Developments in distance protection

The block average comparison principle for distance relay comparators has been successfully applied and well proven for many years. The only significant improvement to the basic scheme has been the introduction of a third signal S3 (I_LZR), to the comparator gate, which improved stability for feeder de-energisation and allowed the introduction of additional characteristics (e.g. directional shaped reactance, etc.). The author describes a method of decreasing the minimum comparator operating time by a factor of two and the practical benefits obtained due to the use of microprocessor technology in the control of a distance protection relay based on the block average comparison principle