The New Zealand harmonic legislationD.A. Bradley, Ph.D., B.Tech., C.Eng., M.I.E.E., P.J. Morfee, B.E., M.E., and

LA. Wilson, B.E., M.E., M.I.P.E.N.Z.

Indexing terms: Power transmission and distribution, Convenors

Abstract: The New Zealand power system, with a number of large rectifier loads and extensive use of audio-frequency power system signalling (ripple control) for load management, presents particular problems to thedesigners of harmonic-control measures. The approach adopted in the Limitation of Harmonic Levels Noticediffers from that adopted in other standards and guidelines in a number of areas, in particular in its adoption ofindividual current and voltage limits for the transmission system, the use of psophometrically weighted limitsfor both current and voltage, the provision of a detailed measurement schedule, and the approach to theequitable sharing of available harmonic capacity. In parallel with the standard, a specially designed monitoringsystem has been developed to gather information on system harmonic behaviour, and to present this informa-tion to a user. A primary role of this equipment will be in the monitoring of power system harmonic conditions,to assess the influence of the legislation in controlling harmonic levels.

List of symbols

E = system phase to phase voltage, kVEDI = equivalent disturbing currentEDV = equivalent disturbing voltageF = 3-phase short-circuit level at point of common

coupling, kVAFt = single-phase short-circuit level, kVAHc = consumer's harmonic allowanceH'c = consumer's discretionary harmonic allowanceImax = maximum standing wave current/„ = harmonic current, AIn\B = consumer's harmonic current allowanceInl = harmonic current limit, AKn = nth harmonic current from a convertor, as a per-

centage of full load currentn = harmonic orderPn = weighting given to frequency 50n in the psopho-

metric weighting tablesS = supply capacity at point of common couplingSc = consumer maximum demand, kVA5L = convertor full load rating, kVAUn = nth harmonic voltage (phase/neutral), as a percent-

age of nominal voltageUnl = harmonic voltage limit (phase/neutral), as a per-

centage of nominal voltageUt = percentage total harmonic distortionVmax = maximum standing wave voltageVnl = harmonic voltage limit, VVnm = measured harmonic voltage, VZn = harmonic impedance of supply system up to point

of common couplingZo = transmission line characteristic impedance

1 Introduction

The increase in levels of power system harmonic contentresulting from the increased use of nonlinear loads, such asconvertors, has led in recent years to the development andadoption of standards, guidelines and regulations, bothnational and international, for the control of harmoniclevels [2-4]. The purpose of these standards is threefold:first, to control the degree of distortion of system harmonic

Paper 3822B (P6/P9), first received 24th August 1984 and in revised form 12th Feb-ruary 1985Dr. Bradley is with the Department of Engineering, University of Lancaster, Bail-rigg, Lancaster LAI 4YR, United Kingdom, Mr. Morfee is with the Mines Division,New Zealand Ministry of Energy, Wellington, New Zealand, and Mr. Wilson iswith the Electricity Division, New Zealand Ministry of Energy, Wellington, NewZealand

current and voltage to a level that the power system cantolerate; secondly, to ensure that consumers are providedwith a supply suitable for their needs, and, finally, toprevent interference with other systems such as telephones.

As there is currently no full understanding of the abilityof a power system to operate in the presence of harmonicdistortion, the formulation of such standards and thesetting of limits is not an easy matter. Local priorities, suchas the use made of power system signalling (ripple control)for load management, will also play a significant role inestablishing the standard.

Thus, although the various standards have a common-ality of approach, they are not identical and indeed couldnot be so, as each represents a compromise for the particu-lar system between the requirement to maintain an undis-torted supply and the ability to use distortion inducingequipment. From this it is clear that no standard is correctin any absolute sense. Furthermore, there exists no evi-dence to suggest that any particular approach to theproblem of the setting of standards has an advantage for aparticular system condition.

New Zealand presents particular problems in the devel-opment of harmonic standards. Although the bulk of theload lies in the North Island, the generation is dominatedby the South Island hydroelectric power stations with theinterisland DC link being used for energy transfer, nor-mally in a northerly direction (Fig. 1). This energy transfersupplies, under normal operation, some 30% of the NorthIsland demand.

