S-transform based directional bus-bar protection

The directional protection of bus-bars using time-frequency transform such as S-transform is presented in the paper. S-transform is used to estimates the phase and amplitude of the fault current signals during fault situations. The difference in phase angle between positive sequence component of the current during fault and pre-fault conditions distinguishes internal faults (bus-bar faults) from external fault and load change situations. The estimated phase difference is positive for outgoing feeders for internal fault, but the same is negative for external and load change conditions. Thus a simple rule base is formulated for bus-bar protection depending upon the difference in phase information of the current signal of the outgoing feeder. The proposed method is tested for different fault situations in bus-bar as well as external fault and loading conditions, and provides accurate results.