GB408956A - Improvements in or relating to electric relays - Google Patents

Abstract

408,956. Electromagnetic relays. WESTINGHOUSE ELECTRIC & MANUFACTURING CO., East Pittsburg, U.S.A.- (Assignees of Smith, R. M. ; 12, Abbott Place, North Arlington, New Jersey, U.S.A.) Oct. 13, 1932, No. 28648. Convention date, Oct. 13, 1931. [Class 38 (v).] An overload relay which is capable of adjustment to obtain a substantially uniform inverse time-current characteristic over through the entire operating range comprises currentresponsive electromagnetic means adapted to operate the relay contacts which are biassed towards the closed position and are held from movement until an electrical quantity such as the current reaches a predetermined value and damping or timing means associated therewith, a resilient coupling being interposed between the electromagnetic operating means and the timing mechanism. As shown in Fig. 2 the relay contact 14 is carried by the armature 9 of the operating electromagnet 2 which is energized by the load circuit, a spring 21 having a substantially constant force biassing the contact 14 towards the fixed contact 16. The armature is connected by a spring 27 to a pivoted arm 31 secured to a ratchet wheel 42. On rotation of the ratchet wheel in an anticlockwise direction pawls 43 are engaged and drive through gearing 44, 45 an eddy-current braking disc 46 movable between the poles of permanent magnets 52. The arm 31 is however connected by a link 83 to the pivoted armature 65 of an initiating electromagnet 59, a powerful spring 77 normally holding the parts in the position shown and preventing movement of the armature 9 of the timing mechanism. On the occurrence, however, of a predetermined current strength the electromagnet 61 attracts its armature and frees the operating and timing mechanism. The various factors controlling the speed of the contact closure are each separately adjustable, viz., the pull of the magnet 3 by tappings 81, the strength of the spring 21 assisting closure and the amount of retardation of the timing mechanism by adjustment of the magnetic circuit of magnets 52 so that any desired inverse-time characteristic throughout the entire operating range may be obtained. Adjustment of tappings on the initiating electromagnet 61 may be utilized to vary the range of operation, and this element may alternatively be made responsive to voltage or impedance.