GB259979A - Improvements in means for detecting an earth leakage in high tension cables - Google Patents

Abstract

259,979. Akt.-Ges. Brown, Boveri, et Cie. Oct. 14, 1925, [Convention date]. Detecting, indicating, and locating faults. - In order to detect selectively a faulty section of a high-tension conductor connecting a plurality of central stations, devices are provided for measuring the higher harmonic component of the earth leakage current and also devices by which the distribution of these higher harmonic currents over the various central stations can be varied for locating the fault. As shown, two stations A, B are connected by three-phase high-tension conductors R, S, T, in the first-named of which is a fault E to earth. The presence of the earth leakage is detected at station A by means of a telephone HA, which can be connected successively to the secondary windings of transformers in the lines R, S, T, thereby detecting in which line the fault occurs. At a point C between the stations A, B is a choking-coil D consisting preferably of transformers having normally short-circuited secondary windings. In order to determine on which side of the point C the fault lies, the short-circuit is temporarily opened, whereby the effective inductance is increased, particularly for higher harmonic currents, which therefore flow almost exclusively through the station A. The telephone HA therefore indicates, by increased sound, the presence of a fault between the points A, C. The opening and closing of the short-circuiting switch K may be controlled telephonically from the stations A, B. A periodic method of working may be arranged, for example the choking coil may be alternately closed for 20 seconds and opened for 5 seconds.