MANAGINGHARMONICSMANAGINGHARMONICSA guide to EA Engineering Recommendation G5/4

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ScopeThe Guide considers the installation of singleor multiple drive systems, and providesinformation on the manner in whichapplications for connection should be madewith the appropriate utility.

(i)

ForewordThis Guide is a simple authoritativeintroduction to good practice in theapplication of variable speed drives, softstarters and load regulators in compliancewith the requirements of the UnitedKingdom electricity supply utilities.

It is the result of work undertaken byGAMBICA members, interpreting theappropriate documents.

The guide should be read in conjunctionwith the Electricity Association (EA)Engineering Recommendation G5/4, whichwas introduced on the 1st. March 2001. TheRecommendation will be followed by anextensive supporting guide ETR 122.

The documents are published by The Electricity Association, 30 Millbank,London SW1P 4RD.

ContentsFOREWORD (i)

SCOPE (i)

INDEX (iii)

1.0 BASIS 11.1 Why change? 1

2.0 HARMONIC CURRENT & VOLTAGE 2

3.0 DRIVE BASICS 33.0.1 Single Phase 33.0.2 Three Phase 3

3.1 DRIVE TYPES 33.1.1 6 pulse 33.1.2 Multi-pulse 43.1.3 Active Rectification 43.1.4 Filters 4

4.0 SOFT STARTERS & LOAD CONTROLLERS 44.1 Controller Basics 54.1.1 Single Phase 54.1.2 Three Phase 54.2 Controller Types 54.2.1 Motor Controllers 54.2.2 Optimising Motor Controllers 64.2.3 Load Controllers 6

5.0 POINT OF COMMON COUPLING 6

6.0 STAGES 76.1 Stage 1 86.1.1 IN ≤ 16 A 86.1.2 16 A < IN < 75 A 86.1.3 IN > 75 A or Multiple Equipments 9

(iii)

Contents (continued)

6.0 STAGES (continued)6.1.4 Stage 1 Typical Drive Loads 96.1.5 Filtering 116.2 Stage 2 126.2.1 Stage 2 Typical Drive Loads 206.3 Stage 3 156.3.1 General 16

7.0 MEASUREMENTS 16

8.0 RESOLUTION OF PROBLEMS 17

9.0 SUMMARY 189.1 The Equipment Supplier 189.2 The Supply Utility 189.3 The User 189.4 Competence 18

APPENDIX 1 19Request to Connect Non-linear Load and Response from NOC

APPENDIX 2 21Harmonic Prediction

(iv)

The intention of the new EA EngineeringRecommendation G5/4 is to try to ensurethat the levels of harmonics in the PublicElectricity Supply do not constitute aproblem for other users of that supply.

This is a primary function of ElectromagneticCompatibility Management and Regulation.

The principle embodied in G5/4 is to settarget levels for the harmonic currentsimposed on a network, which are intendedto place limits for the overall voltagedistortion in a network at planning levelswhich are applied to achieve compatibility.

G5/4 identifies consumers by their point ofcommon coupling (PCC) to the supply, andapplies its limits at that point.

G5/4 therefore applies to every consumerconnected to the Public Electricity Supply,including:

Domestic Commercial, shop and office consumers Industrial users.

It is the consumer’s responsibility to ensurethat the appropriate procedures to agreeconnection of new loads are followed.

It is also very important that consumersunderstand the responsibilities placed onthem by the supply utilities to avoid thepossibility of having to implement costlyremedial measures in the event of a problem.

1.1 Why change?

EA Engineering Recommendation G5/4replaces G5/3, which was in place since 1976,and has seen a vast expansion of thenumbers of rectifiers used both industrially, interms of drives and controls, rail tractionsupplies, in the office environment within ITand in domestic appliances.

There has been a tendency for distortionlevels, especially the 5th harmonic, toincrease, although it is generally consideredthat consumer equipment is the main sourceof this distortion.

G5/4 also introduces areas new to regulationin the UK, including sub-harmonics,interharmonics, and voltage notching.

From the point of view of the user, amodern, well designed drive system will notnormally produce significant levels ofinterharmonics or cause notching outside ofthe permitted levels and they are thereforenot considered in further detail in this guide.

In the United Kingdom, it is possible topurchase electricity from one company, thePublic Electricity Supplier (PES), and to haveit delivered by another company, theNetwork Operating Company (NOC). It isthe NOC who must agree connection ofharmonic producing loads.

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1.0 Basis

The harmonic levels within an individualconsumer’s network are not covered by thisguide, and must be judged solely by theinfluence they will have at the point ofcommon coupling, and the ability of otherequipment on the network to operatesatisfactorily.

Typically the voltage distortion limits of BSEN 50160 Table 1 should be acceptablewithin a single user's site. This would permitup to 8% total harmonic voltage distortion,including up to 6% of 5th. harmonic.

Any rectifier will generate harmonic currentson a network, although they will vary inmagnitude according to the design of thespecific circuit. It is important that allestimates, calculations, and limits assume abalanced voltage supply. Even a small

imbalance can cause large changes in drawncurrent, particularly with uncontrolled bridgerectifiers, and the harmonic performance ofthe drive equipment will deteriorate in suchconditions. Discussion with the NOC mustemphasis this unbalanced situation whichcould affect meeting predicted harmonicvalues.

Rectifiers are incorporated in the majority ofdomestic and office machines, ranging fromTVs, through computers and washingmachines to cordless telephones, as well asindustrial PLCs and drive systems.

All supply systems also have ‘natural’harmonics, introduced by the generators andtransformers, and may also have resonantfrequencies caused by a combination of thecapacitances and inductances of the system.

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It is the harmonic voltage at a given point inthe supply network that determines the riskof disturbance to the load at that point.

The part of that voltage which results fromthe harmonic producing load, is caused bythe voltage drop from the supply impedance,due to the individual harmonic currentsgenerated by the load.

Generally the harmonic currents generatedby a load are controlled by its circuit design,and these can be predicted with a reasonabledegree of confidence by its manufacturer.

They will be affected to some extent by thesupply impedance, especially for small drives,which often use little or no inductance in thed.c. link.

The supply impedance is primarily a functionof the electricity distribution network, andcan normally be predicted by the networkoperator for the fundamental.

