ML19276F309

LER 79-005/03L-0 on 790223:2A Recirculation Motor Generator Field Breaker Opened,Causing Flow Mismatch.Caused by Loosening of Coupling Between Main Shaft & Recirculation Motor Generator Set Tachometer.Tachometer Coupling Reset

ML19276F309
Person / Time
Site:	Quad Cities
Issue date:	03/12/1979
From:	Reed M COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19276F306	List: ML19276F305 ML19276F309
References
LER-79-005-03L-03, LER-79-5-3L-3, NUDOCS 7903280336
Download: ML19276F309 (2)

Text

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-] i t} While o,pe ra t i ng Unit Two at a steady state load, the 2A Reci rculation Motor Generatori m ,3  ; field breaker opened. When the MG Set generator field breaker opened, the 2A l ntai l Recirculation pump coasted down to zero speed causing a flow mismatch (T.S. 3.6.H.). l

,3,3 The 2B Recirculation pump speed was immediately reduced to minimize flow mismatch. l

,3  : ,3 l There were no safety implications due to this occurrence. l t

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, i; j An investication of the field breaker trio revealed that the Reci rculation MG Set 1 j tachometer coupling to the main shaf t had come loose. The tachcreter couplina was (

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repaired and the 2A Recirculat i on MG Set restarted. Once restarted a dynamic analysis

,, l was performed on the tachoneter to MG Set coupling. Work request 1264-79 has been i

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l. LER NUMBER: LER/R0 79-05/03L-0 ll. LICENSEE NAME: Commonwealth Edison Company Quad-Ci ties Nuclear Powe r S tation Ill. FACILITY NAME: Unit Two IV. DOCKET NUMBER: 050-265 V. EVENT DESCRIPTION:

On February 23, 1979 at 5:40 a.m., while operating Unit Two at a steady state load of 773 MWe, the 2A Reci rculation Motor Generator field breaker opened. The Uni t Operator immediately reduced the 2B Recirculation Pump to 45% of full flow, and the unit stabilized at 325 MWe. An attempt was made to restart the 2A Reci rculation MG Set but an incomplete sequence alarm was received. Work Request 1002-79 was immediately written to investigate and repai r the problem. This investigation revealed a loose tachometcr coupling which caused the field breaker to open.

A similar event occurred on October 13, 1977 and was reported in R0 77-34/03L.

VI. PROBABLE CONSEQUENCES OF THE OCCURRENCE:

When the MG Set generator field breaker cpened, the 2A Reci rcu-lation Pump coasted down to zero speed causing reactor power to decrease. Since the 2B Recirculation Pump speed was reduced to 452 immediately, there were no safety implications due to this occurrence.

Vll. CAUSE:

An investigation of the field breaker trip revealed that the Recirculation MG Set tachometer coupling to the main shaft had come loose due to vibration. The excessive vibration is believed to be caused by misalignment of the tachometer to the main generator shaft.

Vill. CORRECTIVE ACTION:

The immediate corrective action was to runback the 2B Reci rcu-lation Pump flow. The tachometer coupling was repai red and the 2A Recirculation MG Set restarted at 8:30 a.m. on February 23 Once the MG set was restarted a dynamic analysis was performed on the tachometer to MG set coupling. This analysis indicated that an alignment adjustment will be necessary.

Work request 1264-79 has been wri tten to properly align the tachometer during the next convenient outage.