GB251292A - Improvements in and relating to the protection of electric systems against excess voltages - Google Patents

Abstract

251,292. International General Electric Co., Inc., (Assignees of Allgemeine Elektricitõts Ges.). April 23, 1925, [Convention date]. Protective. arrangements against excess voltages, particularly applicable to telephone lines but applicable also to power transmission lines. An impedance 12, Fig. 1, is inserted in the vicinity of the working apparatus, between the conductor branches 11, which in the case illustrated are telephone wires, and an earthed protection device 14 of the spark gap type is connected to a selected point on the impedance so that the balancing current through the apparatus T is very low. The lines may be connected to the instruments T through transformers 15 as shown in Fig. 2. Where the outgoing and return conductors have unequal electrical constants, the point of connection to the impedance is displaced from the central point to balance this inequality. Fig. 4 shows four conductors with a common return 16 protected by a single protective device 14 at each end. The inductive resistances 12 are tapped in the ratio 1 to 4 and led through a zig-zag choke coil 19 with four limbs to an artificial neutral point to which the protection device is connected. The multiple zig-zag choke may be replaced by several singlelimb choke coils. In addition to the protection described, the lines may be further protected by protective devices Sa, Sb, Fig. 10. directly connected to the lines and having a higher setting than the protective devices connected to the inductances.