Patent GB-473778-A (GB)
Title: Improvements in or relating to apparatus for protecting poly-phase alternating current electric circuits
IPC: H01H83/22
Filed: 1936-05-28
Abstract: 473,778. Electrically-released switches; protective cut-out arrangements. BROOKHIRST SWITCHGEAR, Ltd., and LANCELEY, C. May 28,1936, No. 15043. [Class 38 (v)] Polyphase A.C. circuits, supplying motors, for example, are protected against overloads and single-phasing. The contacts 57, 58 in the maintaining-coil circuit of the control switch are normally held closed by the engagement of a lever 69a with a detent surface 66 on a lever 59 which is pivoted at 60 and carries contact 58. Lever 59 is urged to open position by a spring 61 which is anchored at 62 to lever 59 and at 63 to a bracket 64, and a pushbutton 72 is provided for resetting the contact 58. Lever 69a and a lever 69 are pivoted at 68 and provided with mutually-inclined slots in which a pin 69c is movable for adjusting the tripping point. The lever 69 is tripped by an ambient-temperature compensating bimetal element 70 on a collar 49 on a slidable secondary bar 39, through which collar also slides a primary bar 38 which is threaded to receive three discs 47 and lock nuts 48. The bars are guided at 45, 46, and 38 has a collar engaging bar 39 so that when 38 is moved to the left, it carries 39 with it. Levers 52 pivoted to blocks on bar 38 are adapted to engage abutments 56 on bar 39. The discs 47 and upper ends of levers 52 co-operate with the free ends of U-shaped bimetal elements 38a which are anchored to blocks 39. Heating coils 40, one in each phase, are wound on asbestos formers 41 and connected at their ends to terminals 43 and to blocks 39 at 42. When the motor is brought into operation with conditions normal, elements 38a move together to the left carrying the two bars 38, 39 with them, but not far enough to produce tripping. If, however, a phase is faulty the lever 52 of that phase will, by the movement of bar 38, engage its element 38a and be rotated, so moving bar 39 to trip the switch. If, during operation, the current in any phase falls unduly, the element 38a of that phase will move to the right to swing the associated lever 52, and as movement of bar 38 is prevented by the engagement of discs 47 with the other elements 38a, the bar 39 is moved to trip. On overload in any phase, the element of that phase moves bar 38, and hence also bar 39, to effect tripping. The strip 70 is of the same thermal characteristics as strips 38a, but is arranged to move in the opposite direction. Alternatively, a wedgeshaped member on a compensating strip may be interposed more or less between the bar and trip lever in accordance with ambient temperature, Fig. 1 (not shown). Fig. 3 shows a modified arrangement of trip lever and compensating strip. The latter is shown at 83 as secured at its upper end to lever 73a engaging notch 66, and as engaging at its free end between parts 80a, 80c on arm 80 pivoted at 81 to lever 73a. The latter is urged anticlockwise by a spring, and is pivoted at 74. Also pivoted at 74 is the lever 75 which is engaged by the secondary bar 39, this lever being urged by a spring 76b against a stop 76a. Pivoted to 75 at 78 is an arm 77 carrying a surface 77a, which is adapted to engage the upper end of 80 and, through 80a, 80c and strip 83, rotate 73a into releasing position. The arm 77 is adjustable relatively to arm 75 by means of a slot in the former and a pin 86 rotatable with respect to the latter. The strip 83 is arranged to bend and rotates lever 80 about pivot 81 so that the distance between 77a and 80 is independent of ambient temperature. The lever 59 may be automatically reset by the return movement of one of the operating bars, as by means of a pivoted lever or ratchet or like unidirectional mechanism.