11a harmonics

8/3/2019 11a Harmonics

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Harmonics In AC SystemsHarmonics In AC Systems

An IntroductionAn Introduction


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HarmonicsHarmonics an introductionan introduction

Modern electronic power control devices widelyModern electronic power control devices widelyusedused

Major disadvantage is that the switching ofMajor disadvantage is that the switching ofsemi conductors generates harmonicssemi conductors generates harmonics

Because current in these systems is interruptedBecause current in these systems is interruptedby a switching action, the current containsby a switching action, the current contains

frequency components that are multiples of thefrequency components that are multiples of the

power system frequencypower system frequency


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High frequency harmonic currents causeHigh frequency harmonic currents causeproblems:problems:

Excessive heat losses in transformers, cables,Excessive heat losses in transformers, cables,other componentsother components

Control, protection and metering devices do notControl, protection and metering devices do notfunction as required (nuisance tripping, etc.)function as required (nuisance tripping, etc.)

Telecommunication & data networks subject toTelecommunication & data networks subject to

interference and disturbanceinterference and disturbance


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Particular problem where the networkParticular problem where the networkcontains power factor correctioncontains power factor correction

capacitorscapacitors

This can form a parallel resonant circuitThis can form a parallel resonant circuitat harmonic frequencyat harmonic frequency

Results in harmonics being amplifiedResults in harmonics being amplified


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Sensitive equipmentSensitive equipment CommunicationsCommunications

VHF radioVHF radio

AIS systemsAIS systems

RadarRadar

ComputersComputers

Control systemsControl systems

Monitoring systemsMonitoring systems

Navigation systemsNavigation systems


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The ProblemThe Problem

To start with a simple example:To start with a simple example:


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The ProblemThe Problem Linear LoadLinear Load

Four-wire System - Linear Phase Currents Return via NeutralConductor where Balanced Phase Current Cancel Out

ABS GUIDANCE NOTES ON CONTROL OF HARMONICS IN ELECTRICAL POWER SYSTEMS . 2006


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The ProblemThe Problem Non linear (switching) LoadNon linear (switching) Load

Triplen Harmonics Add Up Cumulatively in Neutral conductorswith Single-phase Nonlinear Loads in Four-wire System

ABS GUIDANCE NOTES ON CONTROL OF HARMONICS IN ELECTRICAL POWER SYSTEMS . 2006


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Problems most often caused by the 3rd, 5th, 7th,

11th, 13th order harmonics


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5th order

harmonic

removed


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TerminologyTerminology

FundamentalFundamental The basic designed supply frequencyThe basic designed supply frequency

HarmonicsHarmonics Waveforms at an exact multiple of theWaveforms at an exact multiple of the

fundamental frequencyfundamental frequency

OrderOrder

Indication of the frequency of a specificIndication of the frequency of a specificharmonicharmonic


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ExamplesExamples

FundamentalFundamental 60 Hz60 Hz 33rdrd order harmonicorder harmonic 180 Hz180 Hz

66thth

order harmonicorder harmonic 360 Hz360 Hz

FundamentalFundamental 330 Hz330 Hz 33rdrd order harmonicorder harmonic 990 Hz990 Hz

66thth order harmonicorder harmonic 1980 Hz (1.98 kHz)1980 Hz (1.98 kHz)


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Major CauseMajor Cause

High speed electronic switchingHigh speed electronic switching ThyristorsThyristors

Controlled rectifiersControlled rectifiers

InvertersInverters

Power transistorsPower transistors

Propulsion PWM invertersPropulsion PWM inverters

DCDCAC power inverters in UPS unitsAC power inverters in UPS units

All produce reflected currentsAll produce reflected currentsAt time of switchingAt time of switching


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Harmonics In 3Harmonics In 3--phase Systemsphase Systems

Even numbersEven numbers Self cancelling in all AC systemsSelf cancelling in all AC systems

Multiples of threeMultiples of three Self cancelling in 3Self cancelling in 3--phase systemsphase systems

Leaving 5, 7, 11, 13, 17, 19, 23Leaving 5, 7, 11, 13, 17, 19, 23

60Hz system60Hz system 300Hz, 420Hz, 660Hz, 780Hz, 1020Hz300Hz, 420Hz, 660Hz, 780Hz, 1020Hz