In both islands generation tends to be remote from thecentres of load, with resulting long transmission lines withrelatively low fault level. In addition, the South Islandpower system normally operates with in excess of 50% ofthe generated power supplying two large rectifier loads in"the form of the DC link and an aluminium smelter atTiwai Point. These factors, taken together with the exten-sive use made of ripple control for load management,combine to make the system particularly vulnerable toharmonic effects. This was demonstrated on the introduc-tion of the DC link in 1965 when, prior to the commis-sioning of the filters, operation of the link interfered withthe control of the street lighting system in Blenheim, some450 km to the north. The areas around Dunedin andInvercargill similarly experienced problems with ripplecontrol and with communication interference with theadvent of the Tiwai Point smelter. In addition, there havebeen on several occasions failures of capacitors associatedwith tuned stoppers or blocking circuits owing to high har-monic levels.

IEE PROCEEDINGS, Vol. 132, Pt. B, No. 4, JULY 1985 111

Although the large scale effects have, in the main, beencontrolled by filtering, their presence, together with a rapid

..PQlmerston North

0 Haywards

ftnristchurch

unedin

Fig. 1 Map of New Zealand showing the DC linkDC link: 600 M W, 500 k V

total length = 609.2 km(Benmore-Haywards)

growth in the use of solid state controllers, resulted in thedevelopment of the New Zealand harmonic legislation [1]which was gazetted in December 1981 and came into forcein December 1982.

2 The Limitation of Harmonic Levels Notice 1981

This Notice sets limits to the levels of harmonic currentand voltage on the New Zealand public electricity supplynetwork, at all voltage levels down to and including400/230 volts, but specifically excluding signals introducedonto the system for the purpose of load control. TheNotice itself can be considered in three parts. First, thepermitted harmonic levels on systems of 66 kV and above,i.e. the transmission system; secondly, the levels for volt-ages below 66 kV, i.e. the distribution system, and finally aschedule setting out the requirements of measuring systemsto be used to assess compliance with the condition of theNotice.

Furthermore, the Notice is supported by documentsgiving guidance on the application of the Notice, with par-ticular emphasis on the assessment of convertor sizes andthe use of instrumentation.

2.1 Transmission system limitsTable 1 shows the maximum permitted harmonic voltagelevels at any point of common coupling in the transmis-sion system. Along with these limits on the individual har-monic components of voltage, a limit value of 1 % on anyphase is set for a psophometrically weighted component ofvoltage. This component, referred to as the equivalent dis-turbing voltage EDV, is calculated using eqn. 1 and isbased on the psophometric weighting table of the CCITT

Table 1: Transmission system harmonic voltage limits

Harmonic Voltage limit (phase to earth harmonicorder n voltage expressed as a percentage of the

nominal phase to earth system voltage)

3579

11131517 to 2123 to 49

2468 and 10

12 to 50

2.31.41.00.80.70.60.50.40.31.20.60.40.30.2

Table 2: Transmission system, consumer harmonic currentlimits

Harmonic Harmonic current limit, A at nominalorder n system voltage)

220 kV 110 kV 66 kV

3579

1113151719 and 212325 to 492468

1012 and 1416 and 1820 to 50

5.73.42.51.91.61.41.21.00.90.80.72.91.51.00.80.60.50.40.3

Table 3: EDI limits

Nominal system EDI,voltage, kV

66110220

0.81.32.6

2.91.71.31.00.80.70.60.50.50.40.41.50.80.50.40.30.30.20.2

A

1.71.10.80.60.50.40.40.30.30.30.30.90.50.30.30.20.20.20.2

directives concerning the protection of communicationlines from interference from electricity lines [5]

50

EDV = 6.25 x 10 (nPn Uf (1)n = 2

The limits on the harmonic current that may be permittedto flow between any consumer and that consumer's pointof common coupling are given in Table 2. In addition, apsophometrically weighted current, the equivalent dis-turbing current EDI, is specified by eqn. 2 with limits as setout in Table 3.

