ML20206S084
| ML20206S084 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley, Millstone, Peach Bottom, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Fermi, Catawba, Saint Lucie, Grand Gulf, Arkansas Nuclear, Susquehanna, Summer, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Crystal River, Vogtle, Duane Arnold, Clinton, San Onofre, Cook, Rancho Seco, McGuire, 05000000, Zimmer, 05000360, Fort Saint Vrain, Shoreham, Trojan |
| Issue date: | 06/30/1986 |
| From: | Kaiser A BBC BROWN BOVERI, INC. (FORMERLY BROWN BOVERI CORP. |
| To: | Taylor J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| REF-PT21-86, REF-PT21-86-253-000 PT21-86-253, PT21-86-253-000, NUDOCS 8607070287 | |
| Download: ML20206S084 (5) | |
Text
Grown Bover.
BBC i
eso ~ eovee, Switchgear Products Group esc arown Boveri,Inc.
Spring House, PA 19477 Phone:(215)628-7400 June 30, 1986 Mr. J. M. Taylor, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D C 20555
Subject:
BBC Brown Boveri K600/K800 Circuit Breakers Possible Cut Wires in Wire Harness (10CFR Part 21 Report)
Dear Mr. Tayler:
This report is a follow-up to a 10CFR Part 21 Report issued by Northeast Utilities, Millstone Nuclear Power Station, Unit 3 to the NRC Region 1 Office, May 9, 1986.
The report identified a condition in the type K600S circuit breakers supplied by BBC Brown Boveri, wherein a contvol wire harness containing eight (8) wires which run from various components in the circuit breaker to the auxiliary switch on a support shelf on the top left front side of the breaker came into direct contact with a racking gear inside the breaker. Although the harness was wrapped with a plastic spiral wrap, the gear teeth had worn through this material and severed the wire to the shunt trip coil. The wire grounded on the gear which opened the fuses.
This condition could result in the following safety implications depending upon which wire is cut.
l 1.
Failure of the charging motor to charge the breaker closing springs.
1 2.
Failure of the closing latch release coil resulting in loss of remote closing of the circuit breaker.
3.
Loss of the shunt trip capability (local and remote opening function).
4.
Loss of local and remote breaker "open" green light indications.
None of the malfunctions identified above would prevent the circuit breaker from l
l tripping due to an overcurrent or fault condition.
The wiring for these functions is on the other side of the circuit breaker in a separate wiring harness.
I Normally the wiring harness is secured to the underside of the auxiliary switch support plate by a plastic wire clamp which locates (with a self tapping screw) the wire harness such that it keeps it free and clear of the racking gears.
It appears, that in some breakers at Millstone Unit 3 this wire clamp was not located correctly, which permitted the wire harness to come in contact with one of the racking gears.
There are two flat gears that fit up against the front plate of the breaker. One of these gears drives a worm gear, which in turn drives a helical gear that operates the racking cams.
It is the contact with this helical gear (which is mounted vertically) that can cut into the wire harness.
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BBC BROWN BOVERI Mr. J. M. Taylor June 30, 1986 Page 2 There is an opening in the left side plate of the breaker, on the top, near the auxiliary switch, through which an inspection can be performed to determine that the wire harness has not been damaged by the helical gear.
If the spiral wrap or the wire harness shows signs of weaf or contact with the gear, corrective action is required.
If the control wire harness is free and clear of the racking gear no further action is required. The harness is secured to the underside of the auxiliary switch support plate by a wire clamp and to the side of the breaker by wire ties and cannot move to come in contact with the racking gear.
At Millstone Unit 3 the condition was corrected by moving the mounting screw for the plastic wire clamp on the underside of the auxiliary switch support plate, toward the center of the breaker to move the wire harness away from the gear. This, however, could put stress on the wire terminals at the auxiliary switch.
BBC Brown Boveri has designed a gear guard (Part Number 715616-A) to provide protection of the wire harness only in those cases where inspection has revealed that there is contact of the harness with the gear resulting in damage to the harness.
Field installation of this kit is not required if inspection reveals that the wire harness is not in contact with the gear.
It should be noted that the type K600 and K800 circuit breakers have been in use since 1958 with little or no problem with cut wires.
In 1981, an incident of a shunt trip coil wire being cut by the racking gear was reoorted by San Onofre (Southern California Edison). At that time the shunt trip wires were not encapsulated fully in the spiral wrap. The field solution was to pull these two wires away from the racking gears with a plastic tie wrap through holes in the side plate of the breaker.
