05000259/FIN-2015007-03
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Finding | |
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| Title | Procurement of Electrical Equipment for Ungrounded Electrical Systems |
| Description | The team identified an unresolved item (URI) related to the licensees procurement of electrical equipment for ungrounded electrical systems. The 480 VAC system for each unit consists of 480-V Load Center Unit Substations with each substation consisting of 4160-480-V transformers, primary terminal box, and close-coupled or bus duct connected 480-V, metal-enclosed switchgear. The 480-VAC distribution system is three-phase ungrounded. Each substation bus is normally fed from its own transformer, with an alternate source consisting either of an adjacent 480-VAC bus section or of another transformer serving as standby. Ventilated dry-type transformers are three-phase, delta-delta configuration so that the 480 VAC system is ungrounded. Ungrounded systems are susceptible to overvoltage conditions resulting from a single line to ground fault. A line to ground fault will result in a sustained higher voltage to ground on the ungrounded phases. Industry standard IEEE 242 (Buff Book) Protection and Coordination of Industrial and Commercial Power Systems, section 8.2.5 Ungrounded Systems stated if this ground fault is intermittent or allowed to continue, the system could be subjected to possible severe overvoltages to ground, which can be high...(cause line to ground voltages several times normal voltage on all three phases). Because of the potential for overvoltage conditions, specifications, purchase orders or procurement documents for equipment such as motors, cables, and switchgear should identify that the equipment is intended for use on an ungrounded system. The team requested the original specifications for the installed BFN safety-related motors BFN-2-MTR-068-0003; 2-FCV-68-3 (Recirc Pump 2A Disch VLV) fed from the 480V Reactor MOV Board 2E and, BFN-3-MTR-073-0002; 3-FCV-73-2 (HPCI Steam Line INBD Isolation VLV) fed from the 480V Reactor MOV Board 3A to determine if the intended service condition as a 480 VAC ungrounded system was appropriately identified. The team reviewed Procurement Engineering Group packages CRP205J - PO 733602 and CFK570P PO 836093 for the safety-related motors and determined that the ungrounded system requirement was not identified. Equipment intended for service on ungrounded systems is designed to withstand the sustained higher line to ground voltages than can occur on grounded systems. These insulation systems are not typically provided unless the purchaser specifies an ungrounded system. Industry standard NEMA MG 1 Motors and Generators, section 14.31 Machines Operating On An Ungrounded System stated: Alternating-current machines are intended for continuous operation with the neutral at or near ground potential. Operation on ungrounded systems with one line at ground potential should be done only for infrequent periods of short duration, for example as required for normal fault clearance. If it is intended to operate the machine continuously or for prolonged periods in such conditions, a special machine with a level of insulation suitable for such operation is required. The motor manufacturer should be consulted before selecting a motor for such an application. The NRC will review the licensees responses to follow-up questions asked during a conference call with the licensee on January 21, 2016. Based on this future review, the NRC will make a determination if the licensee properly procured electrical components for ungrounded systems. More information is needed to determine if more than a minor performance deficiency or violation exists associated with this issue, thus a URI is being opened. |
| Site: | Browns Ferry  |
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| Report | IR 05000259/2015007 Section 1R21 |
| Date counted | Dec 31, 2015 (2015Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.21M |
| Inspectors (proximate) | A Blamey A Ruh D Dumbacher D Terry-Ward G Ottenberg J Seat R Baldwin R Williams T Stephend Terry-Wardg Ottenberg J Bartley M Yeminy R Patterson W Deschaine |
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Finding - Browns Ferry - IR 05000259/2015007 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Browns Ferry) @ 2015Q4
Self-Identified List (Browns Ferry)
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