Improvements in protective relay arrangements for polyphase electrical systems

摘要

220,329. Metropolitan-Vickers Electrical Co., Ltd., (Assignees of Crichton, L. N.). Aug. 11, 1923, [Convention date]. Protective arrangements.-Polyphase electric distributing systems with an earthed neutral are protected against earth faults by a wattmetertype relay having a current winding in circuit with the common neutral conductor between the usual current transformers and the overload relays and a potential winding connected in closed delta relation with the secondary windings of potential transformers in the power circuit. As applied to the protection of two parallel feeders 3, 4 supplied from the generator 1 having an earthed neutral and supplying the power circuit 2, two forms 9, 12 of wattmeter-type earth-fault relay are shown for the respective feeders 3, 4. The current coil 14 of the relav 9 is in the neutral conductor from the current transformers in the feeder 3 and the potential coil 15 is connected in closed delta with the secondaries of potential transformers in the supply circuit. The coils are energized only when an earth fault occurs, and the relay closes its contacts to trip the circuit. breaker only when the fault is on the feeder 3. Faults on the feeder 4 serves to reinforce the open position. The relay 12 for protecting the feeder 4 is provided with additional contacts controlled by an additional current coil. Both sets of contacts must be closed before the relav circuit is closed, and the additional set is only closed when the earth current attains a predetermined value.