A practical approach in substation capacitor bank applications to calculating, limiting, and reducing the effects of transient currents

When two or more capacitor banks are paralleled on a common bus, the back-to-back switching of a bank against one or more already energized banks can produce high peak transient in-rush current values. Typically, these currents can exceed the available fault current levels previously present at the bus. The presence of inductance and capacitance together makes the transients oscillatory. Because of close circuit coupling, the transient frequency is generally several kHz or higher and usually decays to zero in a fraction of a 60 Hz cycle. The relatively high level and short duration of these currents can damage substation and control equipment necessitating that appropriate precautions be taken during the design process. This paper explores the methods for estimating capacitor bank transient currents, based on ANSI/IEEE C37.012-1979, for various sizes, voltages, and configurations of real world capacitor bank installations. Also discussed are the various accepted and applied methods for limiting substation equipment susceptibility to transients, as well as reducing the magnitude of the transients themselves.<>