Patent ID: 11936181
Assignee: S&C ELECTRIC COMPANY
Field: Electrical machinery, apparatus, energy (Electrical engineering)
Classification: CPC H  G | IPC G  H

Claim 0:
1. A method for identifying an earth fault in a resonant grounded medium voltage network, the network including a power source that serves a plurality of three-phase feeders and a rapid earth fault current limiting (REFCL) compensation system, each feeder including at least one switching device, wherein the method is performed in one or more of the switching devices, the method comprising:
deriving a zero-sequence real power from a complex phase voltage to ground on each phase and a complex current on each phase;
aligning the zero-sequence real power in time with a magnitude of a zero-sequence voltage provided by the REFCL compensation system;
determining when the zero-sequence real power exceeds a predetermined zero-sequence real power threshold;
determining when the zero-sequence voltage exceeds a predetermined zero-sequence voltage threshold;
delaying the magnitude of the zero-sequence voltage for a predetermined period of time when the zero-sequence voltage exceeds the predetermined zero-sequence voltage threshold; and
determining that the fault is occurring when both the time aligned zero-sequence real power exceeds the zero-sequence real power threshold and the magnitude of the zero-sequence voltage exceeds the zero-sequence voltage threshold for the predetermined period of time at the same time.