There are three levels of supply impedancewhich are of importance:

The minimum level, which would allow the highest possible fault current to flow

The normal running level The maximum level, which would allow

the highest possible harmonic voltages to appear.

The minimum value is needed to enable thedesign of switch and control gear to beevaluated to withstand a potential faultoccurrence. This level is frequently

2.0 Harmonic Current & Voltage

misquoted to correspond only to thestandard capabilities of switch and controlgear, but the correct values are needed topredict the maximum harmonic currents.

The other values represent the normalrunning range, which are needed to predictthe harmonic distortion.

In practice, the system impedance will varyover the course of the day, and the networkoperator must predict the most appropriatefigure as a basis for calculation.

While the system impedance or fault levelcan be predicted for the fundamentalfrequency, it is also probable that theimpedance will vary relative to the frequency.

This variation can become a source ofresonance at some point within thedistribution network.

It is very important to try and identifypotential sources of resonance, such aspower factor correction and long MV supplycables, to ensure that these can be includedin calculation models.

The method of representing the systemimpedance is often by the maximum power that can flow in a fault condition, thisis the system fault level, and is usually quotedin MVA.

The higher the fault level the lower thesource impedance.

The G5/4 document uses fault level as themeasure of source impedance for Stage 1 &2 assessments.

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3.0 Drive BasicsMost variable frequency drives operate byusing a bridge rectifier to convert theincoming AC voltage into a DC voltage. Theinverter of the drive then converts the DCvoltage into a controlled voltage andfrequency for speed control of the motor.

There are a multiplicity of drive topologies,the following gives a brief outline of some ofthe more commonly encountered types:

3.0.1 Single PhaseA typical single phase input frequencyconverter will be provided with a 4-diode fullwave rectifier, feeding an uncontrolled d.c.link, with capacitor energy storage.

This should generate no even harmoniccurrents but with odd harmonics from 3rdupwards, the magnitude depending oninternal impedances.

3.0.2 Three PhaseThree phase supplies will normally be used forindustrial power solutions, and will use at leastsix semiconductors connected in a bridge.

3.1 Drive Types

3.1.1 6 pulseA typical voltage source a.c. drive fitted witha 6-diode full wave rectifier, feeding anuncontrolled d.c. link, with capacitor energy

For the purposes of G5/4, semiconductormotor controllers (soft starters) and loadcontrollers, which comply with EN 60947-4-2and EN 60947-4-3, can be considered as a.c.regulators and the limits for these devicesgiven in G5/4 will apply.

Motor and load controllers rated at morethan 16A will have to be considered under

the same stages of assessment as for drives.Motor and load controllers rated at less than16A that comply with the requirements ofEN61000-3-2 are exempt from assessmentand can be used without restriction.However, devices rated at less than 16A thatdo not comply with EN61000-3-2 will beclassified as professional equipment and willneed to be assessed as for controllers rated

storage, will generate no even harmonics, notriplen (multiples of 3rd) harmonics, only oddharmonics from the 5th upwards. Again themagnitude will depend on the internalimpedances of the system.

Typical d.c. drives (and some 4 quadrant a.c.drives) use a full wave thyristor rectifier.These will generate no even or triplenharmonics, only odd harmonics from 5thupwards, the magnitude again depending oninternal impedances.

3.1.2 Multi-pulse12, (or 18 or 24) pulse full wave rectifier, withphase shifted supplies.

Multi-pulse rectifiers generate no even ortriplen harmonics, only odd harmonics fromthe (n – 1) (where n is the pulse number)upwards, the magnitude depends on internalimpedances.

3.1.3 Active RectificationMost active rectifiers are based on aninverter working in reverse, with enhancedd.c. link voltage. Sometimes known asharmonicless rectifiers, regenerative rectifiersor unity power factor rectifiers.

Small amplitude residual low frequencyharmonics and inter-harmonics will occur.

In all cases, some residual even and lowerorder odd harmonics may occur due tosupply imbalances, and manufacturingtolerances in the individual components used.These are difficult to predict, and aregenerally so small as to be insignificant.

Different manufacturers may also applydifferent terminology to the different types ofrectification described.

3.1.4 FiltersIn addition to connecting rectifiers to anetwork, it is possible to fit filters, and theapplication of active and passive harmonicfiltering as an independent means ofattenuation or as part of a power factorcorrection scheme may provide a cost-effective solution to meeting the planninglevels.

The addition of filters can change the systemnetwork characteristics, and thereforerequires a great deal of care.

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4.0 Soft starters and Load controllers

greater than 16A. In practice, non-optimisingmotor controllers rated less than 16A willprobably comply with EN61000-3-2, whereasload controllers rated up to 16A, andoptimising motor controllers rated at morethan 5A are unlikely to meet the harmonicemissions requirements of EN61000-3-2 andwill require assessment.

4.1 Controller BasicsThere are a number of controller topologies,but all employ self-commutatingsemiconductor switches, either as a singleelement or, more usually, as an anti-parallelpair inserted in each phase connection to thecontrolled motor or load.

Controllers having switches controlling eachhalf-wave of the power wave are said to befully-controlled, whereas those controllingonly one half-wave of the power wave with asingle switch element paralleled by anuncontrolled diode for the other half-wave inthe phase connections are known as halfcontrolled types.

Because they do not produce evenharmonics, fully-controlled versions will havea less severe harmonic spectrum than theirhalf-controlled variants. A brief outline ofsome of the more commonly encounteredtypes is given:

4.1.1 Single PhaseA typical fully-controlled single-phase inputcontroller will be provided with a singlesemiconductor switch in the line connectionto a single-phase load.

This should generate no even harmoniccurrents; only with odd harmonics from 3rdupwards, the magnitude depending oninternal impedances.

4.1.2 Three PhaseThree phase supplies will normally be used forindustrial power applications and will usesemiconductor switches either in two or threephases. Optimising motor controllers, whichuse phase control techniques to reduce thevoltage supplied to a running motor, willalways employ full control to all three phases.

A typical three-phase, fully controlled, a.c.semiconductor motor or load controller, fittedwith a 6-pulse thyristor bridge will notgenerate even or triplen (multiples of 3rd)harmonics, but only odd harmonics from the5th upwards. Again the magnitude will dependon the internal impedances of the system.

