ASSESSMENT OF AEOLIAN ASSESSMENT OF AEOLIAN VIBRATION SEVERITYVIBRATION SEVERITYVIBRATION SEVERITYVIBRATION SEVERITY
Umberto CosmaiUmberto CosmaiConvenor CIGRE WG B2.25Convenor CIGRE WG B2.25
Bangkok 28 February 2009Bangkok 28 February 2009
Study Committee B2Technical Advisory Group B2-AG-06
Modern structures slender plain with lowModern structures slender plain with lowModern structures, slender, plain, with low Modern structures, slender, plain, with low internal damping, are very sensitive to windinternal damping, are very sensitive to wind--
induced motionsinduced motionsinduced motions. induced motions.
Study Committee B2 - Technical Advisory Group B2-AG-06
The overhead transmission lines are the mechanical The overhead transmission lines are the mechanical structures with the greatest extension of slender flexible structures with the greatest extension of slender flexible
elements:elements:elements:elements:
the conductorsthe conductors
Study Committee B2 - Technical Advisory Group B2-AG-06
highly exposed to natural windhighly exposed to natural wind
Overhead conductors are subjected to various wind induced Overhead conductors are subjected to various wind induced vibrations and oscillations.vibrations and oscillations.
Th ll d “ li ib ti ” th t t dTh ll d “ li ib ti ” th t t dThose called “aeolian vibrations” are the most recurrent and Those called “aeolian vibrations” are the most recurrent and the most dangerousthe most dangerous
for the fast accumulation of fatigue cycles (vibration frequencies for the fast accumulation of fatigue cycles (vibration frequencies 55÷÷120 Hz)120 Hz)
d hi h b di t t th fitti ld hi h b di t t th fitti l
Study Committee B2 - Technical Advisory Group B2-AG-06
and high bending stress at the fitting clamps.and high bending stress at the fitting clamps.
These motions, if not mitigated within safety limits, can These motions, if not mitigated within safety limits, can determine fatigue failures of the conductor strands, determine fatigue failures of the conductor strands,
damages to other line componentsdamages to other line componentsd bl kd bl k t f th lit f th li
Study Committee B2 - Technical Advisory Group B2-AG-06
and blackand black--out of the lines.out of the lines.
Fatigue failure of a conductor strand due to aeolian vibrationFatigue failure of a conductor strand due to aeolian vibration
Typical fragile shape i.e. without deformation of the material Typical fragile shape i.e. without deformation of the material th f tth f t
Study Committee B2 - Technical Advisory Group B2-AG-06
near the fracture area.near the fracture area.
Fatigue failures can interest several strandsFatigue failures can interest several strands
Study Committee B2 - Technical Advisory Group B2-AG-06
in the outer and inner layer of the conductorin the outer and inner layer of the conductor
Study Committee B2 - Technical Advisory Group B2-AG-06
Fatigue failures develop at points where the motion is Fatigue failures develop at points where the motion is constrained e.g. where the conductor is secured to fittingsconstrained e.g. where the conductor is secured to fittings
Typical location are: suspension clamps, damper and Typical location are: suspension clamps, damper and spacer clamps, etc.spacer clamps, etc.
Study Committee B2 - Technical Advisory Group B2-AG-06
p p ,p p ,
Another damaging effect of conductor vibration is the Another damaging effect of conductor vibration is the loosening of fittings clamps not suitably designed or loosening of fittings clamps not suitably designed or
incorrectly installed. incorrectly installed.
Study Committee B2 - Technical Advisory Group B2-AG-06
The loosening of a spacer damper clamp, for example, The loosening of a spacer damper clamp, for example, determines, determines,
at the beginning, the abrasion of the conductor outer layer due at the beginning, the abrasion of the conductor outer layer due t th l lidi tt th l lidi t
Study Committee B2 - Technical Advisory Group B2-AG-06
to the clamp sliding movements.to the clamp sliding movements.
Increasing the looseness, the strands are broken by the Increasing the looseness, the strands are broken by the hammering of the clamp.hammering of the clamp.
If left unattended this process will lead to theIf left unattended this process will lead to the complete complete
Study Committee B2 - Technical Advisory Group B2-AG-06
conductor failure.conductor failure.
Fittings whose natural vibration frequency fall in the range of Fittings whose natural vibration frequency fall in the range of conductor vibration frequencies may fail for fatigue. conductor vibration frequencies may fail for fatigue.
Ni ht i d iNi ht i d i
Study Committee B2 - Technical Advisory Group B2-AG-06
Night warning deviceNight warning device
Vibration dampers incorrectly dimensioned or wrongly Vibration dampers incorrectly dimensioned or wrongly distributed can fail for fatigue while protecting the conductor.distributed can fail for fatigue while protecting the conductor.
