US 6,518,767 B1Granted

Line differential protection system for a power transmission line

AssigneeSchweitzer Engineering Laboratories, Inc.

InventorsJeffrey B. Roberts, Gabriel Benmouyal, Hector Altuve-Ferrer, Ralph Folkers, Demetrios Tziouvaras

Life of this patent

Estimating the term…

Loading patent…

Abstract

In a power line current differential protection system, all three phase current values (IA, IB and IC) are obtained from both the local end and the remote end of a power transmission line. The magnitude of the ratio of the remote current values to the local current values are calculated. Also, the angle difference between the local and the remote current values for each phase are calculated. Comparison elements then compare the ratio and angle values against preselected values which establish a restrain region in the current ratio plane. Current values which result in the ratio being within the region do not result in a tripping signal for the circuit breaker on the power transmission line, while current values which result in a ratio outside of the region result in a tripping of the circuit breaker. Similar circuitry is used for negative sequence current quantities, with the negative sequence preselected values being set substantially lower to produce a more sensitive response to possible faults in the line.

Claims28

Dependent claims

A system for current differential protection for a power transmission line, comprising:

means for determining phase current values at local and remote ends of a transmission line;
means for calculating the magnitude value of the ratio of the remote phase current values and the local phase current values;
means for calculating the angle difference value between the remote current and local current values;
comparison elements for comparing the ratio magnitude value and the angle value against preselected values which establish a phase region in a current ratio plane within which tripping of a circuit breaker for the transmission line is restrained, wherein when the ratio magnitude value and angle value are not within the established phase region, an output signal is developed which is a tripping signal for the circuit breaker and wherein when the ratio magnitude value and the angle value are within the established region, no trip signal is produced;
means for determining a selected one of (1) negative sequence current values and (2) zero sequence current values at local and remote ends of the transmission line;
means for calculating the magnitude value of the ratio of the remote selected sequence current values and the local selected sequence current values;
means for calculating the angle difference value between the local and remote selected sequence current values;
and
comparison elements for comparing the ratio magnitude value and the angle value against preselected values which establish a selected sequence restraint region in the current ratio plane, wherein when the ratio magnitude value and angle value are outside of the sequence region, an output signal is developed which is a tripping signal for the circuit breaker, and wherein when the ratio magnitude value and angle value are within the sequence region, no trip signal is produced.

6 more elements

A system for current differential protection for a power transmission line, comprising:

means for determining positive sequence current values at local and remote ends of a transmission line;
means for calculating the magnitude value of the ratio of the remote positive sequence current values and the local positive sequence current values;
means for calculating the angle difference value between the remote current and local current values;
comparison elements for comparing the ratio magnitude value and the angle value against preselected values which establish a phase region in a current ratio plane within which tripping of a circuit breaker for the transmission line is restrained, wherein when the ratio magnitude value and angle values are not within the established phase region, an output signal is developed which is a tripping signal for-the circuit breaker and wherein when the ratio magnitude value and the angle value are within the established region, no trip signal is produced;
means for determining a selected one of (1) negative sequence current values and (2) zero sequence current values at local and remote ends of the transmission line;
means for calculating the magnitude value of the ratio of the remote selected sequence current values and the local selected sequence current values;
means for calculating the angle difference value between the local and remote selected sequence current values;
and
comparison elements for comparing the ratio magnitude value and the angle value against preselected values which establish a selected sequence restraint region in the current ratio plane, wherein when the ratio magnitude value and angle value are outside of the selected sequence region, an output signal is developed which is a tripping signal for the circuit breaker, and wherein when the ratio magnitude value and angle value are within the selected sequence region, no trip signal is produced.

6 more elements

Dependencies are inferred from the claim text.