Patent GB-395706-A (GB)
Title: Improvements in or relating to protective arrangements for electric power transmission systems
IPC: H02H7/26
Filed: 1932-01-18
Abstract: 395,706. Protective cut-out arrangements. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and GARRARD, C. C., c/o General Electric Co., Witton, Birmingham. Jan. 18, 1932, No. 1521. [Class 38 (v).] In a protective arrangement for selectively cutting out a section of a ring main or other transmission system, and employing directional relays for preventing cutting out of a section when fault current is flowing out of that end of the section where the relay is located, undesired cutting out of a section where the directional relay has its voltage coils energized from that side of a power transformer remote from the system and when the transformer is disconnected for repairs &c., is prevented when the section is carrying a fault current of which the directional relay would, if energized, prevent the disconnection. The directional relay at the far end of the next section is employed for this purpose and causes the injection of carrier currents into the line to control the section which would, otherwise, be cut out. As applied to an arrangement of the general character, shown in Fig. 4 of Specification 378,006, the section 1 extends between stations 3, 4, the bus-bars 2, 2 of which are connected through circuit-breakers 28 and isolating switches 27 to power transformers 26, the remote or low-tension sides of which supply the potential coils of directional overload relays 18. Associated with each station is a pair of equipments 10, 11 and 12, 13, each comprising a transmitter 14, receiver 15, control relay 16, and overload relay 17. The circuit of the trip coils 9 of the breakers 7 is from the upper bus-bar through contacts 33 of overload relay 17, contacts 20 of relay 16, and contacts 24 of the receiver 15, this circuit being made by 17 for the breakers at each end of a section when the fault is in that section. If the fault current flows through the section 1 and out at the right-hand end (say), the relay 18 of equipment 12 acts before the relays 17 of the section 1, closes its contacts 34, and energizes relay 16 over contacts 24 of equipment 12. This breaks the circuit of trip coil 9 at 20, and at 21 makes the circuit of transmitter 14 which in turn operates the receiver 15 of equipment 11 and breaks at 24 the circuit of the trip coil 9 at that end. If the transformer 26 is disconnected from the right-hand end of section 1, the relay 18 of equipment 12 would be unable to prevent disconnection of a through left-to-right fault. The back contacts 29 .. 32 are therefore adapted, alternatively or together, on opening either or both of switches 27, 28, to connect contacts 25 of equipment 12 in parallel with contacts 21 of equipment 13 and contacts 25 of equipment 13 in parallel with contacts 21 of equipment 12. The relay 18 at the right-hand end of section 6 then operates the receiver 15 of equipment 13, which at contacts 25 makes the circuit of transmitter 14 of equipment 12, which in turn operates the receivers 18 at both ends of section 1 and prevents the latter from being cut out. The Specification refers also to the use of pilot wires.