GB667256A - Improvements in and relating to electrical protective systems using directional current relays - Google Patents

Abstract

667,256. Protective cut-out arrangements. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 5, 1950. [Jan. 27, 1949] No. 316/50. Class 38 (v). A bus-bar 5 fed by source lines 1 ... 4 and supplying feeders 6 ... 8 is protected against an internal fault by directional relays 16 ... 19 having operating windings 32 and opposed polarizing windings 31, 33, having equal turns. The windings 33 of all the relays are connected in series so as to be fed by the sum of the currents in the current transformer secondaries 20 ... 23, in the respective lines, and the windings 31 are connected in series with the respective windings 32, so as to be fed by the current in that line, the net .polarizing effect of the relay of any one line being therefore normally the sum of the currents of the other lines. The relays 16 .. 19 have series-connected, normally-closed contacts 35 in parallel with normally-closed contacts 34 of respective overload relays 24 ... 27, the group of contacts 34, 35 being connected in series with parallel-connected normally-open contacts 37 of relays 24 ... 27 in a D.C. supply circuit 40 for a relay 38 having contacts 39 in the trip circuit 48 of circuit-breakers 9 ... 15. On an internal fault, e.g. at Y, the directional relays are unaffected, but one or more of the overload relays operates to open its contact 34 and close its contact 37, thereby energizing relay 38 and tripping the circuit-breakers. On a fault on a source line, e.g. at X on line 1, the current in coil 32 of the relay 16 reverses and the contacts 35 open. Similarly, relay 24 is energized and opens its contact 34 thereby keeping the circuit 40 open. If a fault occurs on one of the feeders 6 ... 8, the appropriate overload relay 28 ... 30 opens its contact 36 in the circuit 40. A directional relay is provided for each of at least two of the phases of the source lines.