ABSTRACT

This chapter focuses on the general characteristics of faults and analysis of common fault types with suggestions on how to reduce them. A fault always involves a short circuit between energized phase conductors or between a phase and ground. A fault may be a bolted connection or may have impedance in the fault connection. There are many causes of faults on distribution circuits. A large Electric Power Research Institute study (EPRI) was done to characterize distribution faults in the 1980s at 13 utilities monitoring 50 feeders. The EPRI study surveyed utilities and found evidence that a market for fault-current limiters exists if a device had low-enough cost and was robust enough. Faults are either temporary or permanent. Determining the percentage of faults that are temporary versus permanent is complicated. The magnitude of fault current is limited only by the system impedance and any fault impedance. The system impedance includes the impedances of wires, cables, and transformers back to the source.