In all cases, some residual even and lower-order odd harmonics may occur due tosupply imbalances and manufacturingtolerances in the individual components used.These are difficult to predict, but aregenerally so small as to be insignificant.

4.2 Controller Types

4.2.1 Motor ControllersBecause motor starting currents aremeasured in multiples of motor full-loadcurrent, the harmonic effects of motorcontrollers are at their greatest during themotor starting and accelerating phase.However, provided the controller ramp-timeis set at three seconds or less, the effects canbe ignored. When longer ramp-times arenecessary due to higher inertia loads, orwhere motors with larger inertia rotors areinvolved, G5/4 accepts the use of softstarting ‘infrequently’ on a ‘conditional’ basis.With this concession, most soft starterinstallations will not need specialconsiderations. However, if a challenge arises,consumers will need specific information

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The implementation of G5/4 depends ondefining the ‘point of common coupling’.

This is not necessarily the voltage level atwhich the equipment is connected.

regarding the levels and harmonic spectrumof the type of controller being used.

4.2.2 Optimising MotorControllers Optimising motor controllers will introduceodd harmonics (5th and higher) while theoptimising function is active during normalrunning. However, the harmonic effects aregreatest at the lightest loads of the motor,and since the harmonic currents are relatedto a line current which is significantly lessthan the motor full-load current (typically35% or lower), the effects at the PCC will beminimal except in unusual circumstances.

4.2.3 Load ControllersLoad controllers are used to regulate theenergy supplied to a wide variety of non-motor loads, ranging from control of resistiveloads such as lighting arrays, furnaces, etc tonon-resistive loads such as capacitor banks.The harmonic effects of load controllers arepresent all the while the load is beingcontrolled and depend on the degree andnature of the control. Broadly speaking, thereare two types of control method:

1. ‘Burst firing’ where energy is supplied to theload in a sequence of very short periods ofa variable number of full cycles and,

2. ‘Phase control’, where energy is passedcontinuously to the load throughsemiconductor switches with variable delaysapplied to the turn-on of the devices.

Burst firing is most frequently used for theregulation of resistive loads such as furnaces,and usually involves firing the semiconductordevices at the corresponding voltage zerocrossings of the supply. In this type ofcontroller, the harmonic effects are relativelybenign however, flicker and voltage dropeffects can be significant.

Where phase controlled controllers areemployed, the harmonic spectrum is directlyrelated to the firing angle of thesemiconductor switches in the main circuits.Fully-controlled systems will only generateodd harmonics. If there is no neutralconnection, there will be no triplenharmonics with only the 5th and higherharmonics being of concern. Before anyassessment of the distortion effects of thistype of controller can be made, detailedknowledge of the application and theanticipated range of control are required.

Half-controlled systems have a wider harmonicspectrum and will include even harmonics. Forthis reason, half-controlled systems are usuallylimited to low-power applications. Providedthe application will allow the harmonics to berestricted to the requirements of IEC 61000-3-2, they can be installed without reference tothe supply authority. If this is not the case,then detailed knowledge of the applicationand the anticipated range of control arerequired before the processes outlined inG5/4 can be applied.

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5.0 Point of Common Coupling

The Point of Common Coupling (PCC) isthe point at which a consumer is connectedto other consumers on the Public ElectricitySupply.

Generally in the United Kingdom, consumerswith connected loads of less than around 15 kVA will normally be connected at 230 V single phase and up to 300 kVA at 400 V.

Consumers, with higher power demands, willnormally be connected to the mediumvoltage network by a dedicated transformer,

in which case this medium voltage level willbe their point of common coupling, e.g. if asite is fed by a dedicated distributiontransformer with nominal ratio 11 kV/420 Vand no other consumers are fed by the 400 V system, then the PCC is at 11 kV.

The NOC will apply G5/4 at the point ofcommon coupling (PCC).

The levels of harmonic current and voltage atintermediate points in a consumer’s ownnetwork are solely at the discretion of theconsumer.

G5/4 defines three stages of assessment,which increase in complexity.

It is important to note that these stages donot correspond totally to those in theprevious document,The ElectricityAssociation Engineering RecommendationG5/3, or to those in the various EN and IECstandards.

In addition, while the Planning Levels forvoltage distortion have remained the samefor low1 and medium voltage, and have evenincreased at high voltage, the limits for somespecific harmonic currents have reducedsubstantially, especially for the 5th harmonic.

Where a user wishes to install newequipment to extend an existing installation,and where agreement to connect has alreadybeen established under previous rules, it ispossible that the connection of additional

equipment could involve a new and lowerlimit being applied to the whole installationunder the terms of a new agreement.

This would be retrospective, and thereforedifficult to enforce.

In these circumstances agreement to connectwithout increase in the aggregate harmoniccurrent loading should be forthcoming,although the overall connection may be for ahigher power.

Where a user wishes to replace existingequipment with new equipment of similarfunctionality, there should be no need torepeat the application procedure, ifdocumentary evidence exists that the levelsof harmonic currents generated by the newequipment do not exceed the existing levels.

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6.0 Stages

1Low voltage Un <1000 V, medium voltage 1000 < Un <35000 V, high voltage 35000< Un

6.1 Stage 1

Under G5/4 Stage 1, only connections to 230 V single phase and 400 V three phasesupplies are considered.

G5/4 assumes that there will be no morethan four harmonic producers connected toa single supply source (distributiontransformer) when considering Stage 1connections. The ‘available’ levels of harmonic current per point of connectionhave been split in accordance with thisassumption.

6.1.1 IN <– 16 A2

Under the EMC Directive, any equipment withnominal current less than or equal to 16 A RMS(per phase), and which meets HarmonisedEuropean Standard EN 61000-3-2, will carry a‘CE mark’ to this directive and may beconnected without further assessment.3

Where a number of items of equipment areinstalled, the aggregate of the rated currentsmust be less than or equal to 16 A, and eachindividual piece of equipment must alsocomply with EN 61000-3-2.4

Basically, this standard covers domesticequipment such as televisions, washingmachines, etc. and it is also these deviceswhich are responsible for the bulk ofharmonic voltage distortion throughout thenetwork.

