US1918368A - Electric switch and means to delay the successive opening thereof - Google Patents

Description

July 18, 1933. AINSWQRTH 1,918,368

ELECTRIC SWITCH AND IEANS TO DELAY THE SUCCESSIVE OPENING THEREOF Filed May 31, 1929 Irzven 202.

mi) MM Patented July 18, 1933 UNITED STATES PATENT OFFICE CHESTER D. AINSWOBTH, OF WOLLASTON, MASSACHUSETTS, ASSIGNOB TO CONDIT ELECTRICAL MANUFACTURING CORPORATION, OF SOUTH BOSTON, MASSACHUSETTS,

A CORPORATION OF MASSACHUSETTS ELECTRIC SWITCHAND MEANS T DELAY THE SUCCESSIVE OPENING THEREOF Application filed May 31,

This invention relates to electro1nagnetically controlled electric switches and to closing and opening apparatus and clrcults therefor. V

It frequently happens that an operative, especially with switches adapted for the control of industrial apparatus, as motors, re peatedly opens and close the switch rapidly when there is no need for it, thereby unnecessarily heating the contact members of the switch and drawing destructive arcs between them and also placing unusual demands upon the circuit of the switch and the apparatus associated therewith.

It is an object of the present invention to provide an electric switch'and its control apparatus and circuits with means so arranged that after the switchhas once been opened, it

can not again be reclosed untilthe expiration of a predetermined time interval, which interval is adapted to be suflicientlylong to permit the contact members to become cool and the hot arc gases to be dissipated.

The switch with which'the present invention'particularly is concerned is an electro magnetically operated switch having an electro-magnet that is adapted to be energized to close the switch and to be maintained energized for so long as the switch is to be held closed. The control apparatus for such a switch includesa push button operated circuit controller to insure the initial energization of the electro magnet and the closing of the switchand a second push button operated circuit controller that is adapted to be operated to break the circuit of the electro-magnet V and permit the switch to open. The first or V is normally closed.

1929. Serial No. 367,433.

switch for a predetermined time interval after it has been opened under load.

A further object of the invention is generally to improve the construction and opera tionof electric switches and control apparatus and systems therefor.

Fig 1 is adiagrammatic illustration of the switch and its control apparatus and circuits embodying the present invention. 7

Fig. 2 is similar to Fig. 1 except that a modified arrangement is provided for preventing rapid reclosing operations of the switch. f

Fig. 3 is a modification of Fig. 1 wherein a normally open thermal relay is substituted for the electro-magnetic relay.

The switch with which the present invention is particularly concerned includes a movable bridging member which is adapted to be moved upwardly to engage and bridge the stationary contact members 12 which are included in series with one of the circuit conductors 14 of the herein shown single phase circuit that includes the other conductor 16. The switch may control the supply of power to any power consuming device as the motor 18. While the switch here-shown is illustrated as being in but one conductor of the circuit, it is to be understood that the switch can have cooperating contact members ar ranged in all. of the conductors of the circuit as is common practice. The bridging member 10 is mounted on an insulating bar 20 carried by the switch arm 22 which is pivoted loosely at its free end to one leg of an electro-magnet 24 which has an actuating winding 26. The arrangementis such that when said winding is energized, the electr c-magnet attracts the lever 22 and moves the bridging member into engagement with the fixed contact member 12. thereby closing the switch. The switch is held closed by maintaining the electro-magnet energized. The circuit of the electro-magnet is controlled by a pair of pushbutton con trolled circuit controllers, there being the starting push button 28 which is arranged to initially energize the magnet to efl'ect the closing of the switch and a second or stopping push button 30 which serves to efi'ect the de' 1,a1a,m' Oi i at the opening f" thermal element comprises a metal'strip that j is of twq mmhgving we f xpansim' secured flu m mmfillwfi amiomaw'mm 58 which are infilmidgin the c'bndue- P tty aw firm 2 18pontrols inring Elation with said elemen fi. Said im gpeeificaillyto I In the modification illustrated in Fig.2, the electro-magnetic relay 60 is replaced by a normally-closed thermal relay 70 which is vhereshown as identical with the construction troller and the electro-magnet winding.

