Impact of miscoordination of electric protective devices on nuclear power generating stations

摘要

A review of various reports indicated miscoordination of electrical protective devices has been an issue at some nuclear power generating stations. This study revealed that design errors were the root cause of miscoordination of electric protective devices. These errors could have been avoided if the time current coordination characteristics were accurately plotted. Time-current coordination characteristics must be revised when new loads are added to an existing electrical distribution system. The critical clearing time between the characteristics of protective devices must be maintained. The motor accelerating curves and motor thermal capability curves should be plotted during the design stage. The motor accelerating curves should be plotted at 75% voltages rather than at 100% voltages for Class lE motors and at 80% voltages for Balance of Plant (non-Class 1E) motors rather than at 100% voltages. Modifications to Appendix R to 10 Codes of Federal Regulation Part 50 require coordination of protective devices for high impedance faults (fire produces a high impedance fault).