Distance relay system

Claim 2

A distance relay system, having a distance relay, for use in a three phase electric power system comprising: first means for deriving from said power system a voltage having an amplitude and a phase respectively in proportion to and lagging by 90* behind the amplitude and phase of a line-to-line voltage; and second means for deriving from said power system a current having an amplitude and a phase respectively in proportion to and equal to the amplitude and phase of a negative-sequence current relative to the remaining phase free from the protection taken as a reference, whereby the impedance from the location of said relay to the fault location is derived from the ratio of said voltage and current respectively derived by the first and second means so as to protect the electric power system.

Claim 3

A distance relay system according to claim 1, in which said impedance is determined by a phase comparator circuit which compares the phase of a factor IZ-V for distance measurement with the phase of a polarity voltage V, where V is the voltage derived by said first means, I is the current derived by said second means, and Z is a setting impedance.

Claim 4

A distance relay system, having a distance relay, for use in a three phase electric power system comprising: first means for deriving a voltage having an amplitude and a phase respectively in proportion to and equal to the amplitude and the phase of a line-to-ground voltage of the phase chosen as the subject to the protection; and second means for deriving a current having an amplitude and a phase respectively in proportion to and equal to the amplitude and phase of a negative-sequence current relative to said phase chosen as the subject to the protection and taken as a reference; whereby an impedance from the location of said relay to the fault location is derived from the ratio of said voltage and current respectively derived by the first and second means so as to protect the electric power system.

Claim 5

A distance relay system, having a distance relay, for use in a three phase electric power system comprising: first means for deriving a voltage having an amplitude and a phase respectively in proportion to and equal to the amplitude and the phase of a line-to-ground voltage of the phase chosen as the subject to the protection; and second means for deriving a current having an amplitude and a phase respectively in proportion to and equal to the amplitude and phase of a negative-sequence current relative to said phase chosen as the subject to the protection and taken as a reference; whereby an impedance from the location of said relay to the fault location is derived from the ratio of said voltage and current respectively derived by the first and second means so as to protect the electric power system.

Claim 6

A distance relay system according to claim 3, in which said impedance is determined by a phase comparator circuit which compares the phase of a factor IZ-V for distance measurement with the phase of a polarity voltage V, where V is the voltage derived by said first means, I is the current derived by said second means, and Z is a setting impedance.

Claim 7

A distance relay system for use in a three phase electric power system comprising A three phase voltage transformer having primary windings connected to the respective phase lines of said power system and corresponding secondary windings inductively coupled to said primary windings, a three phase current transformer having three windings coupled to the respective phase lines of said power system, a first phase shifter providing a leading phase shift of 120* connected to one of the windings of said current transformer, a second phase shifter providing a leading phase shift of 240* connected to a second winding of said current transformer, and a distance relay connected to the secondary windings of said voltage transformer to obtain a voltage signal and connected to said current transformer windings through said first and second phase shifters to obtain a current signal so as to provide an impedance indication based on said voltage and current signals.

Claim 8

A distance relay system for use in a three phase electric power system comprising A three phase voltage transformer having primary windings connected to the respective phase lines of said power system and corresponding secondary windings inductively coupled to said primary windings, a three phase current transformer having three windings coupled to the respective phase lines of said power system, a first phase shifter providing a leading phase shift of 120* connected to one of the windings of said current transformer, a second phase shifter providing a leading phase shift of 240* connected to a second winding of said current transformer, and a distance relay connected to the secondary windings of said voltage transformer to obtain a voltage signal and connected to said current transformer windings through said first and second phase shifters to obtain a current signal so as to provide an impedance indication based on said voltage and current signals.

Claim 9

A distance relay system as defined in claim 5 wherein said distance relay includes a phase comparator circuit, relay transformer means responsive to said current and voltage signals for providing a phase signal IZ-V for distance measurement with the phase of the voltage signal, where X is a setting impedance, said comparator circuit being connected to said relay transformer means so as to be responsive to said phase signal and said voltage signal.

Claim 10

A distance relay system as defined in claim 5 further including a third phase shifter connected to the secondary windings of said voltage transformer providing a lagging phase shift of 90* to the voltage signal applied to said distance relay.