Document: NUREG-0800
Document ID: 97120913-d26f-4324-ab62-22f3f5b73925
Document Type: srp
Title: and 8.3.2.
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0636/ML063600410.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.3.1
CFR Part: 
CFR Title: 

Content:
ol number. 8.2-30 Revision 4 - March 2007 APPENDIX A GUIDELINES FOR GENERATOR CIRCUIT BREAKERS/LOAD BREAK SWITCHES 1. Background Generator circuit breakers have been used in nuclear generating station designs (McGuire, Catawba) as a means of providing immediate access of the onsite ac power systems to the offsite circuits by isolating the unit generator from the main step-up and unit auxiliary transformers and allowing backfeeding of power through these circuits to the onsite ac power system. Generator load break switches can also be used as a means of providing access to the offsite circuits as described above, but only on a delayed basis. Since this is a new design feature, the staff made the use of generator circuit breakers and load break switches a generic safety issue (NUREG-0933, Item B-53). In the case of McGuire and Catawba, References 1, 2, and 3, an expert consultant was retained to evaluate the generator circuit breaker verification testing program and its results. These guidelines are formalization of the results of that extensive work. Also guidelines for the load break switches are incorporated, as these devices have some common functional requirements as generator breakers as described above. The staff has made a determination that only devices that have the capability of interrupting the system maximum available fault current, i.e., circuit breakers, will be approved as a means of isolating the unit generators from the offsite power system in order to provide immediate access in accordance with GDC 17. This is necessary because a non fault current interrupting device, i.e., load break switch, must delay its trip for electrical faults until the switchyard circuit breakers have interrupted the current. Following opening of the load break switch, the switchyard circuit breakers must then be reclosed to establish offsite power to the unit. A generator circuit breaker, however, could interrupt the fault current and isolate the unit generator at the same