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Frequency And AmplitudeFrequency And Amplitude

Higher frequency, lower amplitudeHigher frequency, lower amplitudeAmplitude varies as the inverse of the orderAmplitude varies as the inverse of the order

55thth

order harmonicorder harmonicAmplitude = 1/5Amplitude = 1/5 fundamentalfundamental

Applies toApplies to Harmonic currentsHarmonic currents

Resulting EMFResulting EMF


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FundamentalFundamental

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Fundamental + 5Fundamental + 5thth OrderOrder


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Fundamental + 5Fundamental + 5thth & 7& 7thth OrdersOrders

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FundamentalFundamental

+ 5+ 5thth

77thth

& 11& 11thth

OrdersOrders

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All Orders Up To 17All Orders Up To 17thth


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OutOut--ofof--phase Harmonicsphase Harmonics

Harmonics so far in phaseHarmonics so far in phase Regular waveform distortionRegular waveform distortion

Out of phase harmonicsOut of phase harmonics Irregular waveform distortionIrregular waveform distortion


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55thth Order, Lagging 0.8Order, Lagging 0.8

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55thth & 7& 7thth; Lagging 0.8; Lagging 0.8

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All To 17All To 17thth; Lagging 0.8; Lagging 0.8

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Significant EffectsSignificant Effects

Inductive heatingInductive heating

Electromagnetic equipmentElectromagnetic equipment

Motors, transformers, generators, relays, coilsMotors, transformers, generators, relays, coils

Other current carrying devicesOther current carrying devices

Conductors, breakers, fusesConductors, breakers, fuses

Adjacent partsAdjacent parts Steel enclosures, conduit, mounting platesSteel enclosures, conduit, mounting plates


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Other EffectsOther Effects

Voltage distortionVoltage distortion Unpredictable equipment operationUnpredictable equipment operation

Tripping circuit breakersTripping circuit breakers

Flickering fluorescent lightsFlickering fluorescent lights

Fuses blowing for no reasonFuses blowing for no reason

Excessive neutral currentsExcessive neutral currents

Equipment overheatingEquipment overheating

Equipment failureEquipment failure


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Harmonic DistortionHarmonic Distortion

Various calculated valuesVarious calculated values Based on RMS valuesBased on RMS values

Total harmonic content (THC)Total harmonic content (THC)

Effective value of distorted voltageEffective value of distorted voltage Total harmonic distortion (THD)Total harmonic distortion (THD)


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Total Harmonic ContentTotal Harmonic Content

Total harmonic content (THC)Total harmonic content (THC) EEHH == (E(EH5H5 + E+ EH7H7 + E+ EH11H11 ))

WhereWhere EEHnHn is the RMS value of the nis the RMS value of the nthth orderorder

ExampleExample EF = 660 VEF = 660 VRMSRMS

55thth and 11and 11thth harmonics presentharmonics present

EEHH

== (E(EH5H5

+ E+ EH11H11

) =) = (132(132 + 60+ 60) =) =

145V145VRMSRMS


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Effective ValueEffective Value

Effective value of distorted voltageEffective value of distorted voltage EEFF+ E+ EHH

From previous exampleFrom previous example EEFF = 660V= 660V

EEHH = 145V= 145V

Effective value =Effective value = (660(660 + 145+ 145) =) =675.7V675.7VRMSRMS


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Total Harmonic DistortionTotal Harmonic Distortion

TToottaall hhaarrmmoonniicc ddiissttoorrttiioon (THD)n (THD) Most commonly usedMost commonly used measuremeasure

Ratio of harmonic value to fundamentalRatio of harmonic value to fundamental

From previous exampleFrom previous example 145/660 = 21.97%145/660 = 21.97%

EEHH

EEFF


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THD LimitsTHD Limits

Generally accepted limits for most systemsGenerally accepted limits for most systems 25% action must be takenaction must be taken

Limit setLimit set Depends on equipment fittedDepends on equipment fitted

Classification / makers may require lower limitClassification / makers may require lower limit


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How do you detect or measureHow do you detect or measure

harmonics?harmonics?