EDI = 6.25 x 10 - 5SO

n = 2(2)

2.2 Distribution system limitsThe limits for the distribution system are defined in termsof permitted levels of harmonic voltage distortion. Theyare 4% of any odd harmonic, and 2% of any even harmo-nic. Additionally, a limit of 5% is placed on the total har-

178 IEE PROCEEDINGS, Vol. 132, Pt. B, No. 4, JULY 1985

monic distortion (THD) as calculated by eqn. 3:

(3)

2.3 The measurement scheduleThe measurement schedule sets down the followingrequirements for the measuring system, including trans-ducers:

(a) The error in measuring a constant harmonic voltageshall not exceed 0.1% of the nominal phase to earthsystem voltage

(b) the error in measuring a constant harmonic currentshall not exceed 0.2 A

(c) the selectivity of the measuring system shall be suchthat a signal with a 50 Hz separation from that being mea-sured shall have a minimum attenuation of 40 dB

(d) the measuring system shall either have a measure-ment time constant of between 0.08 s and 0.12 s, inclusive,or shall average the input over 4, 5 or 6 cycles of the actualsystem frequency

(e) when a constant harmonic signal in the range 100-2500 Hz is applied to the measuring system, the maximumindication by overshoot shall not exceed the steady stateindication by more than 5%.

3 Background to the Notice

3.1 Transmission system current and voltage limitsThe transmission system limits are based on the estab-lishment of levels of harmonic voltage which are accept-able both in terms of the level of interference and the costof controlling the harmonics. The choice of these levelswas influenced by a number of factors:

(i) the amplitudes of the harmonics produced by themajority of nonlinear loads tend to vary inversely with fre-quency

(ii) the cost of introducing harmonic filtering variesinversely with increasing frequency

(iii) the susceptibility of communication circuits, such astelephone, increases with frequency

(iv) the observed levels of odd and even harmonics.

These all tend to suggest that the levels introducedshould be weighted to allow higher amplitudes for lower asopposed to higher harmonic frequencies.

Such experience with problems of harmonic interferencethat was available tended to suggest that the maximumallowable voltage for harmonics with frequencies between850 Hz and 1150 Hz should be in the range 0.3-0.4% ofthe fundamental or nominal system voltage. As a conse-quence a limit of one third of 1% of the fundamentalvoltage was chosen, at a frequency of 100 Hz. The limitsfor other frequencies were then weighted inversely with fre-quency and an additional factor of one-third applied toeven harmonics. This results in the expressions of eqns. 4and 5 for the levels of odd and even harmonics, expressedas percentages of the fundamental voltage:

Odd harmonics

Un = 20/(3n)%

Even harmonics

Un = 20/(9n)%

(4)

(5)

These equations are used to generate the values of Table 1,with values rounded up to the nearest 0.1%.

Once the harmonic voltage limits had been established,it was necessary to determine the allowable harmonic cur-rents at the point of common coupling, such that theallowable harmonic voltage was not exceeded on thesystem.

Direct connection of a distorting load to a transmissionsystem can give rise to standing waves on transmissionlines, causing amplification of harmonic voltages and cur-rents at remote points. These conditions can arise whentransmission lines are not terminated in their characteristicimpedance, and their length at harmonic frequencies isclose to a quarter wavelength or multiple thereof. Thiscondition has arisen in New Zealand and caused problems.For this reason harmonic current limits were also intro-duced for the transmission system.

If a standing wave condition existed there would be avoltage maximum Vmax and a voltage minimum Vmin

separated by a quarter wavelength. The requirement isthat Vmax for any individual harmonic should not exceedthe allowable harmonic level.

Should a point of common coupling coincide at a parti-cular harmonic frequency with a voltage maximum forthat frequency, then the requirement that the harmonicvoltage should not exceed the limit value at the point ofcommon coupling would be sufficient. If, however, thepoint of common coupling coincides with a voltageminimum, then the current limit must ensure that therelated voltage maximum does not exceed the specifiedlimits.

The current at a voltage minimum, which is a currentmaximum, is defined in terms of the characteristic imped-ance of the transmission line by eqn. 6:

/ — V 17 (6)lmax ~ vmaxl£j0 W

For typical transmission lines at 66 kV and above, thevalue of the characteristic impedance normally lies in therange 300-400 Q.

