Document: NUREG-0800
Document ID: e1169529-d2cb-4947-9efe-b23d927f4aa9
Document Type: srp
Title: NUREG40800
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052350520.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8
CFR Part: 
CFR Title: 

Content:
ion to the undervoltage scheme provided to detect loss of offsite power at the Class 1E buses, a second level of undervoltage protection with time delay should also be provided to protect the Class 1E equipment; this second level of undervoltage protection shall satisfy the following criteria: a) The selection of undervoltage and time delay setpolnts shall be determined from an analysis of the voltage requirements of the Class 1E loads at all onsite system distribution levels; b) Two separate time delays shall be selected for the second level of undervoltage protection based on the following conditions: 1) The first time delay should be of a duration that established the existance of a sustained degraded voltage condition (i.e., something longer than a motor starting transient). Following this delay, an alarm in the control room should alert the operator to the degraded condition. The subsequent occurrence of a safety injection actuation signal (SIAS) should immediately separate the Class 1E distribution system from the offsite power system, 2) The second time delay should be of a limited duration such that the permanently connected Class 1E loads will not be damaged. Following this delay, if the operator has failed to restore 8A-13 Rev. o - July 1981 adequate voltages, the Class 1E distribution system should be automatically separated from the offsite power system. Bases and justification must be provided in support of the actual delay chosen. c) The voltage sensors shall be designed to satisfy the following applicable requirements derived from IEEE Std. 279-1971, "Criteria for Protection Systems for Nuclear Power Generating Stations": 1) Class 1E equipment shall be located at and electrically 2) An Independent scheme shall the Class 1E power system. 3) The undervoltage protection a per bus basis to preclude source; utilized and shall be physically connected to the Class 1E switchgear. be provided for each division of shall include coincidence logic on spurious