Research ArticleElectromagnetic Interference between Cranes andBroadcasting Antennas
V Javor
Faculty of Electronic Engineering University of Nis A Medvedeva 14 18000 Nis Serbia
Correspondence should be addressed to V Javor vesnajavorelfakniacrs
Received 22 July 2015 Accepted 18 October 2015
Academic Editor Felipe Catedra
Copyright copy 2015 V Javor This is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
An interesting phenomenon was noticed in some cases by workers operating with cranes in electromagnetic field of broadcastingantennas They experienced electrical shock or burning pain at distances of kilometers away from powerful transmitters becausecranes act as unintentional receiving antennas The solution to this problem depends on dimensions and positioning of thecrane structure electromagnetic field strength at the site frequency and directional characteristic of the transmitting antennaElectromagnetic interference between such structures is analyzed in this paper Computational results for the induced currentsand voltages in crane treated as wire antenna problem are determined using integrodifferential equations for the current alongconductive structure satisfying boundary condition for the electric field Pointmatchingmethod as theMethod ofMoments (MoM)is applied for solving these equations and polynomial approximation of the current is used Results are presented for different cranestructures and possible solutions to this problem are given
1 Introduction
When considering interference between natural electro-magnetic sources of disturbances (terrestrial as lightningdischarges or extraterrestrial as cosmic radiation and solarwind) and various man-made objects (such as equipmentelectronic devices electric systems power lines commu-nication and automation systems and installations) thekey issues are electromagnetic field strength amplitudes ofvoltages and currents electrical properties of the mediumdimensions and positioning of the structure distances andfrequency An adequate modeling would take into accounta wide variety of configurations of the observed systemsIn the last few decades rapid advance has been achieveddue to development of numerical programs and moderncomputers possibilities The analysis in this paper is basedon the wire antenna approach and the ground is treated asperfectly conducting Finite ground conductivity has someinfluence on induced voltages and currents so it could beconsidered using the same procedure as in this paper butthe solution to this problem is what matters However theseelectromagnetic interference (EMI) problems were rarelynoticed and described just in a few papers [1ndash7] Large
conductive structures permanently or temporarily positionedin electromagnetic field of powerful medium wave (MW)transmitters if their dimensions are of the order of wave-length might be dangerous for humans and equipment AMtransmission is nowadays mostly used for sports news andtalk radio whereas FM is better for sound Digital audiobroadcasting is advancing in many countries all over theworld Although there is a shift to higher frequencies for allsystems MW transmitters are still in operation throughoutthe world AM carrier frequencies are assigned to stationsin the frequency range from 531 to 1611 kHz and just inEurope there are still more than a hundred of them withpower ranging from 1 kW to 1MW [8] depending on thetargeted area (local regional or international)
2 Some EMI Problems
The lifting crane of height 60m and jib of length about25m was operating in Progar (Serbia) 8 km away from thetransmitter when the problem was noticed by crane workersThemeasured open-circuit voltagewas 450V Radio Belgradewas operating at the frequency119891=684 kHzup to 1999 havingpowerful 2 MW transmitter and main antenna of height ℎ =
Hindawi Publishing CorporationInternational Journal of Antennas and PropagationVolume 2015 Article ID 452962 10 pageshttpdxdoiorg1011552015452962
2 International Journal of Antennas and Propagation
Z
C
(a)
(b)
(c)
Figure 1 Possible places (a) (b) and (c) for inserting impedanceinto the crane contour
Figure 2 Rail-mounted 65 t crane in Tenerife (Spain)
230m (half-wave monopole) The electric field strength was1198640= 21Vm at the cranersquos site The solution to that problem
was an egg-insulator inserted above the hook (Figure 1)thus disturbing the resonance of the formed contour Thelimitation of this solution is its mechanical strength
Values of the induced voltages were measured in somesimilar situations throughout the world There are rail-mounted container cranes in the harbor of Tenerife Spainhaving 305m span and capacity of 65 t At one of them theindustrial bus was faulty each timewhen it was in the positionto take the load from ship or if its spreader descended nearcontainers Sensors and actuators were grounded to the cranestructure but the problem in control system persisted In2013 the induced current of 500mA was measured as wellas 50V voltage at the frequency 119891 = 621 kHz due to AMantenna broadcasting at this frequency (Spanish nationalradio broadcast) from the nearby mountain [6] When theylubricated the wires of steel cables supporting the spreaderand thus isolated the spreader from crane structure byinserting some impedance the problem was temporarilysolved The crane structure is presented in Figure 2 and theinstrument measuring the induced voltage is presented inFigures 3 and 4The further work presented in this paper wasinitiated by coworking on this problem
At the island Oahu (Hawaii) the crane operator experi-enced electrical shock while using it to lower steel peelingsinto the canal [2] The crane had the boom of 335m length
Figure 3 Measurement site
Figure 4 Instrument measuring induced voltage of about 50V atabout 621 kHz
and was near transmitter broadcasting five AM and one FMchannel at the frequencies from 30 to 100MHz with the totalpower 117 kW and antenna of height ℎ = 122m
In 50 t rough-terrain crane in Japan [3] induced voltagesin the hook up to 12 kV and several amperes measured in theboom of this crane were noticed It was positioned in the farfield of the transmitter operating at frequency 119891 = 624 kHzat the distance where the measured electric field was 119864
0=
079Vm The case is examined further in this paper In [3]the solution to put acrylic plate under outrigger floats is givenand also another solution to add a plain knit grounding wirein the hook was suggested
On the building site in Rio de Janeiro (Brazil) wheretwo cranes were used workers reported electrical shock andskin burns when they touched the boom of the large crawlercrane and electronic systems of the smaller truck-basedcrane became inoperative [7] The grounding of the vehicledid not solve the problem It was due to AM transmittersoperating with the power of 100 kW at 119891
1= 1280 kHz (station
1) and at 1198912= 900 kHz (station 2) approximately 230 meters
from the building site Practical solution to the problem wasa coil wounded around the hydraulic jack of the crane withone end connected to the hook and the other grounded to anearby point
EMI problem was noticed also by workers using a largecrane during the assembly phase of the turbine componentwhile building wind power plant in Turkey [5] nearby AMtransmitter operating at 119891 = 702 kHz with the power of550 kW Steel tower of the turbine had 80 meters of heightand the rotor with three blades 44 meters long The mainboom of the crane was 110m long and there was also a shorterauxiliary boom Crane site was 8 km from the transmitterAdditional grounding was used to mitigate the inducedeffects
International Journal of Antennas and Propagation 3
Z
Boom
Wire
x y
z
120593
120579
r
h1
h2
Jib
h3
2a1
2a2
2a3
Figure 5 Simple wire antenna model of the crane in externalelectromagnetic field
All the mentioned problems may be treated as receivingwire antenna in external electromagnetic field so that someof the codes may be used as NEC [9] AWAS [10] andso forth Programs AWAS and SPAN [11] are used in thispaper to calculate induced currents and voltages for the givenexamples
3 Crane Acting as Receiving Antenna inExternal Electromagnetic Field
To model the crane structure as wire antenna in externalelectromagnetic field it is necessary to determine if the fieldis near or far For all the mentioned cases the constructionwork is done in the far field of transmitting antenna at afew hundreds of meters or even kilometers away [12 13]Near field is in fact prohibited area with electric field valuesmuch over the occupationalcontrolled limits according toregulations It should be noticed that mentioned problemsoccur in the area with electric field values below the publiclimits for these frequencies [14] Let us assume that receivingantenna is in a plane wave electromagnetic field so thatelectric field is
119864119904= 1198640
sdot exp [minus119895119896 (119909 sin 120579 cos120593 + 119910 sin 120579 sin120593 + 119911 cos 120579)] (1)
where 120579 and 120593 are spherical coordinates 119909 119910 and 119911 areDescartes coordinates given in Figure 5 119864
0is the maximum
electric field strength 119896 = 2120587120582 is the phase constant120582 = 119888119891is the wavelength and 119888 is the speed of light
The crane is treated as wire antenna structure at perfectlyconducting ground To model a 50 t rough-terrain crane [3]with cylindrical segments the boom segment is taken ofheight ℎ
= 48m and radius 1198863= 15 cm This is the first examined
crane denoted by case A For the second examined cranedenoted by case B lengths are the same for all segmentsbut radii are 119886
1= 15 cm 119886
2= 10 cm and 119886
3= 25 cm The
hook is at height 25m above the ground in both cases Ifusing FDTD method as in [3] calculated induced voltagesare about 600V whereas measured results from [3] are upto 12 kV and induced currents are of several amperes if themaximum electric field is 119864
0= 079Vm and 119891 = 624 kHz
Results for this crane are calculated in this paper using AWAS[10] based on Pocklingtonrsquos equation [15] and polynomialapproximation of the currents [16] The induced voltages aregiven in Table 1 for case A and in Table 2 for case B for therange of frequencies of interest and the three propagationdirectionsThese show that frequencies producing the largestvoltages differ in the two cases so as themaximumof inducedvoltages At119891 = 727 kHzmaximumvoltage119880maxA = 116198Vis calculated in case A whereas at 119891 = 676 kHz voltage119880maxB= 143324V in case B both for the propagation directions120579 = 1205872 120593 = 0
The induced currents along the structure are given inFigures 6ndash11 starting from the base of the boom along the jiband down the wire to the hook at the end These results aregiven in Figure 6 for the electric field 119864
120579= 079Vm 119864
120593= 0
for the propagation directions 120579 = 0 120593 = 0 in Figure 7 for120579 = 1205872 120593 = 0 and in Figure 8 for 120579 = 1205872 120593 = 1205872 forcase A (total length along the crane in that case is 1245m)For 119864
120579= 0 119864120593= 0 120579 = 0 120593 = 1205872 there are no voltages or
currents induced but this is not the case in real situation Infact 120579 is near 1205872 and any 120593may exist during crane operationas both antenna structures are vertically positioned at theground
It is shown that at some frequencies the phenomenon willnot be noticed at all The maximum of induced current at thebase of the boom is about 5 amperes and it occurs for thefrequency 119891 = 727 kHz and the propagation directions 120579 =
4 International Journal of Antennas and Propagation
Figure 6 Induced currents versus length from the boom base caseA directions 120579 = 0 120593 = 0
1205872 120593 = 0 in case A This current is about 57 amperes for119891 = 676 kHz in case B It should be noticed that for plusmn30 kHzcurrents along the structure are about one-half of the value at119891 = 727 kHz as shown in Figure 7
There is a difference in current results at segmentsbeginningsends if compared to FDTD results [3] Thereare no discontinuities in currents results due to Kirchhoff rsquoslaw for currents at nodes which is satisfied in the appliedprocedure The chosen polynomial degree is 119899 = 3 In case Bfor plusmn30 kHz currents along the structure are about one-thirdof the value at 119891 = 676 kHz as shown in Figure 10 Resonant
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
120579 = 1205872 120593 = 0
700kHz650kHz600kHz550kHz500kHz
1000 kHz900kHz800 kHz750kHz727kHz
0
1
2
3
4
5
Curr
ent (
A)
Figure 7 Induced currents versus length from the boom base caseA directions 120579 = 1205872 120593 = 0
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
700kHz650kHz600kHz550kHz500kHz
1000 kHz900kHz800 kHz750kHz727kHz
0
1
2
3
4
5
Curr
ent (
A)
120579 = 1205872 120593 = 1205872
Figure 8 Induced currents versus length from the boom base caseA directions 120579 = 1205872 120593 = 1205872
characteristics of this structure may be noticed also in resultsfor the induced voltages versus frequency in Figures 12 and13 for the two cases A and B
From the calculation of induced currents and voltages forthese two cases it may be noticed that the change in segmentscross section dimensions has great influence Change ofwire diameter determined also with mechanical constraintschanges resonant frequency and in this way the problem
International Journal of Antennas and Propagation 5
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
120579 = 0 120593 = 0
00
05
10
15
20
25
Curr
ent (
A)
Figure 9 Induced currents versus length from the boom base caseB directions 120579 = 0 120593 = 0
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
0
1
2
3
4
5
6
Curr
ent (
A)
120579 = 1205872 120593 = 0
Figure 10 Induced currents versus length from the boom base caseB directions 120579 = 1205872 120593 = 0
might be mitigated Another approach may be an adequatechoice of crane configuration after the structure is analyzedand induced voltages and currents are computed
4 Computation Procedure Based onHallenrsquos Equation
Magnetic vector-potential of a wire antenna structure with119899 linear cylindrical segments having current distribution
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
0
1
2
3
4
5
6
Curr
ent (
A)
120579 = 1205872 120593 = 1205872
Figure 11 Induced currents versus length from the boom base caseB directions 120579 = 1205872 120593 = 1205872
120579 = 1205872 120593 = 1205872
120579 = 0 120593 = 0
120579 = 1205872 120593 = 0
600 700 800 900 1000500Frequency (kHz)
0
200
400
600
800
1000
1200
1400
Volta
ge (V
)
Figure 12 Open-circuit voltage in case A for 119864120579= 079Vm 119864
120593= 0
and propagation directions 120579 = 0 and 120593 = 0 120579 = 1205872 and 120593 = 0120579 = 1205872 and 120593 = 1205872
119868119911119898
(1199111015840119898) along 119898th segment is obtained as the sum of 119899
components Each component 119860(119911119898) is in the direction of
119898th segment having length ℎ119898and radius 119886
119898 so that
119860 (119911119898) =120583
4120587intℎ119898
0
119868119911119898
(1199111015840119898)exp (minus119895119896119903
119898119898)
119903119898119898
d1199111015840119898 (2)
6 International Journal of Antennas and Propagation
120579 = 1205872 120593 = 1205872
120579 = 0 120593 = 0
120579 = 1205872 120593 = 0
600 700 800 900 1000500Frequency (kHz)
0
200
400
600
800
1000
1200
1400
1600
Volta
ge (V
)
Figure 13 Open-circuit voltage in case B for 119864120579= 079Vm 119864
120593= 0
and propagation directions 120579 = 0 and 120593 = 0 120579 = 1205872 and 120593 = 0120579 = 1205872 and 120593 = 1205872
where 119903119898119898= [119909119898
2 + 119910119898
2 + (119911119898minus 1199111015840119898)2]12 is the distance
between the point 119872(119909119898 119910119898 119911119898) and the point 119875(0 0 1199111015840
119898)
along the axis of the119898th segment for119898 = 1 119899The total magnetic vector-potential is
119860 =119899
sum119898=1
119860 (119911119898) (3)
Descartes components of magnetic vector-potential originat-ing from the 119897th segment current are recalculated into the119898thsegment Descartes coordinate system as
119860119909119898
= sum119897119897 =119898
sin120595119897119898
sin 120579119897119898119860 (119911119897)
119860119910119898
= minus sum119897119897 =119898
cos120595119897119898
sin 120579119897119898119860 (119911119897)
119860119911119898
= 119860 (119911119898) + sum119897119897 =119898
cos 120579119897119898119860 (119911119897)
(4)
where 120579119897119898 120595119897119898 and 120593
119897119898are Eulerrsquos angles between the
119897th and 119898th segments of Descartes coordinate systemsBoundary condition for the tangential component of electricfield at the conductive surface and Lorenz gauge condition areused so that
In (8)119885(119894) is the concentrated impedance at point 119911119898
(119894) alongthe 119894th segment for 119894 = 1 119899
119911 where 119899
119911is the total
number of concentrated impedances for that segment Thissystem of equations is solved by Point matching method asthe Method of Moments (MoM) [18] and matching pointsare equidistantly positioned at the surface of each segmentincluding the beginnings and ends of segments Currentsare assumed to be distributed along the axes of segmentsalthough they are flowing along the conductive surface of
International Journal of Antennas and Propagation 7
the structure in order to avoid singularities in integralsDistributions of the currents are unknowns and they areapproximated by polynomials [16]
The distance between the matching point119872(119909119898 119910119898 119911119898)
at 119898th segment surface and the point 119875119897(0 0 1199111015840
119897) along the
axis of 119897th segment where the elementary current source ispositioned for 119897 = 119898 is
119875119887(119909119887119897119898 119910119887119897119898 119911119887119897119898) is the beginning of the 119897th segment
that is its coordinate system origin recalculated into the119898th segment coordinate system Kirchhoff rsquos current law issatisfied for all the nodes For 119899
119863antenna segments incident
to node119863 Kirchhoff rsquos law is119899119863
sum119903=1
119899119903
sum119904=1
119861119903119904(119911119903
ℎ119903
)119904
= 0 (13)
for unknown complex coefficients119861119903119904and chosen polynomial