Study Committee B2 - Technical Advisory Group B2-AG-06
Five methods are commonly used for the assessment of Five methods are commonly used for the assessment of vibration severity on overhead transmission line conductors: vibration severity on overhead transmission line conductors:
1.1. Analytical prediction of vibration intensityAnalytical prediction of vibration intensity
2.2. Tests on outdoor experimental spansTests on outdoor experimental spans2. 2. Tests on outdoor experimental spansTests on outdoor experimental spans
3.3. Laboratory tests on short spans Laboratory tests on short spans
44 Vibration measurements on actual linesVibration measurements on actual lines4. 4. Vibration measurements on actual linesVibration measurements on actual lines
5. 5. Conductor inspections on actual linesConductor inspections on actual lines
Each method offers its own contribution to the total picture. Each method offers its own contribution to the total picture. Although they are interAlthough they are inter--related, their limitations and concepts related, their limitations and concepts
are somewhat differentare somewhat different
Study Committee B2 - Technical Advisory Group B2-AG-06
are somewhat different. are somewhat different.
Analytical prediction of vibration intensityAnalytical prediction of vibration intensity
Study Committee B2 - Technical Advisory Group B2-AG-06
The most comprehensive medium to predict the vibration The most comprehensive medium to predict the vibration behaviour of a conductor is the computer simulation behaviour of a conductor is the computer simulation
f d b f ifi tf d b f ifi tperformed by means of specific computer programs.performed by means of specific computer programs.
Others methods based on abacus diagrams andOthers methods based on abacus diagrams andOthers methods based on abacus, diagrams and Others methods based on abacus, diagrams and nomographs can only provide qualitative information. nomographs can only provide qualitative information.
For example, the procedure proposed by CIGRE TF 22.11.04 in For example, the procedure proposed by CIGRE TF 22.11.04 in the brochure titled “Safe Design Tension with Respect to the brochure titled “Safe Design Tension with Respect to
Aeolian Vibration” can usefully determine whether additionalAeolian Vibration” can usefully determine whether additionalAeolian Vibration can usefully determine whether additional Aeolian Vibration can usefully determine whether additional damping (normal or special)damping (normal or special) is required or not but can not is required or not but can not
provide data about the damping system to apply. provide data about the damping system to apply.
Study Committee B2 - Technical Advisory Group B2-AG-06
Computer analysis is mainly used at design stageComputer analysis is mainly used at design stage
to anticipate the vibration behaviour of single and bundledto anticipate the vibration behaviour of single and bundledto anticipate the vibration behaviour of single and bundled to anticipate the vibration behaviour of single and bundled conductorsconductors
d t d fi h th t it bl d id t d fi h th t it bl d iand to define, when necessary, the most suitable damping and to define, when necessary, the most suitable damping system.system.
Calculations are based on the energy balanceCalculations are based on the energy balancebetween the energy introduced by the wind and the between the energy introduced by the wind and the
energy dissipated by the vibrating conductorsenergy dissipated by the vibrating conductorsenergy dissipated by the vibrating conductorsenergy dissipated by the vibrating conductors
with and without and relevant damping units.with and without and relevant damping units.
Study Committee B2 - Technical Advisory Group B2-AG-06
Vibration analysis of a bare conductorVibration analysis of a bare conductor
Analytical model Analytical model Vib. frequencies Vib. frequencies yyof the conductorof the conductor
Model of theModel of the
and wave lengthsand wave lengths
Antinode Antinode Model of the Model of the windwind vibration vibration
amplitudesamplitudes
Analytical model Analytical model of suspension of suspension arrangementarrangement
Max strains at the Max strains at the suspension clampsuspension clamp
Computer Computer analysisanalysis
Study Committee B2 - Technical Advisory Group B2-AG-06
arrangementarrangement
Vibration analysis of a single conductor withVibration analysis of a single conductor withVibration analysis of a single conductor with Vibration analysis of a single conductor with additional dampingadditional damping
Vib f iVib f iAnalytical model of Analytical model of the conductorthe conductor
Vib. frequencies Vib. frequencies and wave lengthsand wave lengths
Vib amplitude ofVib amplitude ofModel of the windModel of the wind
Analytical model ofAnalytical model of
Vib. amplitude of Vib. amplitude of the antinodes and the antinodes and of the dampersof the dampers
Computer Computer Analytical model ofAnalytical model of
Analytical model of Analytical model of the damper(s)the damper(s) Strains at suspen. Strains at suspen.
