GB652374A - An improved system of electric lighting and improved apparatus for use therewith - Google Patents

Abstract

652,374. Electricity supply; supply systems for space discharge lamps ; transformers. COTTON, H. July 25, 1947, Nos. 20147 and 31912. [Classes 38 (ii) and 38 (iv)] Installation wiring; transformer arrangements; voltage accommodation.-An electric lighting system suitable for coal mines and other areas where sparking must be avoided comprises an insulated cable supplied with a constant alternating current which by electromagnetic induction energizes at any selected point in the cable length at least one detachable lamp unit comprising a gas discharge or incandescent lamp 6 connected across a winding 5 on a magnetic core 4 provided with a detachable yoke 7 to enable the cable to be passed into and out of the aperture of the core. A multicore cable having its cores a-d series-connected to form a continuous conductor may be used to reduce the supply current required which is preferably derived from the secondary winding 2 of a high reactance " constant current " transformer 1 which also enables the usual ballast for discharge lamps to be dispensed with. Protection against excess voltage, excess current and earth leakage is effected by switching means included in the primary circuit of the transformer 1 actuated by coils connected respectively across the secondary winding 2, in the primary circuit and between the " earthed " mid-point of the secondary winding and a conductive screen surrounding the cable. The excess current trip is provided with a time lag to afford time to connect one or more lamps when the supply is made with no-load applied. The two parts of the magnetic core (Fig. 5, not shown), may be separated by two magnetizable plates which extend into the core aperture between the cable and winding 5 with a small air gap between them filled in or covered over by a strip of non-conducting and non-magnetizable material. The part of the core carrying the winding 5, which may be of the core or shell type, also carries the lamp housing comprising a transparent shield surrounding the incandescent or one or more series-connected discharge lamps associated with the usual starting switches. The detachable yoke which may be wedge-shape may be hinged or anchored to the core and held in the closed position by a clasp, or clamping cams operated by pivoted levers.