Fast and Sensitive Time-Domain Protection of Shunt Capacitor Banks

Protection of shunt capacitor bank is important for identifying an internal fault to improve its service reliability. This paper presents a time-domain protection of shunt capacitor banks with wye connection. The proposed method is sensitive to a single element failure in the capacitor bank and takes decision within a quarter cycle. The superimposed current in time-domain is computed using the subtraction of calculated current from the measured one in each phase of the capacitor bank. The superimposed component of current is zero for normal operation and non-zero for internal fault conditions. Both open and short circuit faults in the capacitor bank can be identified by the proposed method. Using the change in equivalent capacitance in each phase of the shunt capacitor bank, the number of failed capacitor element is obtained. Various cases; symmetrical fault, system voltage unbalance and poor transient response of capacitor voltage transformers are tested to validate the performance of the proposed method and found to be accurate. The issue with division operation in time-domain is also addressed in the paper.