Corrective action in the factory was to enclose the shunt trip wires inside the spiral wrap and make sure the routing of the harness was clear of the gear.
An inspection to make sure the there is clearance between the control wire harness and the racking gear should be performed at normal maintenance intervals, and any time replacement parts are installed or wiring modifications are made.
This inspection should be performed on electrically operated (E.0.) breakers of the K600 and K800 types, not just the K600S.
The K1600 circuit breakers, because of their larger size, have adequate clearance and do not require inspection. Also, K600 mechanical operated breakers do not require inspect. ion, since there is no wire harness in the area of the racking gears.
Although Millstone Unit 3 reported this condition as being generic, BBC Brown Boveri believes the condition where the harness is coming into direct contact with the gears is limited in scope.
BBC BROWN BOVERI Mr. J. M. Taylor June 30, 1986 Page 3 Examination of some of the K600S breakers at Millstone Unit 3 revealed that there was a larger than normal (oval-shaped) hole due to a manufacturing anomaly, for the wire harness to pass through the support plate to the auxiliary switch (on the left side of the breaker). This could contribute to the misrouting of the control wire harness.
Normally this wire access hole is 1-1/8" in diameter with a rubber grommet to protect the harness.
An inspection was also conducted at Nine Mile Point Unit 2 (Niagara Mohawk) on some K600S circuit breakers manufactured in approximately.the same time period (1982 and 1983) as those at Miilstone Unit 3.
This inspection, though limited in scope, did not
]
reveal the same conditions that were observed at Millstone Unit 3.
There was adequate clearance between the gec and the wiring harness, and there was no damage to the spiral wrap or wires in each of the breakers inspected.
Users of K600 and K800 electrically operated circuit breakers should consider conducting a visual inspection for clearance between the wiring harness and racking gear. Those units where inspections were previously conducted for the condition noted at San Onofre (Southern California Edison) in early 1981 should require reinspection only if replacement parts have been installed or modifications have been made to the circuit breakers since that time.
The location of K-Line circuit breakers that are being utilized in Nuclear Safety Related applications is shown in Attachment "A" of this report. This is a total list of K-Line circuit breakers and will therefore include those units that may have been subject to similar inspection based on a BBC Brown Boveri recommendation in April, 1981.
It ' uo includes K1600, K2000, K3000, and K4000 circuit breakers which do not require an inspection because there is no potential problem with the wire harness routing.
Q
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mwr A. F. KAISER, President Switchgear Products Group AFK/jm Attachment
i A:TTAC HM E N T- " A "
Location of BBC Brown Boveri K-Line Circuit Breakers in Nuclear-Safety Related applications.
Arizona Public Service Palo Verde 1, 2, & 3-l Arkansas Power & Light Company Arkansas Nuclear 1 j
Carolina Power & Light Brunswick 1 & 2 i
Cincinnati Gas & Electric Zimmer l
Cleveland Electric Illuminating Perry.
. Consumers Power Palisades '
. Detroit Edison Fermi 2 Duke Power Oconee 1, 2 & 3 Duke Power McGuire 1 & 2 Duke Power Catawba 1 & 2 1
Duquesne Light Company Beaver Valley l
Florida Power Corporation Crystal River Florida Power & Light Company
. Turkey Point Florida Power & Light Company St. Lucie Georgia Power Company Vogtle Gulf States Utilities Company River Bend Illinois Power Clinton Indiana & Michigan Electric Company Cook Iowa Electric Light & Power' Company Arnold Long Island Lighting Company Shoreham Mississippi Power & Light Grand Gulf Niagara Mohawk Power Corporation Nine Mile. Point 2 4
j Northeast Utilities Millstone 3 Pennsylvania Power & Light Susquehanna Philadelphia Electric Company Peach Bottom Philadelphia Electric Company Limerick Portland General Electric Trojan Public Service Colorado Ft. St.Vrain Public Service Indiana Marble Hill Public Service New Hampshire Seabrook 1
+'*
1 Public Service Electric & Gas Salem Sacramento Municipal Utility District Rancho Seco South Carolina Electric & Gas Summer Southern California Edison San Onofre 2 & 3 TVA Hartsville TVA Phipps Bend TVA Yellow Creek Virginia Electric & Power Company Surry i
Virginia Electric & Power Company North Anna Washington Public Power Supply System WNP-2 j
,h i
e 2
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