Protective relay apparatus and method for providing single-pole tripping

Claim 2

Protective relay apparatus for detecting a single-phase-to-ground fault in a three-phase electrical power system and for identifying the faulted phase conductor, said protective relay apparatus comprising: means for providing a first phasor signal representative of unbalanced current in the three-phase electrical power system, means for providing a second phasor signal for each phase conductor representative of a negative sequence component of an electrical quantity for each phase conductor; means for providing a third phasor signal for each phase conductor representative of a quadrature voltage for each phase conductor advanced by a predetermined number of electrical degrees; coincidence means for determining the coincidence of said first, second, and third phasor signals for each phase conductor; said coincidence means providing a signal indicating the occurrence of a single-phase-to-ground fault on an identified phase conductor when the phase angles of said first, second, and third phasor signals for the identified phase conductor have a predetermined relationship.

Claim 3

The protective relay apparatus of claim 1 wherein the negative sequence component is the negative sequence current.

Claim 4

The protective relay apparatus of claim 1 wherein the negative sequence component is the negative sequence voltage rotated by 90° counterclockwise.

Claim 5

The protective relay apparatus of claim 1 wherein the quadrature voltage is the line-to-line voltage having a phase angle normal to the phase angle of the phase conductor being monitored.

Claim 6

The protective relay apparatus of claim 1 wherein the predetermined number of electrical degrees for each quadrature voltage is 30 electrical degrees counterclockwise.

Claim 7

The protective relay apparatus of claim 1 wherein the predetermined relationship of the phase angles is the phase angles all being within a predetermined number of electrical degrees of one another.

Claim 8

The protective relay apparatus of claim 4 wherein the predetermined number of electrical degrees is 60 electrical degrees.

Claim 9

Protective relay apparatus for detecting a single-phase-to-ground fault in a three-phase electrical power system having phase conductors A, B, and C, phase voltages V A , V B , and V C , and phase currents I A , I B , and I C , said protective relay apparatus comprising: means providing a first phasor signal representative of the sum of the phase currents I A , I B , and I C ; means providing second, third, and fourth phasor signals representative of a negative sequence component referenced to the phase conductors A, B, and C, respectively; means providing fifth, sixth, and seventh phasor signals representative of -V C , -V A , and -V B , respectively; first detector means for providing a signal indicating a single-phase-to-ground fault on the phase A conductor when said first, second, and fifth phasor signals are within a predetermined number of electrical degrees of one another; second detector means for providing a signal indicating a single-phase-to-ground fault on the phase B conductor when said first, third, and sixth phasor signals are within a predetermined number of electrical degrees of one another; third detector means for providing a signal indicating a single-phase-to-ground fault on the phase C conductor when said first, fourth, and seventh phasor signals are within a predetermined number of electrical degrees of one another.

Claim 10

Protective relay apparatus for detecting a single-phase-to-ground fault in a three-phase electrical power system having phase conductors A, B, and C, phase voltages V A , V B , and V C , and phase currents I A , I B , and I C , said protective relay apparatus comprising: means providing a first phasor signal representative of the sum of the phase currents I A , I B , and I C ; means providing second, third, and fourth phasor signals representative of a negative sequence component referenced to the phase conductors A, B, and C, respectively; means providing fifth, sixth, and seventh phasor signals representative of -V C , -V A , and -V B , respectively; first detector means for providing a signal indicating a single-phase-to-ground fault on the phase A conductor when said first, second, and fifth phasor signals are within a predetermined number of electrical degrees of one another; second detector means for providing a signal indicating a single-phase-to-ground fault on the phase B conductor when said first, third, and sixth phasor signals are within a predetermined number of electrical degrees of one another; third detector means for providing a signal indicating a single-phase-to-ground fault on the phase C conductor when said first, fourth, and seventh phasor signals are within a predetermined number of electrical degrees of one another.

Claim 13

The method of claim 9 wherein the negative sequence component is the negative sequence current.

Claim 14

The method of claim 9 wherein the negative sequence component is the negative sequence voltage rotated by 90° counterclockwise.