United States Nuclear Regulatory Commission - Protecting People and the Environment

W15 Adequacy of Station Electric Distribution System Voltages—Degraded Voltage Protection

The Office of Nuclear Reactor Regulation, Division of Engineering, Electrical Engineering Branch will conduct a panel session to discuss the existing regulatory requirements and staff guidance to ensure automatic protection of safety buses and loads from degraded voltages. Since degradation of the offsite power system can lead to or cause the failure of redundant Class1E safety-related electrical equipment, the NRC requires all licensees to install degraded voltage protection schemes. NRC’s letter to licensees dated June 2, 1977, regarding sustained degraded voltage conditions at the offsite power sources, and generic letter 79–36 dated August, 8, 1979, “Adequacy of Station Electric Distribution Systems Voltages“ provided guidance on evaluating the performance of electric power systems with regard to voltage drop calculations. Recent regional inspection findings have identified inconsistent interpretations of the NRC requirements and guidance for the implementation of degraded voltage protection schemes. Both the NRC and invited industry representatives will present their perspectives on resolving this issue.


  George Wilson – Branch Chief, Division of Engineering, NRC/NRR




Swagata Som – NRC/NRR, tel: (301) 415- 8491, e-mail: Swagata.Som@nrc.gov

Carla Roquecruz – NRC/NRR, tel: (301) 415-1455, e-mail: Carla.Roquecruz@nrc.gov

Page Last Reviewed/Updated Thursday, March 29, 2012