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With care!With care!

Normally only possible to measure atNormally only possible to measure atvoltages below 690 Volts acvoltages below 690 Volts ac


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AEMC 3945 Connected On-site Illustrating Wrap-aroundRogowski-type, AmpFlex 6500 A Current Probes


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Typical analysis by software:Typical analysis by software:

Real TimeCurrentWaveformsviaComputer


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Typical analysis by software:Typical analysis by software:

Real TimeComputerDisplay ofHarmonicCurrents


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Typical analysis by software:Typical analysis by software:Unbalance inReal Time viaComputer


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Minimising Harmonic EffectMinimising Harmonic Effect

Circuit designCircuit designAdditional inductanceAdditional inductance

Phase shift transformersPhase shift transformers

Increase number of converter pulsesIncrease number of converter pulses

Use dedicated (clean) power suppliesUse dedicated (clean) power supplies Negates the advantage of single power sourceNegates the advantage of single power source

operationoperation Harmonic filtersHarmonic filters


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Equipment design:Equipment design:

Increase number of pulses; example use aIncrease number of pulses; example use a

1212--pulse drive instead of a 6pulse drive instead of a 6--pulse drive.pulse drive. Harmonics produced higher up the orderHarmonics produced higher up the orderwhere they will have less effectwhere they will have less effect


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Where harmonics are too high, filtersWhere harmonics are too high, filtersmust be used, either;must be used, either;

Passive filtrationPassive filtration

OrOr

Active filtrationActive filtration


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Phase ShiftingPhase Shifting

Phase shift can be accomplished using a starPhase shift can be accomplished using a star--deltadeltatransformertransformer

Cancellation of 5Cancellation of 5thth & 7& 7thth harmonic currentsharmonic currents


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12-pulse A.C. PWM with double wound phase

shift transformer


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Comprises a double-wound isolating transformer

with 30 degrees phase shift between the star and

delta secondary windings,


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Comprises a double-wound isolating transformer with 30

degrees phase shift between the star and delta secondary

windings,

Two 6-pulse input bridges, an interbridgereactor, a DC bus and an inverter bridge.


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Passive Harmonic FiltersPassive Harmonic Filters

Consist of a series circuit of reactors &Consist of a series circuit of reactors &capacitorscapacitors

Tuned resonant circuitsTuned resonant circuits

Absorb unwanted frequenciesAbsorb unwanted frequencies

RLC circuitRLC circuit (resistance, inductance, capacitance)(resistance, inductance, capacitance)


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Consist of a series circuit of reactors &Consist of a series circuit of reactors &capacitorscapacitors


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High voltage

harmonic filter


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Harmonic Mitigating TransformersHarmonic Mitigating Transformers

Using a DeltaUsing a Delta--ZigZagZigZag transformer it is possible to achievetransformer it is possible to achievea 30a 30 phase shiftphase shift

Overlaying the waveforms can provide some harmonicOverlaying the waveforms can provide some harmonic

cancellationcancellation


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B Wave Shape With No Phase Shift;A Wave Shape Phase Shifted By 30


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The Combination of The B And 30Phase Shifted A Wave Shapes.


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When the two are combined cancellation of

the 5th, 7th, 17th, and 19th harmonics occurs.


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Another phase shift could further

improve the waveform


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Combination of Two A+B Wave ShapesWith One Of The Two Phase Shifted By 15


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Cancels out the harmonics


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BUT the cost-benefit does notgenerally justify this extra stage


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Active Harmonic FiltersActive Harmonic Filters

Principle:Principle:

Measures the harmonic content andMeasures the harmonic content and

Actively generates a harmonic currentActively generates a harmonic currentspectrum in opposite phase.spectrum in opposite phase.

Original harmonics therefore cancelled out.Original harmonics therefore cancelled out.


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ABB PQFA Active Filter system


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ABB PQFA Active Filter system

The PQF system is basically a compensating current generator


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Phase shifttransformers

cycloconverters

Motor-generator set

for clean AC supply

Double windingsynchronous motor

Propulsion motorexcitation

CPP

Example - Electric Propulsion System

11a harmonics

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