Breaker failure protection

Mains decoupling relay (Relay Code 78) This protection is applicable when the captive generator is hooked up with the main bus. The relay trips the incoming breaker instantaneously on failure of the main supply. Otherwise on rapid restoration of the... 

EGSG Idaho s Idaho National Engineering Laboratory reviewed Licensee Event Reports (LERs), both qualitatively and quantitatively, to extract reliability information in support of the USNRC s effort to gather and analyze component failure data for U.S. commercial nuclear power plants. LERs describing failures or command faults (failure due to lack of needed input) for selected components have been analyzed in this program. Separate reports have been issued for batteries and battery chargers, control rods and drive mechanisms, diesel generators, ISC, Inverters, primary containment penetrations, protective relays and circuit breakers, pumps, and valves. 

Failure of a circuit breaker, automatic circuit protection device is expected to occur 0.001 times per demand or electrical over cunent event The amount of the additional current caused by an electrical short is not known but it is assumed to be in excess of the current required to cause the circuit breaker to remove power from the circuit. 

Have a supply of circuit breakers, fuses, GFCIs, etc., on hand to explain their functions for protecting workers. Promote the fact that these are only mechanical devices and subject to failure. The best accident preventive methods are stiU correct installation of temporary wiring and safe work places and practices. 

In the event of accidents with unauthorized addition of reactivity or loss of heat removal, complete failure of protective systems and operator inaction on primary circuit pressure increase, the plant will be tripped by a direct-acting pressure-actuated power breaker cutting supplies to the control rod drives. 

If instead of step starting, the operator applies full motor load to a stationary, fully loaded conveyor, one of two things will occur (1) the drive motor s circuit breaker will trip as a result of excessive amp load, or (2) the shear pin installed to protect the conveyor will fail. Either of these failures adversely impacts production. 

This subsection should provide information relevant to the plant on the off-site electrical power systems. It should include a description of the off-site power systems, with emphasis on features for control and protection (breaker arrangements, manual and automatic disconnect switches) at the interconnection to the on-site power system. Special emphasis should be put on all design provisions used to protect the plant from off-site electrical disturbances and to maintain power supply to in-plant auxiliaries. Information on grid reliability should also be provided and any design specific provisions necessary to cope with frequent grid failures should also be described. 

Protection Against Short-circuit Current. A short circuit is a special case of excess current. However, a short-circuit failure differs from overload in that damage to the circuit and cables occurs very rapidly. Protective devices must therefore be able to respond quickly to these failures. As far as any type of fuse is concerned a short-circuit failure will cause it to operate more rapidly because of the increased thermal effect. Circuit-breakers, on the other hand, usually have a separate part of their operating characteristic which is specifically designed for short-circuit failures. A miniature... 

On February 26, 1983, NRC investigators discovered that a similar failure had occurred on at Salem 1 on February 22, 1983. Based on a computer printout of February 22 events, it was evident that on that day (as on February 25) the two reactor trip breakers failed to open upon receipt of an automatic trip signal from the reactor protection system. The operators initiated a manual trip even though they were unaware that the automatic trip had failed. 

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