Under this standard, drives are considered tobe professional equipment, and with a ratedinput over 1 kW they are at presentaccepted with no limits under this standard.

If the equipment is a conventional inverterload, and the combined total rating is

under 5 kVA for a single-phase supply, it mayagain be connected without furtherassessment.5

6.1.2 16 A < IN < 75 AFor three phase supplies, a maximum total of 12 kVA of standard 6-pulse diode rectifierloads can be connected without furtherassessment.6

Any single piece of equipment between 16 A and 75 A nominal current which meets Stages 1 or 2 of Technical Report IEC 61000-3-4 (which will be replaced in due course by the standard IEC 61000-3-12)can be connected without further assessment.7

This standard allows a single 6-pulse dioderectifier frequency converter with a.c. or d.c.chokes rated at up to 1/350 of the fault level,to be connected without further assessment.(As G5/4 assumes a fault level of 10 MVA ona 400 V network, this will permit a drive upto approximately 30 kVA).8

The procedures detailed refer to a singleconsumer having single items of harmonicgenerating equipment installed to a singlepoint of common coupling.

2 IN = Rated current drawn3 G5/4 Clause 6.24 EN 61000-3-2 A14 20005 G5/4 Clause 6.3.1.16 G5/4 Table 67 G5/4 Clause 6.38 IEC 61000-3-4 Table 3, based on10 MVA Fault Level

6.1.3 IN > 75 A or MultipleEquipmentsThe sum of the harmonic currents generatedby all the equipment connected to a single

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point of common coupling can be calculatedand checked to be below G5/4 Table 7.

This restricts the total amount of equipmentthat can be installed by a single consumerunder the Stage 1 procedure, and includesmultiple equipments meeting the harmonisedstandard EN 61000- 3-2.

One possible problem area in this procedureis where the standing voltage distortion levelis already close to or above the planning level (5%).

In this case, the Network Operator reservesthe right to examine any additional loadunder the Stage 2 procedure.

If a Table 7 assessment needs to be made,the drive supplier will normally provide theappropriate data for individual drives

It must also be remembered that G5/4 Table7 is based on a system fault level of 10 MVAat 400 V.

This is fairly typical for an urban supplysystem. However, this must be confirmed bythe supply utility.

If the fault level varies from this base levelthe figures in Table 7 may be varied pro-rata,as will the powers that can be connected.

It is the responsibility of the supply utility toadvise the effective peak, normal running andminimum running fault levels.

This information also has implications to the electrical safety of the consumer’sequipment.

6.1.4 Stage 1Typical Drive LoadsWhen the levels of harmonics generated bydifferent types of drive rectifiers areconsidered, at the base fault level for thesystem, we may expect to be able toconnect the following powers:

6 pulse diode –30 kW limited by the 5th harmonic

12 pulse diode – 300 kW limited by the 23rd harmonic

Active Rectifier – possibly up to 500 kW.

To calculate the resulting level, the arithmeticsum of all the harmonics for a number ofdrives is taken. A typical calculation exampleis shown in Figure 1.

In practice, there will be a co-incidencefactor, depending on the relative loading andmethod of connection of each specificrectifier, giving a small safety margin in thecalculation.

This co-incidence factor may need to bemore carefully considered as phase shiftingand consequent summation or subtractioncan occur between industrial and domesticloads.

With an uncontrolled rectifier, the 5th, 11th,and 17th (6n – 1) harmonics, on a threephase system, will always be in phase, whilstthe 7th, 13th, and (6n + 1) harmonics willvary in phase with the relative loading of therectifier. In addition, the harmonics generatedon a single-phase (phase/neutral) networkwill also be phase displaced to the harmonicsgenerated by a three phase (phase/phase)system.

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Guidance to harmonic co-incidence factorswas given in G5/3 Table A3, however, G5/4now refers to IEC 61000-3-6.

Practical experience suggests for a number ofunequally loaded uncontrolled (diode)rectifiers, the (6n – 1) harmonics will alwaysbe in phase and currents should be summed arithmetically.

The (6n + 1) harmonics, however, will vary inphase and current cancellation will allow areduction from the arithmetic sum by afactor of up to 10%.

Application Example of Table 7Figure 1 shows the summation of harmonics, without the use of co-incidencefactors.

While it is possible to calculate values toseveral decimal places, in practice it isimpossible to measure even small systems to

better than one decimal place.This should beconsidered when calculating the margin.

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DomesticLoad

Drive 1 Drive 2 Drive 3 SumG5/4

Margin(Lighting, Table 7PCs. Etc)

Rating (kVA) 11 80 260Motor Power

(kW)7.5 55 200

Rectifier Type 6 p diode 12 p diode ActiveCurrent (A) (A) (A) (A) (A) (A)

HarmonicFundamental 12.4 12.0 83.6 299 407 N/A

I3 11.0 Negligible Negligible 0.15 11.15 48.1 37.0I5 8.0 4.8 2.0 1.53 16.33 28.9 12.6I7 4.8 1.73 1.03 1.34 8.9 41.2 32.2I9 2.2 Negligible Negligible 0.28 2.48 9.6 7.1I11 1.0 0.54 5.2 1.3 8.04 39.4 31.4I13 0.9 0.17 3.76 0.75 5.58 27.8 22.2I17 0.8 0.28 0.19 0.8 2.07 13.6 11.5I19 0.5 0.24 0.14 0.26 1.14 9.1 8.0I23 0.4 0.17 0.83 0.81 2.21 7.5 5.3I25 0.3 0.28 0.72 0.9 2.2 4.0 1.8I29 0.2 0.1 0.06 1.75 2.11 3.1 0.9I31 0.2 0.09 0.06 0.64 0.99 2.8 1.8I35 0.1 0.08 0.44 1.13 1.75 2.3 0.55I37 0.1 Negligible 0.38 1.32 1.7 2.1 0.4I41 0.08 Negligible Negligible 0.92 1.0 1.8 0.8I47 0.07 Negligible Negligible 0.27 0.34 1.4 1.1I49 0.09 Negligible 0.22 0.63 0.94 1.3 0.4

Figure 1. Example of Table 7 Calculation

For even harmonics and triplens, due tothree phase loads, the values will normally benegligible and need not be recorded.

