Schweitzer Engineering Laboratories, Inc.

Joseph B Mooney

Edmund O Schweitzer, Iii

Armando Guzman-Casillas

Jeffrey B Roberts

Gabriel Benmouyal

Luther S Anderson

An apparatus and method compensate for the sensitivity of at least one 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 apparatus includes a first delta filter configured to remove a first pre-fault current from a first fault current of the transmission line to derive a compensated first current phasor. The apparatus also includes a second delta filter configured to remove a second pre-fault current from a second fault current of the transmission line to derive a compensated second current phasor. The compensated first and second current phasors are provided to the at least one line current differential element to compensate the sensitivity of the at least one line current differential element.

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

The system is used in a distance-type protective relay which includes a calculation circuit responsive to voltage and current values from a power line to produce a quantity which is analogous to the distance between the relay and a fault on the line, referred to as an m quantity. This quantity is then applied to a distance element/circuit for comparison of said quantity with a setting reach value for a zone one distance protection to determine whether the fault is within zone one protection. The system includes a filter circuit which filters the quantity before it reaches the distance element, resulting in a smoothing of said quantity and rejection of noise therefrom. The system further includes a control circuit which determines whether the filter is to be used in the system in a particular situation, depending upon whether when the value of the quantity is above a selected percentage of the setting reach value.

Protective relay for power systems having fault distance measurement filter logic

The system includes a plurality of protection application elements to accomplish various power system protection functions, including for example line protection, line fault location, current direction determination, breaker protection and synchronism check, among others. The system includes local sources of current and voltage information for the protective functions as well as a receiving section for receiving such current and voltage values from a remote source, such as another protection device, as well as other necessary input information for the protective functions. A selection logic section is responsive to the output of the protective function elements, as well as the local and remote data to determine whether the primary or local sources are to be used. The outputs of the protective function elements are used by an output section to control circuit breakers and the like and are also transmitted, with the local and remote source quantities, to other protective devices.

Voltage and current source selection system for use in the protection, automation and control of an electric power system

The system includes an enable signal applied to an output AND element. A comparator compares the voltage ratio of selected measured and calculated phase-to-phase or single phase voltages against a threshold value. An AND gate is responsive to a high signal from the comparator and indications of a three pole open condition, a single pole open condition for selected poles, and a loss of potential condition. A high output from the AND gate is applied to a timer, which produces a high output for a short period of time, which controls the output element. The output element provides a blocking signal for the protective elements under particular conditions and a permissive signal under other conditions.

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Colfax, WA, United States of America

Joseph B Mooney