& damper clamps& damper clampspp
analysisanalysisAnalytical model of Analytical model of
the suspension the suspension clampclamp
Number and Number and positioning of the positioning of the dampersdampers
Study Committee B2 - Technical Advisory Group B2-AG-06
pp
Vibration analysis of a bundled conductorVibration analysis of a bundled conductorVibration analysis of a bundled conductor Vibration analysis of a bundled conductor with spacer damperswith spacer dampers
Vib frequenciesVib frequenciesAnalytical model of Analytical model of
the conductorthe conductor
Vib. frequencies Vib. frequencies and wave lengthsand wave lengths
Model of the windModel of the wind Max and min vib. Max and min vib. Model of the wind Model of the wind for bundlesfor bundles
Analytical modelAnalytical model M iM i
amplitude of the amplitude of the antinodesantinodes
Computer Computer
Analytical model Analytical model and distribution of and distribution of the spacer dampers the spacer dampers
Max strains at Max strains at suspension and suspension and spacer clampsspacer clampspp
analysisanalysisAnalytical model of Analytical model of the suspension the suspension arrangementarrangement
p pp pMax spacer clamp Max spacer clamp amplitude and amplitude and
Study Committee B2 - Technical Advisory Group B2-AG-06
arrangementarrangement arm rotationarm rotation
O td t t t tiO td t t t tiOutdoor test stationsOutdoor test stations
Study Committee B2 - Technical Advisory Group B2-AG-06
Outdoor test stations exposed Outdoor test stations exposed to natural wind have been to natural wind have been built in several Countries built in several Countries
worldworld--widewide
for research and for research and development purposesdevelopment purposes
and for the comparative and for the comparative evaluation of damping evaluation of damping
t d ft d fsystems proposed for systems proposed for important transmission line important transmission line
projects. projects.
Study Committee B2 - Technical Advisory Group B2-AG-06
These stations allow an These stations allow an t i ti ti ft i ti ti faccurate investigation of accurate investigation of
conductor vibrationsconductor vibrations
as they can be fully as they can be fully instrumented withinstrumented withinstrumented with instrumented with
recording and recording and monitoring systems.monitoring systems.
Study Committee B2 - Technical Advisory Group B2-AG-06
The high costs involved in The high costs involved in these test stationsthese test stations
can be afforded only by can be afforded only by Power Authorities and Power Authorities and
Research InstitutesResearch InstitutesResearch InstitutesResearch Institutes
or justified in some major or justified in some major j jj jtransmission line projects. transmission line projects.
Study Committee B2 - Technical Advisory Group B2-AG-06
Laboratory test spansLaboratory test spans
Study Committee B2 - Technical Advisory Group B2-AG-06
Vibration tests on laboratory spans (30Vibration tests on laboratory spans (30÷÷90 m)90 m)C t t t i
Tension clampRigid clamp Conductor
Shaker
Constant tension device
Rigid clampTension clamp
Free span 30÷90mConcrete block Concrete
block
provide data about conductor selfprovide data about conductor self--damping, fatigue damping, fatigue endurance of conductorendurance of conductor--clamp systemsclamp systemsand effectiveness of vibration dampers.and effectiveness of vibration dampers.
Study Committee B2 - Technical Advisory Group B2-AG-06
and effectiveness of vibration dampers.and effectiveness of vibration dampers.
Extremity block of a laboratory test spanExtremity block of a laboratory test span
T iT i TensionTension Ri idRi idTension Tension devicedevice
Tension Tension clampclamp
Rigid Rigid clampclamp
Study Committee B2 - Technical Advisory Group B2-AG-06
accelerometeraccelerometer
conductor clampconductor clampload cellload cell
spring steel bandsspring steel bands
flexibleflexibleflexible flexible connection connection between between
shaker and shaker and conductorconductor
Study Committee B2 - Technical Advisory Group B2-AG-06
InIn--span transducersspan transducersInIn--span transducersspan transducersFor the measurement of vibration levels along the span For the measurement of vibration levels along the span
miniature accelerometers are normally usedminiature accelerometers are normally used
accelerometeraccelerometer
miniature accelerometers are normally used.miniature accelerometers are normally used.
Contactless displacement transducers (laser or eddy Contactless displacement transducers (laser or eddy
Study Committee B2 - Technical Advisory Group B2-AG-06
current based) are also used on very light conductors.current based) are also used on very light conductors.
Test span layout for conductor self-damping measurementsTest span layout for conductor self damping measurements in accordance with IEEE 664 Standard
AccelerometersTest span ShakerTest span
Load cell
Power amplifier
Waveform generatorg
Computer OscilloscopeTransducer amplifiers
DAC interface
amplifiers
Study Committee B2 - Technical Advisory Group B2-AG-06
DAC interface
Effectiveness test on vibration dampers in accordance with IECEffectiveness test on vibration dampers in accordance with IECEffectiveness test on vibration dampers in accordance with IEC Effectiveness test on vibration dampers in accordance with IEC 61897 and IEEE 664 Standards61897 and IEEE 664 Standards
The power dissipated by the conductor plus damper is compared with the The power dissipated by the conductor plus damper is compared with the p p y p p pp p y p p ppower introduced by the windpower introduced by the wind
for a certain number of tunable harmonic vibrations of the span, at constant for a certain number of tunable harmonic vibrations of the span, at constant speed or constant bending strains.speed or constant bending strains.speed or constant bending strains.speed or constant bending strains.
Tension clampRigid clamp C d t
Constant tension device
Rigid clampTension clamp
Strain gauges accelerometers
Rigid clamp ConductorShaker
Rigid clamp
damper load cell
Free span 30÷90mConcrete block Concrete
block
cell
The power dissipated by the conductor plus damper shall be greater thanThe power dissipated by the conductor plus damper shall be greater than
Study Committee B2 - Technical Advisory Group B2-AG-06
The power dissipated by the conductor plus damper shall be greater than The power dissipated by the conductor plus damper shall be greater than power introduced by the wind. power introduced by the wind.
