GB680336A - Improvements in electrically operated time delay devices - Google Patents

Abstract

680,336. Automatic circuit-breakers; electromagnetic switches. FOSTER TRANSFORMERS & SWITCHGEAR, Ltd., and BAGNALL, R. I. June 20, 1950 [June 21, 1949], No. 16450/49. Class 38 (v) An electromagnetic time delay device primarily for overload tripping functions in circuit-breaker, has two windings 9, 10 which act differentially on a common armature and have, or form parts of circuits having, different temperature coefficients so that as their temperature rises under overload conditions, the distribution of current in the two windings changes and the armature is operated to produce tripping. In Fig. 1 the windings 9, 10 are wound on opposing magnet cores 5, 6 on a common yoke 4 on which the armature 7 is pivoted. The windings are connected in parallel and the winding 9 is in series with a resistance 11 having a high positive temperature coefficient, whilst the winding 10 may be in series with a resistance 12 having a low positive or a negative temperature coefficient. The armature is initially against an adjustable stop 8 and may be normally biased by springs or gravity. Under overload conditions, the heating of the resistances and windings by the excessive current causes the reduction of the current in winding 9 relative to that in winding 10, so that the force exerted :by the latter overcomes that of the former and the bias to move the armature 7 to its alternative position against the core 6. In Fig. 2 the windings 9, 10 are of unequal cross-section and wound on a common tube former 14 on a yoke 4 having a limb 13 extending between the windings. The plunger-type armature 15 acts on a striker pin 16 and a resistance strip 18 of low positive or negative temperature coefficient is connected in series with the larger coil 10. in each case the coil 10 may have more turns than the coil 9 so as to produce an ininstantantaneous action under very heavy overload conditions and to assist in producing in inverse time delay with reference to the magnitude of the current.