GB355738A - Improvements in or relating to overload switches - Google Patents

Abstract

355,738. Protective cut-out arrangements; electromagnetic switches. IGRANIC ELECTRIC CO., Ltd., 147, Queen Victoria Street, London, and WRIGHT, S. R., 113, London Road, Bedford. May 28, 1930, No. 16442. [Class 38 (v).] An overload protection device for polyphase circuits comprises individual overload coils for connection in the respective phases, and a common slow - moving element (dashpot plunger) which moves slowly in response to an applied force and acts to delay interruption of a circuit on low overloads, but not on high overloads, in any or all of the phases. For high overloads a separatelyacting device is provided to act instantaneously. An overload switch for use in a 3-phase circuit comprises coils 1 arranged at the apices of a triangle and symmetrical about the stem 3 of the plunger of a dashpot 4, the stem 3 being connected by a plate 6 to reduced extensions 5 of the plungers 2 of coils 1. A further armature 7 having brass sleeves 8 extending into the coils 1 carries three contacts 10 each normally engaging a contact 11 and connected so that the three are in series in the winding of a main contactor, which is opened on overload, due to downward movement of the armature 7 against the action of springs 9 if the overload is heavy, or, if the overload is slight, due to upward movement of the plungers 2 under the retarding action of the dashpot 4 until the plungers strike the sleeves 8 to move the armature 7. If the heavy overload occurs in only one phase, the armature 7 tilts so that one pair of contacts 10, 11 will be opened. The dashpot 4 is adjustable as to time-lag and is arranged to give a rapid final movement. A contactor coil 23, Fig. 5, is energized by a starting button 26 to start a motor, energization of coils 1 in the motor circuit raising plungers 2 to close contacts 21 and establish a maintaining circuit for the coil 23. If voltage failure occurs, one or other of the switches 21 open to disconnect the motor by de-energizing the coil 23. Contacts 22 are opened on overload which, if heavy, causes a spring 25 to stretch and enable the armature 19 and rod 24a to move independently of the dashpot 4a and rod 24b, whereas if the overload is light, members 19, 24a, 24b move together under the restraint of the dashpot. In Fig. 6 the coil 23 is in series with a manual switch 26a and switches 21 each comprising contact arms pivoted at x, y and interlocked as shown diagrammatically. On energizing the coils 1, the plungers 2 rise and lift the respective contact arms which still remain in engagement, but voltage failure in one phase causes the lever arm of the corresponding switch 21 to open and de-energize the winding 23, the switch 21 being held open by a gravity latch pivoted to the upper contact arm. Overload causes the upper arm of the middle switch 21 to rise and get latched open, the latches in each case requiring to be reset before further energization of the coil 23 can be effected. The arms of the switches 21 can, alternatively, be spring-controlled. In Figs. 12 and 14, a V-shaped member 34 pivoted at the axis X-X is urged by a spring so that contacts on its ends engage contacts at one end of the arms 36 pivoted intermediate their ends, the other ends resting under collars 35 on the no-volt plungers. This switch is in series with a coil 23 and contacts 39 of a relay 40 across lines L<1>, L<2>, the relay 40 being under the control of a manual switch 26a. When the contactor 23 closes its contacts 23a and energizes the coils 1, the collars 35 are lifted, causing the arms 36 to be rotated by the member 34, without however breaking contact. Voltage failure in a line causes the corresponding plunger to move its collar 35 which acts on the arm 36 to move the member 34 from the other contact and break the circuit of coil 23. An overload device similar to that of Fig. 5 is provided to lift the member 34 on overload, the member being maintained by a hand-freed latch. By connecting the circuits of coils 23, 40 to different lines, it is impossible to re-energize the contactor until the failure is remedied. In a further form the contactor is controlled from a starting button which is shorted bv an extra contact on the contactor when the latter operates. In Figs. 16 and 17, a plate 34a is pivoted at X and urged downwards by a spring to bridge contacts 38. A collar 35 on each plunger 2 engages in its lower position a lever 42 which lifts the plate 34a. In its upper position, a plate 44 is engaged by the collars 35 to lift a plate 34b from bridging across parallel contacts 38. A spring- latch 45, pivoted at 46 normally bears on the collar 35 associated with the line L<1> and plate 44, as shown, so that when the collar is down and the plate up, the latch can come between them. When the coils 1 are energized the plungers 2 rise allowing the plate 34a to fall and, later, causing plate 34b to rise. Voltage failure in line L<2> or L<3> causes the appropriate plunger 2 to fall and raise the plate 34a which breaks the circuit of coil 23 whereby the other plungers fall. The plate 34b also recloses its contacts as the plate 44 engages the latch 45 before the collar 35 releases it. Re-energization cannot be effected until the line L<2> or L<3> is again restored. If, however, the voltage failure is in line L<1>, the collar 35 drops and allows the latch 45 to function, as the plate 44 will be held by the other collars until the coil 23 is de-energized. The latch is removed by a button 48 raising the arm 34a, the button also serving to release the catch Z holding up the overload device when the latter has operated to raise the arm 34a.