GB728002A - Improvements in and relating to electrical frequency responsive relays - Google Patents

Abstract

728,002. Electromagnetic relays. ENGLISH ELECTRIC CO., Ltd. Sept. 18, 1953 [Sept. 19, 1952], No. 23566/52. Class 38 (5). A frequency responsive relay which may be adapted to operate for under frequency or over frequency conditions comprises a magnetic core 1 having three pairs of poles a, b, c, d, and e, f, the outer pole pairs being shaded by windings 3 connected in series with a capacitor 4, a tapped inductor 5 being included in the shading circuit of the pole pairs c, d. The core 1 is energized by a winding 2 and the pole pairs a, b, and c, d, produce oppositely-acting torques on an aluminium disc 6 rotatable on a shaft 9 between the pole gaps, the two torques being equal when the frequency is normal, e.g. 50 c.p.s. The shading circuit of pole pair a, b, is tuned for a frequency below normal, e.g. 40 c.p.s., whereas the shading circuit of pole pair c, d, is tuned for a frequency above normal, e.g. 55-65 c.p.s. Hence in an under frequency relay, Fig. 2, or an over frequency relay, Fig. 3, a contact arm 8 on the shaft 9 is moved against a return spring 7 to bridge a pair of contacts 10 in response to under frequency or over frequency conditions, respectively. Graphs (Figs. 4, 5, not shown). show the operating torques of the shaded pole pairs plotted against frequency.