Digital differential relaying scheme for teed circuits based on voltage and current signal comparison

The authors describe the basis of an alternative approach to the problem of differential protection of teed feeders that involves deriving signals which are functions of both voltages and currents. It is shown that this approach obviates the need for bias to compensate for capacitance spill current, thus improving the overall performance of the relay. Methods are outlined for compensating for the variable responses of practical transducers. Other practical considerations include the means developed for signal compression to simplify the digital hardware requirements and reduce the bandwidth requirements for digital communication between the three ends. The protection is developed using CAD techniques, and the methods proposed are readily implemented using present generation signal processing hardware