GB509558A - Improvements in and relating to electric power transmission systems - Google Patents

Abstract

509,558. Converting. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 10, 1938, No. 29335. Convention date, Oct. 9, 1937. Addition to 456,222. [Class 38 (ii)] A power transmission system comprising, as in the parent Specification, a high voltage constant current direct current transmission line and translating circuits connecting it, at each end, to separate constant voltage alternating current systems, is provided with a plurality of translating circuits at each end and switching means to control the current level in the constant current circuit so as to reduce losses under light load conditions. One end of a constant current direct current line 3 is connected to a constant voltage alternating current system 1 through a pair of translating circuits. Switches 9, 25<1> permit connection of the constant voltage alternating current system 1 to the constant voltage terminals of monocyclic networks 4, 24 respectively. In another position, switch 25<1> short-circuits the monocyclic network 24 and an isolating switch 28 is provided adjacent to, the constant current terminals of this network. The constant current terminals of networks 4, 24 are connected through constant current alternating current circuits 10, 27, which may be interconnected by switch 31, to the primaries of transformers 11, 29 respectively. The secondaries of these transformers are connected to electric valve rectifiers (or inverters) 14, 30, respectively, connected in series across the constant current direct current transmission line 3. Similar terminal apparatus, associated with the constant voltage alternating current system at the other end of the line, is shown in Fig. 1 (not shown in full). Under normal load conditions, switches 9, 25<1> are closed and switch 31 open so that power is supplied independently through the two translating circuits to the constant current direct current circuit. Under light load conditions losses may be reduced by moving switch 25<1> to its short-circuiting position and dosing switch 31, whereupon the currents in the transformers 11, 29 and the transmission line 3 are reduced to half their previous value. As an alternative to short-circuiting the network 24, switches 25<1> and 28 may be operated to isolate it completely. Fig. 2 ( not shown) shows a form of the translating circuit in which control of the current level in the constant current circuit may be effected, either by switching reactances in parallel either with the capacitative or inductive elements of a monocyclic network, or by series-parallel control of a plurality of primary windings of a polyphase transformer in the constant current alternating current circuit.