Upgrading intertie protection to meet Texas public utility commission rules

The 51N/32 combination functioned as a 67N directional overcurrent ground relay. In order to safely export power to the utility, safeguards had to be installed immediately. As part of the power contract, transfer trip equipment had to be installed at each utility substation and at the plant site to provide fast tripping of the intertie circuit breakers. Due to the long lead-time for procurement of transfer trip equipment and installation, immediate action was taken to prevent any power from exporting. Since the current protection relays did not give enough flexibility for additional trip set points, a microprocessor based multifunction relay was considered as an interim option.