Ch t i ti f th f ti b h i fCh t i ti f th f ti b h i fCharacterization of the fatigue behaviour of a Characterization of the fatigue behaviour of a conductorconductor
Pneumatic tensioning systemDynamometer
Amplitude measuring system
Rubber dampers
Suspension clamp
End clamp
Turnbuckle
Slider
Wire break detectionVibrator
Active length : 7 m2 m 2 m
Turnbuckle
5.5
Laboratory fatigue tests Laboratory fatigue tests y gy gResonant type test Resonant type test
benchesbenches
Study Committee B2 - Technical Advisory Group B2-AG-06
Vibration measurements on existing Vibration measurements on existing OHTLOHTLOHTLOHTL
Study Committee B2 - Technical Advisory Group B2-AG-06
Conductor vibration measurements on actual lines are Conductor vibration measurements on actual lines are usually performed: usually performed:
O liO liOn new linesOn new lines-- as final check of the damping systemas final check of the damping system-- to compare different damping systemsto compare different damping systems
On lines in operationOn lines in operationpp-- for assessment of vibration intensityfor assessment of vibration intensity
to evaluate the conductor residual lifeto evaluate the conductor residual life-- to evaluate the conductor residual lifeto evaluate the conductor residual life-- to investigate the cause of damagesto investigate the cause of damages
Study Committee B2 - Technical Advisory Group B2-AG-06
The direct method to evaluate the conductor vibration severity The direct method to evaluate the conductor vibration severity is the measurement of the conductor bending strain at the is the measurement of the conductor bending strain at the
clamp mouthclamp mouthclamp mouth,clamp mouth,
performed by means of strain gauges glued on the outer performed by means of strain gauges glued on the outer layer strandslayer strandslayer strands. layer strands.
This technique, had been used for a limited period of time but This technique, had been used for a limited period of time but then was abandoned in favour of methods more suitable for then was abandoned in favour of methods more suitable for
fi ld li tifi ld li ti
Study Committee B2 - Technical Advisory Group B2-AG-06
field application.field application.
Aeolian vibration measurement on actual linesAeolian vibration measurement on actual linesperformed by means of specific recordersperformed by means of specific recorders
has been widely used for the last 45 yearshas been widely used for the last 45 years..
Study Committee B2 - Technical Advisory Group B2-AG-06
These vibration measurements are based on the These vibration measurements are based on the bending bending amplitude methodamplitude method proposed by the IEEE paper 31 TP 65proposed by the IEEE paper 31 TP 65--
156 1965156 1965156, 1965 156, 1965
89 mm
Yb
89 mm
The bending amplitude YThe bending amplitude Ybb is the peak to peak vibration is the peak to peak vibration g pg p bb p pp pamplitude measured at 89 mm (3.5 inches) amplitude measured at 89 mm (3.5 inches)
from the last point of contact between the conductor and the from the last point of contact between the conductor and the suspension clampsuspension clamp
Study Committee B2 - Technical Advisory Group B2-AG-06
suspension clamp.suspension clamp.
The bending amplitude is easier to measure than theThe bending amplitude is easier to measure than theThe bending amplitude is easier to measure than the The bending amplitude is easier to measure than the bending strainbending strain
bendingbending amplitude
89 m
bending strain
In a number of cases, the bending amplitude can be converted In a number of cases, the bending amplitude can be converted i t b di t i i th P ff b d S t (P&S)i t b di t i i th P ff b d S t (P&S)into bending strain using the Poffemberger and Swart (P&S) into bending strain using the Poffemberger and Swart (P&S)
formula.formula.In other cases, the conversion factor can be determined by In other cases, the conversion factor can be determined by
f l b t t tf l b t t t
Study Committee B2 - Technical Advisory Group B2-AG-06
means of laboratory tests.means of laboratory tests.
Bending Amplitude RecordersBending Amplitude RecordersBending Amplitude RecordersBending Amplitude Recorders
HILDAOntario Hydro Recorder TVM 90
Scolar
Pavica
IIIRibe LVR
Vibrec 400 Vibrec 500
Study Committee B2 - Technical Advisory Group B2-AG-06
Only Vibrec500 and Pavica are still available on the marketOnly Vibrec500 and Pavica are still available on the market.
Modern aeolian vibration recorders are a microprocessor Modern aeolian vibration recorders are a microprocessor based, battery powered, selfbased, battery powered, self--contained devices. The battery contained devices. The battery
autonomy is 3autonomy is 3--6 months6 monthsautonomy is 3autonomy is 3 6 months.6 months.
Vibration Vibration b at ob at osensorsensor
Temperature probeTemperature probeWind sensorWind sensor
Study Committee B2 - Technical Advisory Group B2-AG-06
VIBREC|500 WT
The most recent version of the vibration recorder Vibrec 500 The most recent version of the vibration recorder Vibrec 500 allows wireless connection with the ground instrumentation.allows wireless connection with the ground instrumentation.