degree 119899119903in the approximation of current along the 119903th
segment Coordinate of the beginningend of 119903th segment is119911119903and ℎ119903is the segment length Electric potential is calculated
sdot sin [119896 (119911119898minus 119904)] d119904 minus
119899119885
sum119894=1
119885(119894)119868 (119911119898
(119894))
sdot cos [119896 (119911119898minus 119904)]
(14)
5 Tower Crane and Turn-OverCrane Examples
More complex crane structures are modelled and system of(8) is solved for each example using the presented procedureSome interesting results for tower crane and turn-over crane[1] are obtained For the crane in Figure 14 in far electromag-netic field 119864
120579= 1Vm 119864
120593= 0 for 119891 = 1MHz and different
propagation directions effective current along main towersegment of the height 119897 = 34m is presented in Figure 15 for
1m
46m
23m
22m6m
34m
15m
01m01m
Z
01m
Figure 14 Tower crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
10 20 300Distance along the tower segment l (m)
0
50
100
150
200
250
300
Indu
ced
curr
entI
ef(m
A)
Figure 15 Induced current along the main tower segment of thetower crane
the polynomial degree 119899 = 5 and impedance 119885 = 100Ω Ifthe turn-over crane given in Figure 16 is in the same field theeffective current along boom segment of the height 119897 = 32mis presented in Figure 17
For 119891 = 1MHz the wavelength is 120582 = 300m Theresults for different frequencies are analyzed and it is obtainedthat for the tower crane example the maximum currentsalong the structure and maximum touch voltages at the hookare at 119891 = 7258 kHz and for the turn-over crane are at119891 = 149MHz Eight segments and seven nodes were chosento model the tower crane at perfectly conducting groundwhereas six segments and six nodes were chosen for the turn-over crane
6 Reloading Bridge and Portal-HarborCrane Examples
It is important to consider reloading bridges portal-harborcranes and container cranes as they may be permanently inthe field of MW transmitter a few kilometers from the cranersquos
8 International Journal of Antennas and Propagation
32m
01m05m
91m
01m
5m
1m
12m
16m
03m
Z
Figure 16 Turn-over crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
0
5
10
15
20
25
30
35
Indu
ced
curr
entI
ef(m
A)
5 10 15 20 25 300Distance along the boom segment l (m)
Figure 17 Induced current along the boom segment of the turn-over crane
site Electric fields in such cases are often of the order of Vmdepending on the transmitter power and vicinity Positions ofsuch cranes should be carefully selected based on modelingof the specific problem Induced effects may pose great riskin some cases [19 20]
An example of the reloading bridge with its dimensionsis given in Figure 18 Portal-harbor crane of dimensions verysimilar to the described rail-mounted container crane ispresented in Figure 19 For these cranes positioned in thefar field for 119864
120579= 1Vm 119864
120593= 0 120579 = 1205872 and 120593 =
1205872 touch voltages and induced currents are calculated forthe polynomial degree 119899 = 5 and impedance 119885 = 1000ΩResults are presented in Figures 20 and 21 Induced voltagefor the portal-harbor crane is about 50V for frequency 119891 =621 kHz as measured in Tenerife (Spain) although this is justa simplified model
The impedancewhichmodels a human touching the hookmay be chosen according to the frequency of interest andusing results from [21ndash25]
It may be concluded that the reloading bridge is moresuitable as it has less resonant frequencies smaller values of
32m5m 5m
7m5m
35m38m38m30m
5m5m01m
Z
Figure 18 Reloading bridge model
15m005m
10m
2m
2m
1m1m
2m18m
7m
3m16m
5m
1m
Z
Figure 19 Portal-harbor crane model
induced currents and smaller values of touch voltages exceptin the narrow bandwidth around resonant frequency
7 Conclusion
Currents up to several amperes and touch voltages up to about1 kVmay be induced in large cranes nearbyMW transmittersAt such frequencies these values may result in electricalshock painful burns and dangerous involuntary movementsof workers but also in faults in the automation and controlsystems of cranes Analysis of such problems is presented inthis paper as well as results for induced current and voltagesfor different configurations of crane structures
Current distribution along the crane structure is deter-mined using wire antenna model of the crane and elec-tromagnetic theory approach Currents along segments areapproximated by polynomials System of integral equationsfor the currents is solved using Point matching methodResults are in agreement with measured currents and volt-ages
This approach may be used to analyze specific prob-lems especially before positioning of reloading bridges andcontainer cranes nearby MW transmitters Some practicalsolutions to this problem are also given in the paper
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This paper is in the frame of research within ProjectsHUMANISM III 44004 and TR33008 (2011ndash2015) financed
International Journal of Antennas and Propagation 9
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
0
50
100
150
200
250
300
350
U (V
)
10 15 20 25 30 35 40 45 5005f (MHz)
Figure 20 Induced voltage for reloading bridge and portal-harborcrane versus 119891
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
10 15 20 25 30 35 40 45 5005f (MHz)
0
50
100
150
I (m
A)
Figure 21 Induced current for reloading bridge and portal-harborcrane versus 119891
by Ministry of Education Science and Technological Devel-opment of the Republic of Serbia
References
[1] V Javor ldquoThe calculation and elimination of undesirable elec-tromagnetic field influence on cranesrdquo in Proceedings of the4th International Conference on Telecommunications in ModernSatellite Cable and Broadcasting Services (TELSIKS rsquo99) pp628ndash631 Nis Serbia October 1999
[2] T Denton ldquoRadiofrequency energy poses unseen hazardrdquoOccupational Hazards vol 64 no 12 pp 45ndash47 2002
[3] T Hajime ldquoElectromagnetic disturbance of large-scale cranedue to medium wave broadcasting and countermeasuresrdquoResearchReports ofNational Institute of Industrial Safety 2003
[4] R G Olsen J B Schneider and R A Tell ldquoRadio frequencyburns in the power system workplacerdquo IEEE Transactions onPower Delivery vol 26 no 1 pp 352ndash359 2011
[5] F Ustuner ldquoPractical papers articles and application notesinteraction of an AM broadcast transmitter with a large crane
posing health hazards a real-world event analysisrdquo IEEE Elec-tromagnetic Compatibility Magazine vol 1 no 2 pp 41ndash492012
[6] V Javor andM Saranac ldquoElectromagnetic disturbances in con-ductive structures nearby transmitting antennasrdquo inProceedingsof the 21st International Conference on Software Telecommuni-cations and Computer Networks (SoftCOM rsquo13) pp 1ndash5 IEEEPrimosten Croatia September 2013
[7] M B Perotoni and R M Barreto Resolving Safety-Critical EMIProblems between AMTransmitters and Cranes Using a 3D FieldSolver High Frequency Electronics 2014
[8] httpsenwikipediaorgwikiList of European mediumwave transmitters
[9] G J Burke and A J Poggio ldquoNumerical electromagneticscode (NEC)-method of momentsrdquo Tech Rep 116 Naval OceanSystems Center San Diego Calif USA 1981
[10] A R Djordjevic M B Bazdar T K Sarkar and R F Har-rington AWAS for Windows Analysis of Wire Antennas andScatterers Software and Userrsquos Manual Artech House BooksBoston Mass USA 1995
[11] V Javor and D Velickovic ldquoComputer package for analysis oflightning electromagnetic field distribution for cage conductorstructuresrdquo in Proceedings of the 26th International Conferenceon Lightning Protection (ICLP rsquo02) Proceedings of Papers pp382ndash387 Cracow Poland September 2002
[12] O P Gandhi and I Chatterjee ldquoRadio-frequency hazards in theVLF to MF bandrdquo Proceedings of the IEEE vol 70 no 12 pp1462ndash1464 1982
[13] W Congjiang L Deming W Shuquan W Baosheng andH Baoge ldquoEnvironmental impact of electromagnetic radiationfrom the 10kWmedium wave transmitter of Weihai Broadcast-ing Stationrdquo Journal of Environmental Sciences vol 7 no 4 pp461ndash467 1995
[14] IEEE C951-2005 IEEE Standard for safety levels with respectto human exposure to radio frequency electromagnetic fields3 kHz to 300GHz IEEE 2005
[15] H C Pocklington ldquoElectrical oscillations in wiresrdquo Proceedingsof the Cambridge Philosophical Society Mathematical and Phys-ical Sciences vol 9 pp 324ndash332 1897
[16] B D Popovic ldquoPolynomial approximation of current along thinsymmetrical cylindrical dipolesrdquoProceedings of the Institution ofElectrical Engineers vol 117 no 5 pp 873ndash878 1970
[17] E Hallen ldquoTheoretical investigations into the transmitting andreceiving qualities of antennasrdquo Nova Acta Regiae SocietatisScientiarum Upsaliensis Ser IV vol 11 no 4 pp 1ndash44 1938
[18] R F Harrington Field Computation by Moment Methodssection 62 Macmillan New York NY USA 1968
[19] I R Bradby Practical Experience in Radio Frequency InducedIgnition RiskAssessment for COMAHDSEARCompliance Sym-posium Series no 154 ABB Engineering Services 2008
[20] X-T Huang ldquoStudy on the influence of induced high-voltagesurge to tower crane by Baise MW broadcasting station and itsprotectionrdquo Journal of Safety Science and Technology no 2 pp146ndash151 2010
[21] H Kanai I Chatterjee and O P Gandhi ldquoHuman bodyimpedance for electromagnetic hazard analysis in the VLFto MF bandrdquo IEEE Transactions on Microwave Theory andTechniques vol 32 no 8 pp 763ndash772 1984
[22] D A Hill and J A Walsh ldquoRadio-frequency current throughthe feet of a grounded humanrdquo IEEE Transactions on Electro-magnetic Compatibility vol 27 no 1 pp 18ndash23 1985
10 International Journal of Antennas and Propagation
[23] I Chatterjee D Wu and O P Gandhi ldquoHuman bodyimpedance and threshold currents for perception and pain forcontact hazard analysis in the VLF-MF bandrdquo IEEE Transac-tions on Biomedical Engineering vol 33 no 5 pp 486ndash4941986
[24] Y Kamimura K Komori M Shoji Y Yamada S Watanabeand Y Yamanaka ldquoHuman body impedance for contact currentmeasurement in Japanrdquo IEICE Transactions on Communica-tions vol 88 no 8 pp 3263ndash3267 2005
[25] V De Santis P A Beeckman D A Lampasi and M FelizianildquoAssessment of human body impedance for safety requirementsagainst contact currents for frequencies up to 110MHzrdquo IEEETransactions on Biomedical Engineering vol 58 no 2 pp 390ndash396 2011
2 International Journal of Antennas and Propagation
Z
C
(a)
(b)
(c)
Figure 1 Possible places (a) (b) and (c) for inserting impedanceinto the crane contour
Figure 2 Rail-mounted 65 t crane in Tenerife (Spain)
230m (half-wave monopole) The electric field strength was1198640= 21Vm at the cranersquos site The solution to that problem
was an egg-insulator inserted above the hook (Figure 1)thus disturbing the resonance of the formed contour Thelimitation of this solution is its mechanical strength
Values of the induced voltages were measured in somesimilar situations throughout the world There are rail-mounted container cranes in the harbor of Tenerife Spainhaving 305m span and capacity of 65 t At one of them theindustrial bus was faulty each timewhen it was in the positionto take the load from ship or if its spreader descended nearcontainers Sensors and actuators were grounded to the cranestructure but the problem in control system persisted In2013 the induced current of 500mA was measured as wellas 50V voltage at the frequency 119891 = 621 kHz due to AMantenna broadcasting at this frequency (Spanish nationalradio broadcast) from the nearby mountain [6] When theylubricated the wires of steel cables supporting the spreaderand thus isolated the spreader from crane structure byinserting some impedance the problem was temporarilysolved The crane structure is presented in Figure 2 and theinstrument measuring the induced voltage is presented inFigures 3 and 4The further work presented in this paper wasinitiated by coworking on this problem
At the island Oahu (Hawaii) the crane operator experi-enced electrical shock while using it to lower steel peelingsinto the canal [2] The crane had the boom of 335m length
Figure 3 Measurement site
Figure 4 Instrument measuring induced voltage of about 50V atabout 621 kHz
and was near transmitter broadcasting five AM and one FMchannel at the frequencies from 30 to 100MHz with the totalpower 117 kW and antenna of height ℎ = 122m
In 50 t rough-terrain crane in Japan [3] induced voltagesin the hook up to 12 kV and several amperes measured in theboom of this crane were noticed It was positioned in the farfield of the transmitter operating at frequency 119891 = 624 kHzat the distance where the measured electric field was 119864
0=
079Vm The case is examined further in this paper In [3]the solution to put acrylic plate under outrigger floats is givenand also another solution to add a plain knit grounding wirein the hook was suggested
On the building site in Rio de Janeiro (Brazil) wheretwo cranes were used workers reported electrical shock andskin burns when they touched the boom of the large crawlercrane and electronic systems of the smaller truck-basedcrane became inoperative [7] The grounding of the vehicledid not solve the problem It was due to AM transmittersoperating with the power of 100 kW at 119891
1= 1280 kHz (station
1) and at 1198912= 900 kHz (station 2) approximately 230 meters
from the building site Practical solution to the problem wasa coil wounded around the hydraulic jack of the crane withone end connected to the hook and the other grounded to anearby point
EMI problem was noticed also by workers using a largecrane during the assembly phase of the turbine componentwhile building wind power plant in Turkey [5] nearby AMtransmitter operating at 119891 = 702 kHz with the power of550 kW Steel tower of the turbine had 80 meters of heightand the rotor with three blades 44 meters long The mainboom of the crane was 110m long and there was also a shorterauxiliary boom Crane site was 8 km from the transmitterAdditional grounding was used to mitigate the inducedeffects
International Journal of Antennas and Propagation 3
Z
Boom
Wire
x y
z
120593
120579
r
h1
h2
Jib
h3
2a1
2a2
2a3
Figure 5 Simple wire antenna model of the crane in externalelectromagnetic field
All the mentioned problems may be treated as receivingwire antenna in external electromagnetic field so that someof the codes may be used as NEC [9] AWAS [10] andso forth Programs AWAS and SPAN [11] are used in thispaper to calculate induced currents and voltages for the givenexamples
3 Crane Acting as Receiving Antenna inExternal Electromagnetic Field
To model the crane structure as wire antenna in externalelectromagnetic field it is necessary to determine if the fieldis near or far For all the mentioned cases the constructionwork is done in the far field of transmitting antenna at afew hundreds of meters or even kilometers away [12 13]Near field is in fact prohibited area with electric field valuesmuch over the occupationalcontrolled limits according toregulations It should be noticed that mentioned problemsoccur in the area with electric field values below the publiclimits for these frequencies [14] Let us assume that receivingantenna is in a plane wave electromagnetic field so thatelectric field is
119864119904= 1198640
sdot exp [minus119895119896 (119909 sin 120579 cos120593 + 119910 sin 120579 sin120593 + 119911 cos 120579)] (1)
where 120579 and 120593 are spherical coordinates 119909 119910 and 119911 areDescartes coordinates given in Figure 5 119864
0is the maximum
electric field strength 119896 = 2120587120582 is the phase constant120582 = 119888119891is the wavelength and 119888 is the speed of light
The crane is treated as wire antenna structure at perfectlyconducting ground To model a 50 t rough-terrain crane [3]with cylindrical segments the boom segment is taken ofheight ℎ
= 48m and radius 1198863= 15 cm This is the first examined
crane denoted by case A For the second examined cranedenoted by case B lengths are the same for all segmentsbut radii are 119886
1= 15 cm 119886
2= 10 cm and 119886
3= 25 cm The
hook is at height 25m above the ground in both cases Ifusing FDTD method as in [3] calculated induced voltagesare about 600V whereas measured results from [3] are upto 12 kV and induced currents are of several amperes if themaximum electric field is 119864
0= 079Vm and 119891 = 624 kHz
Results for this crane are calculated in this paper using AWAS[10] based on Pocklingtonrsquos equation [15] and polynomialapproximation of the currents [16] The induced voltages aregiven in Table 1 for case A and in Table 2 for case B for therange of frequencies of interest and the three propagationdirectionsThese show that frequencies producing the largestvoltages differ in the two cases so as themaximumof inducedvoltages At119891 = 727 kHzmaximumvoltage119880maxA = 116198Vis calculated in case A whereas at 119891 = 676 kHz voltage119880maxB= 143324V in case B both for the propagation directions120579 = 1205872 120593 = 0
The induced currents along the structure are given inFigures 6ndash11 starting from the base of the boom along the jiband down the wire to the hook at the end These results aregiven in Figure 6 for the electric field 119864
120579= 079Vm 119864
120593= 0
for the propagation directions 120579 = 0 120593 = 0 in Figure 7 for120579 = 1205872 120593 = 0 and in Figure 8 for 120579 = 1205872 120593 = 1205872 forcase A (total length along the crane in that case is 1245m)For 119864
120579= 0 119864120593= 0 120579 = 0 120593 = 1205872 there are no voltages or
currents induced but this is not the case in real situation Infact 120579 is near 1205872 and any 120593may exist during crane operationas both antenna structures are vertically positioned at theground
It is shown that at some frequencies the phenomenon willnot be noticed at all The maximum of induced current at thebase of the boom is about 5 amperes and it occurs for thefrequency 119891 = 727 kHz and the propagation directions 120579 =
4 International Journal of Antennas and Propagation
Figure 6 Induced currents versus length from the boom base caseA directions 120579 = 0 120593 = 0
1205872 120593 = 0 in case A This current is about 57 amperes for119891 = 676 kHz in case B It should be noticed that for plusmn30 kHzcurrents along the structure are about one-half of the value at119891 = 727 kHz as shown in Figure 7
