GB265952A - Improvements in and relating to protective systems for electric distribution systems - Google Patents

Abstract

265,952. British Thomson-Houston Co., Ltd., (Assignees of Summerhayes H. R.). Feb. 13, 1926, [Convention date]. Cut-out systems. - In protective arrangements for busbars and controlling apparatus arranged in sections, an earthed bus-bar is provided for each section or for each phase of a section, which is arranged to carry any leakage current from the oil switches, isolating switches, current transformers, bus-bar supports &c. in that section, the flow of such leakage current causing the tripping of all the switches connecting that section to other sections. As shown in Fig. 1 applied to a three - phase star - connected system with earthed neutral the section 2 is connected to adjacent sections 1 and 3 by oil switches 4, 6 and isolating switches 5, 7. Section 2 is supplied by a generator 20 through oil switches 24 and isolating switches 25 and supplies feeders 11, 12 through oil switches 14, 17, isolating switches 15, 18 and current transformers 13, 16. The feeders 11, 12 may be first connected to a group feeder bus-bar which is connected in turn to the main bus-bar, which may itself be duplicated. Each phase A, B, C of each of the sections 1, 2, 3 is provided with an earthed bus-bar 31, 32, 33 which as shown for the section 2 is connected to the corresponding oil switch tanks and operating mechanisms, isolating switch bases, current transformer casings and bus-bar insulator supports. When current flows to earth through any of the earthed bus-bars one or more of the relays 45, 47 are operated through current transformers 44, 46 so completing the energizing circuit of a relay 50 which in turn completes the energizing circuits of tripping coils 29 corresponding to all the circuit-breakers to connect the section to other sections so that the affected section is thereupon completely isolated. As shown the tanks of the circuit-breakers 4, 6 interconnecting adjacent sections are not connected to the earthed bus-bars of either section, but in a modified form in which adjacent sections are interconnected by two series connected circuitbreakers the casing of each circuit-breaker is connected to the earthed bus-bar of the adjacent section. Where the neutral of the supply is not earthed, protection on fault is obtained by the operation of relays due to the increased capacity current in the earthed bus-bars resulting from faults to earth.