Th t i t d d bTh t i t d d b
Study Committee B2 - Technical Advisory Group B2-AG-06
The autonomy is extended above one year.The autonomy is extended above one year.
VIBREC|500 WIRELESS CONNECTIONVIBREC|500 WIRELESS CONNECTION
SEARCHFOUNDVR500WT
Study Committee B2 - Technical Advisory Group B2-AG-06
The recorder is installed on the suspensionThe recorder is installed on the suspension clamp.
898989 89 mmmm
The vibration sensor is positioned at 89 mm from the last point of The vibration sensor is positioned at 89 mm from the last point of
Study Committee B2 - Technical Advisory Group B2-AG-06
contact between the conductor and the suspension clamp.contact between the conductor and the suspension clamp.
On small conductors and On small conductors and shield wires as well as at shield wires as well as at
damper and spacer damper and spacer clamps vibration recorders clamps vibration recorders
with split sensor can bewith split sensor can bewith split sensor can be with split sensor can be usedused..
Study Committee B2 - Technical Advisory Group B2-AG-06
Another type of vibration recorder is installed on the Another type of vibration recorder is installed on the conductor, with the clamp positioned at 89 mmconductor, with the clamp positioned at 89 mm
89 mm
from the last point of contact between the conductor and from the last point of contact between the conductor and
Study Committee B2 - Technical Advisory Group B2-AG-06
the suspension clamp.the suspension clamp.
The tip of the vibration sensor is positioned at the last point of The tip of the vibration sensor is positioned at the last point of contact between the conductor and the suspension clamp.contact between the conductor and the suspension clamp.
This vibration recorder measures the soThis vibration recorder measures the so--called “inverted called “inverted b di lit d ”b di lit d ”
Study Committee B2 - Technical Advisory Group B2-AG-06
bending amplitude”.bending amplitude”.
Due to its low weight (about 0.6Kg) this recorder can be Due to its low weight (about 0.6Kg) this recorder can be installed along the span near dampers, spacers and other installed along the span near dampers, spacers and other
fitting clamps.fitting clamps.
For small conductors a version with split sensor is also For small conductors a version with split sensor is also
Study Committee B2 - Technical Advisory Group B2-AG-06
ppavailable.available.
I t ti l St d d d d ti f liI t ti l St d d d d ti f liInternational Standards and recommendations for aeolian International Standards and recommendations for aeolian vibration measurements on overhead transmission linesvibration measurements on overhead transmission lines
IEEEIEEE paperpaper 31 TP 6531 TP 65 156 1965156 1965IEEE IEEE paper paper 31 TP 6531 TP 65--156, 1965 156, 1965 Standardization of conductor vibration measurementsStandardization of conductor vibration measurements
CIGRE SC22 WG04 CIGRE SC22 WG04 Recommendations for the evaluation of the lifetime of transmission Recommendations for the evaluation of the lifetime of transmission line conductorsline conductorsELECTRA nELECTRA n°°63, 197963, 1979
CIGRE SC22 WG11 CIGRE SC22 WG11 Guide to vibration measurements on overhead linesGuide to vibration measurements on overhead linesELECTRA nELECTRA n°°163 1995163 1995ELECTRA nELECTRA n 163, 1995163, 1995
IEEE Par P1368 2006IEEE Par P1368 2006Guide for Aeolian Vibration Field Measurements of Overhead Guide for Aeolian Vibration Field Measurements of Overhead
Study Committee B2 - Technical Advisory Group B2-AG-06
Conductors Conductors
Evaluation criteria of conductorEvaluation criteria of conductorEvaluation criteria of conductor Evaluation criteria of conductor
vibration severity vibration severity
Study Committee B2 - Technical Advisory Group B2-AG-06
E l ti it i f th ib ti it fE l ti it i f th ib ti it fEvaluation criteria of the vibration severity for Evaluation criteria of the vibration severity for aluminium based conductorsaluminium based conductors
IEEE 1966IEEE 1966 Criterion of the maximum allowable Criterion of the maximum allowable bending strain.bending strain.
EPRI & IEEE 2006EPRI & IEEE 2006 Criterion of the maximum allowable Criterion of the maximum allowable bending amplitude.bending amplitude.Criterion of the maximum allowableCriterion of the maximum allowable
CIGRECIGRE Criterion of the accumulation of fatigueCriterion of the accumulation of fatigue
Criterion of the maximum allowable Criterion of the maximum allowable bending stress.bending stress.
CIGRE CIGRE Criterion of the accumulation of fatigue Criterion of the accumulation of fatigue (lifetime calculation based on Miner (lifetime calculation based on Miner hypothesis and a “Universal” conductor hypothesis and a “Universal” conductor SS N Curves called Safe Border Line)N Curves called Safe Border Line)
Study Committee B2 - Technical Advisory Group B2-AG-06
SS--N Curves called Safe Border Line).N Curves called Safe Border Line).