There is a difference in current results at segmentsbeginningsends if compared to FDTD results [3] Thereare no discontinuities in currents results due to Kirchhoff rsquoslaw for currents at nodes which is satisfied in the appliedprocedure The chosen polynomial degree is 119899 = 3 In case Bfor plusmn30 kHz currents along the structure are about one-thirdof the value at 119891 = 676 kHz as shown in Figure 10 Resonant
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
120579 = 1205872 120593 = 0
700kHz650kHz600kHz550kHz500kHz
1000 kHz900kHz800 kHz750kHz727kHz
0
1
2
3
4
5
Curr
ent (
A)
Figure 7 Induced currents versus length from the boom base caseA directions 120579 = 1205872 120593 = 0
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
700kHz650kHz600kHz550kHz500kHz
1000 kHz900kHz800 kHz750kHz727kHz
0
1
2
3
4
5
Curr
ent (
A)
120579 = 1205872 120593 = 1205872
Figure 8 Induced currents versus length from the boom base caseA directions 120579 = 1205872 120593 = 1205872
characteristics of this structure may be noticed also in resultsfor the induced voltages versus frequency in Figures 12 and13 for the two cases A and B
From the calculation of induced currents and voltages forthese two cases it may be noticed that the change in segmentscross section dimensions has great influence Change ofwire diameter determined also with mechanical constraintschanges resonant frequency and in this way the problem
International Journal of Antennas and Propagation 5
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
120579 = 0 120593 = 0
00
05
10
15
20
25
Curr
ent (
A)
Figure 9 Induced currents versus length from the boom base caseB directions 120579 = 0 120593 = 0
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
0
1
2
3
4
5
6
Curr
ent (
A)
120579 = 1205872 120593 = 0
Figure 10 Induced currents versus length from the boom base caseB directions 120579 = 1205872 120593 = 0
might be mitigated Another approach may be an adequatechoice of crane configuration after the structure is analyzedand induced voltages and currents are computed
4 Computation Procedure Based onHallenrsquos Equation
Magnetic vector-potential of a wire antenna structure with119899 linear cylindrical segments having current distribution
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
0
1
2
3
4
5
6
Curr
ent (
A)
120579 = 1205872 120593 = 1205872
Figure 11 Induced currents versus length from the boom base caseB directions 120579 = 1205872 120593 = 1205872
120579 = 1205872 120593 = 1205872
120579 = 0 120593 = 0
120579 = 1205872 120593 = 0
600 700 800 900 1000500Frequency (kHz)
0
200
400
600
800
1000
1200
1400
Volta
ge (V
)
Figure 12 Open-circuit voltage in case A for 119864120579= 079Vm 119864
120593= 0
and propagation directions 120579 = 0 and 120593 = 0 120579 = 1205872 and 120593 = 0120579 = 1205872 and 120593 = 1205872
119868119911119898
(1199111015840119898) along 119898th segment is obtained as the sum of 119899
components Each component 119860(119911119898) is in the direction of
119898th segment having length ℎ119898and radius 119886
119898 so that
119860 (119911119898) =120583
4120587intℎ119898
0
119868119911119898
(1199111015840119898)exp (minus119895119896119903
119898119898)
119903119898119898
d1199111015840119898 (2)
6 International Journal of Antennas and Propagation
120579 = 1205872 120593 = 1205872
120579 = 0 120593 = 0
120579 = 1205872 120593 = 0
600 700 800 900 1000500Frequency (kHz)
0
200
400
600
800
1000
1200
1400
1600
Volta
ge (V
)
Figure 13 Open-circuit voltage in case B for 119864120579= 079Vm 119864
120593= 0
and propagation directions 120579 = 0 and 120593 = 0 120579 = 1205872 and 120593 = 0120579 = 1205872 and 120593 = 1205872
where 119903119898119898= [119909119898
2 + 119910119898
2 + (119911119898minus 1199111015840119898)2]12 is the distance
between the point 119872(119909119898 119910119898 119911119898) and the point 119875(0 0 1199111015840
119898)
along the axis of the119898th segment for119898 = 1 119899The total magnetic vector-potential is
119860 =119899
sum119898=1
119860 (119911119898) (3)
Descartes components of magnetic vector-potential originat-ing from the 119897th segment current are recalculated into the119898thsegment Descartes coordinate system as
119860119909119898
= sum119897119897 =119898
sin120595119897119898
sin 120579119897119898119860 (119911119897)
119860119910119898
= minus sum119897119897 =119898
cos120595119897119898
sin 120579119897119898119860 (119911119897)
119860119911119898
= 119860 (119911119898) + sum119897119897 =119898
cos 120579119897119898119860 (119911119897)
(4)
where 120579119897119898 120595119897119898 and 120593
119897119898are Eulerrsquos angles between the
119897th and 119898th segments of Descartes coordinate systemsBoundary condition for the tangential component of electricfield at the conductive surface and Lorenz gauge condition areused so that
In (8)119885(119894) is the concentrated impedance at point 119911119898
(119894) alongthe 119894th segment for 119894 = 1 119899
119911 where 119899
119911is the total
number of concentrated impedances for that segment Thissystem of equations is solved by Point matching method asthe Method of Moments (MoM) [18] and matching pointsare equidistantly positioned at the surface of each segmentincluding the beginnings and ends of segments Currentsare assumed to be distributed along the axes of segmentsalthough they are flowing along the conductive surface of
International Journal of Antennas and Propagation 7
the structure in order to avoid singularities in integralsDistributions of the currents are unknowns and they areapproximated by polynomials [16]
The distance between the matching point119872(119909119898 119910119898 119911119898)
at 119898th segment surface and the point 119875119897(0 0 1199111015840
119897) along the
axis of 119897th segment where the elementary current source ispositioned for 119897 = 119898 is
119875119887(119909119887119897119898 119910119887119897119898 119911119887119897119898) is the beginning of the 119897th segment
that is its coordinate system origin recalculated into the119898th segment coordinate system Kirchhoff rsquos current law issatisfied for all the nodes For 119899
119863antenna segments incident
to node119863 Kirchhoff rsquos law is119899119863
sum119903=1
119899119903
sum119904=1
119861119903119904(119911119903
ℎ119903
)119904
= 0 (13)
for unknown complex coefficients119861119903119904and chosen polynomial
degree 119899119903in the approximation of current along the 119903th
segment Coordinate of the beginningend of 119903th segment is119911119903and ℎ119903is the segment length Electric potential is calculated
sdot sin [119896 (119911119898minus 119904)] d119904 minus
119899119885
sum119894=1
119885(119894)119868 (119911119898
(119894))
sdot cos [119896 (119911119898minus 119904)]
(14)
5 Tower Crane and Turn-OverCrane Examples
More complex crane structures are modelled and system of(8) is solved for each example using the presented procedureSome interesting results for tower crane and turn-over crane[1] are obtained For the crane in Figure 14 in far electromag-netic field 119864
120579= 1Vm 119864
120593= 0 for 119891 = 1MHz and different
propagation directions effective current along main towersegment of the height 119897 = 34m is presented in Figure 15 for
1m
46m
23m
22m6m
34m
15m
01m01m
Z
01m
Figure 14 Tower crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
10 20 300Distance along the tower segment l (m)
0
50
100
150
200
250
300
Indu
ced
curr
entI
ef(m
A)
Figure 15 Induced current along the main tower segment of thetower crane
the polynomial degree 119899 = 5 and impedance 119885 = 100Ω Ifthe turn-over crane given in Figure 16 is in the same field theeffective current along boom segment of the height 119897 = 32mis presented in Figure 17
For 119891 = 1MHz the wavelength is 120582 = 300m Theresults for different frequencies are analyzed and it is obtainedthat for the tower crane example the maximum currentsalong the structure and maximum touch voltages at the hookare at 119891 = 7258 kHz and for the turn-over crane are at119891 = 149MHz Eight segments and seven nodes were chosento model the tower crane at perfectly conducting groundwhereas six segments and six nodes were chosen for the turn-over crane
6 Reloading Bridge and Portal-HarborCrane Examples
It is important to consider reloading bridges portal-harborcranes and container cranes as they may be permanently inthe field of MW transmitter a few kilometers from the cranersquos
8 International Journal of Antennas and Propagation
32m
01m05m
91m
01m
5m
1m
12m
16m
03m
Z
Figure 16 Turn-over crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
0
5
10
15
20
25
30
35
Indu
ced
curr
entI
ef(m
A)
5 10 15 20 25 300Distance along the boom segment l (m)
Figure 17 Induced current along the boom segment of the turn-over crane
site Electric fields in such cases are often of the order of Vmdepending on the transmitter power and vicinity Positions ofsuch cranes should be carefully selected based on modelingof the specific problem Induced effects may pose great riskin some cases [19 20]
An example of the reloading bridge with its dimensionsis given in Figure 18 Portal-harbor crane of dimensions verysimilar to the described rail-mounted container crane ispresented in Figure 19 For these cranes positioned in thefar field for 119864
120579= 1Vm 119864
120593= 0 120579 = 1205872 and 120593 =
1205872 touch voltages and induced currents are calculated forthe polynomial degree 119899 = 5 and impedance 119885 = 1000ΩResults are presented in Figures 20 and 21 Induced voltagefor the portal-harbor crane is about 50V for frequency 119891 =621 kHz as measured in Tenerife (Spain) although this is justa simplified model
The impedancewhichmodels a human touching the hookmay be chosen according to the frequency of interest andusing results from [21ndash25]
It may be concluded that the reloading bridge is moresuitable as it has less resonant frequencies smaller values of
32m5m 5m
7m5m
35m38m38m30m
5m5m01m
Z
Figure 18 Reloading bridge model
15m005m
10m
2m
2m
1m1m
2m18m
7m
3m16m
5m
1m
Z
Figure 19 Portal-harbor crane model
induced currents and smaller values of touch voltages exceptin the narrow bandwidth around resonant frequency
7 Conclusion
Currents up to several amperes and touch voltages up to about1 kVmay be induced in large cranes nearbyMW transmittersAt such frequencies these values may result in electricalshock painful burns and dangerous involuntary movementsof workers but also in faults in the automation and controlsystems of cranes Analysis of such problems is presented inthis paper as well as results for induced current and voltagesfor different configurations of crane structures
Current distribution along the crane structure is deter-mined using wire antenna model of the crane and elec-tromagnetic theory approach Currents along segments areapproximated by polynomials System of integral equationsfor the currents is solved using Point matching methodResults are in agreement with measured currents and volt-ages
This approach may be used to analyze specific prob-lems especially before positioning of reloading bridges andcontainer cranes nearby MW transmitters Some practicalsolutions to this problem are also given in the paper
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This paper is in the frame of research within ProjectsHUMANISM III 44004 and TR33008 (2011ndash2015) financed
International Journal of Antennas and Propagation 9
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
0
50
100
150
200
250
300
350
U (V
)
10 15 20 25 30 35 40 45 5005f (MHz)
Figure 20 Induced voltage for reloading bridge and portal-harborcrane versus 119891
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
10 15 20 25 30 35 40 45 5005f (MHz)
0
50
100
150
I (m
A)
Figure 21 Induced current for reloading bridge and portal-harborcrane versus 119891
by Ministry of Education Science and Technological Devel-opment of the Republic of Serbia
References
[1] V Javor ldquoThe calculation and elimination of undesirable elec-tromagnetic field influence on cranesrdquo in Proceedings of the4th International Conference on Telecommunications in ModernSatellite Cable and Broadcasting Services (TELSIKS rsquo99) pp628ndash631 Nis Serbia October 1999
[2] T Denton ldquoRadiofrequency energy poses unseen hazardrdquoOccupational Hazards vol 64 no 12 pp 45ndash47 2002
[3] T Hajime ldquoElectromagnetic disturbance of large-scale cranedue to medium wave broadcasting and countermeasuresrdquoResearchReports ofNational Institute of Industrial Safety 2003
[4] R G Olsen J B Schneider and R A Tell ldquoRadio frequencyburns in the power system workplacerdquo IEEE Transactions onPower Delivery vol 26 no 1 pp 352ndash359 2011
[5] F Ustuner ldquoPractical papers articles and application notesinteraction of an AM broadcast transmitter with a large crane
posing health hazards a real-world event analysisrdquo IEEE Elec-tromagnetic Compatibility Magazine vol 1 no 2 pp 41ndash492012
[6] V Javor andM Saranac ldquoElectromagnetic disturbances in con-ductive structures nearby transmitting antennasrdquo inProceedingsof the 21st International Conference on Software Telecommuni-cations and Computer Networks (SoftCOM rsquo13) pp 1ndash5 IEEEPrimosten Croatia September 2013
[7] M B Perotoni and R M Barreto Resolving Safety-Critical EMIProblems between AMTransmitters and Cranes Using a 3D FieldSolver High Frequency Electronics 2014
[8] httpsenwikipediaorgwikiList of European mediumwave transmitters
[9] G J Burke and A J Poggio ldquoNumerical electromagneticscode (NEC)-method of momentsrdquo Tech Rep 116 Naval OceanSystems Center San Diego Calif USA 1981
[10] A R Djordjevic M B Bazdar T K Sarkar and R F Har-rington AWAS for Windows Analysis of Wire Antennas andScatterers Software and Userrsquos Manual Artech House BooksBoston Mass USA 1995
[11] V Javor and D Velickovic ldquoComputer package for analysis oflightning electromagnetic field distribution for cage conductorstructuresrdquo in Proceedings of the 26th International Conferenceon Lightning Protection (ICLP rsquo02) Proceedings of Papers pp382ndash387 Cracow Poland September 2002
[12] O P Gandhi and I Chatterjee ldquoRadio-frequency hazards in theVLF to MF bandrdquo Proceedings of the IEEE vol 70 no 12 pp1462ndash1464 1982
[13] W Congjiang L Deming W Shuquan W Baosheng andH Baoge ldquoEnvironmental impact of electromagnetic radiationfrom the 10kWmedium wave transmitter of Weihai Broadcast-ing Stationrdquo Journal of Environmental Sciences vol 7 no 4 pp461ndash467 1995
[14] IEEE C951-2005 IEEE Standard for safety levels with respectto human exposure to radio frequency electromagnetic fields3 kHz to 300GHz IEEE 2005
[15] H C Pocklington ldquoElectrical oscillations in wiresrdquo Proceedingsof the Cambridge Philosophical Society Mathematical and Phys-ical Sciences vol 9 pp 324ndash332 1897
[16] B D Popovic ldquoPolynomial approximation of current along thinsymmetrical cylindrical dipolesrdquoProceedings of the Institution ofElectrical Engineers vol 117 no 5 pp 873ndash878 1970
[17] E Hallen ldquoTheoretical investigations into the transmitting andreceiving qualities of antennasrdquo Nova Acta Regiae SocietatisScientiarum Upsaliensis Ser IV vol 11 no 4 pp 1ndash44 1938
[18] R F Harrington Field Computation by Moment Methodssection 62 Macmillan New York NY USA 1968
[19] I R Bradby Practical Experience in Radio Frequency InducedIgnition RiskAssessment for COMAHDSEARCompliance Sym-posium Series no 154 ABB Engineering Services 2008
[20] X-T Huang ldquoStudy on the influence of induced high-voltagesurge to tower crane by Baise MW broadcasting station and itsprotectionrdquo Journal of Safety Science and Technology no 2 pp146ndash151 2010
[21] H Kanai I Chatterjee and O P Gandhi ldquoHuman bodyimpedance for electromagnetic hazard analysis in the VLFto MF bandrdquo IEEE Transactions on Microwave Theory andTechniques vol 32 no 8 pp 763ndash772 1984
[22] D A Hill and J A Walsh ldquoRadio-frequency current throughthe feet of a grounded humanrdquo IEEE Transactions on Electro-magnetic Compatibility vol 27 no 1 pp 18ndash23 1985
10 International Journal of Antennas and Propagation
[23] I Chatterjee D Wu and O P Gandhi ldquoHuman bodyimpedance and threshold currents for perception and pain forcontact hazard analysis in the VLF-MF bandrdquo IEEE Transac-tions on Biomedical Engineering vol 33 no 5 pp 486ndash4941986
[24] Y Kamimura K Komori M Shoji Y Yamada S Watanabeand Y Yamanaka ldquoHuman body impedance for contact currentmeasurement in Japanrdquo IEICE Transactions on Communica-tions vol 88 no 8 pp 3263ndash3267 2005
[25] V De Santis P A Beeckman D A Lampasi and M FelizianildquoAssessment of human body impedance for safety requirementsagainst contact currents for frequencies up to 110MHzrdquo IEEETransactions on Biomedical Engineering vol 58 no 2 pp 390ndash396 2011
International Journal of Antennas and Propagation 3
Z
Boom
Wire
x y
z
120593
120579
r
h1
h2
Jib
h3
2a1
2a2
2a3
Figure 5 Simple wire antenna model of the crane in externalelectromagnetic field
All the mentioned problems may be treated as receivingwire antenna in external electromagnetic field so that someof the codes may be used as NEC [9] AWAS [10] andso forth Programs AWAS and SPAN [11] are used in thispaper to calculate induced currents and voltages for the givenexamples
3 Crane Acting as Receiving Antenna inExternal Electromagnetic Field
To model the crane structure as wire antenna in externalelectromagnetic field it is necessary to determine if the fieldis near or far For all the mentioned cases the constructionwork is done in the far field of transmitting antenna at afew hundreds of meters or even kilometers away [12 13]Near field is in fact prohibited area with electric field valuesmuch over the occupationalcontrolled limits according toregulations It should be noticed that mentioned problemsoccur in the area with electric field values below the publiclimits for these frequencies [14] Let us assume that receivingantenna is in a plane wave electromagnetic field so thatelectric field is
119864119904= 1198640
sdot exp [minus119895119896 (119909 sin 120579 cos120593 + 119910 sin 120579 sin120593 + 119911 cos 120579)] (1)
where 120579 and 120593 are spherical coordinates 119909 119910 and 119911 areDescartes coordinates given in Figure 5 119864
