Schweitzer Engineering Laboratories, Inc.

Ralph W Folkers

Jeffrey B Roberts

Gabriel Benmouyal

Edmund O Schweitzer, Iii

Armando Guzman-Casillas

Demetrios A Tziouvaras

Hector J Altuve-Ferrer

Provided is a compensated inverse-time undervoltage load shedding system and method for use in an electrical power system. The compensated inverse-time undervoltage load shedding system includes a compensation element for determining a compensated value and an inverse-time undervoltage element operatively coupled to the compensation element and enabled based on the compensated value. When enabled, the inverse-time undervoltage element calculates a load shedding time delay value based on the compensated value, and determines a load shedding signal based on the load shedding time delay value. An associated load of the electrical power system is shed based on the load shedding signal. The compensation element may determine the compensated value using a voltage magnitude, a rate-of-change of power system voltage over time, a weighted rate-of-change of power system voltage over time, a current magnitude, a weighted current magnitude, and an impedance phasor value, to name a few.

Compensated inverse-time undervoltage load shedding systems

In a power line current differential protection system, all three phase current values (I , I and I ) 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.

Line differential protection system for a power transmission line

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Pullman, WA, United States of America

Ralph W Folkers