GB237334A - Improvements in alternating current relays - Google Patents

Abstract

237,334. British Thomson-Houston Co., Ltd., and Fitzgerald, A. S. April 22,1924. Alternating - current relays; polarized and tuned relays; automatic circuit-breakers, &c.- A polarized alternating- current relay comprises an operating winding arranged to magnetize an unmagnetized reed of magnetic material symmetrically disposed in an air-gap of a magnetic circuit, which includes a permanent or an electromagnet, the reed having a natural frequency substantially equal to that of the operating current. The relay may open or close circuits or may actuate trip devices of circuit - breakers or latches. The non - magnetized reed 12 of magnetic material is secured to a plug 17 and symmetrically disposed in the airgap 29 between poles 14 of permanent magnets 19 of cobalt steel. The reed carries a contact 26 co-operating with a fixed contact 25 that is adjustable to prevent the reed touching the poles 14, and is surrounded by an operating coil 11. In operation, when the coil 11 is excited by a predetermined value of current, the reed vibrates in synchronism and its amplitude rapidly increases until the contacts 25, 26 engage. The gap 29 is made relatively large to avoid damping by the permanent magnet of the fire-oscillation of the reed when maximum sensitivity is required. When the relay is required to be sensitive to a frequency varying slightly either way from the normal frequency, the gap is chosen sufficiently small to allow limited damping, or alternatively, a variable magnetic shunt may be used to vary the permanent field through the reed. Either or both poles 14 may be adjustably mounted on the magnet 19 to ensure that the reed is centrally disposed between them. When the frequency is liable to vary over a wide range, two or more reeds may be used, arranged to resonate at a slightly different frequency, or there may be used two or more relays connected in series or parallel and each having a reed tuned to a different frequency.