Protective relaying methods and apparatus
AssigneeWestinghouse Electric Corp.
InventorWalter A. Elmore
Life of this patent
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Abstract
Methods and apparatus for detecting a single-phase-to-ground fault on a three-phase electrical power system, and for identifying a faulted phase. A single-phase-to-ground fault is correctly distinguished from other faults, including phase-to-phase-to-ground faults, even with transmission lines which utilize series capacitors, by taking into consideration the phase-to-phase voltage which is in quadrature with the voltage to ground of the monitored phase.
Claims11
Apparatus for detecting a single-phase-to-ground fault in a three-phase electrical power system, comprising:
- means providing a first phasor signal responsive to unbalanced current in the three-phase system,
- means providing a second phasor signal indicative of a negative sequence quantity, referenced to the phase being monitored,
- means providing a third phasor signal responsive to the quadrature voltage of the phase being monitored,
- comparison means comparing the phase angles of said first, second and third phasor signals,
- said comparison means providing a signal which indicates a single-phase-to-ground fault on the three-phase system, with the fault being on the phase being monitored, when the phase angles have a predetermined relationship.
Apparatus for detecting a single-phase-to-ground fault in a three-phase electrical power system having phases A, B and C, phase voltages V.sub.A, V.sub.B and V.sub.C, line voltages V.sub.AB, V.sub.CA and V.sub.BC, and phase currents I.sub.A, I.sub.C and I.sub.B, and for identifying the faulted phase, comprising:
- means providing a first phasor signal responsive to the sum of the phase currents I.sub.A, I.sub.B and I.sub.C,
- means providing second, third and fourth phasor signals responsive to a negative sequence quantity referenced to phases A, B and C, respectively,
- means providing fifth, sixth, and seventh phasor signals responsive to V.sub.BC, V.sub.CA and V.sub.AB, respectively,
- first detector means for providing an output signal indicating a phase A-to-ground fault when said first, second and fifth phasor signals are within a predetermined number of electrical degrees of one another,
- second detector means for providing an output signal indicating a phase B-to-ground fault when said first, third and sixth phasor signals are within said predetermined number of electrical degrees of one another,
- and third detector means for providing an output signal indicating a phase C-to-ground fault when said first, fourth and seventh phasor signals are within said predetermined number of electrical degrees of one another.
A method of detecting a single-phase-to-ground fault in a three-phase electrical power system, comprising the steps of:
- providing a first phasor signal responsive to the sum of the three phase currents in the three-phase system,
- providing a second phasor signal indicative of a predetermined negative sequence quantity, referenced to the phase being monitored,
- providing a third phasor signal responsive to the quadrature voltage for the phase being monitored,
- comparing the phase angles of said first, second and third phasor signals,
- and providing a signal indicating a single-phase-to-ground fault of the monitored phase when the step of comparing the phase angles detects a predetermined phase angle relationship.
Dependencies are inferred from the claim text.