The 3rd harmonic and other triplens willoccur on most three phase networks due tovoltage imbalance and phase sequenceeffects of the supply system at the rectifierterminals. These cannot be readily quantifiedby calculation. In addition, single phase loadsmay result in some triplen contribution.

G5/4 permits any two harmonics between6th and 19th to exceed the limit by 10% or0.5 A, whichever is the greater.

G5/4 also permits any four harmonics abovethe 19th to exceed the limit by 10% or 0.1 A, whichever is the greater.

In each case, the uncertainty of themeasurement may well be greater than thesevalues.

Beyond the 25th harmonic, the values areonly indicative until 2005, when they willbecome limits, unless experience shows themto be unrealistic.

These values are normally extremely low.The currents are also significantly attenuatedby the distribution system, and do notnormally cause problems with the exceptionof a possibility of interference with olderanalogue telephone installations.

The example in Figure 1, which consists ofover 250 kW of converter fed motor loads,meets the current limits for each harmonicand should therefore be acceptable forconnection at Stage 1.

The chart, which is based on a simplespreadsheet model, provides a ready meansof presenting the appropriate data.

6.1.5 FilteringIf alternative means of harmonic attenuationare being utilised, such as a closed loop activeharmonic filter, which will inject anti phaseharmonics, the attenuation of this device canbe shown as a negative value in this table.

When calculating a suitable filter theharmonic generation of the rectifier against atrue sinusoid should be considered, as themeasured harmonic currents from a rectifierwill be lower when a standing distortionexists on a network. As the filter will resultin an improved network distortion the actualabsorption may be higher thanmeasurements predict.

The same principle may also be applied toopen loop active and tuned filters if the loadis non-dynamic. However, tuned filters mayalso import harmonic load.

The addition of tuned filters must be verycarefully considered, especially withconventional voltage source PWM drives.

These filters consist of an LC (inductor andcapacitor) network, tuned close to aharmonic frequency (typically 225 -235 Hzon a 50 Hz network) to provide a lowimpedance path to allow controlledharmonic current flow.

The filter is therefore inherently capacitivebelow the tuned frequency and reactiveabove. The low impedance at the tunedpoint may also allow harmonic currents to

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be imported from other parts of a network.

As a diode rectifier presents very littlefundamental reactive load to compensate, itis relatively easy to create a system that canachieve a leading power factor, which in turnmay set up a resonant condition with the d.c.link components and result in prematuredrive or filter failure.

The use of this type of filter with a d.c. driveprovides a convenient and cost-effectivemeans of controlling both power factor andharmonic load.

The use of power factor correction capacitorswithout de-tuning is not recommended onany circuits that may have a harmonic content,as they will appear as a low impedance pathfor any harmonics on that network.

If the connection is not acceptable at Stage 1or is at Medium Voltage, it is possible toconsider a Stage 2 assessment.

6.2 Stage 2

If the levels of harmonics exceed those forStage 1, or the standing distortion is alreadyclose to the planning level, or the point ofcommon coupling is at medium voltage (6.6 kV to 22 kV), then a different procedureis called for.

Firstly, for an MV PCC, if the total ofconverter loads is lower than 130 kVA of 6 pulse or 250 kVA of 12 pulse diode rectifier,there is no need for further assessment.

Otherwise the Network Operator is obligedto determine the network backgroundvoltage distortion.

This should be a measured value, and for abalanced load application should record as avery minimum the primary odd distortingharmonics, up to the 25th, plus the totalharmonic distortion (THD) from 2nd to50th harmonic.

The peak values of voltage harmonicdistortion on the UK network will usuallyoccur on a Saturday or Sunday evening, whenvery high levels of domestic televisionviewing co-incide with minimal levels ofgeneration.

The measurements should therefore betaken over a period of seven days, to allowthe results to be assessed realistically.

Under G5/4, if the measured distortion on anetwork is less than 75% of the planninglevel for voltage distortion, then a summationof currents can be used and compared withG5/4 Table 12.

Within the scope of G5/4, there is theprovision to allow the background level to beassessed on the basis of the level that is notexceeded for 95% of the time.

If the equipment will not be in continuousoperation, the background should only beconsidered for the hours and days of theweek that the equipment will be operated.

As an example, taking an 11 kV point ofcommon coupling, if the measured THD isless than 3% - that is less than 75% of theplanning level at 4%, and the 5th harmonicdistortion is less than 2.25% (75% of 3%),then we can apply G5/4 Table 12, as shownin Figure 2.

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The planning levels for THD are the same asthe former G5/3 levels for 400 V and 11 kVnetworks (5% and 4%), however, maximum5th harmonic content is now introduced (4% and 3%).

The values of current permitted in G5/4Table 12 are substantially lower than theprevious G5/3 Stage 2 limits.

6.2.1 Stage 2 Typical Drive LoadsThe current levels in Table 12 of G5/4

correspond typically to the following levels ofsingle rectifier load:

6 pulse diode – 185 kW limited by the 5th harmonic

12 pulse diode – 2000 kW limited by the 25th harmonic

24 pulse diode – 2400 kW limited by the 25th harmonic

Active Rectifier – possibly up to 3150 kW.

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Drive 1 Drive 2 Drive 3G5/4

Table 12

Rating (kVA) 260 2750 3000Motor Power (kW) 175 2000 2400

Rectifier Type 6 p diode 12 p diode 24 p diodeCurrent (A) (A) (A)

HarmonicFundamental 9.9 110.5 132.6 N/A

I3 Negligible Negligible Negligible 6.6I5 3.7 2.6 2.7 3.9I7 1.6 1.3 1.5 7.4I9 Negligible Negligible Negligible 1.8I11 0.8 6.2 1.4 6.3I13 0.5 4.3 1.0 5.3I17 0.4 0.2 0.2 3.3I19 0.2 0.2 0.2 2.2I23 0.1 1.0 1.1 1.8I25 0.1 1.0 1.0 1.0I29 0.1 0.1 0.1 0.8I31 Negligible 0.1 0.1 0.7I35 0.1 0.5 0.3 0.6I37 Negligible 0.4 0.3 0.5I41 Negligible Negligible Negligible 0.4I47 Negligible 0.3 0.3 0.3I49 Negligible 0.3 0.3 0.3

Figure 2. Comparison of typical rectifier harmonic loads at 11 kV with G5/4 Table 12

A clear exchange of information is needed inorder that the drive supplier should be ableto offer the most cost-effective solution.

