Application of Point on Wave Switching for Mitigation of Transients During Charging of Power Transformer in Presence of Large Capacitive Component

Abstract

Point on wave switching is widely accepted as mitigation technique for inrush reduction during transformer and capacitor switching. Ideal targets for transformer switching are voltage peak without considering residual flux whereas capacitors banks are switched at voltage zero. There are several cases where large capacitive component is directly connected to transformer due to commercial issues. In these conditions, the default strategies for capacitor/transformer are not effective and target needs to be modified so as to achieve minimum inrush current. This paper evaluates the controlled switching strategies for transformer with large capacitor bank. The technique has been verified from field tests, simulated in PSCAD software and found quite effective. The subject configuration is constrained by low short circuit strength of grid which lead to severe voltage dip beyond acceptable limits. Therefore, the motive of installing CSD in such environment is not only to reduce inrush current rather targeted for improvement in power quality. Different cases has been considered for confirming the validity of proposed methodology. Besides reducing inrush effect, suggested methodology is also helpful in increasing power quality in terms of total harmonics distortion and voltage dip.