Puget Sound Energy, Auburn Power Factor Capacitor Bank Harmonic Resonance Investigation

Puget Sound Energy is a utility company serving Western Washington. They installed two capacitor banks at the Boeing Auburn Plant main substations. The purpose of these capacitors was to correct the power factor at the Auburn Plant. There were concerns about the potential of harmonic sources and possible resonance problems.

Puget Sound Energy hired Power Systems Engineering to perform a harmonic analysis study to determine the resonance point of the capacitors and transformers. The transformers and capacitors together acted as tuned 5th harmonic filters. They provide a low impedance path for 5th harmonic currents in the utility distribution system.

Power Systems Engineering's engineer recommended that the capacitor banks be de-tuned by removing a portion of the capacitance. This eliminated the problem and cleaned up the voltage sine wave and lowered the %THD.

Puget Sound Energy is a utility company serving Western Washington. They noticed that the voltage had an excessive amount of harmonics and the %THD exceeded the IEEE-519 guidelines.

Puget Sound Energy hired Power Systems Engineering, to model their distribution system from the Greenwater Substation to the Crystal Mountain Ski Resort. The purpose of this study was to determine why the voltage distortion was so high at the location.

The engineers at Power Systems Engineering found that due to the underground cable capacitance and system transformers, the system was tuned to the 5th harmonic. The ski resort has numerous variable speed drives that produce 5th harmonic currents. These currents along with the system tuned to the 5th harmonic caused the high %THD.

Power Systems Engineering worked with the utility to redesign the distribution system and to shift the system resonant point to an even number.