Limiting the harmonic current at the point of commoncoupling to (harmonic voltage limit)/400 A would nor-mally be sufficient to ensure that the harmonic voltagelimits were not exceeded elsewhere on the network. Thisargument, however, does not take into account the possi-bility that harmonic currents produced by multiple harmo-nic sources could summate at some point in the networkand produce harmonic voltages in excess of the limit. Onthe other hand, in a branching network, the harmonic cur-rents will be dispersed as they propagate through thenetwork, whereas the diversity between the various harmo-nic sources reduces the possibility of direct addition of har-monic currents [6, 7].

Operational experience with the New Zealand transmis-sion system showed that it was appropriate to furtherreduce the harmonic current limits at the point of commoncoupling by a factor of 1.25 to accommodate these effects.This results in the limits for odd and even harmonic cur-rents of eqns. 7 and 8, respectively:

Odd harmonics

* 155Similarly, for even harmonics,

Inl = £/(39n)

= £ / ( 1 3 n )

(8)

Application of these equations produces the current limitsof Table 2.

IEE PROCEEDINGS, Vol. 132, Pt. B, No. 4, JULY 1985 179

3.2 Psophometrically weighted current and voltagelimits

Interference on communications circuits is a function ofthe coupling between the power and communications cir-cuits and the sensitivity of the receiver/human ear com-bination. The psophometrically weighted EDV and EDI ofeqns. 1 and 2 were developed to take account of this possi-bility.

4 Guidelines for the application of the Limitationof Harmonic Levels Notice

Part 2 of the Notice provides guidance on the implementa-tion of the terms of the Notice. It is intended to assistsupply authorities, consumers and manufacturers in assess-ing how the limits apply to their equipment, the resolutionof problems, and the measurement of harmonic levels. Acode of practice for the sharing of responsibility betweenconsumers at a point of common coupling, and rules forestablishing acceptable sizes for convertor installations, areincluded.

4.1 Convertor sizing

4.1.1 Harmonic allowance: The harmonic allowance[1, 8] is intended to provide an equitable means of divid-ing the harmonic capacity of a point of common couplingbetween connected consumers while ensuring that the har-monic limits are not exceeded. This is achieved by allocat-ing a harmonic allowance to each consumer in proportionto their maximum demand. The basic harmonic allowancefor any consumer is defined by eqn. 9:

common coupling. In this case it is appropriate for thisexcess capacity to be distributed amongst consumersaccording to eqn. 10:

H'c =

where

(10)

sc = scl

Hc = SJS (9)

The individual, consumer maximum demands (Sc) can bemeasured by one of the methods established in the NewZealand Electrical Wiring Regulations, 1976.

In some cases the sum of consumer maximum demandswill be less than the supply capacity of the point of

This discretionary allowance may be altered with the con-nection of additional load.

The harmonic allowance is applied to the consumers onboth the transmission and distribution systems, supportedas necessary by harmonic penetration studies.

4.1.2 Convertor sizing: Most of the harmonic distortionin the supply network is caused by convertors of varioustypes. Using a simplified theory an acceptable size for aparticular convertor can be established, in terms of theshort-circuit level at the point of common coupling.

Part 2 of the Notice develops multiplying factors forvarious convertor types, so that an effective size can beestablished for multiconvertor installations.

The assessment of allowable convertor sizes in the dis-tribution system applies the consumers harmonic allow-ance to the maximum effective installation size applicableat his point of common coupling.

The simplified theory is based on the assumption thatthe distribution systems impedance is predominantlyinductive, and hence proportional to frequency, and thatthere are no resonance effects [1, 8]. The relationshipbetween harmonic current and voltage under these condi-tions for a 3-phase convertor is given by eqn. 11:

Un = l00y/3nInE/F (11)

Table 4 indicates the likely level of harmonic currents gen-erated by various types of convertor equipment. These aretaken as being related to the convertor full-load rating byeqn. 12:

(12)

Table 4: Harmonic currents for typical semiconductor convertors expressed aspercentages of full load current K

Order ofharmonic

13579

1113151719212325272931333537394143454749

Effective

2

number of phases

Uncontrolled Controlled

100.030.517.511.0

6.84.53.02.11.51.31.00.80.70.50.40.30.250.20.20.150.150.150.10.10.1

100.033.320.013.510.0

7.76.35.24.53.93.43.02.72.42.22.01.81.41.41.31.21.11.01.00.9

(pulses)

