Patent GB-444418-A (GB)
Title: Improvements in protective arrangements for electric power transmission systems
IPC: H02H7/26
Filed: 1934-11-28
Abstract: 444,418. Protective cut-out systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and WILSON, W., and CLIFF, J. S., c/o General Electric Co., Ltd., Witton, Birmingham. Nov. 28, 1934, No. 34223. [Class 38 (v)] A discriminative protective arrangement for a sectionalized transmission system comprises two channels of communication extending between the ends of a section, one channel being controlled at one section-end by relay means responsive to circuit conditions thereat and the other being controlled at the other section-end by relay means responsive to circuit conditions thereat. A control is normally transmitted over a channel but is interrupted on the occurrence of an external fault under the control of power flowing to the fault, for the purpose of preventing isolation of a section-end. The channels may be existing telephone or telegraph circuits. The apparatus shown for one end of a section 1 is duplicated at the other end and the control is exerted by means of voice-frequencies transmitted by a transmitter 5 and received by the receiver 4 at the far end. Current transformers 28, 30 feed, respectively, the overload coils 32, 35 and current coils 33, 36 of directional relays which close their contacts 17, 18 with incoming power. In the neutral are connected the earth-leakage relay coil 37 in series with the current coil 38 of the directional earth-leakage relay which closes contacts 23 with incoming leakage power. Contacts 12, 14 of overload relays are adapted to open with, say, 125 per cent overload, and contacts 11, 13 to close with, say, 150 per cent overload. The contacts 21 of the earth-leakage relay open with a relatively small, and contacts 20 close at a higher, value of residual current. Contacts 11, 13, 20 are connected in parallel in a circuit containing the trip coil 3 of breaker 2, contacts 48, which, with contacts 47 controlling the transmitter 5, are normally held closed by coil 24 in series with the normallyclosed contacts 12, 21, 14, and contacts 49 normally held closed by the coil 25 energized by the receiver 4. With a fault outside the section, say the right, the coil 24 at the righthand end is de-energized and opens at 48 the trip circuit at that end to prevent its isolation. Contacts 47 are also opened to interrupt the transmission of the control, whereby the trip circuit at the left-hand end is opened at contacts 49. At the same time, the receiver relay at the left-hand end closes contacts 50 to energize coil 51 of the relay 8 which closes contacts 52, 53 with a time-lag. Closure of 52 would make a parallel circuit about the opened contacts 49 and so cause tripping, but by grading the lags of relays 8, it can be ensured that only the faulty section is cut out. Closure of contacts 53 energizes an alarm 54 which may be utilized to indicate failure of the receiver or transmitter or the channel between them. On fault in the section 1, coils 24, 25 both remain operated, contacts 48, 49 remain closed and closure of one or more contacts 11, 13, 20 produces tripping. The leakage relays may be substituted by an overload and directional relay operating as in the other phases. Also, contacts 47, 48 may be adapted to close on deenergization of 24, which will then be connected in series with directional-relay contacts which close with outgoing power, and with overload-relay contacts which close at a lower value of overload than that at which contacts in series with the trip coil close.