The drive supplier is only indirectly a party tothe application of G5/4, however, in practiceto achieve the optimal solution the customer

If the distortion, present before the new loadis connected, exceeds 75% of theappropriate voltage planning level or thecurrents exceed the Table 12 limits, then, it isnecessary to determine the voltagedistortion that is likely to be generated bythe new load, and to predict the overalllevels of voltage distortion that will result.

In this case the predicted harmonic currentsfor the load as calculated by themanufacturer should be submitted to thesupply utility for them to calculate the effectof the proposed new load.

The harmonic currents are used to calculatethe resultant voltage distortion, however,G5/4 uses some correction factors to allow

for possible system resonances in making thiscalculation.

At 400 V the voltages generated by harmoniccurrents of the 7th order and above arereduced by 50%, and for 6.6 kV, 11 kV, and 22 kV systems voltages generated by harmoniccurrents up to the 7th order are doubled.

If the resultant THD and the level of 5thharmonic remain within the planning levels,then connection should be agreed.

Typical examples of a voltage distortioncalculation are given in Figure 3, based on the6 pulse drive shown in Figure 2, with thesystem impedances typical in a 100 MVAfault level system.

14

Harmonic Current (A) VoltageCorrection Corrected

% VoltageFactor Voltage

Fundamental 9.9 110005 3.7 34.45 2 68.9 0.627 1.6 20.80 2 41.6 0.3811 0.8 16.31 1 16.3 0.1513 0.5 12.05 1 12.0 0.1117 0.4 12.60 1 12.6 0.1119 0.2 7.04 1 7.0 0.0623 0.1 4.26 1 4.3 0.0425 0.1 4.63 1 4.6 0.0429 0.1 5.37 1 5.4 0.0535 0.1 6.48 1 6.5 0.06

THD 0.77%

Figure 3. Voltage Distortion Calculation

RectifierRating

260 kVA

should encourage direct involvement andgood communication between the utility andthe supplier.

There are a number of techniques available tominimise harmonics and potential supplyproblems.These consist of modifications of thenetwork or the drive, and range from phaseshifting, through multi-pulse rectifiers, to filters.

The sequence for exchange of informationshould preferably be as shown in theAppendices. It must always be rememberedthat the time scale for this exchange is criticalto avoid unreasonable delays inimplementation of a project.

6.3 Stage 3

If the levels of harmonics exceed those forStage 2, or if the point of common couplingis at 33 kV or over, then a different andsubstantially more complex procedure iscalled for.

In this case, measurements to determine thedistortion of the local network, at least up tothe 33 kV level are needed, together withdetailed information on the systemimpedances.

This information is then used in constructinga computer model, showing the inter-relationship of the consumers’ network andthe local supply network, to enable theeffects of the new harmonic sources to bemodelled.

Currently there is little standardisedmethodology for undertaking this type of

study, and this needs to be establishedbetween the NOC, the consumer, and thedrive supplier.

A number of proprietary programs areavailable for network studies; most weredeveloped to enable the safety of a systemto be established by calculating worst casefault levels, and establishing the protectiveequipment co-ordination. Each of theseprograms has both strengths and limitations.It is therefore important that the mosteffective software and correct form of studyis selected and undertaken.

Within the model, account may be taken ofthe variation of existing and predictedharmonic levels with time of day, and/or dayof the week. This may be useful if a clearcorrelation can be established between theexisting levels and the effect of the proposedload.9

According to G5/4, it is the responsibility ofthe network operating company (NOC) tocarry out these calculations, and todetermine whether the proposed load isacceptable for connection.

In practice, even with the most precisesoftware, the validity of the model willdepend absolutely on the accuracy ofinformation input.

In practice, the user will need to plan theinstallation in advance to be sure that it willbe accepted. This means that the

15

9G5/4 Para 8.3.2

Measurements can be taken of supplyimpedances and both harmonic currents andvoltages using proprietary equipment.

The most common form of measurement isthe voltage distortion over a period of time,and while G5/3 accepted measurements over24 hours, G5/4 now looks to a seven dayrecord in order to establish the worst caseoperating conditions.

The accuracy of any measurement is limitedby the measuring equipment, and themethod of measurement.

At low voltage, it is normal to take directvoltage measurements, but currentmeasurements are normally made indirectlyby a current transformer, Hall effecttransducer, or Rogowski coil.

At medium and high voltage, themeasurement voltage and currenttransformers forming the switchgearprotection or metering provisions arenormally the only facilities available to beutilised, adding their inaccuracies. They alsoplace limitations in terms of the phase shift

between current and voltage transformers,and the numbers of CTs and VTs fitted.

Most of these devices are not designed tomeasure accurately at frequencies other thanthe fundamental and any inaccuracies due tothe methods of magnetic coupling must alsobe considered.

The equipment or an associated computerprogram undertakes a Fourier Analysis of theresultant waveform, and logs the results.

The standard for making measurements iscurrently the harmonised European StandardEN 61000-4-7, which defines the class ofaccuracy for measuring instruments.

The harmonic current measurementtolerances may be greater than the actualvalues in G5/4 Tables 7 and 12 at higherfrequencies when measuring larger loads.

This may limit the validity of measurementsto show compliance with Table 7 or Table 12for higher power levels.

information, which will be used by the NOCto carry out the estimation, must be madeavailable during the planning phase.

These studies are inevitably time consumingand costly, and the apportionment of thesecosts must also be established.

6.3.1 GeneralIf a drive installation is to be run for less than24 hours daily, it is quite possible to consideronly the standing distortion during theproposed operating period.

16

7.0 Measurements

G5/4 is a process for permitting connectionof new non-linear loads to the publicelectricity supply.

If it is applied consistently, it is unlikely thatproblems will arise after installation andcommissioning.

Firstly, it is critically important that adequateand sufficient information is available at theoutset of a project, and that this informationis provided in a timely manner.

