Power Systems Application Brief
Queensland Electricity Commission
The Queensland Electricity Commission investigates and locates
problems in the power systems of Australia.
Brisbane, QLD Australia
A new power system for a coal mining railway in Queensland met with
problems when the filter capacitors used to control the power supply
quality mysteriously failed catastrophically. The cause was a large
sixth harmonic (300 Hz) resonance condition set up between a 50 kV
railway supply harmonic filter and the power system. Not only did this
failure result in major financial problems, it also posed a challenging
problem to the resident power transmission engineers.
Power utilities worldwide experience problems related to harmonic
distortion of voltage waveforms. A non-linear element will cause a
non-sinusoidal current to be drawn from the power supply, which can
lead to capacitor failures and interference with communication circuits
- not to mention catastrophic failures.
Signal Analysis Tools Required
To ensure adequate quality of supply, utilities try to keep harmonic
distortion below levels specified by published standards, such as the
Australian Standard 2279 and the American IEEE 519 Standard. If the
levels specified in the standard are exceeded - even if nothing fails -
field investigations are performed to locate offending harmonic
sources. These investigations require a combination of power
engineering and signal analysis skills, and tools to match.