05000285/LER-1980-021-03, /03L-0:on 800910,transformer T4 of DG-1 Failed. Transformer Feeds Diesel Oil Immersion Heater & Alarm Relays.Caused by Moveable Armature Located on Immersion Heater Contractor.Armature Repaired
| ML19347A931 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 09/11/1980 |
| From: | Mueller R OMAHA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| Shared Package | |
| ML19347A923 | List: |
| References | |
| LER-80-021-03L, LER-80-21-3L, NUDOCS 8009300539 | |
| Download: ML19347A931 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| 2851980021R03 - NRC Website | |
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U. S. NUCLEAR REGULATORY COMMIMlUN RfRC FORM 366 (7 77)
LICENSEE EVENT REPORT CONTROL BLOCK: l l
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60 61 DOCKET NUMSER 68 69 EVENT DATE 74 75 REPORT DATE 80 EVENT DESCRIPTION AND PROBABLE CONSEoVENCES Oio Transformer (T4) of DG-1 failed. This transformer feeds the control circuitry for
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the 15 kw diesel oil imersion heater as well as supplying power to alarm relays for 1O lai !
the following items:
low lube oil pressure, low lube oil level, hiah and/or low I
10141 I lube oil temperature, water temperature, water level and water pressure. Durino I
iO Isi I the time of the transformer failure, DG-2 as well as the 161 kv and 345 kv systems 1
IO te i I were available and operable.
In addition. DG-1 was considered inoperable only durind
!O I7I I the time that the transformer and associated eouipment were bei~ o chanaed out, i.e.
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i c ie i i only while DG-1 was in " Local Maintenance".
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40 41 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS IilOII A moveable armature located on the immersion heater cnntactor was lonso nn the olunadr li li 1 I shaft & therefore. causina a slicht bindina orablem nn the enntactnr_
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iii2i l oostulated that this bindino of the contactor caused the contactor control trans-I li13i I former to draw excessive current and eventually fail. The moveable armature was re-I ii,4i I paired and the diesel satisfactorily tested and returned to service.
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LER 80-021 Omaha Public Power District Fort Calhoun Station Unit No. 1 Docket No. 05000285 ATTACHMENT NO. 1
Safety Analysis
The Fort Calhoun Station Unit No.1 Engineered Safety Features System is so designed that no single failure can prevent the safe shut-down of the plant if necessary.
During the time diesel generator DG-1 was inoperable, diesel generator DG-2 was operable as were the 161 KV and 345 KV supplies thus providing more than adequate capability for safe shutdown of the plant should the unlikely event of an accident occur.
It should be pointed out that DG-1 was considered inoperable only during the time that the transforner was being changed out since this transformer only feeds the oil immersion heater for DG-1 and associated annunciation. Should the need have arisen, DG-1 would still have automatically started per engineered safeguards and performed its design function as described in the Final Safety Analysis Report.
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LER 80-021 Omaha Public Power District Fort Calhoun Station Unit No.1 Docket No. 05000285 ATTACHMENT NO. 2
Corrective Action
M.0. #7057 was written to investigate possible causes for the failure of the control transformer. As a result, it was discovered that a moveable armature (moveable in the vertical direction) was loose on the immersion heater contgetor's giunger shaft, thus allowing the armature to rotate from 0 to 360 horizontally with respect to the plunger shaft. Normally, when the contactor is picked up or energized the plunger shaft is drawn vertically via magnetic forces until the armature mates with a designated seating surface on the contactor and correspondingly the main. contacts are completely closed. However, if the armature is allowed to rotate horizontally such that when the annature and plunger shaft are magnetically drawn upwards, the armature does not mate with its designated contactor seating surface; the "esult is armature binding and partial closure of the contact main contacts.
Further the control transformer 5.ill draw excessive amps as it tries to fully close the contactor contacts.
To correct the problem, the armature was secured to the plunger shaft in such a position that proper seating between the armature and armature seating surface of the contact would be achieved.
As a further consequence of this problem, the emaining diesel con-trol panel (DG-2) was inspected for a similar problem. However, the armature shaft was found to be firmly riveted to the plunger shaft.
The failed control transformer was replaced with an electrically i
equivalent transformer (See EEAR FC-80-101). Any wires or relays which may have been damaged by the transformer overheating were also replaced with identical equipment. The diesel was satisfactorily tested and returned to service.
No further action is planned or scheduled in conjunction with this event.
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o LER 80-021 2
Omaha Public Power District Fort Calhoun Station Unit No.1 Docket NO. 05000285 ATTACHMENT NO. 3 Faiare Data This is the second failure of this type at the Fort Calhoun Station.
The first being documented per LER 80-014.
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