GB350009A - Improvements in the automatic isolation of parallel three-phase electric power transmission lines - Google Patents

Abstract

350,009. Protective cut-out systems. VICTORIA FALLS & TRANSVAAL POWER CO., Ltd., Consolidated Buildings, Fox Street, Johannesburg, South Africa. March 4, 1930, No. 7104. Convention date, Dec. 21, 1929. [Class 38 (v).] For the protection of long parallel-connected transmission lines 4, 5 connecting bus-bars 2, 3 an electrically-interlocked, discriminating, faultprotection relay-arrangement 12, 13, 19 is provided to open one only of the circuit-breakers 7, 9 at the generator end. Underload relays 38, 39 are provided to open the corresponding circuit-breaker 8 or 10 at the far end. The relay 19, which may be a reverse-power relay but is shown as an earthleakage relay, closes on fault one of its sets of contacts 19, 20 or 21, 22 and completes a local circuit to energize one of the time-lay relays 12, 13 through the normally-closed lower contacts of the other relay. If the fault is on the feeder 4, contacts 20, 21 are closed and the relay coil 23 energized through the contacts 29, 30 of the other relay. The relay 12 closes at once and completes the tripping circuit for the circuit-breaker 7. If a fault appears on the feeder 5 (now carrying the load) its circuit-breaker will not be tripped until the relay 12, under retardation, has closed the contacts 27, 28 again. This time interval is long enough normally for the fault to be burnt out. At the far end of the feeder 6 current supplied to the fault from the healthy feeder is of substantially reduced value in at least one of the conductors (i.e. the healthy conductor-the system is not applicable to the unusual case of a fault on all three conductors) and, in consequence, one or other of the low load relays 42 releases its armature to complete the tripping circuit of the circuit-breaker 8. If a period of low load may be normal to the system the contacts of an additional relay 47 is included in the tripping circuit. This relay is energized from all three phases like an earthleakage relay and closes only on fault. The system is stated to be applicable to more than two parallel feeders.