A new sequence detection relay with quadrilateral characteristic.

A new static distance relay working on the principle of sequence detection is reported in the paper. The three-input sequence detector developed in the paper is simple and convenient to employ in obtaining the popular quadrilateral characteristic. The relay employs semi-conductor devices throughout and operates in less than a cycle.
The E.H.V., long, heavily loaded transmission lines are usually protected by means of distance relays. A static distance relay employing phase comparator may either work on the principle of cosine comparison (Adamson and Wedepohl 1956, Humpage and Sabberwal 1965) or sine comparison. The principle of sequence detection is reported by Thakkar and Parathasarathy (1970) where it is shown that the required characteristic may be obtained by detecting the sequence of the selected mixed signals. Thakkar and Parathasarathy (1970) further present the mathematical basis of the relay working on the principle of sequence detection and describes two schemes of practical circuitry of the relay. It is necessary to employ separate phase comparator for every pair of input signals in the first scheme resulting in the costly construction of the relay. The second scheme employs flip-flop circuits in the detection of the sequence requiring less number of circuit components. However, it suffers from the disadvantage that its time of operation increases unduly to two cycles. [ABSTRACT FROM AUTHOR]