Patent GB-383308-A (GB)
Title: Improvements in or relating to protective arrangements for electric power transmission systems
IPC: H02H7/26
Filed: 1931-08-01
Abstract: 383,308. Protective cut-out arrangements. KAPP, R. A., CARROTHERS, C. G., 25, Randolph Crescent, and GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, both in London. Aug. 1, 1931, No. 22008. [Class 38 (v).] A section of a transmission system has protective means adapted to operate only if there is a fault in the section, and further protective means which operates less quickly than the first means and tends to become effective in response to a fault whether the fault is in the section or not, but is rendered ineffective unless the fault is in the section. At each end of the section of an overhead ring main or network of a three-phase earthed system is a group of three directional overload elements and overload elements, one for each of the phases, having directional contacts 11, which close when the power is incoming, and overload contacts 10, 9 which are normally closed and open, respectively. In parallel with contacts 9 are contacts 16, tripping contacts 18, trip coil 6 of the breakers 4, 5 and back contacts 7 of the breaker which open when the latter opens. The contacts 16 are controlled by a 'differential relay 17 which is in turn controlled by contacts 35, 36 such that, when both halves of its winding are energized, it does not operate, but when the lower half is energized, contacts 16 are opened and contacts 33 are closed. Sources 22, 23 of carrier currents of different frequency are connected to the line through couplers 20, and a third frequency current is adapted to be injected from sources 24 on closure of contacts 33. The operating means 26, 27 of tripping and control relays 19, 25 are tuned to the frequency of the source 22 or 23 at the other end, and the operating means 31 of a lockout relay 30 is tuned to the frequency of the source 24. With a fault in the section, the directional contacts 11 at both ends close and energize relays 8 whereby both contacts 39 are closed to transmit currents from the sources 22, 23 to the opposite ends, whereby relays 19, 25 at both ends are operated. Since both halves of relays 17 are energized by contacts 11 and contacts 35, 36 (closed by relay- 25), the relay 17 remains unoperated and contacts 16 remain closed, so that closure of contacts 18 of relay 19 closes the trip coil circuits and opens both breakers. If either breaker failed to open, the time-delay relay 14 energized in parallel with the coil 8 would eventually close its contacts 37 and make the trip circuit. In the event of a through fault, say from left to right, the contacts 11, 9 at the left end would close and energize the coils 8, 13, thereby energizing relays 19, 25 at the right-hand end. As in this case the right-hand contacts 11 do not close and as contacts 10 open, the lower half alone of relay 17 at that end is energized and closes the contacts 33, whereby the source 24 is connected to the lockout relays 30 at both ends, the relay 30 at the left end opening contacts 38 to prevent energization of the trip coil 6 by closure of the contacts 37 of timelag relay 13. The contacts 16 at the right-hand end open and prevent tripping of the breaker at that end should reversal of power flow occur on clearing of the fault before the trip relay 19 has reopened, as in Specification 376,409. If a fault occurs in the section fed from, say, the left end only, the right-hand relay 17 does not operate as contacts 10 remain closed, but the trip coil 6 of breaker 5 is energized over contacts 18, and so is the coil 8 at that end, so that a control current is sent back to the left end to trip the breaker 4. The Specification refers also to other forms of remote control, to leakage relays instead of one of the directional and overload elements, to different settings of the directional and overload elements, and to Specification 378,006.