Power Distribution HarmonicsCase Study of 285-3F Chiller Plant

Michael W. HarmonPrinciple Engineer

Savannah River Nuclear Solutions, LLCSavannah River Site

May 5, 2011

Las Vegas, Nevada

2011 Department of Energy Facility Representative / Safety System Oversight Workshop

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What are Harmonics?

Distorted electrical waveforms that introduce inefficiencies into your electrical system.

Harmonic Order Frequency 1 (fundamental) 60Hz 2 120Hz 3 180Hz 5 300Hz 7 420Hz N N * Fundamental

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Distorted Waveforms

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Some Sources of Harmonics

Non Linear Loads• Solid State Motor Drives (VFDs)• Rectifiers/Inverters (largest source) • Switch / Pulsed Circuits• UPS systems• Computer power supplies• Arc devices – arc furnaces, welders• Fluorescent lighting – electronic ballasts

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Some Harmonic Related Symptoms • Electronic Equipment Misoperation (which relies on voltage zero

crossing detection or is sensitive to wave shape) • Incorrect Readings on Meters • Circuit Breaker Misoperation• Protective Relays Misoperation• Blown Capacitor Fuses• Neutral Overheating (3rd Harmonic)• Motor / Generator/ Transformer* Overheating• Interference with Communication Circuits

* Dry-Type Transformer – Heat of 30% of the equivalent additional load

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285-3F Chiller Plant

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285-3F Chillers and Switchgear

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Basic Single Line

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Highlights of Events• Several previous single line outages for a new facility tie-in with no

perceived harmonic affects

• Another single line feed was initiated Monday morning (September 13, 2010). Chillers 1,2 and 3 shutdown and would not restart. Chiller 4 was locked out for maintenance. Found same 120V control fuse blown in all three chiller control circuits. The fuses were replaced which cleared the alarm interlock allowing for the chillers to be restarted.

• The chillers operated for several hours however at 1430 hours all chillers shutdown again.

• After second shutdown, the green OK light on all three PS/UV relays was not illuminated and all three relays had phase unbalance targets. The alarm interlock would not clear therefore the chillers would not start.

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Highlights of Events• Was this outage different from previous outages?

– Initially told by the Utility Group there was no difference.

• Analytical Labs had high priority samples which had to be analyzed. With no chiller plant operations, the temperature is too high for lab instrumentation to operate. All sample analysis stopped.

• A Dranetz electrical monitor was connected to the control circuit of Chiller 1. The initial data indicated a very small harmonic component which was not an immediate concern. The older Dranetz being used was not abled to event on harmonics.

• The PS/UV relay green lights were cycling on and off every 2 – 8 hours. The relays were removed, bench tested and found to be functioning correctly.

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Highlights of Events• Experiencing numerous conflicting symptoms and results• Finally came back to the original question at the beginning. Was this outage different from

previous outages? – After a more detailed look by the Utility Group the answer was yes.

• What was different?– Unlike the other outages, this time there was only one 115kV/13.8kV transformer in service

and BOTH 13.8kV capacitor banks (used for Power Factor correction) in service. • Utility Group temporarily place the second 115kV/13.8kV transformer in service and the green OK

lights returned on the PS/UV relays.• As a verification, the second 115kV/13.8kV transformer was removed from service and the green

OK lights went out. • That unique and seldom used transformer/capacitor bank configuration was just enough to amplify

harmonics already in the system to the level that the Chiller PS/UV relays dropped out (no green OK lights).

• Harmonics are amplified by harmonic resonance. PF correction brings together system capacitance and inductance. There is a frequency at which the capacitors are in parallel resonance with the supply. If that frequency occurs at, or close to, an existing system harmonics then large harmonic currents will be generated thus causing large harmonic voltage disturbances.

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Dranetz Tapes C-Phase Only

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Dranetz Tapes C-Phase Only

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Dranetz Tapes C-Phase Only

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Harmonics Configuration Results

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Path Forward and Conclusions

• The Utility Group will now administratively control the transformer/capacitor bank configuration (most economical solution)

• The Utility Group has purchased new monitoring equipment and has started taking baseline harmonic levels in each area

• The Utility Group is polling facilities across the site to collect data on all harmonic producing equipment in operation. New utility request form has been modified to include the listing of any new harmonic equipment to be installed

• We generally don’t think about harmonics however with modern electronics, VFDs, etc. the problem will get more attention in the future

• I don’t believe we have a serious harmonics situation yet. The PS/UV relay reactions are a “red flag up the pole” for future awareness

• IEEE-519 sets voltage and current distortion limits for harmonics

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Power Distribution Harmonics

Questions or Comments