White Paper: Passive filter to improve power quality at Tekapo B hydro power station
July 15, 2020
Stephen Butler

New Zealand’s aging hydroelectric stations are undergoing refurbishment. This includes replacing excitation systems with modern power electronic-based solutions.

The stations’ auxiliary power supply is critical for ensuring a secure power supply for the stations’ operation. However, the exciters can cause issues with power quality that in turn can cause issues for auxiliary systems, which are sensitive to poor power quality.

Station auxiliary power quality issues have been experienced for many years at the Tekapo B Hydro Power Plant. After excitation system upgrades in 2013, there was a slight improvement in the power quality but, on occasion, electronic component failures on UPS and battery charger systems were still occurring. Due to these ongoing failures, it was decided to source the station auxiliary supply from the local distribution network as an interim measure. The continued equipment failures prompted an in-depth analysis of the station auxiliary power quality.

PSC identified the cause as high voltage spikes resulting from a high-frequency resonance between the fast switching of the high-powered excitation system and the auxiliary supply network.

PSC investigated power quality issues and developed a practical solution. Our approach included:

  • Measuring and analyzing the voltage waveforms of the auxiliary power system using a high-resolution scope
  • Development of an Electromagnetic Transient (EMT) model in PSCAD/EMTDC to replicate the interaction of the auxiliary power system and the static excitation system
  • Development of a passive filter in PSCAD
  • Design and construction of a passive filter
  • Implementation and testing

This paper highlights the real-world issues of power quality and considerations for station upgrades. It explores the use of EMT-type simulation for design and the installation of a practical solution to resolve power quality issues.

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