Maximum and minimum short circuit currents must be calculated before installing an electric system. The maximum short-circuit current corresponds to a short-circuit in the immediate vicinity of the downstream terminals of the protection device. It must be calculated accurately and used within a safety margin. A minimum short-circuit current is essential when selecting a time-current curve for the circuit breakers and fuses. We use earthing systems to limit phase to ground fault currents. Multiple, distant neutral earths on an electrical network may give rise to circulating zero sequence currents, and have implications for the earth fault level and associated protection. An embedded generator (EG) may be required to provide a point of neutral earthing along with an existing utility-network earth and such cases present challenges which may be overcome using modem protection relays.
Key words: Petersen coil, neutral grounding resistor, artificial neutral.
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