Shunt Capacitor Banks Online Monitoring Using a Superimposed Reactance Method

A new indicating quantity, named superimposed reactance (SR), is presented in this paper to determine failed capacitor elements' involved phase and number in shunt capacitor banks (SCBs). The proposed quantity is estimated using available measurements to the unbalance protection function of SCBs numerical protective relays. The proposed SR adopts calibrating factors for element failures online monitoring and can provide live report of the number of failed capacitor elements. The proposed method applications are: faster identifying SCBs faulty units, for fuseless and internally fused designs, and planning preventive/scheduled maintenance for all types of unit designs including externally fused units. With integration of these applications into protection intelligent electronic devices that provide captured and time-tagged event records via communication protocols for HMIs and SCADA systems, outage times would be reduced and smart grids reliability would be improved. The developed algorithm supports three different grounding arrangements, Wye-ungrounded, Wye-grounded via a low ratio current transformer, and Wye-grounded via a grounding capacitor at the SCB neutral point. Comprehensive simulation and fault-location sensing in PSCAD and MATLAB have verified the proposed algorithm performance. Advantages of the proposed method reports over conventional unbalance relaying alarms are also demonstrated using a commercial relay test results comparison.