0is the maximum
electric field strength 119896 = 2120587120582 is the phase constant120582 = 119888119891is the wavelength and 119888 is the speed of light
The crane is treated as wire antenna structure at perfectlyconducting ground To model a 50 t rough-terrain crane [3]with cylindrical segments the boom segment is taken ofheight ℎ
= 48m and radius 1198863= 15 cm This is the first examined
crane denoted by case A For the second examined cranedenoted by case B lengths are the same for all segmentsbut radii are 119886
1= 15 cm 119886
2= 10 cm and 119886
3= 25 cm The
hook is at height 25m above the ground in both cases Ifusing FDTD method as in [3] calculated induced voltagesare about 600V whereas measured results from [3] are upto 12 kV and induced currents are of several amperes if themaximum electric field is 119864
0= 079Vm and 119891 = 624 kHz
Results for this crane are calculated in this paper using AWAS[10] based on Pocklingtonrsquos equation [15] and polynomialapproximation of the currents [16] The induced voltages aregiven in Table 1 for case A and in Table 2 for case B for therange of frequencies of interest and the three propagationdirectionsThese show that frequencies producing the largestvoltages differ in the two cases so as themaximumof inducedvoltages At119891 = 727 kHzmaximumvoltage119880maxA = 116198Vis calculated in case A whereas at 119891 = 676 kHz voltage119880maxB= 143324V in case B both for the propagation directions120579 = 1205872 120593 = 0
The induced currents along the structure are given inFigures 6ndash11 starting from the base of the boom along the jiband down the wire to the hook at the end These results aregiven in Figure 6 for the electric field 119864
120579= 079Vm 119864
120593= 0
for the propagation directions 120579 = 0 120593 = 0 in Figure 7 for120579 = 1205872 120593 = 0 and in Figure 8 for 120579 = 1205872 120593 = 1205872 forcase A (total length along the crane in that case is 1245m)For 119864
120579= 0 119864120593= 0 120579 = 0 120593 = 1205872 there are no voltages or
currents induced but this is not the case in real situation Infact 120579 is near 1205872 and any 120593may exist during crane operationas both antenna structures are vertically positioned at theground
It is shown that at some frequencies the phenomenon willnot be noticed at all The maximum of induced current at thebase of the boom is about 5 amperes and it occurs for thefrequency 119891 = 727 kHz and the propagation directions 120579 =
4 International Journal of Antennas and Propagation
Figure 6 Induced currents versus length from the boom base caseA directions 120579 = 0 120593 = 0
1205872 120593 = 0 in case A This current is about 57 amperes for119891 = 676 kHz in case B It should be noticed that for plusmn30 kHzcurrents along the structure are about one-half of the value at119891 = 727 kHz as shown in Figure 7
There is a difference in current results at segmentsbeginningsends if compared to FDTD results [3] Thereare no discontinuities in currents results due to Kirchhoff rsquoslaw for currents at nodes which is satisfied in the appliedprocedure The chosen polynomial degree is 119899 = 3 In case Bfor plusmn30 kHz currents along the structure are about one-thirdof the value at 119891 = 676 kHz as shown in Figure 10 Resonant
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
120579 = 1205872 120593 = 0
700kHz650kHz600kHz550kHz500kHz
1000 kHz900kHz800 kHz750kHz727kHz
0
1
2
3
4
5
Curr
ent (
A)
Figure 7 Induced currents versus length from the boom base caseA directions 120579 = 1205872 120593 = 0
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
700kHz650kHz600kHz550kHz500kHz
1000 kHz900kHz800 kHz750kHz727kHz
0
1
2
3
4
5
Curr
ent (
A)
120579 = 1205872 120593 = 1205872
Figure 8 Induced currents versus length from the boom base caseA directions 120579 = 1205872 120593 = 1205872
characteristics of this structure may be noticed also in resultsfor the induced voltages versus frequency in Figures 12 and13 for the two cases A and B
From the calculation of induced currents and voltages forthese two cases it may be noticed that the change in segmentscross section dimensions has great influence Change ofwire diameter determined also with mechanical constraintschanges resonant frequency and in this way the problem
International Journal of Antennas and Propagation 5
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
120579 = 0 120593 = 0
00
05
10
15
20
25
Curr
ent (
A)
Figure 9 Induced currents versus length from the boom base caseB directions 120579 = 0 120593 = 0
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
0
1
2
3
4
5
6
Curr
ent (
A)
120579 = 1205872 120593 = 0
Figure 10 Induced currents versus length from the boom base caseB directions 120579 = 1205872 120593 = 0
might be mitigated Another approach may be an adequatechoice of crane configuration after the structure is analyzedand induced voltages and currents are computed
4 Computation Procedure Based onHallenrsquos Equation
Magnetic vector-potential of a wire antenna structure with119899 linear cylindrical segments having current distribution
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
0
1
2
3
4
5
6
Curr
ent (
A)
120579 = 1205872 120593 = 1205872
Figure 11 Induced currents versus length from the boom base caseB directions 120579 = 1205872 120593 = 1205872
120579 = 1205872 120593 = 1205872
120579 = 0 120593 = 0
120579 = 1205872 120593 = 0
600 700 800 900 1000500Frequency (kHz)
0
200
400
600
800
1000
1200
1400
Volta
ge (V
)
Figure 12 Open-circuit voltage in case A for 119864120579= 079Vm 119864
120593= 0
and propagation directions 120579 = 0 and 120593 = 0 120579 = 1205872 and 120593 = 0120579 = 1205872 and 120593 = 1205872
119868119911119898
(1199111015840119898) along 119898th segment is obtained as the sum of 119899
components Each component 119860(119911119898) is in the direction of
119898th segment having length ℎ119898and radius 119886
119898 so that
119860 (119911119898) =120583
4120587intℎ119898
0
119868119911119898
(1199111015840119898)exp (minus119895119896119903
119898119898)
119903119898119898
d1199111015840119898 (2)
6 International Journal of Antennas and Propagation
120579 = 1205872 120593 = 1205872
120579 = 0 120593 = 0
120579 = 1205872 120593 = 0
600 700 800 900 1000500Frequency (kHz)
0
200
400
600
800
1000
1200
1400
1600
Volta
ge (V
)
Figure 13 Open-circuit voltage in case B for 119864120579= 079Vm 119864
120593= 0
and propagation directions 120579 = 0 and 120593 = 0 120579 = 1205872 and 120593 = 0120579 = 1205872 and 120593 = 1205872
where 119903119898119898= [119909119898
2 + 119910119898
2 + (119911119898minus 1199111015840119898)2]12 is the distance
between the point 119872(119909119898 119910119898 119911119898) and the point 119875(0 0 1199111015840
119898)
along the axis of the119898th segment for119898 = 1 119899The total magnetic vector-potential is
119860 =119899
sum119898=1
119860 (119911119898) (3)
Descartes components of magnetic vector-potential originat-ing from the 119897th segment current are recalculated into the119898thsegment Descartes coordinate system as
119860119909119898
= sum119897119897 =119898
sin120595119897119898
sin 120579119897119898119860 (119911119897)
119860119910119898
= minus sum119897119897 =119898
cos120595119897119898
sin 120579119897119898119860 (119911119897)
119860119911119898
= 119860 (119911119898) + sum119897119897 =119898
cos 120579119897119898119860 (119911119897)
(4)
where 120579119897119898 120595119897119898 and 120593
119897119898are Eulerrsquos angles between the
119897th and 119898th segments of Descartes coordinate systemsBoundary condition for the tangential component of electricfield at the conductive surface and Lorenz gauge condition areused so that
In (8)119885(119894) is the concentrated impedance at point 119911119898
(119894) alongthe 119894th segment for 119894 = 1 119899
119911 where 119899
119911is the total
number of concentrated impedances for that segment Thissystem of equations is solved by Point matching method asthe Method of Moments (MoM) [18] and matching pointsare equidistantly positioned at the surface of each segmentincluding the beginnings and ends of segments Currentsare assumed to be distributed along the axes of segmentsalthough they are flowing along the conductive surface of
International Journal of Antennas and Propagation 7
the structure in order to avoid singularities in integralsDistributions of the currents are unknowns and they areapproximated by polynomials [16]
The distance between the matching point119872(119909119898 119910119898 119911119898)
at 119898th segment surface and the point 119875119897(0 0 1199111015840
119897) along the
axis of 119897th segment where the elementary current source ispositioned for 119897 = 119898 is
119875119887(119909119887119897119898 119910119887119897119898 119911119887119897119898) is the beginning of the 119897th segment
that is its coordinate system origin recalculated into the119898th segment coordinate system Kirchhoff rsquos current law issatisfied for all the nodes For 119899
119863antenna segments incident
to node119863 Kirchhoff rsquos law is119899119863
sum119903=1
119899119903
sum119904=1
119861119903119904(119911119903
ℎ119903
)119904
= 0 (13)
for unknown complex coefficients119861119903119904and chosen polynomial
degree 119899119903in the approximation of current along the 119903th
segment Coordinate of the beginningend of 119903th segment is119911119903and ℎ119903is the segment length Electric potential is calculated
sdot sin [119896 (119911119898minus 119904)] d119904 minus
119899119885
sum119894=1
119885(119894)119868 (119911119898
(119894))
sdot cos [119896 (119911119898minus 119904)]
(14)
5 Tower Crane and Turn-OverCrane Examples
More complex crane structures are modelled and system of(8) is solved for each example using the presented procedureSome interesting results for tower crane and turn-over crane[1] are obtained For the crane in Figure 14 in far electromag-netic field 119864
120579= 1Vm 119864
120593= 0 for 119891 = 1MHz and different
propagation directions effective current along main towersegment of the height 119897 = 34m is presented in Figure 15 for
1m
46m
23m
22m6m
34m
15m
01m01m
Z
01m
Figure 14 Tower crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
10 20 300Distance along the tower segment l (m)
0
50
100
150
200
250
300
Indu
ced
curr
entI
ef(m
A)
Figure 15 Induced current along the main tower segment of thetower crane
the polynomial degree 119899 = 5 and impedance 119885 = 100Ω Ifthe turn-over crane given in Figure 16 is in the same field theeffective current along boom segment of the height 119897 = 32mis presented in Figure 17
For 119891 = 1MHz the wavelength is 120582 = 300m Theresults for different frequencies are analyzed and it is obtainedthat for the tower crane example the maximum currentsalong the structure and maximum touch voltages at the hookare at 119891 = 7258 kHz and for the turn-over crane are at119891 = 149MHz Eight segments and seven nodes were chosento model the tower crane at perfectly conducting groundwhereas six segments and six nodes were chosen for the turn-over crane
6 Reloading Bridge and Portal-HarborCrane Examples
It is important to consider reloading bridges portal-harborcranes and container cranes as they may be permanently inthe field of MW transmitter a few kilometers from the cranersquos
8 International Journal of Antennas and Propagation
32m
01m05m
91m
01m
5m
1m
12m
16m
03m
Z
Figure 16 Turn-over crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
0
5
10
15
20
25
30
35
Indu
ced
curr
entI
ef(m
A)
5 10 15 20 25 300Distance along the boom segment l (m)
Figure 17 Induced current along the boom segment of the turn-over crane
site Electric fields in such cases are often of the order of Vmdepending on the transmitter power and vicinity Positions ofsuch cranes should be carefully selected based on modelingof the specific problem Induced effects may pose great riskin some cases [19 20]
An example of the reloading bridge with its dimensionsis given in Figure 18 Portal-harbor crane of dimensions verysimilar to the described rail-mounted container crane ispresented in Figure 19 For these cranes positioned in thefar field for 119864
120579= 1Vm 119864
120593= 0 120579 = 1205872 and 120593 =
1205872 touch voltages and induced currents are calculated forthe polynomial degree 119899 = 5 and impedance 119885 = 1000ΩResults are presented in Figures 20 and 21 Induced voltagefor the portal-harbor crane is about 50V for frequency 119891 =621 kHz as measured in Tenerife (Spain) although this is justa simplified model
The impedancewhichmodels a human touching the hookmay be chosen according to the frequency of interest andusing results from [21ndash25]
It may be concluded that the reloading bridge is moresuitable as it has less resonant frequencies smaller values of
32m5m 5m
7m5m
35m38m38m30m
5m5m01m
Z
Figure 18 Reloading bridge model
15m005m
10m
2m
2m
1m1m
2m18m
7m
3m16m
5m
1m
Z
Figure 19 Portal-harbor crane model
induced currents and smaller values of touch voltages exceptin the narrow bandwidth around resonant frequency
7 Conclusion
Currents up to several amperes and touch voltages up to about1 kVmay be induced in large cranes nearbyMW transmittersAt such frequencies these values may result in electricalshock painful burns and dangerous involuntary movementsof workers but also in faults in the automation and controlsystems of cranes Analysis of such problems is presented inthis paper as well as results for induced current and voltagesfor different configurations of crane structures
Current distribution along the crane structure is deter-mined using wire antenna model of the crane and elec-tromagnetic theory approach Currents along segments areapproximated by polynomials System of integral equationsfor the currents is solved using Point matching methodResults are in agreement with measured currents and volt-ages
This approach may be used to analyze specific prob-lems especially before positioning of reloading bridges andcontainer cranes nearby MW transmitters Some practicalsolutions to this problem are also given in the paper
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This paper is in the frame of research within ProjectsHUMANISM III 44004 and TR33008 (2011ndash2015) financed
International Journal of Antennas and Propagation 9
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
0
50
100
150
200
250
300
350
U (V
)
10 15 20 25 30 35 40 45 5005f (MHz)
Figure 20 Induced voltage for reloading bridge and portal-harborcrane versus 119891
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
10 15 20 25 30 35 40 45 5005f (MHz)
0
50
100
150
I (m
A)
Figure 21 Induced current for reloading bridge and portal-harborcrane versus 119891
by Ministry of Education Science and Technological Devel-opment of the Republic of Serbia
References
[1] V Javor ldquoThe calculation and elimination of undesirable elec-tromagnetic field influence on cranesrdquo in Proceedings of the4th International Conference on Telecommunications in ModernSatellite Cable and Broadcasting Services (TELSIKS rsquo99) pp628ndash631 Nis Serbia October 1999
[2] T Denton ldquoRadiofrequency energy poses unseen hazardrdquoOccupational Hazards vol 64 no 12 pp 45ndash47 2002
[3] T Hajime ldquoElectromagnetic disturbance of large-scale cranedue to medium wave broadcasting and countermeasuresrdquoResearchReports ofNational Institute of Industrial Safety 2003
[4] R G Olsen J B Schneider and R A Tell ldquoRadio frequencyburns in the power system workplacerdquo IEEE Transactions onPower Delivery vol 26 no 1 pp 352ndash359 2011
[5] F Ustuner ldquoPractical papers articles and application notesinteraction of an AM broadcast transmitter with a large crane
posing health hazards a real-world event analysisrdquo IEEE Elec-tromagnetic Compatibility Magazine vol 1 no 2 pp 41ndash492012
[6] V Javor andM Saranac ldquoElectromagnetic disturbances in con-ductive structures nearby transmitting antennasrdquo inProceedingsof the 21st International Conference on Software Telecommuni-cations and Computer Networks (SoftCOM rsquo13) pp 1ndash5 IEEEPrimosten Croatia September 2013
[7] M B Perotoni and R M Barreto Resolving Safety-Critical EMIProblems between AMTransmitters and Cranes Using a 3D FieldSolver High Frequency Electronics 2014
[8] httpsenwikipediaorgwikiList of European mediumwave transmitters
[9] G J Burke and A J Poggio ldquoNumerical electromagneticscode (NEC)-method of momentsrdquo Tech Rep 116 Naval OceanSystems Center San Diego Calif USA 1981
[10] A R Djordjevic M B Bazdar T K Sarkar and R F Har-rington AWAS for Windows Analysis of Wire Antennas andScatterers Software and Userrsquos Manual Artech House BooksBoston Mass USA 1995
[11] V Javor and D Velickovic ldquoComputer package for analysis oflightning electromagnetic field distribution for cage conductorstructuresrdquo in Proceedings of the 26th International Conferenceon Lightning Protection (ICLP rsquo02) Proceedings of Papers pp382ndash387 Cracow Poland September 2002
[12] O P Gandhi and I Chatterjee ldquoRadio-frequency hazards in theVLF to MF bandrdquo Proceedings of the IEEE vol 70 no 12 pp1462ndash1464 1982
[13] W Congjiang L Deming W Shuquan W Baosheng andH Baoge ldquoEnvironmental impact of electromagnetic radiationfrom the 10kWmedium wave transmitter of Weihai Broadcast-ing Stationrdquo Journal of Environmental Sciences vol 7 no 4 pp461ndash467 1995
[14] IEEE C951-2005 IEEE Standard for safety levels with respectto human exposure to radio frequency electromagnetic fields3 kHz to 300GHz IEEE 2005
[15] H C Pocklington ldquoElectrical oscillations in wiresrdquo Proceedingsof the Cambridge Philosophical Society Mathematical and Phys-ical Sciences vol 9 pp 324ndash332 1897
[16] B D Popovic ldquoPolynomial approximation of current along thinsymmetrical cylindrical dipolesrdquoProceedings of the Institution ofElectrical Engineers vol 117 no 5 pp 873ndash878 1970
[17] E Hallen ldquoTheoretical investigations into the transmitting andreceiving qualities of antennasrdquo Nova Acta Regiae SocietatisScientiarum Upsaliensis Ser IV vol 11 no 4 pp 1ndash44 1938
[18] R F Harrington Field Computation by Moment Methodssection 62 Macmillan New York NY USA 1968
[19] I R Bradby Practical Experience in Radio Frequency InducedIgnition RiskAssessment for COMAHDSEARCompliance Sym-posium Series no 154 ABB Engineering Services 2008