Bending stress/strain safety limitsBending stress/strain safety limitsBending stress/strain safety limitsBending stress/strain safety limits
Bending stress/strain values can be derived from the Bending stress/strain values can be derived from the measured bending amplitudes using the Poffemberger andmeasured bending amplitudes using the Poffemberger andmeasured bending amplitudes using the Poffemberger and measured bending amplitudes using the Poffemberger and
Swartz (P&S) formula or through lab tests. Swartz (P&S) formula or through lab tests.
The P&S formula is valid only for solid metal to metal The P&S formula is valid only for solid metal to metal suspension clamps without armour rods.suspension clamps without armour rods.
General reference limits are available for conventional General reference limits are available for conventional aluminium based conductors.aluminium based conductors.
No internationally accepted reference limits are available for No internationally accepted reference limits are available for other conductors and conductor /clamp combinations.other conductors and conductor /clamp combinations.
Study Committee B2 - Technical Advisory Group B2-AG-06
other conductors and conductor /clamp combinations.other conductors and conductor /clamp combinations.
Bending stress/strain endurance limits for aluminium Bending stress/strain endurance limits for aluminium based conductorsbased conductors
IEEE (1966)IEEE (1966) 150150--200 200 µεµε peak to peakpeak to peak
Utilities Technical SpecificationsUtilities Technical Specifications 151500 300300 peak to peakpeak to peak
EPRI EPRI &&
Bending stress Bending strainBending stress Bending strain
Utilities Technical SpecificationsUtilities Technical Specifications 151500--300 300 µεµε peak to peakpeak to peak
& & IEEEIEEE20062006
MultiMulti--layer ACSR 8.5 MPa 247layer ACSR 8.5 MPa 247µεµε peak to peakpeak to peakMultiMulti--layer layer AAAC 5.7 Mpa AAAC 5.7 Mpa 165 165 µεµε peak to peakpeak to peak
A bending stress/stain endurance limit can be derived from The CIGRE A bending stress/stain endurance limit can be derived from The CIGRE Safe Border Line and usually taken at 5x10Safe Border Line and usually taken at 5x108 8 cycles. This value cycles. This value
correspond to a bending stress of 9.09correspond to a bending stress of 9.09 MPa and to a bending strain ofMPa and to a bending strain of
Study Committee B2 - Technical Advisory Group B2-AG-06
correspond to a bending stress of 9.09correspond to a bending stress of 9.09 MPa and to a bending strain of MPa and to a bending strain of 264 264 µεµε peak to peak.peak to peak.
Bending amplitude endurance limits (EPRI)Bending amplitude endurance limits (EPRI)Bending amplitude endurance limits (EPRI)Bending amplitude endurance limits (EPRI)
Available for Available for 74 ACSR conductors (0.2174 ACSR conductors (0.21-- 0.32mm)0.32mm)4 steel conductors (7 strands) (0 964 steel conductors (7 strands) (0 96 --1 67 mm)1 67 mm)4 steel conductors (7 strands) (0.96 4 steel conductors (7 strands) (0.96 --1.67 mm)1.67 mm)2 AAAC conductors (7 strands) (0.40 2 AAAC conductors (7 strands) (0.40 -- 0.59 mm)0.59 mm)
(a general limit of 0.23mm for ACSR conductors is also provided)(a general limit of 0.23mm for ACSR conductors is also provided)
The limits are valid The limits are valid onlyonly for conventional suspension clamps with and for conventional suspension clamps with and without armour rods.without armour rods.
No specific values are available for other conductors and conductor No specific values are available for other conductors and conductor /clamp combinations. These values can be obtained through /clamp combinations. These values can be obtained through
laboratory testslaboratory tests
Study Committee B2 - Technical Advisory Group B2-AG-06
laboratory tests.laboratory tests.
Conductor lifetime estimationConductor lifetime estimation
Miner’s cumulative damage theory for elastic structures Miner’s cumulative damage theory for elastic structures is suggested by CIGRE to evaluate the conductor is suggested by CIGRE to evaluate the conductor
lifetimelifetime. .
Bending stress/strain values, derived from field Bending stress/strain values, derived from field measurements, can be used to define the curve of the measurements, can be used to define the curve of the stresses accumulated by the conductor in one year of stresses accumulated by the conductor in one year of y yy y
service.service.
Study Committee B2 - Technical Advisory Group B2-AG-06
The curve shows for each stress level “The curve shows for each stress level “σσ” the number of ” the number of cycles “n” to be expected in one year.cycles “n” to be expected in one year.
Study Committee B2 - Technical Advisory Group B2-AG-06
The stress curve is compared with a “universal” SThe stress curve is compared with a “universal” S--N curve N curve known as “safe border line” (or with the Sknown as “safe border line” (or with the S--N curve of the N curve of the specific conductor) showing forspecific conductor) showing for each stress level “each stress level “σσ” the” thespecific conductor) showing for specific conductor) showing for each stress level each stress level σσ the the number of cycles “N” that can be endured indefinitely.number of cycles “N” that can be endured indefinitely.
