GB499540A - Improvements in combinations of electric discharge devices with incandescent filaments in series with them - Google Patents

Abstract

499,540. Supply systems for discharge lamps. GENERAL ELECTRIC CO., Ltd. (Patent-Treuhand-Ges. f³r Elektrische Gl³hlampen) Jan. 6, 1938, No. 418. [Class 38 (iv)] Emergency systems.-An electric discharge lamp is connected in series and structurally combined with a filament which is rendered incandescent by the discharge current and serves, at least in part, as a stabilizing resistance. The filament runs fully loaded or slightly over-loaded and means are provided whereby when the filament burns out it may be replaced,' preferably automatically. In the arrangement described, a substitute filament 8, in combination with devices 9 and 10 which break down under excess voltage, is connected in parallel with a filament 6 which normally functions in series with a H.P.M.V. lamp 1 across the supply terminals 7, 7<1>. The centre points of the filaments 6 and 8 are connected by a conductor 11 so that, as long as filament 6 remains intact, the maximum voltage across either of the devices 9 and 10 is a little less than half the mains voltage and is insufficient to cause their breakdown. A high impedance 5 is connected across electrodes 2, 2<1> of. the lamp 1 so that when, say, the half of filament 6 nearer to 7 burns out, the device 9 is connected across the supply terminals by way of the impedance 5, the intact half of filament 6 and the half of filament 8 nearer to 9. The device 9 then breaks down under full mains voltage and operating conditions are restored with half of filament 8 replacing the broken half of filament 6. If the remaining half of filament 6 breaks, the device 10 will be broken down and the whole of filament 8 brought into operation. The devices 9 and 10 are composed of oxide film which breaks down at a critical voltage. Alternatively any known means of automatically replacing a damaged filament by a sound one may be employed. If the lamp 1 is one in which an outer jacket surrounds an envelope enclosing the discharge, the filaments and all or part of the means for substitution may be located in the space between the envelope and the jacket. More than one substitute filament may be used.