[20] X-T Huang ldquoStudy on the influence of induced high-voltagesurge to tower crane by Baise MW broadcasting station and itsprotectionrdquo Journal of Safety Science and Technology no 2 pp146ndash151 2010
[21] H Kanai I Chatterjee and O P Gandhi ldquoHuman bodyimpedance for electromagnetic hazard analysis in the VLFto MF bandrdquo IEEE Transactions on Microwave Theory andTechniques vol 32 no 8 pp 763ndash772 1984
[22] D A Hill and J A Walsh ldquoRadio-frequency current throughthe feet of a grounded humanrdquo IEEE Transactions on Electro-magnetic Compatibility vol 27 no 1 pp 18ndash23 1985
10 International Journal of Antennas and Propagation
[23] I Chatterjee D Wu and O P Gandhi ldquoHuman bodyimpedance and threshold currents for perception and pain forcontact hazard analysis in the VLF-MF bandrdquo IEEE Transac-tions on Biomedical Engineering vol 33 no 5 pp 486ndash4941986
[24] Y Kamimura K Komori M Shoji Y Yamada S Watanabeand Y Yamanaka ldquoHuman body impedance for contact currentmeasurement in Japanrdquo IEICE Transactions on Communica-tions vol 88 no 8 pp 3263ndash3267 2005
[25] V De Santis P A Beeckman D A Lampasi and M FelizianildquoAssessment of human body impedance for safety requirementsagainst contact currents for frequencies up to 110MHzrdquo IEEETransactions on Biomedical Engineering vol 58 no 2 pp 390ndash396 2011
Figure 6 Induced currents versus length from the boom base caseA directions 120579 = 0 120593 = 0
1205872 120593 = 0 in case A This current is about 57 amperes for119891 = 676 kHz in case B It should be noticed that for plusmn30 kHzcurrents along the structure are about one-half of the value at119891 = 727 kHz as shown in Figure 7
There is a difference in current results at segmentsbeginningsends if compared to FDTD results [3] Thereare no discontinuities in currents results due to Kirchhoff rsquoslaw for currents at nodes which is satisfied in the appliedprocedure The chosen polynomial degree is 119899 = 3 In case Bfor plusmn30 kHz currents along the structure are about one-thirdof the value at 119891 = 676 kHz as shown in Figure 10 Resonant
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
120579 = 1205872 120593 = 0
700kHz650kHz600kHz550kHz500kHz
1000 kHz900kHz800 kHz750kHz727kHz
0
1
2
3
4
5
Curr
ent (
A)
Figure 7 Induced currents versus length from the boom base caseA directions 120579 = 1205872 120593 = 0
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
700kHz650kHz600kHz550kHz500kHz
1000 kHz900kHz800 kHz750kHz727kHz
0
1
2
3
4
5
Curr
ent (
A)
120579 = 1205872 120593 = 1205872
Figure 8 Induced currents versus length from the boom base caseA directions 120579 = 1205872 120593 = 1205872
characteristics of this structure may be noticed also in resultsfor the induced voltages versus frequency in Figures 12 and13 for the two cases A and B
From the calculation of induced currents and voltages forthese two cases it may be noticed that the change in segmentscross section dimensions has great influence Change ofwire diameter determined also with mechanical constraintschanges resonant frequency and in this way the problem
International Journal of Antennas and Propagation 5
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
120579 = 0 120593 = 0
00
05
10
15
20
25
Curr
ent (
A)
Figure 9 Induced currents versus length from the boom base caseB directions 120579 = 0 120593 = 0
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
0
1
2
3
4
5
6
Curr
ent (
A)
120579 = 1205872 120593 = 0
Figure 10 Induced currents versus length from the boom base caseB directions 120579 = 1205872 120593 = 0
might be mitigated Another approach may be an adequatechoice of crane configuration after the structure is analyzedand induced voltages and currents are computed
4 Computation Procedure Based onHallenrsquos Equation
Magnetic vector-potential of a wire antenna structure with119899 linear cylindrical segments having current distribution
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
0
1
2
3
4
5
6
Curr
ent (
A)
120579 = 1205872 120593 = 1205872
Figure 11 Induced currents versus length from the boom base caseB directions 120579 = 1205872 120593 = 1205872
120579 = 1205872 120593 = 1205872
120579 = 0 120593 = 0
120579 = 1205872 120593 = 0
600 700 800 900 1000500Frequency (kHz)
0
200
400
600
800
1000
1200
1400
Volta
ge (V
)
Figure 12 Open-circuit voltage in case A for 119864120579= 079Vm 119864
120593= 0
and propagation directions 120579 = 0 and 120593 = 0 120579 = 1205872 and 120593 = 0120579 = 1205872 and 120593 = 1205872
119868119911119898
(1199111015840119898) along 119898th segment is obtained as the sum of 119899
components Each component 119860(119911119898) is in the direction of
119898th segment having length ℎ119898and radius 119886
119898 so that
119860 (119911119898) =120583
4120587intℎ119898
0
119868119911119898
(1199111015840119898)exp (minus119895119896119903
119898119898)
119903119898119898
d1199111015840119898 (2)
6 International Journal of Antennas and Propagation
120579 = 1205872 120593 = 1205872
120579 = 0 120593 = 0
120579 = 1205872 120593 = 0
600 700 800 900 1000500Frequency (kHz)
0
200
400
600
800
1000
1200
1400
1600
Volta
ge (V
)
Figure 13 Open-circuit voltage in case B for 119864120579= 079Vm 119864
120593= 0
and propagation directions 120579 = 0 and 120593 = 0 120579 = 1205872 and 120593 = 0120579 = 1205872 and 120593 = 1205872
where 119903119898119898= [119909119898
2 + 119910119898
2 + (119911119898minus 1199111015840119898)2]12 is the distance
between the point 119872(119909119898 119910119898 119911119898) and the point 119875(0 0 1199111015840
119898)
along the axis of the119898th segment for119898 = 1 119899The total magnetic vector-potential is
119860 =119899
sum119898=1
119860 (119911119898) (3)
Descartes components of magnetic vector-potential originat-ing from the 119897th segment current are recalculated into the119898thsegment Descartes coordinate system as
119860119909119898
= sum119897119897 =119898
sin120595119897119898
sin 120579119897119898119860 (119911119897)
119860119910119898
= minus sum119897119897 =119898
cos120595119897119898
sin 120579119897119898119860 (119911119897)
119860119911119898
= 119860 (119911119898) + sum119897119897 =119898
cos 120579119897119898119860 (119911119897)
(4)
where 120579119897119898 120595119897119898 and 120593
119897119898are Eulerrsquos angles between the
119897th and 119898th segments of Descartes coordinate systemsBoundary condition for the tangential component of electricfield at the conductive surface and Lorenz gauge condition areused so that
In (8)119885(119894) is the concentrated impedance at point 119911119898
(119894) alongthe 119894th segment for 119894 = 1 119899
119911 where 119899
119911is the total
number of concentrated impedances for that segment Thissystem of equations is solved by Point matching method asthe Method of Moments (MoM) [18] and matching pointsare equidistantly positioned at the surface of each segmentincluding the beginnings and ends of segments Currentsare assumed to be distributed along the axes of segmentsalthough they are flowing along the conductive surface of
International Journal of Antennas and Propagation 7
the structure in order to avoid singularities in integralsDistributions of the currents are unknowns and they areapproximated by polynomials [16]
The distance between the matching point119872(119909119898 119910119898 119911119898)
at 119898th segment surface and the point 119875119897(0 0 1199111015840
119897) along the
axis of 119897th segment where the elementary current source ispositioned for 119897 = 119898 is
119875119887(119909119887119897119898 119910119887119897119898 119911119887119897119898) is the beginning of the 119897th segment
that is its coordinate system origin recalculated into the119898th segment coordinate system Kirchhoff rsquos current law issatisfied for all the nodes For 119899
119863antenna segments incident
to node119863 Kirchhoff rsquos law is119899119863
sum119903=1
119899119903
sum119904=1
119861119903119904(119911119903
ℎ119903
)119904
= 0 (13)
for unknown complex coefficients119861119903119904and chosen polynomial
degree 119899119903in the approximation of current along the 119903th
segment Coordinate of the beginningend of 119903th segment is119911119903and ℎ119903is the segment length Electric potential is calculated
sdot sin [119896 (119911119898minus 119904)] d119904 minus
119899119885
sum119894=1
119885(119894)119868 (119911119898
(119894))
sdot cos [119896 (119911119898minus 119904)]
(14)
5 Tower Crane and Turn-OverCrane Examples
More complex crane structures are modelled and system of(8) is solved for each example using the presented procedureSome interesting results for tower crane and turn-over crane[1] are obtained For the crane in Figure 14 in far electromag-netic field 119864
120579= 1Vm 119864
120593= 0 for 119891 = 1MHz and different
propagation directions effective current along main towersegment of the height 119897 = 34m is presented in Figure 15 for
1m
46m
23m
22m6m
34m
15m
01m01m
Z
01m
Figure 14 Tower crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
10 20 300Distance along the tower segment l (m)
0
50
100
150
200
250
300
Indu
ced
curr
entI
ef(m
A)
Figure 15 Induced current along the main tower segment of thetower crane
the polynomial degree 119899 = 5 and impedance 119885 = 100Ω Ifthe turn-over crane given in Figure 16 is in the same field theeffective current along boom segment of the height 119897 = 32mis presented in Figure 17
For 119891 = 1MHz the wavelength is 120582 = 300m Theresults for different frequencies are analyzed and it is obtainedthat for the tower crane example the maximum currentsalong the structure and maximum touch voltages at the hookare at 119891 = 7258 kHz and for the turn-over crane are at119891 = 149MHz Eight segments and seven nodes were chosento model the tower crane at perfectly conducting groundwhereas six segments and six nodes were chosen for the turn-over crane
6 Reloading Bridge and Portal-HarborCrane Examples
It is important to consider reloading bridges portal-harborcranes and container cranes as they may be permanently inthe field of MW transmitter a few kilometers from the cranersquos
8 International Journal of Antennas and Propagation
32m
01m05m
91m
01m
5m
1m
12m
16m
03m
Z
Figure 16 Turn-over crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
0
5
10
15
20
25
30
35
Indu
ced
curr
entI
ef(m
A)
5 10 15 20 25 300Distance along the boom segment l (m)
Figure 17 Induced current along the boom segment of the turn-over crane
site Electric fields in such cases are often of the order of Vmdepending on the transmitter power and vicinity Positions ofsuch cranes should be carefully selected based on modelingof the specific problem Induced effects may pose great riskin some cases [19 20]
An example of the reloading bridge with its dimensionsis given in Figure 18 Portal-harbor crane of dimensions verysimilar to the described rail-mounted container crane ispresented in Figure 19 For these cranes positioned in thefar field for 119864
120579= 1Vm 119864
120593= 0 120579 = 1205872 and 120593 =
1205872 touch voltages and induced currents are calculated forthe polynomial degree 119899 = 5 and impedance 119885 = 1000ΩResults are presented in Figures 20 and 21 Induced voltagefor the portal-harbor crane is about 50V for frequency 119891 =621 kHz as measured in Tenerife (Spain) although this is justa simplified model
The impedancewhichmodels a human touching the hookmay be chosen according to the frequency of interest andusing results from [21ndash25]
It may be concluded that the reloading bridge is moresuitable as it has less resonant frequencies smaller values of
32m5m 5m
7m5m
35m38m38m30m
5m5m01m
Z
Figure 18 Reloading bridge model
15m005m
10m
2m
2m
1m1m
2m18m
7m
3m16m
5m
1m
Z
Figure 19 Portal-harbor crane model
induced currents and smaller values of touch voltages exceptin the narrow bandwidth around resonant frequency
7 Conclusion
Currents up to several amperes and touch voltages up to about1 kVmay be induced in large cranes nearbyMW transmittersAt such frequencies these values may result in electricalshock painful burns and dangerous involuntary movementsof workers but also in faults in the automation and controlsystems of cranes Analysis of such problems is presented inthis paper as well as results for induced current and voltagesfor different configurations of crane structures
Current distribution along the crane structure is deter-mined using wire antenna model of the crane and elec-tromagnetic theory approach Currents along segments areapproximated by polynomials System of integral equationsfor the currents is solved using Point matching methodResults are in agreement with measured currents and volt-ages
This approach may be used to analyze specific prob-lems especially before positioning of reloading bridges andcontainer cranes nearby MW transmitters Some practicalsolutions to this problem are also given in the paper
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This paper is in the frame of research within ProjectsHUMANISM III 44004 and TR33008 (2011ndash2015) financed
International Journal of Antennas and Propagation 9
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
0
50
100
150
200
250
300
350
U (V
)
10 15 20 25 30 35 40 45 5005f (MHz)
Figure 20 Induced voltage for reloading bridge and portal-harborcrane versus 119891
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
10 15 20 25 30 35 40 45 5005f (MHz)
0
50
100
150
I (m
A)
Figure 21 Induced current for reloading bridge and portal-harborcrane versus 119891
by Ministry of Education Science and Technological Devel-opment of the Republic of Serbia
References
[1] V Javor ldquoThe calculation and elimination of undesirable elec-tromagnetic field influence on cranesrdquo in Proceedings of the4th International Conference on Telecommunications in ModernSatellite Cable and Broadcasting Services (TELSIKS rsquo99) pp628ndash631 Nis Serbia October 1999
[2] T Denton ldquoRadiofrequency energy poses unseen hazardrdquoOccupational Hazards vol 64 no 12 pp 45ndash47 2002
[3] T Hajime ldquoElectromagnetic disturbance of large-scale cranedue to medium wave broadcasting and countermeasuresrdquoResearchReports ofNational Institute of Industrial Safety 2003
[4] R G Olsen J B Schneider and R A Tell ldquoRadio frequencyburns in the power system workplacerdquo IEEE Transactions onPower Delivery vol 26 no 1 pp 352ndash359 2011
[5] F Ustuner ldquoPractical papers articles and application notesinteraction of an AM broadcast transmitter with a large crane
posing health hazards a real-world event analysisrdquo IEEE Elec-tromagnetic Compatibility Magazine vol 1 no 2 pp 41ndash492012
[6] V Javor andM Saranac ldquoElectromagnetic disturbances in con-ductive structures nearby transmitting antennasrdquo inProceedingsof the 21st International Conference on Software Telecommuni-cations and Computer Networks (SoftCOM rsquo13) pp 1ndash5 IEEEPrimosten Croatia September 2013
[7] M B Perotoni and R M Barreto Resolving Safety-Critical EMIProblems between AMTransmitters and Cranes Using a 3D FieldSolver High Frequency Electronics 2014
[8] httpsenwikipediaorgwikiList of European mediumwave transmitters
[9] G J Burke and A J Poggio ldquoNumerical electromagneticscode (NEC)-method of momentsrdquo Tech Rep 116 Naval OceanSystems Center San Diego Calif USA 1981
[10] A R Djordjevic M B Bazdar T K Sarkar and R F Har-rington AWAS for Windows Analysis of Wire Antennas andScatterers Software and Userrsquos Manual Artech House BooksBoston Mass USA 1995
[11] V Javor and D Velickovic ldquoComputer package for analysis oflightning electromagnetic field distribution for cage conductorstructuresrdquo in Proceedings of the 26th International Conferenceon Lightning Protection (ICLP rsquo02) Proceedings of Papers pp382ndash387 Cracow Poland September 2002
[12] O P Gandhi and I Chatterjee ldquoRadio-frequency hazards in theVLF to MF bandrdquo Proceedings of the IEEE vol 70 no 12 pp1462ndash1464 1982
[13] W Congjiang L Deming W Shuquan W Baosheng andH Baoge ldquoEnvironmental impact of electromagnetic radiationfrom the 10kWmedium wave transmitter of Weihai Broadcast-ing Stationrdquo Journal of Environmental Sciences vol 7 no 4 pp461ndash467 1995
[14] IEEE C951-2005 IEEE Standard for safety levels with respectto human exposure to radio frequency electromagnetic fields3 kHz to 300GHz IEEE 2005
[15] H C Pocklington ldquoElectrical oscillations in wiresrdquo Proceedingsof the Cambridge Philosophical Society Mathematical and Phys-ical Sciences vol 9 pp 324ndash332 1897
[16] B D Popovic ldquoPolynomial approximation of current along thinsymmetrical cylindrical dipolesrdquoProceedings of the Institution ofElectrical Engineers vol 117 no 5 pp 873ndash878 1970
[17] E Hallen ldquoTheoretical investigations into the transmitting andreceiving qualities of antennasrdquo Nova Acta Regiae SocietatisScientiarum Upsaliensis Ser IV vol 11 no 4 pp 1ndash44 1938
[18] R F Harrington Field Computation by Moment Methodssection 62 Macmillan New York NY USA 1968
[19] I R Bradby Practical Experience in Radio Frequency InducedIgnition RiskAssessment for COMAHDSEARCompliance Sym-posium Series no 154 ABB Engineering Services 2008
[20] X-T Huang ldquoStudy on the influence of induced high-voltagesurge to tower crane by Baise MW broadcasting station and itsprotectionrdquo Journal of Safety Science and Technology no 2 pp146ndash151 2010
[21] H Kanai I Chatterjee and O P Gandhi ldquoHuman bodyimpedance for electromagnetic hazard analysis in the VLFto MF bandrdquo IEEE Transactions on Microwave Theory andTechniques vol 32 no 8 pp 763ndash772 1984
[22] D A Hill and J A Walsh ldquoRadio-frequency current throughthe feet of a grounded humanrdquo IEEE Transactions on Electro-magnetic Compatibility vol 27 no 1 pp 18ndash23 1985
10 International Journal of Antennas and Propagation
[23] I Chatterjee D Wu and O P Gandhi ldquoHuman bodyimpedance and threshold currents for perception and pain forcontact hazard analysis in the VLF-MF bandrdquo IEEE Transac-tions on Biomedical Engineering vol 33 no 5 pp 486ndash4941986
[24] Y Kamimura K Komori M Shoji Y Yamada S Watanabeand Y Yamanaka ldquoHuman body impedance for contact currentmeasurement in Japanrdquo IEICE Transactions on Communica-tions vol 88 no 8 pp 3263ndash3267 2005