Study Committee B2 - Technical Advisory Group B2-AG-06
The life time, in years, is then calculated as followsThe life time, in years, is then calculated as follows
=1Lifetime
∑=
i
1i
i
NnLifetime
iN
C id i th k bl tt i th d tC id i th k bl tt i th d tConsidering the remarkable scatter in the conductor Considering the remarkable scatter in the conductor fatigue characteristics, conductor life expectancy is fatigue characteristics, conductor life expectancy is
considered to have only qualitative significance.considered to have only qualitative significance.
Study Committee B2 - Technical Advisory Group B2-AG-06
Bending amplitude P&Sor lab tests
Miner’srule
Bending stress/strain
rule
EPRI IEEE CIGRE
Lifetime
E l ti f ib ti it
EPRI limits limits Utility limits
Study Committee B2 - Technical Advisory Group B2-AG-06
Evaluation of vibration severity
Inverted bending amplitude
P&Sor lab tests
Miner’srule
Bending amplitude
Bending stress/strain
Lifetime
EPRI IEEE CIGRElimits
Lifetime
Utility limits
E l ti f ib ti it
EPRI limits limits Utility limits
Study Committee B2 - Technical Advisory Group B2-AG-06
Evaluation of vibration severity
Criteria adopted by the industry for the Criteria adopted by the industry for the evaluation of vibration severity of evaluation of vibration severity of
overhead conductoroverhead conductor
Study Committee B2 - Technical Advisory Group B2-AG-06
C it i f th t f li ib ti itC it i f th t f li ib ti itCriteria for the assessment of aeolian vibration severityCriteria for the assessment of aeolian vibration severityon aluminium based conductors, resulting fromon aluminium based conductors, resulting from
the review of 80 Utility Specificationsthe review of 80 Utility Specifications
Max bending
the review of 80 Utility Specificationsthe review of 80 Utility Specifications
58%
16%
Max bending strain
Max bendingamplitude
6%Lifetime
20%
0% 10% 20% 30% 40% 50% 60% 70%
No requirements
Study Committee B2 - Technical Advisory Group B2-AG-06
Required values of maximum bending strainRequired values of maximum bending strain
60%
Required values of maximum bending strainRequired values of maximum bending strain
50%
60%
51%30%
40%
27%18%10%
20%
*4%
0%150 200 247 300
microstrainmicrostrain peak to peakpeak to peak* * corresponding to 8.5 MPacorresponding to 8.5 MPa
Study Committee B2 - Technical Advisory Group B2-AG-06
p gp g
Criteria for the assessment of aeolian vibrationCriteria for the assessment of aeolian vibrationCriteria for the assessment of aeolian vibration Criteria for the assessment of aeolian vibration severity on steel based shield wires, found in 15 severity on steel based shield wires, found in 15
Utility SpecificationsUtility Specifications
13%Max bendingamplitude
0%
67%
Lifetime
Max bending strain
amplitude
20%
0%
No requirements
Lifetime
0% 10% 20% 30% 40% 50% 60% 70%
Study Committee B2 - Technical Advisory Group B2-AG-06
Required values of maximum bending strain for steelRequired values of maximum bending strain for steelRequired values of maximum bending strain for steel Required values of maximum bending strain for steel based conductors (13 specs reviewed)based conductors (13 specs reviewed)
30%
35%
20%
25%
30%
10%
20%
30%
10%5%
10%
15%
10% 10%
0%
5%
300 400 450 600 1000
i t ii t i k t kk t k
Study Committee B2 - Technical Advisory Group B2-AG-06
microstrainmicrostrain peak to peakpeak to peak
During the survey, it was found that, in the industry, evaluation During the survey, it was found that, in the industry, evaluation criteria of vibration severity are frequently prescribedcriteria of vibration severity are frequently prescribedy q y py q y p
with no consideration of whether the relevant reference limits, with no consideration of whether the relevant reference limits, a ailable in literat rea ailable in literat reavailable in literature,available in literature,
are applicable or not to the specific conductor and/or are applicable or not to the specific conductor and/or d t / l bi tid t / l bi ticonductor/clamp combination.conductor/clamp combination.
CIGRE SC B2 and IEEE WG on Conductor Dynamics are CIGRE SC B2 and IEEE WG on Conductor Dynamics are yycommitted to provide the industry with detailed and committed to provide the industry with detailed and
comprehensive guides on this subject. comprehensive guides on this subject.
Study Committee B2 - Technical Advisory Group B2-AG-06
Subspan oscillation measurementsSubspan oscillation measurements
Study Committee B2 - Technical Advisory Group B2-AG-06
Subspan oscillation has been studied extensively in Subspan oscillation has been studied extensively in p yp ywind tunnels and outdoor test laboratorieswind tunnels and outdoor test laboratories
but to a much lesser extent on actual transmission linesbut to a much lesser extent on actual transmission linesfor lack of suitable instrumentsfor lack of suitable instrumentsfor lack of suitable instruments.for lack of suitable instruments.