6

Uncontrolled

100.0—

17.511.0

—4.53.0

—1.51.3

—0.80.7

—0.40.3

—0.20.2

—0.150.15

—0.10.1

Controlled

100.0—

20.013.5

—7.76.2

—4.53.9

—3.02.7

—2.22.0

—1.61.4

—1.21.1

—1.00.9

12

Uncontrolled

100.0—

2.01.5

—4.53.0

—0.20.15

—0.80.7

—0.050.05

—0.20.2

————

0.10.1

Controlled

100.0—

3.02.0

— •

7.76.2

—0.30.2

—3.02.7

—0.10.1

—1.61.4

————

1.00.9

180 IEE PROCEEDINGS, Vol. 132, Pt. B, No. 4, JULY 1985

From eqns. 11 and 12 the relationship between harmonicvoltage and converter rating is that of eqn. 13:

then

= nKnSJF (13)

For a 12-pulse uncontrolled converter, the worst case isfor the 11th harmonic when

Utl=49.5SJF

Thus, for Uu to be less than the 4% of fundamentalamplitude, as required by the limits,

SL < 0.08IF

Similar analyses for other converter types gives the resultssummarised in Table 5.

Table 5: Maximum size of 3-phase convenor equipment as apercentage of short-circuit level to ensure individual harmo-nic limit is not exceeded

Convenor type Uncontrolled Controlled

6-pulse12-pulse

4.68.1

4.04.7

In addition to the individual harmonic limits the effectof THD in restricting convertor size must be taken intoaccount. From the definition of THD, and using eqn. 13

o / 50° i lr,..~*2 ( 1 4 )

For a 12-pulse uncontrolled convertor

Ut = 10.1SJF

where, for Ut to be less than the 5% limit

SL < 0.071F

Carrying out the same calculation for other convertortypes leads to the results summarised in Table 6.

Table 6: Maximum size of 3-phase convertor equipment as apercentage of short-circuit level to ensure total harmonicdistortion limit is not exceeded

Convertor type Uncontrolled Controlled

6-pulse12-pulse

3.57.1

1.82.7

There is a similar analysis for a single-phase convertorconnected phase to phase using

(15)

and

(16)

Using Table 4, limiting sizes for 2-pulse controlled anduncontrolled convertors of 0.8% and 1.6% of systemshort-circuit level, respectively, are established.

Similarly, for a single phase convertor connected phaseto neutral,

and

(17)

(16)

Assuming the relationship

n = 3nKnSJF (19)

The limiting sizes for 2-pulse controlled and uncontrolledconvertors, connected phase to neutral, can therefore beexpressed as 0.5% and 0.9%, respectively, of system short-circuit current. Combining the results for phase to phaseand phase to neutral conductors gives Table 7.

Table 7: Maximum size of single-phase convertor equipmentas a percentage of 3-phase short circuit level to ensure THDlimit is not exceeded

Convertor type Uncontrolled Controlled

Phase to phase 1.6 0.8Phase to neutral 0.9 0.5

Some consumers will have a mix of convertor types, andto assess the effective installation size, each convertor isadjusted to an equivalent reference convertor size. The ref-erence convertor for a 3-phase system is chosen to be theequivalent size of a 6-pulse controlled convertor thatwould produce the same THD. This is achieved by usingthe results of Tables 6 and 7 to provide a multiplyingfactor for each convertor type, and these are given in Table8. A similar table for a single-phase installation is given inTable 9.

Table 8: Multiplying factors applicable to convertors inassessing effective installation size at a 3-phase point ofcommon coupling

Type ofconvertor

Uncontrolled(no firing angledelay)Controlled(delayed firingangle)

Singlephase toneutral

2.0

3.7

Singlephase tophase

1.1

2.2

3-phase6-pulse

0.5

1.0

3-phase12-pulse

0.25

0.65

Table 9: Multiplying factors applicable to single-phase con-vertors in assessing effective installation size at a single-phase point of common coupling

Controlled Uncontrolleddelayed (no firingfiring angle) angle delay)

