GB552965A - Improvements in or relating to trip devices for electric circuit breakers - Google Patents

Abstract

552,965. Automatic circuit-breakers. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. May 12, 1942, No. 6448. Convention date, May 15. 1941. [Class 38 (v)] A trip device for a multipole breaker comprises a trip bar, an independently-movable trip member for each pole each biased to operate the trip bar, a thermal element for each trip member yieldingly holding the trip member against tripping movement, and an electromagnetic means for each trip member operable to cause tripping movement thereof. The movable contact-arms 25 of all poles are interconnected by bar 75 for collective movement about pivot 79 in a frame 43 to which the operating lever 47 is pivoted at 57. The centre contact-arm has pivoted to it at 67 one link 51 of a toggle; the other link 49 of which fulcrums in the apex 69 of a cradle 55 pivoted in the frame 43 at 56. The cradle is normally latched at 113 so that movement of handle 63 causes a spring 53 anchored between it and the toggle-knee 65 to make and break the toggle to close and open the switch. When the latch 113 releases the cradle, spring 53 acting through the toggle, causes the cradle to rotate clockwise so that a surface 68 thereon engages a pin 66 on toggle lever 51 to break the toggle to the left and open the circuit. The cradle is reset by moving the handle from the mid position, which it assumes on tripping, to the off position, whereby a part 133 engages the cradle to reset it, so that the handle can be returned to the on position to reclose the switch. The latch 113 is moulded integral with a rotatable insulating trip bar 81 having an integral arm 91 for each pole. Each arm is turned up at 95 to engage an aperture in a trip member 93 which engages at one end in a notch 101 in the trip bar and carries an adjustable screw 109 which is pressed by a spring 103 on to the free end of a series bimetal strip 39 adapted to flex downwards when heated. An electromagnetic trip device comprises a U-shaped core 115 surrounding each conductor 31 and an armature 123, the whole being surrounded by a non-magnetic yoke 119 which is apertured to receive a threaded rod 125 having a nut 127 engaging the upper face of member 93. The yoke 119 of the centre pole also seats a compression spring 129 biasing the centre arm 91 upwards. On low overloads, the spring 103 of the overloaded pole provides most of the trip force, which is opposed by the thermal element 39 for a time depending on the intensity of the overload. As the intensity increases, the effect of the electromagnetic trip becomes stronger until at a given overload the tripping is substantially instantaneous, since the armature 123 does not have to flex the elements 39 of unfaulted poles. The individual poles are isolated by partitions 16. 26 in the base and cover, respectively. Specification 549,554 is referred to.