Power System Harmonics - WMEA

1 11/20/2003 10:26:46 1ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewPractical Overview of Mine Practical Overview of Mine Power System Harmonics Power System Harmonics Western Mining Western Mining Electrical Electrical AssociationAssociationTucson, ArizonaTucson, ArizonaNovember 1999 November 199911/20/2003 10:26:46 2ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewHarmonic TopicsHarmonic Topics What are Harmonics ?What are Harmonics ? Where do they come from?Where do they come from? Why worry? Why worry? 10:26:46 3ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewWhat Are Power Line Harmonics ?What Are Power Line Harmonics ? Harmonics are voltages Harmonics are voltages and currents at frequencies and currents at frequencies that are multiples of utility that are multiples of utility Power , 5th and 7th 10:26:46 4ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewWhere Do Harmonics Come From?

2 Where Do Harmonics Come From? Harmonic currents result from loads that Harmonic currents result from loads that draw Power in nondraw Power in non--sinesine--wave format. These are soThese are so--called noncalled non--linear 10:26:46 5ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewSome Specific Harmonic SourcesSome Specific Harmonic Sources Resistance devices Resistance devices --heaters, incandescent heaters, incandescent lampslamps Induction motorsInduction motors Capacitor banksCapacitor banks Transformers during Transformers during energizationenergization Arc welders and arc Arc welders and arc furnacesfurnaces RectifiersRectifiers Computers, switching Computers, switching Power suppliespower supplies DC drives, AC DrivesDC drives, AC Drives Switched cap banksSwitched cap banksLinear load examples:Linear load examples:NonNon--Linear load examples:Linear load examples:11/20/2003 10:26.

3 46 6ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewSome Harmonic ProducersSome Harmonic ProducersHarmonic ProducerHarmonicNotesTransformers during energization2ndGone after secArc Welders and FurnacesBroad spectrum, 2nd, 3rd, 4th, 5th, 7th, 11thFilters usually includedBallasts, electronic3rd, 5th, 7th3rd cancelled in delta transfPlating RectifiersTypical 5th, 7th, 11th, 13th, etc, magnitude 1/nVaries by number of pulsesComputers, switching Power supplies3rd, 5th, 7th3rd cancelled in delta transfDC DrivesTypical 5th, 7th, 11th, 13th, etc, magnitude 1/nVaries by number of pulsesAC drivesTypical 5th, 7th, 11th, 13th, etc,Varies by type, number of pulses, System ZSwitching Cap banksHigh frequencies, depend on systemTransients, induce System resonances11/20/2003 10:26:46 7ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewWhy Worry?

4 Why Worry?OR OR --What makes Power System Harmonics so bad?What makes Power System Harmonics so bad? Capacitors can blow from Capacitors can blow from overvoltageovervoltage Drives can trip offlineDrives can trip offline Transformers can overheat Transformers can overheat --possibly to destructionpossibly to destruction Motors will heat moreMotors will heat more Ballasts can popBallasts can pop Electronics can malfunctionElectronics can malfunction11/20/2003 10:26:46 8ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewA Closer Look: Capacitor Loss A Closer Look: Capacitor Loss from Harmonic Overvoltagesfrom Harmonic OvervoltagesHarmonic Numberof Resonance=Short Circuit MVAC apacitor MVAR Every AC distribution System has Every AC distribution System has distributed inductance L & capacitance inductance L & capacitance C.

5 Adding pf correction caps anywhere in the Adding pf correction caps anywhere in the System will produce a resonant point with System will produce a resonant point with System Lsystem LIF THIS HAPPENS TO CORRESPOND TO A HARMONIC IF THIS HAPPENS TO CORRESPOND TO A HARMONIC CURRENT PRESENT IN THE System , THE RESONANCE CURRENT PRESENT IN THE System , THE RESONANCE WILL PRODUCE BIG VOLTAGES ON THE CAP BANK!WILL PRODUCE BIG VOLTAGES ON THE CAP BANK!11/20/2003 10:26:46 9ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewExample: PF Cap Bank in Example: PF Cap Bank in Harmonic Trouble69 kV1100 MVAsc15 MVA, 5%5 kV5 MVARH armonic TroubleSystem KV = System MVAsc =235 Capacitor Bank Mvar = Harmonic Resonance = !Harmonic Numberof Resonance=Short Circuit MVAC apacitor MVAREQUIVALENT CIRCUIT:235 MVAscCAP BANK AND System Z RESONATE NEAR 7th HARMONIC!

6 ANY DRIVE OR RECTIFIERS ON THE System COULD CAUSE HUGE OVERVOLTAGES!11/20/2003 10:26:46 10ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewSymptoms of Capacitor Series ResonanceSymptoms of Capacitor Series Resonance Voltages across caps measure Voltages across caps measure higher than 10% over nameplate higher than 10% over nameplate rating, scope shows high , scope shows high peaks. Be sure to use TrueBe sure to use True--RMS meterRMS meter OverOver--voltages can come and go with voltages can come and go with operation of harmonic producing operation of harmonic producing Capacitor Cans are swollenCapacitor Cans are swollen Cap Fuses blow, cans failCap Fuses blow, cans fail11/20/2003 10:26:46 11ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewFixing System Resonance ProblemsFixing System Resonance Problems Experiment or calculate to verify Experiment or calculate to verify problemproblem Calculate using simplified approachCalculate using simplified approach Temporarily remove caps and Temporarily remove caps and observe effect.