1.0 0.5

The relationship with the harmonic allowance may beillustrated by the following example. A consumer, with amaximum demand of 3000 kVA and connected to a pointof common coupling rated at 10000 kVA, has 400 kVA of6-pulse uncontrolled and 70 kVA of single phase to neutralconvertor equipment installed, and wishes to install afurther 700 kVA of 12-pulse convertor equipment. Theeffective installation size is, using Table 8,

0.5 x 400 + 2.0 x 70 + 0.65 x 700 = 795 kVA

The consumer's harmonic allowance is

(3000 + 700)/10000 = 0.37

If the point of common coupling has a short-circuit level of100 MVA, the maximum allowable effective installationsize is, from Table 6,

0.018 x 1000000 = 1800 kVA

IEE PROCEEDINGS, Vol. 132, Pt. B, No. 4, JULY 1985 181

The particular consumer's share is

0.37 x 1800 = 666 kVA

As this is less than the effective installation size, the con-sumer is required to take appropriate corrective action,such as the provision of filters, to reduce the levels of theharmonics produced by this installation at the systempoint of common coupling.

4.2 Resolution of problemsWhere the consumer's installation size is greater thanwould be permitted by the analysis of Section 4.1, anumber of actions are possible:

(i) the short-circuit kVA at the point of common coup-ling could be increased

(ii) some convertor load could be transferred to anotherpoint of common coupling

(iii) the effective installation size could be reduced byeliminating some convertors, or increasing pulse numbers

(iv) filtering could be introduced to control harmoniclevels. This would require a new effective installation sizeto be calculated, taking into account the effect of the filter-ing.

4.2.1 Parallel resonance conditions: A parallel resonantcondition may occur in a number of ways within thepower system, or between the power system and a con-sumer's equipment.

Fig. 2 illustrates two examples of parallel resonance.

Iss Cs

III I

C Q

t t

point of common coupling

In

C

load harmonicsource(consumer B)

load

Fig. 2 Conditions for parallel resonance

The harmonic current from consumer B sees a high imped-ance at the point of common coupling due to resonancebetween the system inductance Ls and one or both of thesystem capacitance Cs and the power-factor-correctioncapacitance Ca of consumer A.

The particular resonant condition is established frommeasurements of the harmonic currents in each consumer'sconnection and the harmonic voltage at the point ofcommon coupling. If the harmonic currents in each con-sumer's connection and the voltage are high, indicative ofa high harmonic impedance, resonance within the powersystem is indicated. If a large harmonic current flowing ina consumer's connection is associated with a high harmo-nic voltage at the point of common coupling, then reson-ance between the system inductance and the consumer'scapacitance is indicated.

4.2.2 Harmonic current allowance: The harmoniccurrent allowance is used where problems are being causedby the level of system harmonic content to assess whether

the harmonic current produced by an individual consumeris excessive. The harmonic current allowance is based onthe harmonic allowance of Section 4.1.1, and a harmoniccurrent limit corresponding to that level of harmoniccurrent, which, if flowing through the system impedance,would cause the harmonic voltage limit to be reached atthe point of common coupling. This limiting value of har-monic current is given by eqn. 20:

Inl = Vnl/\Zn\ (20)

The harmonic current allowance for a consumer B is thengiven by eqn. 21:

InlB=I HcB (21)

If a consumer is producing harmonic currents in excess ofthis level, then action will be required to reduce these cur-rents to levels which ensure compliance with the harmonicvoltage limits at the point of common coupling. Theamount by which the consumer's harmonic current shouldbe reduced is given approximately by eqn. 22:

Mn = (Vnm- Vnl)/\Zn\ (22)

If the high harmonic voltage is due to a resonance betweenthe system inductance and a consumer's power-factor-correction capacitor, then the current flowing into thisconsumer will exceed the allowance, and the need toreduce the levels by an appropriate amount would beapplied to that consumer.

Where the resonance is between power-system com-ponents, either the consumer producing the high harmoniccurrent would be required to reduce this current, or thesystem could be detuned if circumstances allowed.

