GB649486A - Improvements in and relating to electrical ballasts particularly for electric discharge devices - Google Patents

Abstract

649,486. Transformers; supply systems for space discharge lamps ; modifying reactive characteristics of electrical circuits. BRITISH THOMSON-HOUSTON CO., Ltd. Sept. 17, 1948, No. 24443. Convention date, Sept. 25, 1947. [Classes 38 (ii) and 38 (iv)] A ballast 1 for an electric discharge lamp 2, which provides an operating current to the lamp at approximately unity and preferably slightly lagging power factor and takes a high power factor current from the supply 13, comprises in combination a transformer and a condenser 5 included in the output circuit of the transformer, the transformer core having a magnetic shunt section 11 to increase the series reactance of the transformer and a high reluctance series section 15 for causing the primary winding 8 to take a high exciting current and neutralize in the input circuit the effect of the capacitive reactance of the output circuit which latter reactance is higher than and preferably twice the transformer series reactance. The transformer may be of the core or shell type, preferably with auto-connected windings separated by the magnetic shunts constituting intermediate legs 11 on the laminated yoke 7 separated from the central limb 17 by or in the case of the core tyre provided with air gaps 16. The high reluctance series section may be obtained by providing punched apertures 15, and bridges 19 in that portion of the central limb carrying the primary winding. 8 or by reducing the width of lamination in that portion of the outer yoke 18 enclosing the primary winding or providing a bridged air gap where outer yoke 18 joins central limb 17 (Fig. 5, not shown). In the case of core-type transformers, the core is formed of pairs of laminations with butt joints at the core ends staggered in alternate laminations, some of which are cut short to form at the centre an aperture through the cone end (Fig. 6, not shown). Additional lamps may be supplied by providing a secondary winding 10 and condenser 6 for each, and in the case of the two lamp ballast the condenser may comprise a single unit with a centre tapping (Fig. 7, not shown).