As drives up to 250 kW or greater areavailable from most suppliers’ stock, or ashort delivery and even drives with ratingsexceeding 1MW, are available within eight orten weeks. Therefore, any delay in theprovision of information could be critical tothe implementation of a project.

Exact calculation of harmonics for drives is adifficult procedure, as the supply impedanceand existing harmonic voltages will influencethe magnitude and direction of harmoniccurrent flow in a rectifier.

This is especially true where there areseveral rectifier combinations, variations inthe supply source fault level, tap-changersettings, and installed power factorcorrection.

If the supply utility is unable to complete thecalculations for a Stage 2 or Stage 3connection, within a reasonable time10, theconsumer should be permitted to undertakethe measurements and to submit calculations.

Normally the equipment manufacturer willbe best placed to carry out the calculationsand simulations. The NOC should providesuch data as is available, includingconfirmation of the fault levels for Stage 1 orStage 2, and the supply impedance model forStage 3.

If a problem does occur, it is most likely to bewhere a measurement is made afterinstallation, and the levels of voltagedistortion are shown to be excessive.

If the current harmonics are within the levelspredicted at the time of approval, it would beunreasonable to ask the consumer tocontribute to remedial measures.

It is therefore incumbent on the parties to anagreement to connect to have a procedurefor arbitration in the event of a problem.

17

8.0 Resolution of Problems

10A maximum time of one month would be reasonable.

The use of intelligent power controllers, suchas variable speed drives and soft starters iswell accepted both in industry and byGovernment as one of the major meansavailable to improve energy efficiency andproductivity. It is also essential to manyindustries to achieve process control, so it isin the interests of all parties to co-operate tofacilitate their use.

This leads to an examination of theresponsibilities of the different partiesinvolved in the use of a drive system.

9.1 The Equipment SupplierThe responsibility of the equipment supplieris to identify the harmonic currentsgenerated by the equipment under definedconditions.

9.2 The Supply UtilityThe responsibility of the Supply Utility is toprovide appropriate details of the network,including the appropriate fault levels innormal and emergency operating conditions,and to identify any known limitations,including existing harmonic levels.

9.3 The UserThe responsibility of the user is to ensurethat the compatibility of his network, andcompliance with the appropriaterequirements.

9.4 CompetenceUnderstanding the propagation of harmonicsis a complex problem, and in general, thedrive manufacturers have the greatestexperience in the application of theirproducts.

GAMBICA drive manufacturers have manyyears of experience at meeting all sorts ofharmonic limitations. However, it can oftenbe time consuming to provide associatedinformation and other assistance.

The manufacturers’ basic responsibility is toprovide the detail as shown in Appendix 2.

However, most manufacturers are able tooffer additional services including systemstudies, and to make appropriatemeasurements at a reasonable cost.

18

9.0 Summary

19

Appendix 1

Request to Connect Non-linear Load

To: A Network Operating Company

From: A consumer company

Contact:Phone No:Fax: E-mail

Installation Site

Voltage at Point of Common Coupling (If known) kV

Connection Substation (If known)

Site Line Diagram, showing connection. Enclosed Not available

Description of loadMotor Rating kW

Motor Voltage V

Converter kVAConverter Rectifier

Interposing Transformer (1)Ratio (no load)

Rating kVAImpedance %

No load loss kWLoad loss kW

Proposed Stage of Connection

Proposed Method of CompliancePower within Table 6 of G.5/4Compliance with Table 7 of G.5/4Compliance with Table 12 of G.5/4

Enclosures Manufacturers prediction Appendix 2

Figure 4. Suggested Format for Application to connect to Supply.

20

Response from NOC

From: A Network Operating Company

To: A consumer

Agreed Point of Common Coupling voltage kV

Connection substation

Fault level (Peak) MVA at PCCFault level (Running) MVA at PCC

Stage of Connection Stage 1/Stage 2/Stage 3

For Stage 2/Stage 3 connection

Existing worst case distortion (THD)Existing worst case 5th harmonic (V5)

95 percentile value of THD for calculation95 percentile value of V5 for calculation

For Stage 3 connectionSupply impedance valuesSupply impedance X/RComplex Impedance + j Ω max

+ j Ω minSpecial conditions

Figure 5. Suggested Format for Application to connect to Supply.

The following information is also anticipated:

i) Any available information regarding major sources of harmonics in the neighbourhoodii) Details of any large consumer in the same network who may be affectediii) Details of any filter networks in the same networkiv) Transient or emergency conditions which may apply additional stress to the system network

- eg: likelihood of lightning strikes, large DOL motor starting loadsv) Details of any suspected resonant conditions within the local network.

In the case of large power installations and a penetration/load flow study being required, fulldetails of each of these will be required.

21

Appendix 2

Harmonic PredictionSupplierType ReferenceLoad power 30 kW

Network and Transformer Data Converter Data

Nominal voltage [V] 11000 400 Converter 40 [kVA](Primary side) (secondary side) Rating

Frequency 50 [Hz] Rectifier Device DiodePrimary Network Sk 100 [MVA] Pulse # 6Transformer Sn 500 [kVA] Lv 440 [uH]Transformer Pk 4.7 [kW] Cdc 1.65 [mF]Transformer Zk 4.5 [%] Udc 540 [V]

Idc 61 [A]Secondary Network Sk 10 [MVA]

ResultCosfii 0.999 THD Current 48.2 %Tot. power factor 0.9 THD Voltage 1.1 %Udmax mot. 98%

Significant Harmonicsh f [Hz] Current [A] Ih /I1 Voltage [V] Uh /U11 50 48.1 100.0 % 399.4 100.0 %5 250 18.9 39.3 % 3.0 0.8 %7 350 9.8 20.3 % 2.1 0.5 %

11 550 4.2 8.8 % 1.4 0.3 %13 650 2.8 5.9 % 1.1 0.3 %17 850 2.1 4.3 % 1.1 0.3 %19 950 1.3 2.8 % 0.8 0.2 %23 1150 1.1 2.4 % 0.8 0.2 %25 1250 0.7 1.4 % 0.5 0.1 %29 1450 0.6 1.2 % 0.5 0.1 %31 1550 0.4 0.8 % 0.4 0.1 %35 1750 0.3 0.6 % 0.3 0.1 %37 1850 0.3 0.6 % 0.3 0.1 %41 2050 0.2 0.3 % 0.2 0.1 %43 2150 0.2 0.5 % 0.3 0.1 %47 2350 0.2 0.3 % 0.2 0.1 %49 2450 0.2 0.4 % 0.3 0.1 %

Figure 6. Suggested Format for Drive Suppliers Response - (Typical data for a 30 kW Drive system).

