Document: NRC Regulatory Guide
Document ID: 1731a882-b0c5-418d-b65e-55646c26be5c
Document Type: regulatory_guide
Title: 03/2007
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0703/ML070380553.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.9
CFR Part: 
CFR Title: 

Content:
diesel generator output breaker. 1.2 When the characteristics of the required emergency diesel generator loads are not accurately known, such as during an early stage of design, each emergency diesel generator selected for an onsite power supply system should have a continuous load rating (as defined in Section 3.2 of IEEE Std 387-1995) equal to the sum of the conservatively estimated connected loads (nameplate rating) that the diesel generator would power at any one time, plus a 10- to 15-percent margin. In the absence of fully substantiated performance characteristics for mechanical equipment such as pumps, the electric motor drive ratings should be calculated using conservative estimates of these characteristics (e.g., pump runout conditions and motor efficiencies of 90 percent or less, and power factors of 85 percent or less). 1.3 During the operating license or combined license stages of review, the maximum design-basis loads should be within the continuous rating (as defined in Section 3.2 of IEEE Std 387-1995) of the diesel generator with sufficient margin (i.e., not less than 5 percent). 1.4 Clause 4.1.2 of IEEE Std 387-1995 pertains, in part, to the starting and load-accepting capabilities of the diesel generator. In conformance with Clause 4.1.2, each diesel generator should be capable of starting and accelerating to rated speed, in the required sequence, all the needed engineered safety features and emergency shutdown loads. The diesel generator should be designed such that the frequency will not decrease, at any time during the loading sequence, to less than 95 percent of nominal and the voltage will not decrease to less than 75 percent of nominal. (A larger decrease in voltage and frequency may be justified for a diesel generator that carries only one large connected load.) Frequency should be restored to within 2 percent of nominal in less than 60 percent of each load-sequence interval for a stepload increase, and less than 80 percent of each