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?

2 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?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.

3 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.

4 AC Drives Switched cap banksSwitched cap banksLinear load examples:Linear load examples:NonNon--Linear load examples:Linear load examples:11/20/2003 10:26:46 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.

5 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?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.

6 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. 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!

7 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!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.

8 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.

9 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.

10 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.