GB925558A - An arrangement for monitoring the operation of tap selector switches - Google Patents

Abstract

925,558. Control of A.C. motors. LICENTIA PATENT - VERWALTUNGS - G.m.b.H. March 16, 1960 [March 23, 1959], No. 9281/60. Class 38 (3). [Also in Group XXXV] An A.C. traction motor is supplied through bus-bars from a transformer and controlled by a tapchanging mechanism which is monitored by detection of the voltage and current carried by the bus-bars to ensure correct opening and closing of the tap selector switches. Off-load selector switches 7, 8, 11, 12 are connected to bus-bars 5, 6, the currents in which are detected by current transformers 20, 21 connected to indicators or control mechanisms (not shown), which allow a switch to close only when no current flows in the bus-bar to which it is connected. The bus-bar potentials are detected by voltage transformers 15, 16 (or a single transformer connected between the bus-bars, Fig. 2, not shown), which indicate proper closing of a selector switch. The load current path may be divided into two parallel branches each tapping then being provided with two selector switches connected to separate bars 28, 29 or 30, 31. The current transformers 56, 57 and 58, 59 then indicate symmetrical current, loading in the pairs of bus-bars, and may be differentially connected to give zero reading under these conditions (Fig. 3, not shown). Two conditions must be satisfied before a tapping is opened: (a) there must be symmetrical current loading in the bus-bar systems; and (b) the voltage transformers must indicate proper closing of the subsequent selector switches. Transductors 54, 55 may be provided to reduce the current before switching so that on load switches 50, 51, 52, 53 operate substantially off-load and may be omitted.