GB652191A - Improvements in or relating to protective systems for polyphase transmission lines - Google Patents

Abstract

652,191. Protective cut-out arrangements. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Oct. 8, 1948, No. 26281. Convention date, Nov. 29, 1947. [Class 38(v)] In a protective system for a three-phase transmission line, similar to that of Specification 651,998, the fault-detector relays FD1 and FD2 each have an operating coil (denoted by FD1 and FD2) and a restraining coil FD1R and FD2R. The operating coils are connected in series and supplied from a network of filter HC B over a non- saturating transformed NST and a rectifier bridge RB. The restraining coils are connected in series in the anode circuit of a triode 9, the grid of which is connected to a tapping on a resistance RO1 fed from the output terminals m, n, of a minimumvoltage network. This network gives at terminals m, n, the smallest of the three phase-to-phase voltages supplied by transformers Ta-Tc. The latter energize rectifier bridges Ba-Bc and condensers Ca-Cc, which are 'shunted by resistors Rr, the potential drops across the latter being applied to terminals m, n, through reverselyconnected rectifiers 6a, 6c. The relays FD1, FD2 thus serve as quasi-impedence relays, the former having a lower current-setting and higher impedance-response than FD2. As in the prior Specification, these relays respectively control the operation of valves V2, V2, and tripping relay R.