4.3 Relaxation of restrain ts

4.3.1 Bursts of harmonic voltages and currents: Devicessuch as a rolling mill may produce a burst of harmonics asa billet hits the rollers. In general, such bursts will be toler-ated provided that the burst duration is less than 2 s, theinterval between the bursts is more than 30 s and there areno more than 10 bursts in a half-hour period. In addition,the harmonics produced by such bursts must not be ofexcessive magnitude, i.e. greater than 4 or 5 times the limit.

4.3.2 Unavailability of harmonic suppressionequipment: Should an unforeseen failure of harmonic sup-pression equipment occur, then the consumer may berequired to take temporary corrective action, such asreducing load at specified times or take co-ordinatedaction with the supply authority. When such equipment isto be taken out of service for maintenance or other pur-poses, this should coincide with periods when theequipment is not needed for harmonic control. When thisis not possible, the consumer should make special arrange-ments with the supply authority.

4.4 Measuring instrumentsA specification for the measuring system to be used toestablish full compliance with the requirements of theNotice is set out in the schedule to the Notice (Section 2.3).The majority of instruments currently in use for harmonicmeasurement are unlikely to meet these requirements in allrespects. These instruments may, however, be used subjectto certain criteria. In particular, in relation to instrumentaccuracy the following criteria are used:

(a) if the instrument reading plus the maximum systemerror in volts (or amperes) is less than the specified limit,

182 IEE PROCEEDINGS, Vol. 132, Pt. B, No. 4, JULY 1985

then the harmonic content may be taken as being belowthis limit

(b) if the instrument reading, less the maximum systemerror in volts (or amperes) is greater than the specifiedlimit, the harmonic content may be taken as being abovethis limit.

Other aspects of harmonic measurements coveredinclude the interpretation of the readings produced by ana-logue instruments whose time constant does not fall withinthe specified limits, and the use of digital instruments sam-pling over differing number of cycles.

5 The MAC-8 measuring system

The MAC-8 measuring system is a New Zealand Elec-tricity designed and built harmonic measurement andanalysis system based on a specially designed mini-computer [9]. It uses fast Fourier transform techniques toperform 20 complete Fourier analyses, each based on fivecycles of the fundamental frequency over the 3-phase cur-rents and voltages, per minute, and is intended to monitorthe system continuously for periods of several weeks.

In its basic form the MAC-8 provides a display of har-monic levels which is updated each minute, generating atotal of 916 items of information every minute, which arethen transferred to a magnetic tape store. These data arethen analysed offline using a mainframe computer toextract the required data by means of an interactiveprogram providing a graphical output [10].

Two MAC-8s are in use by New Zealand Electricity, ina variety of roles ranging from a general monitoring ofsystem harmonic content through enforcement of the legis-lation, to the provision of data for use in the developmentof harmonic penetration studies.

6 Discussion

The New Zealand harmonic legislation as embodied in theLimitation of Harmonic Levels Notice is intended tocontrol harmonic current and voltage levels on both thetransmission and distribution systems. Although the ulti-mate responsibility for the operation of the Notice restswith the Secretary of Energy, responsibility for enforce-ment will be delegated to the Electricity Division of theMinistry of Energy and other electrical supply authorities,with each having responsibility for points of commoncoupling within their own systems. Although the individ-ual supply authorities take supply from, and therefore areconsumers of, the Electricity Division, it is recognised thatthey fulfil what is essentially a distribution role and gener-ally consume little energy themselves. Therefore, whenconsidering the application of limits to electrical supplyauthorities at points of common coupling at 66 kV andabove, the harmonic current limits described in Section 2.1are not applied. The electrical supply authorities do,however, have a responsibility to ensure that the harmonicvoltage limits of the Notice are not exceeded at theirpoints of common coupling.

As yet it is not possible to properly assess the impact ofthe Notice in controlling harmonic levels on the transmis-sion and distribution systems. To provide the necessaryinformation for such an assessment, it is intended to usethe MAC-8 measuring systems to monitor and record har-monic levels at various points on the transmission system,in particular to provide the background informationagainst which changes can be evaluated. Similarly, the

operation of the Notice within the various electrical supplyauthorities and its impact on both the users and suppliersof harmonic generating equipment is to be monitored toassess its effects in these areas. In particular, the nature ofthe corrective measures required, such as the range andtypes of filters employed, and changes to system operatingconditions adopted, should be examined.