7 Remove proven offending cap banksRemove proven offending cap banks OR, Change size of bankOR, Change size of bank OR, Tune the bank with inductorsOR, Tune the bank with inductors11/20/2003 10:26:46 12ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewExample Power SystemExample Power SystemPLANTCONVEYORHV UTILITY MV DISTRIBEXCAVATORSECDFA11/20/2003 10:26:46 13ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewThe Correction DilemmaThe Correction DilemmaA. Harmonic producers such as drives A. Harmonic producers such as drives often need Power factor need Power factor Naked capacitors will likely B. Naked capacitors will likely resonate and cause problemsresonate and cause problems11/20/2003 10:26:46 14ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewTuned Capacitor BanksTuned Capacitor Banks[Also Known As Harmonic Filters][Also Known As Harmonic Filters] Naked capacitors often Naked capacitors often cause resonance problems cause resonance problems on systemon System Inductors and capacitors in Inductors and capacitors in series combinations at series combinations at resonant frequency look resonant frequency look like near zero near zero ohms.

8 If tuned to harmonic If tuned to harmonic frequency, LC filter will act frequency, LC filter will act as sink for that frequencyLResFreq = 1 2pi(LC)^.5 Cas sink for that frequencyDeltaConnectedTunedBank11/20/20 03 10:26:46 15ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewTuned Capacitor BanksTuned Capacitor BanksConfigurationsConfigurationsDelta Connected Tuned Delta Connected Tuned Bank Bank --frequently used in frequently used in LV Connected Tuned Wye Connected Tuned Bank Bank --frequently used frequently used in MV MV 10:26:46 16ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewHarmonic FiltersHarmonic Filters Medium voltage or low voltageMedium voltage or low voltage Tune to below desired trap Tune to below desired trap frequency [example, ]frequency [example, ] Rising temps move up resonanceRising temps move up resonance Filter LC is in parallel with System z Filter LC is in parallel with System z --causing ANOTHER resonant pointcausing ANOTHER resonant point New parallel resonant point is New parallel resonant point is hopefully not on critical frequencieshopefully not on critical frequencies11/20/2003 10:26.

9 46 17ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewMultipulse Rectifier Circuit ComparisonMultipulse Rectifier Circuit Comparison66--PULSE RECTIFIERPULSE RECTIFIER5th, 7th, 11th, 13th,5th, 7th, 11th, 13th,17th, 19th, 23rd, 25th , 19th, 23rd, 25th deg0 deg30 deg30 deg1212--PULSE RECTIFIERPULSE RECTIFIER5th, 7th 90% cancelled5th, 7th 90% cancelledstill have 11th, 13th,still have 11th, 13th,17th, 19th, 23rd, 25th , 19th, 23rd, 25th +20 deg+20 deg0 deg0 deg--20 deg20 degVprim66--RECTRECTBRIDGEBRIDGELOADLOAD 1818--PULSE RECTIFIERPULSE RECTIFIER5th, 7th 11th, 13th5th, 7th 11th, 13th90% cancelled90% cancelledstill have 17th, 19thstill have 17th, 19th23rd, 25th , 25th 10:26:46 18ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewPlating RectifiersPlating Rectifiers Power range 1 Power range 1--10 MVA10 MVA Thyristor [SCR] phase controlledThyristor [SCR] phase controlled Frequently 12 pulse configuration to Frequently 12 pulse configuration to cancel 5th and 7th harmonicscancel 5th and 7th Harmonics Filters are on transformer primary Filters are on transformer primary Small 5th and 7th plus 11th and 13th Small 5th and 7th plus 11th and 13th 10:26.

10 46 19ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewDC DrivesDC DrivesABCABCABCABCP haseVoltagePhaseCurrentsSquare Waves CurrentsMDC Rectified Excavator Drive Phase controlled Phase controlled SCR drives, phase SCR drives, phase amps in square wave amps in square wave blocksblocks Usually have PF Usually have PF comp and Filters comp and Filters Typical 5th, 7th etc at Typical 5th, 7th etc at 1/N magnitude. 1/N magnitude. HF ringing HF ringing Harmonics due to Harmonics due to Switched caps on Switched caps on P&H individually P&H individually LAG PF at stall very LAG PF at stall very poor w/o w/o 10:26:46 20ggGE Industrial SystemsGE Industrial SystemPower SystemHarmonic OverviewHarmonic OverviewSwitched Capacitor BanksSwitched Capacitor BanksOR Contactors or SCR s can be Contactors or SCR s can be Provide automatic compensation Provide automatic compensation of variable PF demandsof variable PF demands Switched banks must be Switched banks must be individually tuned.