GB273452A - Improvements in or relating to electrical protective relays - Google Patents

Abstract

273,452. Ross, T. W., and Metropolitan-Vickers Electrical Co., Ltd. May 28, 1926. Electromagnetic switches; cut-out systems.- A relay is provided, in addition to contacts controlled according to the impedance of the line, with a separate set of contacts which are operated by an overload unaccompanied by a drop in voltage. As shown in the Figure an induction disc 10 controlled by a current coil is geared at 14, 16 to a shaft 18 provided with a return spring 20 and a contact arm 42. Mounted coaxially with the shaft 18 and connected thereto by an arm 24 and a spring 22 is a shaft 26 carrying an armature 28 normally held against the poles 30, 32 of a saturated voltage electromagnet and carrying a second contact arm 34. On overload accompanied by a drop in the voltage the rotation of the disc 10 besides stressing the return spring 20 winds up the spring 22 until the attractive force on the armature 28 is overcome when the contact arm 34 is moved over to engage its contacts, the time of operation being a measure of the overload and the fall in voltage, i.e. of the impedance of the line. If no appreciable fall of voltage occurs, however, the attractive force on the armature is not overcome and the contact arm 42 is moved over to engage its fixed contacts in a time inversely proportional to the current. Either or both sets of fixed contacts may be provided with an adjustable setting indicated as by a dial 50. Specification 216,531 is referred to.