Improved Overcurrent Protection of Capacitor Banks Using Mathematical Morphology

Numerical overcurrent relays used to protect capacitor banks can better discriminate between faults and switching inrush compared to their electromechanical counterparts. However, there is still scope and use for faster and reliable operation. This paper describes the implementation of a filter based on mathematical morphology that creates distinct signatures for capacitor inrush and faults. These signatures are then used to propose a rule-based classification method that can be easily implemented in microprocessor-based relays. Extensive simulations are carried out to test the classification method using waveforms generated from PSCAD/EMTDC simulation of a standardized test system. The classification method is shown to be very reliable, general, and significantly faster than methods currently used or previously proposed.