[25] V De Santis P A Beeckman D A Lampasi and M FelizianildquoAssessment of human body impedance for safety requirementsagainst contact currents for frequencies up to 110MHzrdquo IEEETransactions on Biomedical Engineering vol 58 no 2 pp 390ndash396 2011
International Journal of Antennas and Propagation 5
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
120579 = 0 120593 = 0
00
05
10
15
20
25
Curr
ent (
A)
Figure 9 Induced currents versus length from the boom base caseB directions 120579 = 0 120593 = 0
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
0
1
2
3
4
5
6
Curr
ent (
A)
120579 = 1205872 120593 = 0
Figure 10 Induced currents versus length from the boom base caseB directions 120579 = 1205872 120593 = 0
might be mitigated Another approach may be an adequatechoice of crane configuration after the structure is analyzedand induced voltages and currents are computed
4 Computation Procedure Based onHallenrsquos Equation
Magnetic vector-potential of a wire antenna structure with119899 linear cylindrical segments having current distribution
JibBoomDistance along the structure (m)
20 40 60 80 100 120 1400Wire
676kHz624kHz600kHz550kHz500kHz
1000 kHz900 kHz800kHz700kHz
0
1
2
3
4
5
6
Curr
ent (
A)
120579 = 1205872 120593 = 1205872
Figure 11 Induced currents versus length from the boom base caseB directions 120579 = 1205872 120593 = 1205872
120579 = 1205872 120593 = 1205872
120579 = 0 120593 = 0
120579 = 1205872 120593 = 0
600 700 800 900 1000500Frequency (kHz)
0
200
400
600
800
1000
1200
1400
Volta
ge (V
)
Figure 12 Open-circuit voltage in case A for 119864120579= 079Vm 119864
120593= 0
and propagation directions 120579 = 0 and 120593 = 0 120579 = 1205872 and 120593 = 0120579 = 1205872 and 120593 = 1205872
119868119911119898
(1199111015840119898) along 119898th segment is obtained as the sum of 119899
components Each component 119860(119911119898) is in the direction of
119898th segment having length ℎ119898and radius 119886
119898 so that
119860 (119911119898) =120583
4120587intℎ119898
0
119868119911119898
(1199111015840119898)exp (minus119895119896119903
119898119898)
119903119898119898
d1199111015840119898 (2)
6 International Journal of Antennas and Propagation
120579 = 1205872 120593 = 1205872
120579 = 0 120593 = 0
120579 = 1205872 120593 = 0
600 700 800 900 1000500Frequency (kHz)
0
200
400
600
800
1000
1200
1400
1600
Volta
ge (V
)
Figure 13 Open-circuit voltage in case B for 119864120579= 079Vm 119864
120593= 0
and propagation directions 120579 = 0 and 120593 = 0 120579 = 1205872 and 120593 = 0120579 = 1205872 and 120593 = 1205872
where 119903119898119898= [119909119898
2 + 119910119898
2 + (119911119898minus 1199111015840119898)2]12 is the distance
between the point 119872(119909119898 119910119898 119911119898) and the point 119875(0 0 1199111015840
119898)
along the axis of the119898th segment for119898 = 1 119899The total magnetic vector-potential is
119860 =119899
sum119898=1
119860 (119911119898) (3)
Descartes components of magnetic vector-potential originat-ing from the 119897th segment current are recalculated into the119898thsegment Descartes coordinate system as
119860119909119898
= sum119897119897 =119898
sin120595119897119898
sin 120579119897119898119860 (119911119897)
119860119910119898
= minus sum119897119897 =119898
cos120595119897119898
sin 120579119897119898119860 (119911119897)
119860119911119898
= 119860 (119911119898) + sum119897119897 =119898
cos 120579119897119898119860 (119911119897)
(4)
where 120579119897119898 120595119897119898 and 120593
119897119898are Eulerrsquos angles between the
119897th and 119898th segments of Descartes coordinate systemsBoundary condition for the tangential component of electricfield at the conductive surface and Lorenz gauge condition areused so that
In (8)119885(119894) is the concentrated impedance at point 119911119898
(119894) alongthe 119894th segment for 119894 = 1 119899
119911 where 119899
119911is the total
number of concentrated impedances for that segment Thissystem of equations is solved by Point matching method asthe Method of Moments (MoM) [18] and matching pointsare equidistantly positioned at the surface of each segmentincluding the beginnings and ends of segments Currentsare assumed to be distributed along the axes of segmentsalthough they are flowing along the conductive surface of
International Journal of Antennas and Propagation 7
the structure in order to avoid singularities in integralsDistributions of the currents are unknowns and they areapproximated by polynomials [16]
The distance between the matching point119872(119909119898 119910119898 119911119898)
at 119898th segment surface and the point 119875119897(0 0 1199111015840
119897) along the
axis of 119897th segment where the elementary current source ispositioned for 119897 = 119898 is
119875119887(119909119887119897119898 119910119887119897119898 119911119887119897119898) is the beginning of the 119897th segment
that is its coordinate system origin recalculated into the119898th segment coordinate system Kirchhoff rsquos current law issatisfied for all the nodes For 119899
119863antenna segments incident
to node119863 Kirchhoff rsquos law is119899119863
sum119903=1
119899119903
sum119904=1
119861119903119904(119911119903
ℎ119903
)119904
= 0 (13)
for unknown complex coefficients119861119903119904and chosen polynomial
degree 119899119903in the approximation of current along the 119903th
segment Coordinate of the beginningend of 119903th segment is119911119903and ℎ119903is the segment length Electric potential is calculated
sdot sin [119896 (119911119898minus 119904)] d119904 minus
119899119885
sum119894=1
119885(119894)119868 (119911119898
(119894))
sdot cos [119896 (119911119898minus 119904)]
(14)
5 Tower Crane and Turn-OverCrane Examples
More complex crane structures are modelled and system of(8) is solved for each example using the presented procedureSome interesting results for tower crane and turn-over crane[1] are obtained For the crane in Figure 14 in far electromag-netic field 119864
120579= 1Vm 119864
120593= 0 for 119891 = 1MHz and different
propagation directions effective current along main towersegment of the height 119897 = 34m is presented in Figure 15 for
1m
46m
23m
22m6m
34m
15m
01m01m
Z
01m
Figure 14 Tower crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
10 20 300Distance along the tower segment l (m)
0
50
100
150
200
250
300
Indu
ced
curr
entI
ef(m
A)
Figure 15 Induced current along the main tower segment of thetower crane
the polynomial degree 119899 = 5 and impedance 119885 = 100Ω Ifthe turn-over crane given in Figure 16 is in the same field theeffective current along boom segment of the height 119897 = 32mis presented in Figure 17
For 119891 = 1MHz the wavelength is 120582 = 300m Theresults for different frequencies are analyzed and it is obtainedthat for the tower crane example the maximum currentsalong the structure and maximum touch voltages at the hookare at 119891 = 7258 kHz and for the turn-over crane are at119891 = 149MHz Eight segments and seven nodes were chosento model the tower crane at perfectly conducting groundwhereas six segments and six nodes were chosen for the turn-over crane
6 Reloading Bridge and Portal-HarborCrane Examples
It is important to consider reloading bridges portal-harborcranes and container cranes as they may be permanently inthe field of MW transmitter a few kilometers from the cranersquos
8 International Journal of Antennas and Propagation
32m
01m05m
91m
01m
5m
1m
12m
16m
03m
Z
Figure 16 Turn-over crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
0
5
10
15
20
25
30
35
Indu
ced
curr
entI
ef(m
A)
5 10 15 20 25 300Distance along the boom segment l (m)
Figure 17 Induced current along the boom segment of the turn-over crane
site Electric fields in such cases are often of the order of Vmdepending on the transmitter power and vicinity Positions ofsuch cranes should be carefully selected based on modelingof the specific problem Induced effects may pose great riskin some cases [19 20]
An example of the reloading bridge with its dimensionsis given in Figure 18 Portal-harbor crane of dimensions verysimilar to the described rail-mounted container crane ispresented in Figure 19 For these cranes positioned in thefar field for 119864
120579= 1Vm 119864
120593= 0 120579 = 1205872 and 120593 =
1205872 touch voltages and induced currents are calculated forthe polynomial degree 119899 = 5 and impedance 119885 = 1000ΩResults are presented in Figures 20 and 21 Induced voltagefor the portal-harbor crane is about 50V for frequency 119891 =621 kHz as measured in Tenerife (Spain) although this is justa simplified model
The impedancewhichmodels a human touching the hookmay be chosen according to the frequency of interest andusing results from [21ndash25]
It may be concluded that the reloading bridge is moresuitable as it has less resonant frequencies smaller values of
32m5m 5m
7m5m
35m38m38m30m
5m5m01m
Z
Figure 18 Reloading bridge model
15m005m
10m
2m
2m
1m1m
2m18m
7m
3m16m
5m
1m
Z
Figure 19 Portal-harbor crane model
induced currents and smaller values of touch voltages exceptin the narrow bandwidth around resonant frequency
7 Conclusion
Currents up to several amperes and touch voltages up to about1 kVmay be induced in large cranes nearbyMW transmittersAt such frequencies these values may result in electricalshock painful burns and dangerous involuntary movementsof workers but also in faults in the automation and controlsystems of cranes Analysis of such problems is presented inthis paper as well as results for induced current and voltagesfor different configurations of crane structures
Current distribution along the crane structure is deter-mined using wire antenna model of the crane and elec-tromagnetic theory approach Currents along segments areapproximated by polynomials System of integral equationsfor the currents is solved using Point matching methodResults are in agreement with measured currents and volt-ages
This approach may be used to analyze specific prob-lems especially before positioning of reloading bridges andcontainer cranes nearby MW transmitters Some practicalsolutions to this problem are also given in the paper
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This paper is in the frame of research within ProjectsHUMANISM III 44004 and TR33008 (2011ndash2015) financed
International Journal of Antennas and Propagation 9
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
0
50
100
150
200
250
300
350
U (V
)
10 15 20 25 30 35 40 45 5005f (MHz)
Figure 20 Induced voltage for reloading bridge and portal-harborcrane versus 119891
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
10 15 20 25 30 35 40 45 5005f (MHz)
0
50
100
150
I (m
A)
Figure 21 Induced current for reloading bridge and portal-harborcrane versus 119891
by Ministry of Education Science and Technological Devel-opment of the Republic of Serbia
References
[1] V Javor ldquoThe calculation and elimination of undesirable elec-tromagnetic field influence on cranesrdquo in Proceedings of the4th International Conference on Telecommunications in ModernSatellite Cable and Broadcasting Services (TELSIKS rsquo99) pp628ndash631 Nis Serbia October 1999
[2] T Denton ldquoRadiofrequency energy poses unseen hazardrdquoOccupational Hazards vol 64 no 12 pp 45ndash47 2002
[3] T Hajime ldquoElectromagnetic disturbance of large-scale cranedue to medium wave broadcasting and countermeasuresrdquoResearchReports ofNational Institute of Industrial Safety 2003
[4] R G Olsen J B Schneider and R A Tell ldquoRadio frequencyburns in the power system workplacerdquo IEEE Transactions onPower Delivery vol 26 no 1 pp 352ndash359 2011
[5] F Ustuner ldquoPractical papers articles and application notesinteraction of an AM broadcast transmitter with a large crane
posing health hazards a real-world event analysisrdquo IEEE Elec-tromagnetic Compatibility Magazine vol 1 no 2 pp 41ndash492012
[6] V Javor andM Saranac ldquoElectromagnetic disturbances in con-ductive structures nearby transmitting antennasrdquo inProceedingsof the 21st International Conference on Software Telecommuni-cations and Computer Networks (SoftCOM rsquo13) pp 1ndash5 IEEEPrimosten Croatia September 2013
[7] M B Perotoni and R M Barreto Resolving Safety-Critical EMIProblems between AMTransmitters and Cranes Using a 3D FieldSolver High Frequency Electronics 2014
[8] httpsenwikipediaorgwikiList of European mediumwave transmitters
[9] G J Burke and A J Poggio ldquoNumerical electromagneticscode (NEC)-method of momentsrdquo Tech Rep 116 Naval OceanSystems Center San Diego Calif USA 1981
[10] A R Djordjevic M B Bazdar T K Sarkar and R F Har-rington AWAS for Windows Analysis of Wire Antennas andScatterers Software and Userrsquos Manual Artech House BooksBoston Mass USA 1995
[11] V Javor and D Velickovic ldquoComputer package for analysis oflightning electromagnetic field distribution for cage conductorstructuresrdquo in Proceedings of the 26th International Conferenceon Lightning Protection (ICLP rsquo02) Proceedings of Papers pp382ndash387 Cracow Poland September 2002
[12] O P Gandhi and I Chatterjee ldquoRadio-frequency hazards in theVLF to MF bandrdquo Proceedings of the IEEE vol 70 no 12 pp1462ndash1464 1982
[13] W Congjiang L Deming W Shuquan W Baosheng andH Baoge ldquoEnvironmental impact of electromagnetic radiationfrom the 10kWmedium wave transmitter of Weihai Broadcast-ing Stationrdquo Journal of Environmental Sciences vol 7 no 4 pp461ndash467 1995
[14] IEEE C951-2005 IEEE Standard for safety levels with respectto human exposure to radio frequency electromagnetic fields3 kHz to 300GHz IEEE 2005
[15] H C Pocklington ldquoElectrical oscillations in wiresrdquo Proceedingsof the Cambridge Philosophical Society Mathematical and Phys-ical Sciences vol 9 pp 324ndash332 1897
[16] B D Popovic ldquoPolynomial approximation of current along thinsymmetrical cylindrical dipolesrdquoProceedings of the Institution ofElectrical Engineers vol 117 no 5 pp 873ndash878 1970
[17] E Hallen ldquoTheoretical investigations into the transmitting andreceiving qualities of antennasrdquo Nova Acta Regiae SocietatisScientiarum Upsaliensis Ser IV vol 11 no 4 pp 1ndash44 1938
[18] R F Harrington Field Computation by Moment Methodssection 62 Macmillan New York NY USA 1968
[19] I R Bradby Practical Experience in Radio Frequency InducedIgnition RiskAssessment for COMAHDSEARCompliance Sym-posium Series no 154 ABB Engineering Services 2008
[20] X-T Huang ldquoStudy on the influence of induced high-voltagesurge to tower crane by Baise MW broadcasting station and itsprotectionrdquo Journal of Safety Science and Technology no 2 pp146ndash151 2010
[21] H Kanai I Chatterjee and O P Gandhi ldquoHuman bodyimpedance for electromagnetic hazard analysis in the VLFto MF bandrdquo IEEE Transactions on Microwave Theory andTechniques vol 32 no 8 pp 763ndash772 1984
[22] D A Hill and J A Walsh ldquoRadio-frequency current throughthe feet of a grounded humanrdquo IEEE Transactions on Electro-magnetic Compatibility vol 27 no 1 pp 18ndash23 1985
10 International Journal of Antennas and Propagation
[23] I Chatterjee D Wu and O P Gandhi ldquoHuman bodyimpedance and threshold currents for perception and pain forcontact hazard analysis in the VLF-MF bandrdquo IEEE Transac-tions on Biomedical Engineering vol 33 no 5 pp 486ndash4941986
[24] Y Kamimura K Komori M Shoji Y Yamada S Watanabeand Y Yamanaka ldquoHuman body impedance for contact currentmeasurement in Japanrdquo IEICE Transactions on Communica-tions vol 88 no 8 pp 3263ndash3267 2005
[25] V De Santis P A Beeckman D A Lampasi and M FelizianildquoAssessment of human body impedance for safety requirementsagainst contact currents for frequencies up to 110MHzrdquo IEEETransactions on Biomedical Engineering vol 58 no 2 pp 390ndash396 2011
6 International Journal of Antennas and Propagation
120579 = 1205872 120593 = 1205872
120579 = 0 120593 = 0
120579 = 1205872 120593 = 0
600 700 800 900 1000500Frequency (kHz)
0
200
400
600
800
1000
1200
1400
1600
Volta
ge (V
)
Figure 13 Open-circuit voltage in case B for 119864120579= 079Vm 119864
120593= 0
and propagation directions 120579 = 0 and 120593 = 0 120579 = 1205872 and 120593 = 0120579 = 1205872 and 120593 = 1205872
where 119903119898119898= [119909119898
2 + 119910119898
2 + (119911119898minus 1199111015840119898)2]12 is the distance
between the point 119872(119909119898 119910119898 119911119898) and the point 119875(0 0 1199111015840
119898)
along the axis of the119898th segment for119898 = 1 119899The total magnetic vector-potential is
119860 =119899
sum119898=1
119860 (119911119898) (3)
Descartes components of magnetic vector-potential originat-ing from the 119897th segment current are recalculated into the119898thsegment Descartes coordinate system as
119860119909119898
= sum119897119897 =119898
sin120595119897119898
sin 120579119897119898119860 (119911119897)
119860119910119898
= minus sum119897119897 =119898
cos120595119897119898
sin 120579119897119898119860 (119911119897)
119860119911119898
= 119860 (119911119898) + sum119897119897 =119898
cos 120579119897119898119860 (119911119897)
(4)
where 120579119897119898 120595119897119898 and 120593
119897119898are Eulerrsquos angles between the
119897th and 119898th segments of Descartes coordinate systemsBoundary condition for the tangential component of electricfield at the conductive surface and Lorenz gauge condition areused so that
In (8)119885(119894) is the concentrated impedance at point 119911119898
(119894) alongthe 119894th segment for 119894 = 1 119899
119911 where 119899
119911is the total
number of concentrated impedances for that segment Thissystem of equations is solved by Point matching method asthe Method of Moments (MoM) [18] and matching pointsare equidistantly positioned at the surface of each segmentincluding the beginnings and ends of segments Currentsare assumed to be distributed along the axes of segmentsalthough they are flowing along the conductive surface of
International Journal of Antennas and Propagation 7
the structure in order to avoid singularities in integralsDistributions of the currents are unknowns and they areapproximated by polynomials [16]
The distance between the matching point119872(119909119898 119910119898 119911119898)
at 119898th segment surface and the point 119875119897(0 0 1199111015840
119897) along the
