Protective relay
AssigneeWestinghouse Electric Corp.
InventorMartin T. Bishop
Life of this patent
Estimating the term…
Abstract
A percent unbalance or ratio ground 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, and a restraining quantity responsive to a pre-fault balanced phase current minus the zero sequence current. This restraint torque arrangement causes the relay to operate on true ratio unbalance, regardless of load.
Claims6
A relay for detecting open phases and phase-to-ground faults in a three-phase electrical power system, including high impedance phase-to-ground faults, comprising:
- first means providing a first signal responsive to the zero sequence current flowing in the three-phase electrical power system,
- second means providing a second signal responsive to a phase current with said second means including means responsive to a phase-to-ground fault in said three-phase electrical power system for maintaining the magnitude of said second signal at substantially the same magnitude following said fault as it had prior to said fault,
- third means providing a restraining quantity which varies as a function of the second signal less the first signal,
- fourth means providing an operating quantity which varies as a function of the first signal,
- and translating means responsive to said restraining and operating quantities for providing a predetermined signal when said restraining and operating quantities have a predetermined relationship.
A relay for detecting open phases and phase-to-ground faults in A three-phase electrical power system, including high impedance phase-to-ground faults, comprising:
- first means providing a first signal responsive to the zero sequence current flowing in the three-phase electrical power system,
- second means providing a second signal responsive to a phase current, with the magnitude of the second signal being substantially unaffected by a phase-to-ground fault in said three-phase electrical power systems, said second means including means providing a phase current signal responsive to the current in a predetermined phase, and means responsive to a fault being in the predetermined phase for substracting the first signal from said phase current signal, with the second signal being responsive to the difference,
- third means providing a restraining quantity which varies as a function of the second signal less the first signal,
- fourth means providing an operating quantity which varies as a function of the first signal,
- and translating means responsive to said restraining and operating quantities for providing a predetermined signal when said restraining and operating quantities have a predetermined relationship.
A relay for detecting open phases and phase-to-ground faults in a three-phase electrical power system, including high impedance phase-to-ground faults, comprising:
- first means providing a first signal responsive to the zero sequence current flowing in the three-phase electrical power system,
- second means providing a second signal responsive to a phase current, with the magnitude of the second signal being substantially unaffected by a phase-to-ground fault in said three-phase electrical power system, said second means including first additional means for providing a phase current signal responsive to the current in a first selected phase, and second additional means responsive to a fault being in said first selected phase for causing said first additional means to provide a phase current signal responsive to the current in a second selected phase, with the phase current signal provided by said first additional means being the second signal,
- third means providing a restraining quantity which varies as a function of the second signal less the first signal,
- fourth means providing an operating quantity which varies as a function of the first signal,
- and translating means responsive to said restraining and operating quantities for providing a predetermined signal when said restraining and operating quantities have a predetermined relationship.
A relay for detecting open phases and phase-to-ground faults in a three-phase electrical power system, including high impedance phase-to-ground faults, comprising:
- an electroresponsive induction device having an electroconductive armature mounted for movement, first and second means for providing magnetic fluxes which act on said armature when energized, to produce restraining and operating torques, respectively, and electrical contact means actuatable by said armature to provide a predetermined signal when the restraining and operating torques have a predetermined relationship,
- first means providing a first signal responsive to the zero sequence current flowing in the three-phase electrical power system,
- and second means providing a second signal responsive to a phase current, with said second means including means responsive to a phase-to-ground fault in said three-phase electrical power system for maintaining the magnitude of said second signal at substantially the same value after said fault as it had prior to said fault,
- said first means of the induction device being responsive to the second signal minus the first signal,
- said second means of the induction device being responsive to the first signal.
Dependencies are inferred from the claim text.