Switching Transient of Multi-step 3-Phase Capacitor Bank in 66/11 kV Bhutan Silicon Metal Private Ltd

Abstract

Capacitor banks are finding greater acceptability in application with the integration of many Ferro Silicon Industries in Bhutan; however, switching of capacitor banks is one of the most challenging operations because many inherent characteristics are accompanied with these events that needs to be studied carefully. This paper presents the switching transients of multi-step 3-phase back-to-back capacitor bank of 66/11kV Bhutan Silicon Metal Private Limited. Simulation were carried out to observe the magnitude of peak inrush current, frequency of transient oscillation and peak oscillating voltage during energizing/de-energizing of capacitor banks. The result shows that the magnitude is very high without current limiting reactor but with current limiting reactor the magnitude is reduced to a permissible limit thereby mechanical stresses to the nearby electrical equipment is reduced. Capacitor bank with grounded system is recommended because the transient recovery voltage and the rate of rise of recovery voltage across circuit breaker contact are less than the standard value of 2S kV and the limit of equipment capability 28 kV/75 μs = 0.37 kV/μs as per ANSI C37.06-2000.