Improvements in relay protection to detect faults of Open phase and phase to ground in Electrical Systems

摘要

The invention provides a ratio ground induction disc relay which detects open phase conductors on electrical distribution circuits, as well as single-phase-to-ground faults regardless of fault impedance, by providing an operating quantity responsive to zero sequence current (K|3I0|2), and a restraining quantity responsive to the positive sequence current minus the negative sequence current (K(|I1|2 - |I2|2)). The restraint quantity is provided by an electromagnetic (38) having first and second outer legs and an inner leg. Electrical windings are disposed on only the first and second outer legs, arranged and energized by the three phase currents (IA, IB, IC) to provide equal length flux paths (oA, oB, oC), and thus equal torques, regardless of the faulted phase.