axis of 119897th segment where the elementary current source ispositioned for 119897 = 119898 is
119875119887(119909119887119897119898 119910119887119897119898 119911119887119897119898) is the beginning of the 119897th segment
that is its coordinate system origin recalculated into the119898th segment coordinate system Kirchhoff rsquos current law issatisfied for all the nodes For 119899
119863antenna segments incident
to node119863 Kirchhoff rsquos law is119899119863
sum119903=1
119899119903
sum119904=1
119861119903119904(119911119903
ℎ119903
)119904
= 0 (13)
for unknown complex coefficients119861119903119904and chosen polynomial
degree 119899119903in the approximation of current along the 119903th
segment Coordinate of the beginningend of 119903th segment is119911119903and ℎ119903is the segment length Electric potential is calculated
sdot sin [119896 (119911119898minus 119904)] d119904 minus
119899119885
sum119894=1
119885(119894)119868 (119911119898
(119894))
sdot cos [119896 (119911119898minus 119904)]
(14)
5 Tower Crane and Turn-OverCrane Examples
More complex crane structures are modelled and system of(8) is solved for each example using the presented procedureSome interesting results for tower crane and turn-over crane[1] are obtained For the crane in Figure 14 in far electromag-netic field 119864
120579= 1Vm 119864
120593= 0 for 119891 = 1MHz and different
propagation directions effective current along main towersegment of the height 119897 = 34m is presented in Figure 15 for
1m
46m
23m
22m6m
34m
15m
01m01m
Z
01m
Figure 14 Tower crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
10 20 300Distance along the tower segment l (m)
0
50
100
150
200
250
300
Indu
ced
curr
entI
ef(m
A)
Figure 15 Induced current along the main tower segment of thetower crane
the polynomial degree 119899 = 5 and impedance 119885 = 100Ω Ifthe turn-over crane given in Figure 16 is in the same field theeffective current along boom segment of the height 119897 = 32mis presented in Figure 17
For 119891 = 1MHz the wavelength is 120582 = 300m Theresults for different frequencies are analyzed and it is obtainedthat for the tower crane example the maximum currentsalong the structure and maximum touch voltages at the hookare at 119891 = 7258 kHz and for the turn-over crane are at119891 = 149MHz Eight segments and seven nodes were chosento model the tower crane at perfectly conducting groundwhereas six segments and six nodes were chosen for the turn-over crane
6 Reloading Bridge and Portal-HarborCrane Examples
It is important to consider reloading bridges portal-harborcranes and container cranes as they may be permanently inthe field of MW transmitter a few kilometers from the cranersquos
8 International Journal of Antennas and Propagation
32m
01m05m
91m
01m
5m
1m
12m
16m
03m
Z
Figure 16 Turn-over crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
0
5
10
15
20
25
30
35
Indu
ced
curr
entI
ef(m
A)
5 10 15 20 25 300Distance along the boom segment l (m)
Figure 17 Induced current along the boom segment of the turn-over crane
site Electric fields in such cases are often of the order of Vmdepending on the transmitter power and vicinity Positions ofsuch cranes should be carefully selected based on modelingof the specific problem Induced effects may pose great riskin some cases [19 20]
An example of the reloading bridge with its dimensionsis given in Figure 18 Portal-harbor crane of dimensions verysimilar to the described rail-mounted container crane ispresented in Figure 19 For these cranes positioned in thefar field for 119864
120579= 1Vm 119864
120593= 0 120579 = 1205872 and 120593 =
1205872 touch voltages and induced currents are calculated forthe polynomial degree 119899 = 5 and impedance 119885 = 1000ΩResults are presented in Figures 20 and 21 Induced voltagefor the portal-harbor crane is about 50V for frequency 119891 =621 kHz as measured in Tenerife (Spain) although this is justa simplified model
The impedancewhichmodels a human touching the hookmay be chosen according to the frequency of interest andusing results from [21ndash25]
It may be concluded that the reloading bridge is moresuitable as it has less resonant frequencies smaller values of
32m5m 5m
7m5m
35m38m38m30m
5m5m01m
Z
Figure 18 Reloading bridge model
15m005m
10m
2m
2m
1m1m
2m18m
7m
3m16m
5m
1m
Z
Figure 19 Portal-harbor crane model
induced currents and smaller values of touch voltages exceptin the narrow bandwidth around resonant frequency
7 Conclusion
Currents up to several amperes and touch voltages up to about1 kVmay be induced in large cranes nearbyMW transmittersAt such frequencies these values may result in electricalshock painful burns and dangerous involuntary movementsof workers but also in faults in the automation and controlsystems of cranes Analysis of such problems is presented inthis paper as well as results for induced current and voltagesfor different configurations of crane structures
Current distribution along the crane structure is deter-mined using wire antenna model of the crane and elec-tromagnetic theory approach Currents along segments areapproximated by polynomials System of integral equationsfor the currents is solved using Point matching methodResults are in agreement with measured currents and volt-ages
This approach may be used to analyze specific prob-lems especially before positioning of reloading bridges andcontainer cranes nearby MW transmitters Some practicalsolutions to this problem are also given in the paper
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This paper is in the frame of research within ProjectsHUMANISM III 44004 and TR33008 (2011ndash2015) financed
International Journal of Antennas and Propagation 9
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
0
50
100
150
200
250
300
350
U (V
)
10 15 20 25 30 35 40 45 5005f (MHz)
Figure 20 Induced voltage for reloading bridge and portal-harborcrane versus 119891
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
10 15 20 25 30 35 40 45 5005f (MHz)
0
50
100
150
I (m
A)
Figure 21 Induced current for reloading bridge and portal-harborcrane versus 119891
by Ministry of Education Science and Technological Devel-opment of the Republic of Serbia
References
[1] V Javor ldquoThe calculation and elimination of undesirable elec-tromagnetic field influence on cranesrdquo in Proceedings of the4th International Conference on Telecommunications in ModernSatellite Cable and Broadcasting Services (TELSIKS rsquo99) pp628ndash631 Nis Serbia October 1999
[2] T Denton ldquoRadiofrequency energy poses unseen hazardrdquoOccupational Hazards vol 64 no 12 pp 45ndash47 2002
[3] T Hajime ldquoElectromagnetic disturbance of large-scale cranedue to medium wave broadcasting and countermeasuresrdquoResearchReports ofNational Institute of Industrial Safety 2003
[4] R G Olsen J B Schneider and R A Tell ldquoRadio frequencyburns in the power system workplacerdquo IEEE Transactions onPower Delivery vol 26 no 1 pp 352ndash359 2011
[5] F Ustuner ldquoPractical papers articles and application notesinteraction of an AM broadcast transmitter with a large crane
posing health hazards a real-world event analysisrdquo IEEE Elec-tromagnetic Compatibility Magazine vol 1 no 2 pp 41ndash492012
[6] V Javor andM Saranac ldquoElectromagnetic disturbances in con-ductive structures nearby transmitting antennasrdquo inProceedingsof the 21st International Conference on Software Telecommuni-cations and Computer Networks (SoftCOM rsquo13) pp 1ndash5 IEEEPrimosten Croatia September 2013
[7] M B Perotoni and R M Barreto Resolving Safety-Critical EMIProblems between AMTransmitters and Cranes Using a 3D FieldSolver High Frequency Electronics 2014
[8] httpsenwikipediaorgwikiList of European mediumwave transmitters
[9] G J Burke and A J Poggio ldquoNumerical electromagneticscode (NEC)-method of momentsrdquo Tech Rep 116 Naval OceanSystems Center San Diego Calif USA 1981
[10] A R Djordjevic M B Bazdar T K Sarkar and R F Har-rington AWAS for Windows Analysis of Wire Antennas andScatterers Software and Userrsquos Manual Artech House BooksBoston Mass USA 1995
[11] V Javor and D Velickovic ldquoComputer package for analysis oflightning electromagnetic field distribution for cage conductorstructuresrdquo in Proceedings of the 26th International Conferenceon Lightning Protection (ICLP rsquo02) Proceedings of Papers pp382ndash387 Cracow Poland September 2002
[12] O P Gandhi and I Chatterjee ldquoRadio-frequency hazards in theVLF to MF bandrdquo Proceedings of the IEEE vol 70 no 12 pp1462ndash1464 1982
[13] W Congjiang L Deming W Shuquan W Baosheng andH Baoge ldquoEnvironmental impact of electromagnetic radiationfrom the 10kWmedium wave transmitter of Weihai Broadcast-ing Stationrdquo Journal of Environmental Sciences vol 7 no 4 pp461ndash467 1995
[14] IEEE C951-2005 IEEE Standard for safety levels with respectto human exposure to radio frequency electromagnetic fields3 kHz to 300GHz IEEE 2005
[15] H C Pocklington ldquoElectrical oscillations in wiresrdquo Proceedingsof the Cambridge Philosophical Society Mathematical and Phys-ical Sciences vol 9 pp 324ndash332 1897
[16] B D Popovic ldquoPolynomial approximation of current along thinsymmetrical cylindrical dipolesrdquoProceedings of the Institution ofElectrical Engineers vol 117 no 5 pp 873ndash878 1970
[17] E Hallen ldquoTheoretical investigations into the transmitting andreceiving qualities of antennasrdquo Nova Acta Regiae SocietatisScientiarum Upsaliensis Ser IV vol 11 no 4 pp 1ndash44 1938
[18] R F Harrington Field Computation by Moment Methodssection 62 Macmillan New York NY USA 1968
[19] I R Bradby Practical Experience in Radio Frequency InducedIgnition RiskAssessment for COMAHDSEARCompliance Sym-posium Series no 154 ABB Engineering Services 2008
[20] X-T Huang ldquoStudy on the influence of induced high-voltagesurge to tower crane by Baise MW broadcasting station and itsprotectionrdquo Journal of Safety Science and Technology no 2 pp146ndash151 2010
[21] H Kanai I Chatterjee and O P Gandhi ldquoHuman bodyimpedance for electromagnetic hazard analysis in the VLFto MF bandrdquo IEEE Transactions on Microwave Theory andTechniques vol 32 no 8 pp 763ndash772 1984
[22] D A Hill and J A Walsh ldquoRadio-frequency current throughthe feet of a grounded humanrdquo IEEE Transactions on Electro-magnetic Compatibility vol 27 no 1 pp 18ndash23 1985
10 International Journal of Antennas and Propagation
[23] I Chatterjee D Wu and O P Gandhi ldquoHuman bodyimpedance and threshold currents for perception and pain forcontact hazard analysis in the VLF-MF bandrdquo IEEE Transac-tions on Biomedical Engineering vol 33 no 5 pp 486ndash4941986
[24] Y Kamimura K Komori M Shoji Y Yamada S Watanabeand Y Yamanaka ldquoHuman body impedance for contact currentmeasurement in Japanrdquo IEICE Transactions on Communica-tions vol 88 no 8 pp 3263ndash3267 2005
[25] V De Santis P A Beeckman D A Lampasi and M FelizianildquoAssessment of human body impedance for safety requirementsagainst contact currents for frequencies up to 110MHzrdquo IEEETransactions on Biomedical Engineering vol 58 no 2 pp 390ndash396 2011
119875119887(119909119887119897119898 119910119887119897119898 119911119887119897119898) is the beginning of the 119897th segment
that is its coordinate system origin recalculated into the119898th segment coordinate system Kirchhoff rsquos current law issatisfied for all the nodes For 119899
119863antenna segments incident
to node119863 Kirchhoff rsquos law is119899119863
sum119903=1
119899119903
sum119904=1
119861119903119904(119911119903
ℎ119903
)119904
= 0 (13)
for unknown complex coefficients119861119903119904and chosen polynomial
degree 119899119903in the approximation of current along the 119903th
segment Coordinate of the beginningend of 119903th segment is119911119903and ℎ119903is the segment length Electric potential is calculated
sdot sin [119896 (119911119898minus 119904)] d119904 minus
119899119885
sum119894=1
119885(119894)119868 (119911119898
(119894))
sdot cos [119896 (119911119898minus 119904)]
(14)
5 Tower Crane and Turn-OverCrane Examples
More complex crane structures are modelled and system of(8) is solved for each example using the presented procedureSome interesting results for tower crane and turn-over crane[1] are obtained For the crane in Figure 14 in far electromag-netic field 119864
120579= 1Vm 119864
120593= 0 for 119891 = 1MHz and different
propagation directions effective current along main towersegment of the height 119897 = 34m is presented in Figure 15 for
1m
46m
23m
22m6m
34m
15m
01m01m
Z
01m
Figure 14 Tower crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
10 20 300Distance along the tower segment l (m)
0
50
100
150
200
250
300
Indu
ced
curr
entI
ef(m
A)
Figure 15 Induced current along the main tower segment of thetower crane
the polynomial degree 119899 = 5 and impedance 119885 = 100Ω Ifthe turn-over crane given in Figure 16 is in the same field theeffective current along boom segment of the height 119897 = 32mis presented in Figure 17
For 119891 = 1MHz the wavelength is 120582 = 300m Theresults for different frequencies are analyzed and it is obtainedthat for the tower crane example the maximum currentsalong the structure and maximum touch voltages at the hookare at 119891 = 7258 kHz and for the turn-over crane are at119891 = 149MHz Eight segments and seven nodes were chosento model the tower crane at perfectly conducting groundwhereas six segments and six nodes were chosen for the turn-over crane
6 Reloading Bridge and Portal-HarborCrane Examples
It is important to consider reloading bridges portal-harborcranes and container cranes as they may be permanently inthe field of MW transmitter a few kilometers from the cranersquos
8 International Journal of Antennas and Propagation
32m
01m05m
91m
01m
5m
1m
12m
16m
03m
Z
Figure 16 Turn-over crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
0
5
10
15
20
25
30
35
Indu
ced
curr
entI
ef(m
A)
5 10 15 20 25 300Distance along the boom segment l (m)
Figure 17 Induced current along the boom segment of the turn-over crane
site Electric fields in such cases are often of the order of Vmdepending on the transmitter power and vicinity Positions ofsuch cranes should be carefully selected based on modelingof the specific problem Induced effects may pose great riskin some cases [19 20]
An example of the reloading bridge with its dimensionsis given in Figure 18 Portal-harbor crane of dimensions verysimilar to the described rail-mounted container crane ispresented in Figure 19 For these cranes positioned in thefar field for 119864
120579= 1Vm 119864
120593= 0 120579 = 1205872 and 120593 =
1205872 touch voltages and induced currents are calculated forthe polynomial degree 119899 = 5 and impedance 119885 = 1000ΩResults are presented in Figures 20 and 21 Induced voltagefor the portal-harbor crane is about 50V for frequency 119891 =621 kHz as measured in Tenerife (Spain) although this is justa simplified model
The impedancewhichmodels a human touching the hookmay be chosen according to the frequency of interest andusing results from [21ndash25]
It may be concluded that the reloading bridge is moresuitable as it has less resonant frequencies smaller values of
32m5m 5m
7m5m
35m38m38m30m
5m5m01m
Z
Figure 18 Reloading bridge model
15m005m
10m
2m
2m
1m1m
2m18m
7m
3m16m
5m
1m
Z
Figure 19 Portal-harbor crane model
induced currents and smaller values of touch voltages exceptin the narrow bandwidth around resonant frequency
7 Conclusion
Currents up to several amperes and touch voltages up to about1 kVmay be induced in large cranes nearbyMW transmittersAt such frequencies these values may result in electricalshock painful burns and dangerous involuntary movementsof workers but also in faults in the automation and controlsystems of cranes Analysis of such problems is presented inthis paper as well as results for induced current and voltagesfor different configurations of crane structures
Current distribution along the crane structure is deter-mined using wire antenna model of the crane and elec-tromagnetic theory approach Currents along segments areapproximated by polynomials System of integral equationsfor the currents is solved using Point matching methodResults are in agreement with measured currents and volt-ages
This approach may be used to analyze specific prob-lems especially before positioning of reloading bridges andcontainer cranes nearby MW transmitters Some practicalsolutions to this problem are also given in the paper
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This paper is in the frame of research within ProjectsHUMANISM III 44004 and TR33008 (2011ndash2015) financed
International Journal of Antennas and Propagation 9
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
0
50
100
150
200
250
300
350
U (V
)
10 15 20 25 30 35 40 45 5005f (MHz)
Figure 20 Induced voltage for reloading bridge and portal-harborcrane versus 119891
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
10 15 20 25 30 35 40 45 5005f (MHz)
0
50
100
150
I (m
A)
Figure 21 Induced current for reloading bridge and portal-harborcrane versus 119891
by Ministry of Education Science and Technological Devel-opment of the Republic of Serbia
References
[1] V Javor ldquoThe calculation and elimination of undesirable elec-tromagnetic field influence on cranesrdquo in Proceedings of the4th International Conference on Telecommunications in ModernSatellite Cable and Broadcasting Services (TELSIKS rsquo99) pp628ndash631 Nis Serbia October 1999
[2] T Denton ldquoRadiofrequency energy poses unseen hazardrdquoOccupational Hazards vol 64 no 12 pp 45ndash47 2002
[3] T Hajime ldquoElectromagnetic disturbance of large-scale cranedue to medium wave broadcasting and countermeasuresrdquoResearchReports ofNational Institute of Industrial Safety 2003
[4] R G Olsen J B Schneider and R A Tell ldquoRadio frequencyburns in the power system workplacerdquo IEEE Transactions onPower Delivery vol 26 no 1 pp 352ndash359 2011
[5] F Ustuner ldquoPractical papers articles and application notesinteraction of an AM broadcast transmitter with a large crane
posing health hazards a real-world event analysisrdquo IEEE Elec-tromagnetic Compatibility Magazine vol 1 no 2 pp 41ndash492012
[6] V Javor andM Saranac ldquoElectromagnetic disturbances in con-ductive structures nearby transmitting antennasrdquo inProceedingsof the 21st International Conference on Software Telecommuni-cations and Computer Networks (SoftCOM rsquo13) pp 1ndash5 IEEEPrimosten Croatia September 2013