GAMBICA is the Trade Association for Instrumentation,Control, Automation & Laboratory Technology in the UK. It has a membership of over 300 companies including themajor multinationals in the sector and a significant number ofsmaller and medium sized companies.

The Association's primary objectives are to further thesuccessful development of the industry and to assist itsmember companies through a broad range of services in theUK and overseas. These include the means to influencenational and international technical standards and tocontribute to industry policy at UK and European level,market data services, guidance on both technical andcommercial issues, and participation in export initiatives.

The scope of the Association covers the five principal sectorsof the industry:

Industrial automation products and systems Process measurement and control equipment and systems Environmental analysis and monitoring equipment Laboratory technology Test and measurement equipment for electrical and

electronics industries.

The greatest care has been taken to ensure the accuracy ofthe information contained in this guide, but no liability can be accepted by GAMBICA or their members, for errors of any kind.

The GAMBICA Association LimitedSt George’s House 195-203 Waterloo Road London SE1 8WB

Telephone: +44(0)20 7642 8080 Fax: +44(0)20 7642 8096Email: assoc@gambica.org.uk Web: www.gambica.org.uk

02/02©GAMBICA 2002

ABB Ltd., Automation Technology Products9 The Towers, Wilmslow RoadDidsbury, Manchester M20 2ABTel: +44 (0)161 445 5555Fax: +44 (0)161 448 1089Email: drives.sales@gb.abb.comWeb: www.abb.co.uk

ALSTOM Power Conversion LtdBoughton Road, RugbyWarwickshire CV21 1BUTel: +44 (0)1788 563625Fax: +44 (0)1788 563780Email: general.drives@powerconv.alstom.comWeb: www.alstom.com

Baldor UK LtdMint Motion Centre6 Bristol Distribution ParkHawkley Drive, Bristol BS32 0BFTel: +44 (0)1454 850000Fax: +44 (0)1454 859001Email: sales@baldor.co.ukWeb: www.baldor.co.uk

Control Techniques UKStafford Park 4Telford TF3 3BATel: +44 (0)1952 213700Fax: +44 (0)1952 213701Email: ctdirect@compuserve.comWeb: www.controltechniques.com

Danfoss LtdPerivale Industrial ParkHorsenden Lane SouthGreenford, Middlesex UB6 7QETel: +44 (0)870 241 7200Fax: +44 (0)870 241 7150Email: uk.drives.sales@danfoss.comWeb: www.danfoss.co.uk

Eaton Ltd, Cutler-HammerCarina, Sunrise ParkwayLinford Wood, Milton KeynesBucks MK14 6NRTel: +44 (0)1908 541600Fax: +44 (0)1908 660527Email: Ch-help-uk@eaton.comWeb: www.ch.cutler-hammer.com/global/uk

GE Power Controls LtdHorn House Lane, Knowsley Industrial ParkKirkby, Merseyside L33 7YQTel: +44 (0)870 600 4372Fax: +44 (0)151 549 4546Email: sales@gepc.ge.comWeb: www.gepowercontrols.com

HID Ltd / HitachiShuttleworth CloseGapton Hall Ind Estate Great Yarmouth, Norfolk NR31 0NQTel: +44 (0)1493 442525Fax: +44 (0)1493 442323Email: sales@hid.co.ukWeb: www.hid.co.uk

Hill Graham Controls LtdLincoln Road, CressexHigh Wycombe Bucks HP12 3RBTel: +44 (0)1494 440121Fax: +44 (0)1494 438810Email: hillgraham@compuserve.comWeb: www.hillgraham.com

IMO Precision Controls Ltd100 North Circular RoadStaples Corner, London NW2 7JPTel: +44 (0)208 452 6444Fax: +44 (0)208 450 2274Email: imo@imopc.comWeb: www.imopc.com

Lenze LtdCaxton RoadBedford MK41 0HTTel: +44 (0)1234 321321Fax: +44 (0)1234 261815Email: sales@lenze.co.ukWeb: www.lenze.co.uk

Mitsubishi Electric Europe B.V.Automation Systems DivisionTravellers Lane, HatfieldHerts AL10 8XBTel: +44 (0)1707 276100Fax: +44 (0)1707 278695Web: www.industrial.meuk.co.uk

Moeller Electric LtdPO Box 35, Gatehouse CloseAylesbury, Bucks HP19 8DHTel: +44 (0)1296 393322Fax: +44 (0)1296 421854Email: support@moeller.co.ukWeb: www.moeller.co.uk

Omron Electronics UK Ltd1 Apsley Way Staples CornerLondon NW2 7HFTel: +44 (0)20 8450 4646Fax: +44 (0)20 8450 8087Email: oeeuk_sales@eu.omron.comWeb: www.omron.co.uk

Rockwell Automation LtdPitfield, Kiln FarmMilton Keynes MK11 3DRTel: +44 (0)1908 838800Fax: +44 (0)1908 839699Email: emccourt@ra.rockwell.comWeb: www.automation.rockwell.com

Schneider Electric LtdUniversity of Warwick Science ParkSir William Lyons RoadCoventry CV4 7EZTel: +44 (0)870 608 8 608Fax: +44 (0)2476 417517Web: www.schneider.co.uk

Siemens plcAutomation & DrivesSir William Siemens HousePrincess RoadManchester M20 2URTel: +44 (0)161 446 6400Fax: +44 (0)161 446 5471Email: info@plcman.siemens.co.ukWeb: www.siemens-industry.co.uk

Yaskawa Electric Europe GmbHUnits 2/3 Centurion CourtBrick Close, Kiln FarmMilton Keynes, Bucks MK11 3JATel: +44 (0)1908 565874Fax: +44 (0)1908 565891Web: www.yaskawa.co.uk

LIST OF MEMBERS