PC based protective relaying algorithms for bus bars using digital filters

The paper reports the development of protective relaying algorithms for bus bars using digital filters. An efficient algorithm based on the recursive constraint transfer function model of the IIR band-pass filter has been used to extract the 50 Hz frequency component for realizing the various protective functions for a bus bar. A fourth-order adaptative filter is used for tracking the centre frequency components of voltages and currents. The proposed relaying algorithms provide variable-bias differential protection logic coupled with undervoltage check/neutral current check, features to ensure a high degree of reliability and freedomfrom unwanted tripping of circuit breakers. The developed algorithms have been tested with simulated input signals, reprensting various normal and abnormal bus bar conditions and the scheme as a whole responded efficiently.