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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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HarmonicsHarmonics an introductionan introduction
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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HarmonicsHarmonics an introductionan introduction
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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HarmonicsHarmonics an introductionan introduction
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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The ProblemThe Problem
Problems most often caused by the 3rd, 5th, 7th,
11th, 13th order harmonics
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The ProblemThe Problem
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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-2.5
-2
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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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How do you detect or measureHow do you detect or measure
harmonics?harmonics?
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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How do you detect or measureHow do you detect or measure
harmonics?harmonics?
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How do you detect or measureHow do you detect or measure
harmonics?harmonics?
AEMC 3945 Connected On-site Illustrating Wrap-aroundRogowski-type, AmpFlex 6500 A Current Probes
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How do you detect or measureHow do you detect or measure
harmonics?harmonics?
Typical analysis by software:Typical analysis by software:
Real TimeCurrentWaveformsviaComputer
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How do you detect or measureHow do you detect or measure
harmonics?harmonics?
Typical analysis by software:Typical analysis by software:
Real TimeComputerDisplay ofHarmonicCurrents
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How do you detect or measureHow do you detect or measure
harmonics?harmonics?
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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Minimising Harmonic EffectMinimising Harmonic Effect
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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Minimising Harmonic EffectMinimising Harmonic Effect
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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Minimising Harmonic EffectMinimising Harmonic Effect
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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Minimising Harmonic EffectMinimising Harmonic Effect
Phase ShiftingPhase Shifting
12-pulse A.C. PWM with double wound phase
shift transformer
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Minimising Harmonic EffectMinimising Harmonic Effect
Phase ShiftingPhase Shifting
Comprises a double-wound isolating transformer
with 30 degrees phase shift between the star and
delta secondary windings,
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Minimising Harmonic EffectMinimising Harmonic Effect
Phase ShiftingPhase Shifting
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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Passive Harmonic FiltersPassive Harmonic Filters
Consist of a series circuit of reactors &Consist of a series circuit of reactors &capacitorscapacitors
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Passive Harmonic FiltersPassive Harmonic Filters
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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Harmonic Mitigating TransformersHarmonic Mitigating Transformers
B Wave Shape With No Phase Shift;A Wave Shape Phase Shifted By 30
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Harmonic Mitigating TransformersHarmonic Mitigating Transformers
The Combination of The B And 30Phase Shifted A Wave Shapes.
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Harmonic Mitigating TransformersHarmonic Mitigating Transformers
When the two are combined cancellation of
the 5th, 7th, 17th, and 19th harmonics occurs.
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Harmonic Mitigating TransformersHarmonic Mitigating Transformers
Another phase shift could further
improve the waveform
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Harmonic Mitigating TransformersHarmonic Mitigating Transformers
Combination of Two A+B Wave ShapesWith One Of The Two Phase Shifted By 15
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Harmonic Mitigating TransformersHarmonic Mitigating Transformers
Cancels out the harmonics
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Harmonic Mitigating TransformersHarmonic Mitigating Transformers
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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Active Harmonic FiltersActive Harmonic Filters
Principle:Principle:
ABB PQFA Active Filter system
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Active Harmonic FiltersActive Harmonic Filters
Principle:Principle:
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
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