05000250/FIN-2017008-04
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Finding | |
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| Title | Potential Inadequate Design Control of Current Limiting Reactor |
| Description | Introduction: The team identified an URI associated with potential discrepancies between the licensees design documentation and the installed configuration of busses inside the reactor coil cabinet. Description : The team reviewed the reactor coil layout drawing, showing the location of the reactor coil and bus configuration within the switchgear cabinet and compared the drawing with the photographs available of conditions inside the cabinet, including phase designation marking s provided on the busses, which appeared to indicate a discrepancy between drawings and bus markings. The drawing indicated an incoming bus configuration from front to rear as phase B , phase C , and phase A . However, the photographs indicated markings on the busses themselves as phase A , phase B , and phase C . The trip flags on the overcurrent relays indicate an initial fault starting on phase A . This discrepancy should be reviewed and appropriate corrective actions taken . The team also evaluated the available fault current on the 3A 4kV switchgear to assess the impact of the current limiting reactor ( CLR) on the switchgear and its capacity to withstand short circuit currents imposed on the bus during faults. The vendor indicated that the 3A 4kV switchgear bus high side could withstand 78,000 amperes (A) but the low side could only withstand 60,000 A . The available fault currents in the low side configuration for restoration was determined to be 55,720 A asymmetrical or 35,171 A symmetrical. The team s review of calculation PTN -3FSE -07- 001, Unit 3 - Safety Related AC Electrical Distribution PSB -1, Short Circuit, Voltage Drop and Bus Loading Analysis, indicated an assumed 3A 4kV switchgear bracing for 78,000 A symmetrical to be consistent with a 350 MVA , 4kV breaker. However, other documents indicate a 78,777 A to be an asymmetrical fault current and a 350MVA capability corresponds more 22 closely to 49,000 A symmetrical than the 78,000 A symmetrical. This issue needs further review in order to be fully understood and determine if there are any issues that need to be addressed. The megger test result s provided for the low side of the 3A 4kV switchgear established a 500 megohms (M) resistance measurement between the phase busses as satisfactory. The inspectors noted that other national standards such as the International Testing Association Inc. , Maintenance Testing Specifications , 1997 edition determined that the insulation resistance tests on electrical apparatus and systems recommends a minimum of 1,000 M for an equipment similar to the 3A 4kV switchgear rated for 5,000 V . Finally, t he team identified a potential concern with the design and installation of the CLR unit inside the 3A 4kV switchgear provided with exposed incoming and outgoing 4kV bussing. The 3A 4kV switchgear had thermoplastic insulated bussing throughout the gear except at the CLR coil. There was no industry standard for a required spacing between the bare individual phase busses and grounded surfaces. Information provided indicated a spacing that conformed to accepted industry technical publications. However, other aspects associated with the cabinet construction and room layout of ventilation equipment in this particular case may have contributed to the bus fault. In particular, the louvers in the front and rear of the cabinet allow unimpeded access to the inside of the cabinet and the exposed energized busses. No guidance was provided to maintain the orientation of the bus connection bolts to provide as wide a gap as possible to grounded surfaces. In the case of the 3A 4kV switchgear , photographs showed evidence that the bolts had been installed backwards for the connection to the C phase bus at the rear bottom of the cabinet . This was the flash- over spot where the bus faulted to the metal cabinet. Specifications and drawings associated with this equipment did not provide any guidance on spacing or insulation to be applied to the busses. An URI was opened in order to review the design and configuration of the reactor coil located inside the 3A 4kV switchgear following the completion of the licensees root cause evaluation. This review will be accomplished to determine whether any performance deficiencies exist in the area of design control. (URI 05000250, 251/2017008- 04, Potential Inadequate Design Control of Current Limiting Reactor) |
| Site: | Turkey Point  |
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| Report | IR 05000250/2017008 Section 4OA5 |
| Date counted | Mar 31, 2017 (2017Q1) |
| Type: | URI: |
| cornerstone | No Cornerstone |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 2201/004 |
| Inspectors (proximate) | E Stamm G Crespo J Patel J Reyes L Suggs N Melly |
| INPO aspect | |
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Finding - Turkey Point - IR 05000250/2017008 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Turkey Point) @ 2017Q1
Self-Identified List (Turkey Point)
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