Recently, a subspan oscillation recorder has been made Recently, a subspan oscillation recorder has been made available on the marketavailable on the marketavailable on the market.available on the market.
Study Committee B2 - Technical Advisory Group B2-AG-06
The subspan oscillation recorderThe subspan oscillation recorderThe subspan oscillation recorderThe subspan oscillation recorder
consists of a displacement transducer installed between a consists of a displacement transducer installed between a i f d t h i t ll li di f d t h i t ll li dpair of conductors horizontally alignedpair of conductors horizontally aligned
and connected via cable to the recorder body installed on the and connected via cable to the recorder body installed on the tt
Study Committee B2 - Technical Advisory Group B2-AG-06
nearest spacer.nearest spacer.
Layout of the subspan under testLayout of the subspan under test
displacement displacement transducertransducer
spacerspacer spacerspacer
subspansubspansubspansubspan
recorder recorder bodybodyconnecting cableconnecting cable
Study Committee B2 - Technical Advisory Group B2-AG-06
Vibration recorders are Vibration recorders are generally installed duringgenerally installed duringgenerally installed during generally installed during
an outage of the line.an outage of the line.
Study Committee B2 - Technical Advisory Group B2-AG-06
The installation of the recorders The installation of the recorders can be also performed on live can be also performed on live pp
lines using the bare hand lines using the bare hand technique.technique.
Study Committee B2 - Technical Advisory Group B2-AG-06
Conductor inspectionsConductor inspections
Study Committee B2 - Technical Advisory Group B2-AG-06
Some general procedures are available that are suitable, Some general procedures are available that are suitable, to a limited extent, for assessing the occurrence of to a limited extent, for assessing the occurrence of
conductor damages produced by severe wind induced conductor damages produced by severe wind induced vibrations. They are: vibrations. They are:
Visual inspectionVisual inspection
Thermographic inspectionThermographic inspectione og ap c spect oe og ap c spect o
Radiographic inspectionRadiographic inspection
ElectroElectro--magneticmagnetic--acoustic inspectionacoustic inspection
Study Committee B2 - Technical Advisory Group B2-AG-06
Visual inspectionVisual inspectionVisual inspectionVisual inspectionIt is appropriate when there is a specific evidence that It is appropriate when there is a specific evidence that damages or at least severe vibrations have occurreddamages or at least severe vibrations have occurreddamages or at least severe vibrations have occurred.damages or at least severe vibrations have occurred.
For example, black spots on the surface of the conductors For example, black spots on the surface of the conductors i di t ib tii di t ib ti
Study Committee B2 - Technical Advisory Group B2-AG-06
may indicate severe vibrations.may indicate severe vibrations.
However, stand failures in inner layers can not be visually However, stand failures in inner layers can not be visually detected and strand failures inside clamps and or below detected and strand failures inside clamps and or below
armour rods can be overlooked unless these components arearmour rods can be overlooked unless these components arearmour rods can be overlooked unless these components are armour rods can be overlooked unless these components are removed. removed.
Study Committee B2 - Technical Advisory Group B2-AG-06
Thermographic inspectionThermographic inspection
Can be performed from the ground but can only detect Can be performed from the ground but can only detect j i t bl d t t d f ilj i t bl d t t d f il
Study Committee B2 - Technical Advisory Group B2-AG-06
joints problems and not strand failures. joints problems and not strand failures.
Thermographic inspectionThermographic inspection
Tests demonstrated that failures of up to three strands do not Tests demonstrated that failures of up to three strands do not produce appreciable temperature variationsproduce appreciable temperature variations
Study Committee B2 - Technical Advisory Group B2-AG-06
produce appreciable temperature variations.produce appreciable temperature variations.
Radiographic inspectionRadiographic inspectionRadiographic inspectionRadiographic inspection
Can detect strand failures but it is costly complex and not Can detect strand failures but it is costly complex and not completely reliable. Strand failures are sometimes overlooked.completely reliable. Strand failures are sometimes overlooked.
Study Committee B2 - Technical Advisory Group B2-AG-06
Radiographic inspectionRadiographic inspection
Study Committee B2 - Technical Advisory Group B2-AG-06
Can be performed on energized lines also.Can be performed on energized lines also.
Radiographic inspectionRadiographic inspectionRadiographic inspectionRadiographic inspection
Example of strand failure detected by radiographyExample of strand failure detected by radiography
Study Committee B2 - Technical Advisory Group B2-AG-06
Example of strand failure detected by radiographyExample of strand failure detected by radiography
ElectroElectro--magneticmagnetic--acoustic inspectionacoustic inspection
Can be performed on energized lines to detect strand Can be performed on energized lines to detect strand f il d t l t d if il d t l t d i
Study Committee B2 - Technical Advisory Group B2-AG-06
failures and steel strand corrosion.failures and steel strand corrosion.
Thank you for your attention !Thank you for your attention !Thank you for your attention !Thank you for your attention !
Study Committee B2 - Technical Advisory Group B2-AG-06