GB1262358A - Distance protection apparatus - Google Patents

Abstract

1,262,358. Protective arrangements. COMPAGNIE DES. COMPTEURS. 19 Feb., 1969 [20 Feb., 1968], No. 9046/69. Heading H2K. A distance protective arrangement for a three phase line has means for producing three signals V<SP>1</SP>a, V<SP>1</SP>b, V<SP>1</SP>c which are functions of the voltage and currents of respective phases, and means responsive to the phase sequence of these signals and the phase sequence of one of these signals, e.g. V<SP>1</SP>a, and a signal which is a function of the voltage Vbc between the other two phases. Each of the three signals may have the form V - Z(I + KIr) where V and I are the voltage and current of the respective phase, Z is a replica impedance representative of the impedance of the protected line section, Ir is the zero-sequence current and K is the earth impedance constant. These signals are produced in a circuit arrangement having current and voltage transformers with mutual inductors providing replica impedances, Fig. 1 (not shown). The Figure shows an arrangement in which the signals V<SP>1</SP>a, V<SP>1</SP>b, V<SP>1</SP>c and Vbc are converted to logic signals by amplifiers 9 ... 12 and applied to phase sequence comparators 7, 8. In the event of any fault within the protected section causing asymmetry, i.e. a single or two-phase fault to earth or a fault between two phases, an "O" signal at the output #3 of the comparator 7 causes a "NOR" logic circuit 2<SP>1</SP> to provide a signal to an "OR" circuit which provides an output controlling the operation of a three-phase circuit-breaker (not shown). When a three-phase fault occurs within the protected section, the determination of the phase sequence of Vbc and V<SP>1</SP>a in the comparator 8 provides at output P a "1" signal which is applied to an "AND" logic circuit. 2 together with the "1" signal which exists at output #3 under symmetrical conditions, the "AND" circuit applying a signal to the "OR" circuit 1. If it is desired to obtain a signal identifying any particular single-phase to earth fault, e.g. for operating a single-pole circuit-breaker in the earthed phase, a polarity comparator 6 is provided. This comparator 6 provides an output at G only when its inputs are simultaneously positive or negative, i.e. in the event of faults to earth from one or two phases within the protected section. Logic signals from the three comparators 6 ... 8 are applied to three "AND" circuits, these signals being arranged so that only the relevant "AND" circuit has three "1" signals when a single phase to earth fault exists, as fully described in the Specification.