GB890309A - Improvements in and relating to polyphase protective relay systems - Google Patents

Abstract

890,309. Protective cut-out arrangements. ENGLISH ELECTRIC CO. Ltd. June 3, 1958 [June 7, 1957], No. 18184/57. Class 38 (5). A three-phase distance type protective arrangement has a relay energized by two zero phase sequence compensated signals each being the vector difference between a first signal derived from a respective phase current and representing the impedance of the line between the arrangement and the fault and a second signal derived from the phase-to-neutral voltage of the same phase and a facsimile impedance representing the impedance of the line between the arrangement and the end of the protected section. In Fig. 1, the compensated signals are obtained from mixing transformers 19, 20 having primary windings 19c, 20c energized from current transformers 17c, 17b, primary windings 19d, 20d energized through an auto-transformer 21 by the residual current output of current transformers 17a . . . 17c, and primary windings 19b, 20b energized from voltage transformers through facsimile impedance 24, 25. The compensated signals induced in the secondary windings 19a, 20a are applied to the windings of an induction relay 14, but alternatively a phase comparator of a static type, such as a Hall effect crystal or transistor device, may be used. Two zone operation may be provided by means of a fault detector unit 15 energized from the currents in the phases and controlling a definite time relay 16 which when energized operates a zone switch 28. This switch opens contacts 22, 23 to introduce additional impedances 29, 30 in series with the impedances 24, 25 to extend the reach of the protective arrangement. A single-phase distance relay 13 provides protection against symmetrical threephase-to-ground faults. In an alternative arrangement, Fig. 2 (not shown), the two compensated signals are derived by voltage comparison instead of current comparison as in the arrangement described. The Provisional Specification refers to the use of a phase comparator comprising three transistors, relay operation occurring when the transistors are conductive. This is when the phase angle between the two signals applied to two of the transistors has a chosen polarity depending on the control action of the third transistor or when either signal has a very low value. Specification 890,308 is referred to.