[7] M B Perotoni and R M Barreto Resolving Safety-Critical EMIProblems between AMTransmitters and Cranes Using a 3D FieldSolver High Frequency Electronics 2014
[8] httpsenwikipediaorgwikiList of European mediumwave transmitters
[9] G J Burke and A J Poggio ldquoNumerical electromagneticscode (NEC)-method of momentsrdquo Tech Rep 116 Naval OceanSystems Center San Diego Calif USA 1981
[10] A R Djordjevic M B Bazdar T K Sarkar and R F Har-rington AWAS for Windows Analysis of Wire Antennas andScatterers Software and Userrsquos Manual Artech House BooksBoston Mass USA 1995
[11] V Javor and D Velickovic ldquoComputer package for analysis oflightning electromagnetic field distribution for cage conductorstructuresrdquo in Proceedings of the 26th International Conferenceon Lightning Protection (ICLP rsquo02) Proceedings of Papers pp382ndash387 Cracow Poland September 2002
[12] O P Gandhi and I Chatterjee ldquoRadio-frequency hazards in theVLF to MF bandrdquo Proceedings of the IEEE vol 70 no 12 pp1462ndash1464 1982
[13] W Congjiang L Deming W Shuquan W Baosheng andH Baoge ldquoEnvironmental impact of electromagnetic radiationfrom the 10kWmedium wave transmitter of Weihai Broadcast-ing Stationrdquo Journal of Environmental Sciences vol 7 no 4 pp461ndash467 1995
[14] IEEE C951-2005 IEEE Standard for safety levels with respectto human exposure to radio frequency electromagnetic fields3 kHz to 300GHz IEEE 2005
[15] H C Pocklington ldquoElectrical oscillations in wiresrdquo Proceedingsof the Cambridge Philosophical Society Mathematical and Phys-ical Sciences vol 9 pp 324ndash332 1897
[16] B D Popovic ldquoPolynomial approximation of current along thinsymmetrical cylindrical dipolesrdquoProceedings of the Institution ofElectrical Engineers vol 117 no 5 pp 873ndash878 1970
[17] E Hallen ldquoTheoretical investigations into the transmitting andreceiving qualities of antennasrdquo Nova Acta Regiae SocietatisScientiarum Upsaliensis Ser IV vol 11 no 4 pp 1ndash44 1938
[18] R F Harrington Field Computation by Moment Methodssection 62 Macmillan New York NY USA 1968
[19] I R Bradby Practical Experience in Radio Frequency InducedIgnition RiskAssessment for COMAHDSEARCompliance Sym-posium Series no 154 ABB Engineering Services 2008
[20] X-T Huang ldquoStudy on the influence of induced high-voltagesurge to tower crane by Baise MW broadcasting station and itsprotectionrdquo Journal of Safety Science and Technology no 2 pp146ndash151 2010
[21] H Kanai I Chatterjee and O P Gandhi ldquoHuman bodyimpedance for electromagnetic hazard analysis in the VLFto MF bandrdquo IEEE Transactions on Microwave Theory andTechniques vol 32 no 8 pp 763ndash772 1984
[22] D A Hill and J A Walsh ldquoRadio-frequency current throughthe feet of a grounded humanrdquo IEEE Transactions on Electro-magnetic Compatibility vol 27 no 1 pp 18ndash23 1985
10 International Journal of Antennas and Propagation
[23] I Chatterjee D Wu and O P Gandhi ldquoHuman bodyimpedance and threshold currents for perception and pain forcontact hazard analysis in the VLF-MF bandrdquo IEEE Transac-tions on Biomedical Engineering vol 33 no 5 pp 486ndash4941986
[24] Y Kamimura K Komori M Shoji Y Yamada S Watanabeand Y Yamanaka ldquoHuman body impedance for contact currentmeasurement in Japanrdquo IEICE Transactions on Communica-tions vol 88 no 8 pp 3263ndash3267 2005
[25] V De Santis P A Beeckman D A Lampasi and M FelizianildquoAssessment of human body impedance for safety requirementsagainst contact currents for frequencies up to 110MHzrdquo IEEETransactions on Biomedical Engineering vol 58 no 2 pp 390ndash396 2011
8 International Journal of Antennas and Propagation
32m
01m05m
91m
01m
5m
1m
12m
16m
03m
Z
Figure 16 Turn-over crane model
120579 = 1205872
120579 = 1205874
120579 = 0
120593 = 0
120593 = 1205874
120593 = 1205872
0
5
10
15
20
25
30
35
Indu
ced
curr
entI
ef(m
A)
5 10 15 20 25 300Distance along the boom segment l (m)
Figure 17 Induced current along the boom segment of the turn-over crane
site Electric fields in such cases are often of the order of Vmdepending on the transmitter power and vicinity Positions ofsuch cranes should be carefully selected based on modelingof the specific problem Induced effects may pose great riskin some cases [19 20]
An example of the reloading bridge with its dimensionsis given in Figure 18 Portal-harbor crane of dimensions verysimilar to the described rail-mounted container crane ispresented in Figure 19 For these cranes positioned in thefar field for 119864
120579= 1Vm 119864
120593= 0 120579 = 1205872 and 120593 =
1205872 touch voltages and induced currents are calculated forthe polynomial degree 119899 = 5 and impedance 119885 = 1000ΩResults are presented in Figures 20 and 21 Induced voltagefor the portal-harbor crane is about 50V for frequency 119891 =621 kHz as measured in Tenerife (Spain) although this is justa simplified model
The impedancewhichmodels a human touching the hookmay be chosen according to the frequency of interest andusing results from [21ndash25]
It may be concluded that the reloading bridge is moresuitable as it has less resonant frequencies smaller values of
32m5m 5m
7m5m
35m38m38m30m
5m5m01m
Z
Figure 18 Reloading bridge model
15m005m
10m
2m
2m
1m1m
2m18m
7m
3m16m
5m
1m
Z
Figure 19 Portal-harbor crane model
induced currents and smaller values of touch voltages exceptin the narrow bandwidth around resonant frequency
7 Conclusion
Currents up to several amperes and touch voltages up to about1 kVmay be induced in large cranes nearbyMW transmittersAt such frequencies these values may result in electricalshock painful burns and dangerous involuntary movementsof workers but also in faults in the automation and controlsystems of cranes Analysis of such problems is presented inthis paper as well as results for induced current and voltagesfor different configurations of crane structures
Current distribution along the crane structure is deter-mined using wire antenna model of the crane and elec-tromagnetic theory approach Currents along segments areapproximated by polynomials System of integral equationsfor the currents is solved using Point matching methodResults are in agreement with measured currents and volt-ages
This approach may be used to analyze specific prob-lems especially before positioning of reloading bridges andcontainer cranes nearby MW transmitters Some practicalsolutions to this problem are also given in the paper
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This paper is in the frame of research within ProjectsHUMANISM III 44004 and TR33008 (2011ndash2015) financed
International Journal of Antennas and Propagation 9
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
0
50
100
150
200
250
300
350
U (V
)
10 15 20 25 30 35 40 45 5005f (MHz)
Figure 20 Induced voltage for reloading bridge and portal-harborcrane versus 119891
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
10 15 20 25 30 35 40 45 5005f (MHz)
0
50
100
150
I (m
A)
Figure 21 Induced current for reloading bridge and portal-harborcrane versus 119891
by Ministry of Education Science and Technological Devel-opment of the Republic of Serbia
References
[1] V Javor ldquoThe calculation and elimination of undesirable elec-tromagnetic field influence on cranesrdquo in Proceedings of the4th International Conference on Telecommunications in ModernSatellite Cable and Broadcasting Services (TELSIKS rsquo99) pp628ndash631 Nis Serbia October 1999
[2] T Denton ldquoRadiofrequency energy poses unseen hazardrdquoOccupational Hazards vol 64 no 12 pp 45ndash47 2002
[3] T Hajime ldquoElectromagnetic disturbance of large-scale cranedue to medium wave broadcasting and countermeasuresrdquoResearchReports ofNational Institute of Industrial Safety 2003
[4] R G Olsen J B Schneider and R A Tell ldquoRadio frequencyburns in the power system workplacerdquo IEEE Transactions onPower Delivery vol 26 no 1 pp 352ndash359 2011
[5] F Ustuner ldquoPractical papers articles and application notesinteraction of an AM broadcast transmitter with a large crane
posing health hazards a real-world event analysisrdquo IEEE Elec-tromagnetic Compatibility Magazine vol 1 no 2 pp 41ndash492012
[6] V Javor andM Saranac ldquoElectromagnetic disturbances in con-ductive structures nearby transmitting antennasrdquo inProceedingsof the 21st International Conference on Software Telecommuni-cations and Computer Networks (SoftCOM rsquo13) pp 1ndash5 IEEEPrimosten Croatia September 2013
[7] M B Perotoni and R M Barreto Resolving Safety-Critical EMIProblems between AMTransmitters and Cranes Using a 3D FieldSolver High Frequency Electronics 2014
[8] httpsenwikipediaorgwikiList of European mediumwave transmitters
[9] G J Burke and A J Poggio ldquoNumerical electromagneticscode (NEC)-method of momentsrdquo Tech Rep 116 Naval OceanSystems Center San Diego Calif USA 1981
[10] A R Djordjevic M B Bazdar T K Sarkar and R F Har-rington AWAS for Windows Analysis of Wire Antennas andScatterers Software and Userrsquos Manual Artech House BooksBoston Mass USA 1995
[11] V Javor and D Velickovic ldquoComputer package for analysis oflightning electromagnetic field distribution for cage conductorstructuresrdquo in Proceedings of the 26th International Conferenceon Lightning Protection (ICLP rsquo02) Proceedings of Papers pp382ndash387 Cracow Poland September 2002
[12] O P Gandhi and I Chatterjee ldquoRadio-frequency hazards in theVLF to MF bandrdquo Proceedings of the IEEE vol 70 no 12 pp1462ndash1464 1982
[13] W Congjiang L Deming W Shuquan W Baosheng andH Baoge ldquoEnvironmental impact of electromagnetic radiationfrom the 10kWmedium wave transmitter of Weihai Broadcast-ing Stationrdquo Journal of Environmental Sciences vol 7 no 4 pp461ndash467 1995
[14] IEEE C951-2005 IEEE Standard for safety levels with respectto human exposure to radio frequency electromagnetic fields3 kHz to 300GHz IEEE 2005
[15] H C Pocklington ldquoElectrical oscillations in wiresrdquo Proceedingsof the Cambridge Philosophical Society Mathematical and Phys-ical Sciences vol 9 pp 324ndash332 1897
[16] B D Popovic ldquoPolynomial approximation of current along thinsymmetrical cylindrical dipolesrdquoProceedings of the Institution ofElectrical Engineers vol 117 no 5 pp 873ndash878 1970
[17] E Hallen ldquoTheoretical investigations into the transmitting andreceiving qualities of antennasrdquo Nova Acta Regiae SocietatisScientiarum Upsaliensis Ser IV vol 11 no 4 pp 1ndash44 1938
[18] R F Harrington Field Computation by Moment Methodssection 62 Macmillan New York NY USA 1968
[19] I R Bradby Practical Experience in Radio Frequency InducedIgnition RiskAssessment for COMAHDSEARCompliance Sym-posium Series no 154 ABB Engineering Services 2008
[20] X-T Huang ldquoStudy on the influence of induced high-voltagesurge to tower crane by Baise MW broadcasting station and itsprotectionrdquo Journal of Safety Science and Technology no 2 pp146ndash151 2010
[21] H Kanai I Chatterjee and O P Gandhi ldquoHuman bodyimpedance for electromagnetic hazard analysis in the VLFto MF bandrdquo IEEE Transactions on Microwave Theory andTechniques vol 32 no 8 pp 763ndash772 1984
[22] D A Hill and J A Walsh ldquoRadio-frequency current throughthe feet of a grounded humanrdquo IEEE Transactions on Electro-magnetic Compatibility vol 27 no 1 pp 18ndash23 1985
10 International Journal of Antennas and Propagation
[23] I Chatterjee D Wu and O P Gandhi ldquoHuman bodyimpedance and threshold currents for perception and pain forcontact hazard analysis in the VLF-MF bandrdquo IEEE Transac-tions on Biomedical Engineering vol 33 no 5 pp 486ndash4941986
[24] Y Kamimura K Komori M Shoji Y Yamada S Watanabeand Y Yamanaka ldquoHuman body impedance for contact currentmeasurement in Japanrdquo IEICE Transactions on Communica-tions vol 88 no 8 pp 3263ndash3267 2005
[25] V De Santis P A Beeckman D A Lampasi and M FelizianildquoAssessment of human body impedance for safety requirementsagainst contact currents for frequencies up to 110MHzrdquo IEEETransactions on Biomedical Engineering vol 58 no 2 pp 390ndash396 2011
International Journal of Antennas and Propagation 9
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
0
50
100
150
200
250
300
350
U (V
)
10 15 20 25 30 35 40 45 5005f (MHz)
Figure 20 Induced voltage for reloading bridge and portal-harborcrane versus 119891
Reloading bridgePortal-harbor crane
120579 = 1205872 120593 = 1205872
10 15 20 25 30 35 40 45 5005f (MHz)
0
50
100
150
I (m
A)
Figure 21 Induced current for reloading bridge and portal-harborcrane versus 119891
by Ministry of Education Science and Technological Devel-opment of the Republic of Serbia
References
[1] V Javor ldquoThe calculation and elimination of undesirable elec-tromagnetic field influence on cranesrdquo in Proceedings of the4th International Conference on Telecommunications in ModernSatellite Cable and Broadcasting Services (TELSIKS rsquo99) pp628ndash631 Nis Serbia October 1999
[2] T Denton ldquoRadiofrequency energy poses unseen hazardrdquoOccupational Hazards vol 64 no 12 pp 45ndash47 2002
[3] T Hajime ldquoElectromagnetic disturbance of large-scale cranedue to medium wave broadcasting and countermeasuresrdquoResearchReports ofNational Institute of Industrial Safety 2003
[4] R G Olsen J B Schneider and R A Tell ldquoRadio frequencyburns in the power system workplacerdquo IEEE Transactions onPower Delivery vol 26 no 1 pp 352ndash359 2011
[5] F Ustuner ldquoPractical papers articles and application notesinteraction of an AM broadcast transmitter with a large crane
posing health hazards a real-world event analysisrdquo IEEE Elec-tromagnetic Compatibility Magazine vol 1 no 2 pp 41ndash492012
[6] V Javor andM Saranac ldquoElectromagnetic disturbances in con-ductive structures nearby transmitting antennasrdquo inProceedingsof the 21st International Conference on Software Telecommuni-cations and Computer Networks (SoftCOM rsquo13) pp 1ndash5 IEEEPrimosten Croatia September 2013
[7] M B Perotoni and R M Barreto Resolving Safety-Critical EMIProblems between AMTransmitters and Cranes Using a 3D FieldSolver High Frequency Electronics 2014
[8] httpsenwikipediaorgwikiList of European mediumwave transmitters
[9] G J Burke and A J Poggio ldquoNumerical electromagneticscode (NEC)-method of momentsrdquo Tech Rep 116 Naval OceanSystems Center San Diego Calif USA 1981
[10] A R Djordjevic M B Bazdar T K Sarkar and R F Har-rington AWAS for Windows Analysis of Wire Antennas andScatterers Software and Userrsquos Manual Artech House BooksBoston Mass USA 1995
[11] V Javor and D Velickovic ldquoComputer package for analysis oflightning electromagnetic field distribution for cage conductorstructuresrdquo in Proceedings of the 26th International Conferenceon Lightning Protection (ICLP rsquo02) Proceedings of Papers pp382ndash387 Cracow Poland September 2002
[12] O P Gandhi and I Chatterjee ldquoRadio-frequency hazards in theVLF to MF bandrdquo Proceedings of the IEEE vol 70 no 12 pp1462ndash1464 1982
[13] W Congjiang L Deming W Shuquan W Baosheng andH Baoge ldquoEnvironmental impact of electromagnetic radiationfrom the 10kWmedium wave transmitter of Weihai Broadcast-ing Stationrdquo Journal of Environmental Sciences vol 7 no 4 pp461ndash467 1995
[14] IEEE C951-2005 IEEE Standard for safety levels with respectto human exposure to radio frequency electromagnetic fields3 kHz to 300GHz IEEE 2005
[15] H C Pocklington ldquoElectrical oscillations in wiresrdquo Proceedingsof the Cambridge Philosophical Society Mathematical and Phys-ical Sciences vol 9 pp 324ndash332 1897
[16] B D Popovic ldquoPolynomial approximation of current along thinsymmetrical cylindrical dipolesrdquoProceedings of the Institution ofElectrical Engineers vol 117 no 5 pp 873ndash878 1970
[17] E Hallen ldquoTheoretical investigations into the transmitting andreceiving qualities of antennasrdquo Nova Acta Regiae SocietatisScientiarum Upsaliensis Ser IV vol 11 no 4 pp 1ndash44 1938
[18] R F Harrington Field Computation by Moment Methodssection 62 Macmillan New York NY USA 1968
[19] I R Bradby Practical Experience in Radio Frequency InducedIgnition RiskAssessment for COMAHDSEARCompliance Sym-posium Series no 154 ABB Engineering Services 2008
[20] X-T Huang ldquoStudy on the influence of induced high-voltagesurge to tower crane by Baise MW broadcasting station and itsprotectionrdquo Journal of Safety Science and Technology no 2 pp146ndash151 2010
[21] H Kanai I Chatterjee and O P Gandhi ldquoHuman bodyimpedance for electromagnetic hazard analysis in the VLFto MF bandrdquo IEEE Transactions on Microwave Theory andTechniques vol 32 no 8 pp 763ndash772 1984
[22] D A Hill and J A Walsh ldquoRadio-frequency current throughthe feet of a grounded humanrdquo IEEE Transactions on Electro-magnetic Compatibility vol 27 no 1 pp 18ndash23 1985
10 International Journal of Antennas and Propagation
[23] I Chatterjee D Wu and O P Gandhi ldquoHuman bodyimpedance and threshold currents for perception and pain forcontact hazard analysis in the VLF-MF bandrdquo IEEE Transac-tions on Biomedical Engineering vol 33 no 5 pp 486ndash4941986
[24] Y Kamimura K Komori M Shoji Y Yamada S Watanabeand Y Yamanaka ldquoHuman body impedance for contact currentmeasurement in Japanrdquo IEICE Transactions on Communica-tions vol 88 no 8 pp 3263ndash3267 2005
[25] V De Santis P A Beeckman D A Lampasi and M FelizianildquoAssessment of human body impedance for safety requirementsagainst contact currents for frequencies up to 110MHzrdquo IEEETransactions on Biomedical Engineering vol 58 no 2 pp 390ndash396 2011
10 International Journal of Antennas and Propagation
[23] I Chatterjee D Wu and O P Gandhi ldquoHuman bodyimpedance and threshold currents for perception and pain forcontact hazard analysis in the VLF-MF bandrdquo IEEE Transac-tions on Biomedical Engineering vol 33 no 5 pp 486ndash4941986
[24] Y Kamimura K Komori M Shoji Y Yamada S Watanabeand Y Yamanaka ldquoHuman body impedance for contact currentmeasurement in Japanrdquo IEICE Transactions on Communica-tions vol 88 no 8 pp 3263ndash3267 2005
[25] V De Santis P A Beeckman D A Lampasi and M FelizianildquoAssessment of human body impedance for safety requirementsagainst contact currents for frequencies up to 110MHzrdquo IEEETransactions on Biomedical Engineering vol 58 no 2 pp 390ndash396 2011
