Powersystems have successfully energised a 90 MVA transformer using new point-on-wave technology to limit the inrush current and voltage dip.
Community Windpower engaged Powersystems to build the electrical connection for Aikengall II Wind Farm, a new 60.8 MW wind farm located in East Lothian. As part of the connection works Powersystems provided a 90 MVA 132/33 kV transformer. However, initial simulation studies showed that energisation of the transformer would cause significant voltage dips of up to 18% on the 132 kV grid.
To reduce the inrush current and voltage dip, Powersystems’ engineers recommended installing a 132 kV circuit breaker with segregated phase switching in conjunction with a point-on-wave controller which controls the precise time that each phase is closed.
Inrush current can be reduced and virtually eliminated by closing each phase at the precise moment in time when the voltage waveform from the supply side matches the remanent flux that is left in the transformer. Powersystems used a 132 kV circuit breaker supplied by GE Grid Solutions in conjunction with a Visimax SynchroTeq Plus supplied by Enspec Power to measure the transformer remanent flux and control the closing time.
The SynchroTeq Plus performed remarkably. By the completion of commissioning, the voltage dip on the 132 kV system had been reduced from about 7% during an uncontrolled energisation of the transformer, to 0.6% when energisation was controlled by the SynchroTeq Plus.
This is the first 132 kV transformer in the UK to be controlled by the SynchroTeq Plus and these results show that point-on-wave control technology is now a viable option for mitigating transformer inrush currents even for large grid-scale transformers.