It is not possible within the scope of this paper tocompare the New Zealand Limitation of HarmonicsNotice with other similar regulations such as the UK G5/3[3] or the Australian AS2279 [11]. Indeed, the making ofsuch comparisons in other than very broad terms must beapproached with care because, as has already been stated,each standard or regulation has been developed to meetthe needs of a specific electricity supply system. Where theNew Zealand Notice is felt to provide a particularly novelapproach is not, perhaps, so much in the choice and natureof the limits themselves, but in areas such as the mecha-nism for assessing allowable convertor sizes, the concept ofthe harmonic allowance and provision of detailed mea-surement information, where, in each case, a new approachis adopted.

7 Conclusions

The New Zealand Limitation of Harmonic Levels Noticehas been constructed to meet the specific New Zealandrequirements in harmonic control. In doing so it intro-duces a number of features which distinguish it from other,similar standards and guidelines. In the body of the Noticeitself these are:

(a) the provision of specific, individual limits for harmo-nic current and voltage on the transmission system

(b) the use of psophometrically weighted currents andvoltages

(c) the provision of a detailed measurement schedule.

The guidelines to the Notice provide the details on theimplementation of the notice. Here, the introduction of theconcept of the harmonic allowance provides a novel meansfor trying to ensure a fair distribution of harmonic capac-ity. In developing the concept of the harmonic allowancesome consideration was given to the need to introducediversity into the assessment of convertor sizes. Ultimately,it was felt that the diversity generally inherent in the valuesof maximum allowance was satisfactory in this respect.The use of the effective installation size based on thereduction of all convertor types to a basic reference con-vertor also represents a new departure in such standards.On using the appropriate Tables, the effective convertorsize can be rapidly assessed against the consumer's harmo-nic allowance.

These features, taken together with the considerationgiven to factors such as resonance conditions, theresolution of problems and the application and use of ins-trumentation, give significance to the New Zealandapproach to the problem of harmonic control.

8 Acknowledgments

The authors would like to thank the General Manager ofNew Zealand Electricity for permission to publish thispaper. In addition, Dr. Bradley would like to thankmembers of the engineering staff of New Zealand Elec-tricity for the many helpful and interesting discussions onthis subject, in which they were all involved.

IEE PROCEEDINGS, Vol. 132, Pt. B, No. 4, JULY 1985 183

9 References

1 New Zealand Ministry of Energy Limitation of Harmonic LevelsNotice, 1981

2 BAITCH, T.L.: 'The Australian standard to specify network harmo-nics limits: AS 2279—1979', IEEE Trans., 1982, IA-18, (3), pp.260-267

3 'Limits for harmonics in the United Kingdom electricity supplysystem'. Electricity Council Engineering Recommendation G5/3, Sep-tember 1976

4 DROUIN, G.: 'Present and future European harmonic standards'.Presented at conference on harmonics, UMIST Manchester, Septem-ber 1981, pp. 132-140

5 'Directives concerning the protection of communication lines againstharmful effects from transmission lines'. CCITT document, Interna-tional Communication Union, Geneva, 1963

6 SHERMAN, W.G.: 'Summation of harmonics with random phaseangles', Proc. IEE, 1972,119, (11), pp. 1643-1648

7 ROWE, N.B.: 'The summation of randomly-varying phasors orvectors with particular reference to harmonic levels'. IEE Conf. Publ.110, 1974, pp. 177-181

8 BRADLEY, D.A., MORFEE, P.J., SHIPMAN, J.D., and WILSON,L.A.: 'The New Zealand harmonic legislation and its application toconvertor sizing'. IEE Conf. Publ. 234, Power Electronics and Vari-able Speed Drives, 1984, pp. 163-166

9 WILSON, L.A., and MORFEE, P.J.: 'Harmonics beware', NewZealand Engineering, 1978,33, (7), p. 174

10 BRADLEY, D.A.: 'Graphical presentation of harmonic data'. Pre-sented at international conference on harmonics in power systems,Worcester MA, USA, Oct. 1984, pp. 69-72

11 Australian standard AS2279: 1979. Standards Association of Aus-tralia

184 IEE PROCEEDINGS, Vol. 132, Pt. B, No. 4, JULY 1985