Interface of the Nuclear Plant with the Grid

The PPS is the preferred power supply for the Nuclear Generating Station Class 1E systems, and the PPS circuits are used during all modes of operation to supply power to the Class 1E and non‐Class 1E buses of the plant. Protective systems are provided to minimize the probability of loss of the PPS under fault conditions. High voltage transmission lines are generally protected with redundant high speed relay schemes with reclosing and communication equipment to minimize line outages. The switchyard DC system channels are generally segregated from each other, separated by physical distance and often in separate rooms. The connection between the preferred power supply and the Class 1E power systems should be made at the input terminals of the Class 1E circuit breaker. The switchyard grounding function is to provide a safe path for a ground fault current to ground. Computer programs are available to design and verify the adequacy of ground grids.