GB823044A - Improvements relating to direct current track circuits for railway signalling systems - Google Patents

Abstract

823,044. Railway signalling track circuits. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd., DUCKITT, H., and TILLOTSON, P. Oct. 26, 1956 [Nov. 3, 1955], No. 31462/55. Class 105. In a D.C. track relay circuit having one, viz. 11, of the track rails continuous as the return for the traction A.C. current, the other rail 12 being divided into sections by insulating joints 13, 14, the current feed set comprises two secondary cells 20, 21 arranged to be charged alternately, preferably for equal periods, through a full-wave rectifier 17 from an A.C. source 19, by a time-switch 23 controlling connection of the cells alternately to the track rails and to the rectifier 17 output terminals so that as one cell, e.g. 20, is charging the other cell 21 feeds the track circuit and vice versa and at no time is the rectifier 17 connected across the track rails and no half-wave rectification can take place in the rectifier due to traction A.C. voltage build-up across the rectifier output terminals, which would increase current fed to the track circuit and reduce the sensitivity thereof to the entry of a vehicle into the section. In the event of a breakdown of the A.C. supply 19, the cells 20, 21 are connected to feed the track circuit in parallel. As shown, each of a pair of repeater relays 24, 25 has an energizing circuit which includes a change-over contact device 23a of the time switch 23 so that operation of the switch opens the energizing circuit of one relay, e.g. 24, and closes that of the other relay, viz. 25, whereupon relay 24 releases and at front contacts 24b breaks the charging circuit of the cell 20, at back contacts 24b connects the cell 20 to the track rails and at back contacts 24a connects the relay 25 to the rectifier. Relay 25 picks up and at its back contacts 25b breaks ts feed circuit to the track rails and at its front contacts 25b connects the cell 21 to the rectifier 17 through the changed-over contact 23a. At back contacts 25a the energizing circuit of relay 24 is opened. A variable resistance 22 is included in the charging circuit and a variable resistance 29 regulates the feed of direct current to the track and a protective choke 30 limits any traction A.C. current circulating through the cells. In an alternative embodiment (Fig. 2, not shown) the time switch 23 has associated with each cell a set of changeover contacts operable in sequence as by cam devices so that the contacts associated with the charging cell connects that cell in the feed circuit before the other set of contacts change over to disconnect the feeding cell from the track circuit.