Document: NUREG-0800
Document ID: d9e9d0a9-6390-4154-94dc-7d5e6d8145cd
Document Type: srp
Title: A-C POWER SYSTEMS (ONSITE)
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052350489.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.3.1
CFR Part: 
CFR Title: 

Content:
ccomplished. Because the signal to start the diesel-generator sets is normally derived from undervoltage relays, and under this situation the voltage is maintained above the trip relay settings by the diesel generator under test, the remaining redundant diesel generators will not be commanded to start running. Consequently, the added capacity resulting from the connection of non-safety related loads to the diesel generator under test will cause the tripping of this diesel due to overload. The end result could be the total loss of power to the safety buses. However, this power interruption could be of momentary duration if the .remaining redundant diesel generators are commanded automatically to start by undervoltage relay action Immediately after total power is lost. The diesel generator under test will be inoperable due to the self- locking feature preventing restarting after an overload trlp condition. The reviewer ascertains that the time delay introduced 8.3.1-11 Rev. 2 - July 1981 in making power available to the safety buses as a result of this event is within the response time limits assumed in the accident analyses. Included is verification that subsequent failures such as those resulting from improper electrical relaying coordination and self-locking features will not impair the automatic starting of the remaining redundant diesel generators required to meet minimum safety requirements. If the time delay introduced in making power available to the safety buses is not tolerable, it must be demon- strated that either the probability of occurrence of this event is low when compared to the frequency and duration of testing each diesel, or the design must provide diverse automatic signals, other than undervoltage, to ensure the availability of standby power to the safety buses. As an outcome of reviewing the parallel operation of the offsite and I onsite power systems, the use of the standby power supply diesel- generator sets to supply power to the electrical