With this arrangement, the heating element 72 is normally (lo-energized except for the time that the starting circuit controller is closed. .The relay is so designed that the contact members 74: are'not adapted to separateby the momentary current traversing the conductor 50. the adjustment being such thatthe contacts74 will not open if the starting circuit controller is but momentarily closed, which is all. that is necessary to effect the closing of the switch.

If, however, it is attempted to reclose the SWltCh repeatedly and rapidly by successive operations of the starting push button, the accumulation of heat in the thermal member is adapted to be such that after two or three rapidly repeated operations, the thermal member expands and separates the contact members 74. thereby disabling the holding circuit 48 and preventing further reclosures of the switch until the thermal relay has dissipated its heat. Usually a switch can be opened rapidly a few times under its rated load without undue arcing but if the opening I operations are continued, the accumulation of heat and arc gases thereafter results in destructive arcing. Thus,.the arrangement shown in Fig. 2 will prevent rapidly repeated openings of the switch under load.

The broader idea of preventing the switch from being repeatedly opened rapidly'under load is described and claimed in a copending application of George A. Burnham, Serial No. 367,340, filed May 31, 1929, and assigned to the assignee of this present application.

In Fig. 3, the arrangement is the same as 'in Fig.1 except that a normally-open thermoresponsive relay 80 is substituted for the electro-magnetic relay 60. The electric resistance heating element 82 of said thermal relay is included in series with the closing circuit 48 and thus is maintained heated for so long as the switch is closed. The thermoresponsive element 84 is maintained in flexed condition by the heated element 82 and thereby maintains the contact members 86 in separated condition. When the switch is opened, however, either on overload, or by depressing the stopping button 30, the current flow 1n the closing circuit 48 is interrupted and the thermo-responsive element cools OE and ulti- Inately closes the contacts 86. Until these contacts are closed, however, no effect results from the operation of the starting push button 28 and the period of time required for the contacts 80 to close is adapted to be sufiicient to provide the desired time delay between successive opening and closing operations of the switch.

, I claim:

1. The combination of an electric switch, electromagnetic means for controlling the closing and opening of the switch, closing and opening circuits for said electromagnetic means, closing and opening circuit controllers'associated with said respective circuits, and electrical means also associated with both and energized from one of said circuits arranged to disable the other circuit :for a period of time sufficient to prevent the rapidly and indefinitely repeated opening of the switch.

2. The combination of an electric switch, electro-magnetic means for controlling the closing and opening of the switch, closing and opening circuits for said electro-magnetic means, closing and opening circuit controllers associated with said respective circuits, and electrical means operated by the current in one circuit to disable the other circuit for a period of time suflicient to prevent the rapidly repeated opening of the switch under load. V

3. The combination of an electric switch, electro-magnetic means for controlling the closing and opening of the switch, closing and opening circuits for said electro-magnetic means, closing and opening circuit controllers associated with said respective circuits, separable contact members included in one of said circuits, and means actuated by the current in said other circuit to effect the control of said contact members and delay the successiveopenings of the switch.

4. The combination of an electric switch, electro-magnetic means for governing the closing and opening of the switch, closing and opening circuits for said electro-magnetic means, closing and opening circuit controllers associated with said respective circuits, separable contact members in one of said circuits, and time-delayed means actuated by the current in said other circuit to control said contact members and delay the reclosing of the switch after an opening thereof.

5. The combination of an electric switch, electro-magnetic means for governing the closing and opening of the switch, closing and opening circuits for said electro-magnetic means, closing and opening circuit controllers associated with said respective circuits, and thermally-actuated means controlled by the current in one of said circuits and having control of said other circuit to delay the reclosing of the switch following its opening.

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