Patent GB-376409-A (GB)
Title: Improvements in or relating to protective arrangements for electrical apparatus
IPC: H02H7/26
Filed: 1931-05-01
Abstract: 376,409. Protective cut-out systems. KAPP, R. O., CARROTHERS, C. G., 25, Randolph Crescent, and GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, both in London. May 1, 1931, No. 12913. [Class 38 (v).] In a discriminative protective system of the kind adapted for sectionalized transmission systems and including directional relay means at either end of a section arranged to exert control through a channel of communication extending to the other end of the section, means are provided which, after power has passed through the section to a fault in another section and when the flow of power is interrupted, restore with a time-lag so as to prevent inadvertent cutting out of that section consequent on reversal of power flow in the section. In the Figure the section 1 has breakers 2 at each end, each controlled by normally-open contacts 33 of overload elements 30 and normally-closed contacts 29 of overload relays the operating coils of which are respectively energized by closure of contacts 27, 34 of directional elements, which latter contacts are engageable by movable contacts 28 depending on whether current is flowing, respectively, into or out of the section at that end. The relay groups 24, 25, 26 are associated with the respective phases and the several contacts 29 are in series whereas those 30 are in parallel. When one of the latter closes on an overload passing from left to right and through the section, the relay 19 at the left-hand end closes.. being energized by a battery 35, and moves its member 18 from contacts 13 to contacts 14, thereby establishing a circuit from battery 15 over the lower half of a differential relay 9 and resistance 11. The relay 9 however does not operate as its upper half also is traversed by an equal current over the pilot 6 to the right-hand relay 9, the relay 19 at which end does not operate as power is flowing out of the section at that end. The appropriate contact 29 at the right-hand end opens so that, although contact 17 at that end is closed by contact 10, the circuit of the trip coil 5 is not made. The elements 30 are arranged to close either with a time-lag or at a higher current, or both, as compared with the opening of the contacts 29, and the latter are further arranged to close with a time-lag. Thus, when a fault out of the section is cleared, the tripping of a breaker in the sound section, due to reclosure of contacts 29 before contacts 17 reopen, is prevented. In a modification, Fig. 2 (not shown), a modified arrangement of directional and overload elements is employed, the latter operating independently of the former, and a further relay of the balanced beam type operates to instantaneously open the trip circuit (and reclose with a time-lag) to prevent inadvertent interruption of a sound section on clearance of a fault in another section. Further modifications relate to the use of earth leakage and directional earth leakage elements instead of one of the single-phase directional and overload elements, and in one form carrier currents are superimposed on the line to actuate a preventive relay when the fault is a through one. As in the Figure the relays are suitably time-lagged to prevent undesired opening of a section. The Provisional Specification describes also a protective system for transformers employing earth leakage relays.