System, apparatus and method for compensating the sensitivity of a sequence element in a line current differential relay in a power system

A method for compensating the sensitivity of a line current differential element of a first current differential relay providing differential protection for a transmission line of a power system during a single-phase pole-open condition, the method comprising:

• (a) removing a first pre-fault current from a first fault current of the transmission line to form a compensated first current;
• (b) removing a second pre-fault current from a second fault current of the transmission line to form a compensated second current;
• and
• (c) providing a first phasor representative of the compensated first current and a second phasor representative of the second compensated current to the line current differential element to compensate the sensitivity of the line current differential element.

A system for compensating the sensitivity of a first line current differential sequence element of a local current differential relay, the local current differential relay operatively coupled to a first end of a transmission line of a power system and in communication with a remote current differential relay operatively coupled to a second end of the transmission line, the system comprising:

• a first delta filter operatively coupled to the first line current differential sequence element, the first delta filter comprising a first delay filter configured to receive a first local sequence current phasor at a first time and to generate a first delayed local sequence current phasor at a second time, and a first adder configured to subtract the first delayed local sequence current phasor from a second local sequence current phasor received at the second time to form a compensated local sequence current phasor;
• and
• a second delta filter operatively coupled to the first line current differential sequence element, the first second filter comprising a second delay filter configured to receive a first remote sequence current phasor at the first time and to generate a first delayed remote sequence current phasor at the second time, and a second adder configured to subtract the first delayed remote sequence current phasor from a second remote sequence current phasor received at the second time to form a compensated remote sequence current phasor,
• wherein the first line current differential element is configured to receive each of the compensated local and remote sequence current phasors to compensate the sensitivity of the first line current differential element.

An apparatus for compensating the sensitivity of at least one line current differential sequence element of a local current differential relay during a single-phase pole-open condition of a transmission line of a power system, the local current differential relay operatively coupled to a first end of the transmission line and in communication with a remote current differential relay operatively coupled to a second end of the transmission line, the apparatus comprising:

• a first delta filter configured to subtract a pre-fault local current phasor from each of a plurality a local current phasors derived from instantaneous local current values measured by the local current differential relay during a fault in the transmission line to form a plurality of compensated local current phasors, the pre-fault local current phasor latched into a memory of the first delta filter;
• and
• a second delta filter configured to subtract a pre-fault remote current phasor from each of a plurality a remote current phasors derived from instantaneous remote current values measured by the remote current differential relay during the fault to form a plurality of compensated second current phasors, the pre-fault remote current phasor latched into a memory of the second delta filter,
• wherein the at least one line current differential element is configured to receive pairs of corresponding local and remote sequence current phasors of the plurality of compensated local and remote sequence current phasors to compensate the sensitivity of the at least one line current differential element.

A method for compensating the sensitivity of a line current differential sequence element of a local current differential relay during a single-phase pole-open condition of a transmission line of a power system, the local current differential relay operatively coupled to a first end of the transmission line and in communication with a remote current differential relay operatively coupled to a second end of the transmission line, the method comprising:

• subtracting a pre-fault local current phasor from each of a plurality of local current phasors derived from instantaneous local current values measured by the local current differential relay during a fault in the transmission line to form a plurality of compensated local current phasors, the pre-fault local current phasor stored in a first memory location of the local current differential relay;
• and
• subtracting a pre-fault remote current phasor from each of a plurality of remote current phasors derived from instantaneous remote current values measured by the remote current differential relay during the fault to form a plurality of compensated second current phasors, the pre-fault remote current phasor stored in a second memory location of the local current differential relay,
• wherein pairs of corresponding local and remote sequence current phasors of the plurality of compensated local and remote sequence current phasors are provided to the line current differential element to compensate the sensitivity of the line current differential element.

A system for compensating the sensitivity of a first line current differential sequence element of a local current differential relay, the local current differential relay operatively coupled to a first end of the transmission line and in communication with a remote current differential relay operatively coupled to a second end of the transmission line, the system comprising:

• a first adder, a first memory register and a first delay filter operatively coupled to the first adder and first memory register, the first delay filter configured to delay a local sequence current phasor calculated prior to detecting a fault in the transmission line, the first memory register configured to store the delayed local sequence current phasor to form a stored local sequence current phasor in response to receipt of a latching signal indicating the fault, the first adder configured to subtract one of the delayed local sequence current phasor and the stored local sequence current phasor from each of a plurality of local sequence current phasors calculated after detecting the fault to form a plurality of compensated local sequence current phasors;
• and
• a second adder, a second memory register and a second delay filter operatively coupled to the second adder and the second memory register, the second delay filter configured to delay a remote sequence current phasor calculated prior to detecting the fault, the second memory register configured to store the delayed remote sequence current phasor to form a stored remote sequence current phasor in response to receipt of the latching signal, the second adder configured to subtract one of the delayed remote sequence current phasor and the stored remote sequence current phasor from each of a plurality of remote sequence current phasors calculated after detecting the fault to form a plurality of compensated remote sequence current phasors,
• wherein the first line current differential element is configured to receive pairs of corresponding compensated local and remote sequence current phasors of the plurality of compensated local and remote sequence current phasors to compensate the sensitivity of the first line current differential element.

A method for compensating the sensitivity of a line current differential element of a protective relay providing differential protection for a transmission line of a power system, the method comprising:

• forming a compensated first signal based on a first pre-fault current and a first fault current measured at a first end of the transmission line;
• forming a compensated second signal based on a second pre-fault current and a second fault current measured at a second end of the transmission line;
• and
• providing compensated first and second current phasors to the current differential element thereby compensating the line current differential element, each of the compensated first and second current phasors derived from corresponding compensated first and second signals.