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On 01/10/2001 at approximately 03:00 durin … On 01/10/2001 at approximately 03:00 during surveillance testing of "B" emergency Diesel Generator (EDG), the engine came up to speed but no voltage or frequency was observed. Trouble shooting determined that the cause was a short circuit in two diodes of a diode rectifier bridge, which caused a protective fuse to open.</br></br>This prevented the generator field from flashing. At this same time, the "A" EDG was inoperable due to testing. The plant was shutdown with all fuel removed from the reactor vessel and a time to boil of greater than 25 hours for the Spent Fuel Pool.</br></br>The same problem was discovered previously on the "A" EDG on 12/24/00 but was thought to be a random failure and the other train of ESF power was still operable. At that time the diodes and fuse were replaced.</br></br>The rectifier bridge is a generator component that assured DC power was supplied as input power for the manual voltage regulator motor operated potentiometer (MOC-2). The rectifier provided DC output regardless of whether AC or DC input power was supplied. After their failure, these diodes were removed and sent off for analysis. The cause of failure was determined to be an over-voltage condition that could not be replicated either on the EDG or in the Electric Shop.</br></br>The diode rectifier bridges have been removed from these circuits on both EDGs since they are not necessary. V. C. Summer uses only DC power as the input to the MOC.ses only DC power as the input to the MOC. +
On 01/10/2001 at approximately 03:00 durin … On 01/10/2001 at approximately 03:00 during surveillance testing of "B" emergency Diesel Generator (EDG), the engine came up to speed but no voltage or frequency was observed. Trouble shooting determined that the cause was a short circuit in two diodes of a diode rectifier bridge, which caused a protective fuse to open.</br></br>This prevented the generator field from flashing. At this same time, the "A" EDG was inoperable due to testing. The plant was shutdown with all fuel removed from the reactor vessel and a time to boil of greater than 25 hours for the Spent Fuel Pool.</br></br>The same problem was discovered previously on the "A" EDG on 12/24/00 but was thought to be a random failure and the other train of ESF power was still operable. At that time the diodes and fuse were replaced.</br></br>The rectifier bridge is a generator component that assured DC power was supplied as input power for the manual voltage regulator motor operated potentiometer (MOC-2). The rectifier provided DC output regardless of whether AC or DC input power was supplied. After their failure, these diodes were removed and sent off for analysis. The cause of failure was determined to be an over-voltage condition that could not be replicated either on the EDG or in the Electric Shop.</br></br>The diode rectifier bridges have been removed from these circuits on both EDGs since they are not necessary. V. C. Summer uses only DC power as the input to the MOC.ses only DC power as the input to the MOC. +
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