US1951243A

US1951243A - Circuit breaker releasing mechanism

Info

Publication number: US1951243A
Application number: US652225A
Authority: US
Inventors: Charles H Hodgkins
Original assignee: Bryant Electric Co
Current assignee: Bryant Electric Co
Priority date: 1933-01-17
Filing date: 1933-01-17
Publication date: 1934-03-13
Anticipated expiration: 1951-03-13

Description

March 13, 1934. Q HQDGKINS 1,951,243

CIRCUIT BREAKER RELEASING MECHANISM Filed Jan. 17, 1935 CURRENT CURRENT INVENTOR CHARLES H. HODGKINS BY HIS ATTORNEYS Patented-Mar. 13, 1934 PATENT OFFICE 1,951,243 CIRCUIT BREAKER RELEASING MECHANISM Charles H. Hodgkins, Fairfield, Conn, assignor to The Bryant Electric Company, Conn., a corporation of Connecticut Bridgeport,

Application January 11,1933, Serial No. 652,225

12 claims.

This invention relates to current-responsive means for causing the opening of a circuit breaker upon the occurrence of predetermined current conditions in the circuit controlled by the circuit breaker. More particularly this invention relates to a circuit breaker releasing means embodying more than one bimetallic element, which elements are caused to flex upon the occurrence of excess current, and one of which controls a varying of the rate of flexure, upon occurrence of a predetermined excess of current.

My inventionis particularly useful when it is desired to change the overload time trip characteristics of circuit breakers which have overload tripping means which are responsive to thermal conditions ina circuit. My invention may 'be applied to existing switches; or it may be incorporated into switches during their manufacture to avoid the necessity of carrying in stock a large number of thermal elements each hav-.

ing a different characteristic, as has been done in the past when it has been desired to have v switches which opened at different current values.

It is an object of this invention to provide a releasing mechanism for circuit breakers, the characteristics of which mechanism will change upon the occurrence oi. a predetermined current value in the circuit, whereby the opening of the circuit breaker may be hastened or retarded.

Another object is to provide means, applicable to thermally-actuable tripping means for circuit breakers, for changing the characteristics of the tripping means.

Another object is to provide means applicable to thermally-actuable tripping means for circuit breakers, for increasing or decreasing the time lag between occurrence of an overload condition and tripping of the circuit breaker.

Other objects and advantages of this invention will be described in connection with the accompanying drawing.

In the drawing:-

Figure 1 illustrates diagrammatically a circuit breaker controlled by a tripping mechanism in which the time lag is decreased for high current values; a

Figure 2 is a graph showing a typical curve resulting from the invention as shown in Figure 1;

Figure 3 illustrates diagrammatically a circuit breaker controlled by another form of tripping mechanism in which the time lag is increased; and

Figure 4 is a graph showing a typical curve resulting from the invention shown in Figure 3.

Referringto the drawing a switch lever 10 pivotally mounted at 12 is normally biased to opencircuit position by a spring 14 but is held in closedcircuit position by a thermally responsive bimetallic element 16 mounted at one end upon a stationary support 18 but having its other end freeto flex in a well known manner as the element is subjected to an increased temperature. A contact 20 is mounted upon and insulated from the switch lever 10 and connected by a conductor 22 to a source of power. The contact 20 while in closed circuit position of the circuit breaker engages afixed contact 24 suitably mounted upon a stationary support 26 and connected by a conductor 28 to one end 29 of a resistance unit forming a heater element 30 which is positioned adjacent to but not touching the bimetallic element 16 in order that the heat generated may cause heating of the bimetallic element; The other end 31 of the heater element may be connected to an electric motor 32 or other translating de- 76 vice which is also connected to the source 01 .power by a conductor 34, The construction as thus far described is well known in the art. In operation, when the element 16 is sufllciently heated it will bend down away from the lever 80 10 releasing the lever which will then snap away from contact 24 under the influence of spring 14.

In order to decrease the time taken to open the circuit breaker a fixed contact 40 is connected to the heater element 30 at some point interme- 86 diate its

ends

29 and 31. The exact point of connection of the contact 40 to the heater element 30 will be determined by the decrease in time lag which is desired. The contact 40 is normally engaged by a movable contact 42 mounted upon a 90 bimetallic element 44 which in turn is mounted at one end upon a fixed support 46. The bimetallic element 44 is placed adjacent to, but not touching, the heater element 30 in order that upon the occurrence of a rise in temperature of the heater element 30 the bimetallic element 44 may be caused to flex away from the contact 40. A conductor 48 connects the fixed end of the bimetallic element 44 with one end of the heater element 30.

The bimetallic element 44 is constructedto flex more, upon a less degree of heat, than the bimetallic element 16 in order to separate the contacts 42 and 40 upon the generation of a less degree of heat than is required to cause sufllcient flexing of the bimetallic element 16 to open the switch. By reason of this construction of the bimetallic element the current which is normally shunted through the auxiliary bimetallic element 44 is caused to go through the whole of the heater element 30. Since the current remains substantially the same even though the whole heater 30 is placed in the circuit it will be obvious that an increase in the amount of heat will result from the full current traversing the whole of the heater element 30. As a result of this increase in heat, the bimetallic element 16 will be caused to flex more rapidly and to a greater extent and will thereby more quickly permit the separation of the

switch contacts

22 and 24 under the influence of spring 14. Referring to Figure 2, the typical curve shown therein is plotted against current and time. The break in the curve indicates the value at which the shunt is removed from the heater element.

Referring now to Figures 3 and 4 it will be noted that the switch, bimetallic trip 16, heater, motor and connections therebetween are illustrated as in Figure 1 and therefore it will not be necessary to again describe this construction. The construction shown in Figure 3 differs from that shown in Figure 1 in the respect that a movable'contact 52, which is located upon one end of an auxiliary bimetallic element 54 whose other end is mounted upon a fixed support 56, is normally disengaged from the fixed contact which is connected intermediate the

ends

31 and 29 of the heater element 30. In this form as in the form of Figure 1, the fixed end of the auxiliary bimetallic element is connected with one end of the heater element 30. The auxiliary bimetallic element 54 is constructed so as to flex toward contact 50 upon less amount of heat than is required for the bimetallic element 16 to bend and release the switch arm 10. Thus the contact 52 .will'engage the contact 50 and form a shunt around a portion of the heater element 30 thereby reducing the amount of heat generated in the element 30 and consequently retarding the flexing of the bimetallic element 16. Thus the time taken for the separation of the

switch contacts

22 and 24 will be increased. Figure 4 shows the typical curve of the Figure 3 combination, in which the current is plotted against time. The break in the curve indicates the value at which a portion of the heater element is shunted. It will be noted that this break proceeds in the opposite direction from the break shown in Figure 2, because in the Figure 3 combination the time lag is increased'while in the Figure 1 combination the time lag is decreased.

The contact 42 is preferably mounted upon a leaf spring 43 in order for it to have firm engagement with the stationary contact 40 without placing the thermo-bar 16 under unnecessary strain, and in order to avoid the necessity of fine adjustments of the thermo-bar to get a firm contact without exerting unnecessary strain on the thermo-bar.

From the foregoing it will be apparent that I" have provided a simple and effective way of varying the tripping value of mechanism for opening circuit breakers upon the occurrence of overload conditions.

Modifications and changes within the scope of my invention will occur to'those skilled in the art. Therefore I have shown my invention diagrammatically and do not limit myself to the exact form illustrated.

I claim:-

1. An overload tripping means for a circuit breaker comprising a plurality of heat responsive devices, means energized by current in the circuit to be controlled and associated with said devices for subjecting them to the thermal e le t ofoverload current in said circuit, one of said devices being movable to cause tripping of the circuit breaker upon overload, another of said devices being movable upon a less overload than said tripping device to vary the thermal effect of the current upon said tripping device.

2. An overload tripping means for a circuit breaker comprising a pluralityof heat responsive devices, means energized by current in the circuit to be controlled and associated with said devices for subjecting them to the thermal effect of overload current in said circuit, one of said devices being movable to cause tripping of the circuit breaker upon overload, another of said devices being movable upon a less overload than said tripping device to increase the thermal effect of the current upon said tripping device.

3. An overload tripping means for a circuit breaker comprising a plurality of heat responsive devices, means energized by current in the circuit to be controlled and associated with said devices for subjecting them to the thermal effect of overload current in said circuit, one of said devices being movable to cause tripping of-the circuit breaker upon overload, another of said devices being movable upon a less overload than said tripping device to decrease the thermal effect of the current upon said tripping device;

4. An overload tripping device for circuit breakers comprising a plurality of thermally responsive means one of which is movable on overload to cause tripping of the circuit breaker, current responsive heat-generating means associated with said thermally responsive means, and means controlled by'one of said thermally responsive means to vary the amount of-heat generated in said heat-generating means upon the occurrence of a predetermined-current in said heat generating means.

5. An overload tripping device for circuit breakers comprising a plurality of thermally responsive elements, current responsive heat generating means associated with said elements, one of said elements being movable to,cause tripping of the circuit breaker on overload, the other of said elements opening a shunt circuit around a part of said heating device upon the occurrence of a predetermined current in the heating device for increasing the amount of heat generated.

6. An overload tripping device for circuit breakers comprising a plurality of thermally responsive elements, current responsive heat-generating means associated with said elements, one of said elements being movable to cause tripping of the circuit breaker, the other of said elements closing a shunt circuit around a part of said heating means upon the occurrence of a predetermined current in the heating means for decreasing the amount of heat generated.

7. An overload tripping device for circuit breakers comprising a plurality of thermally responsive elements of different characteristics, a heater element adjacent said thermally responsive elements and means controlled by one oi said thermally responsive elements shunting a i sponsive elements of different characteristics, a

heater element for causing bending of said elements, one of said elements holding a switch in closed circuit position, the other of said elements controlling a shunt circuit for varying upon cur ence of a predetermined current therein the amount of heat generated in said-heater element.

9. An overload tripping device for circuit breakers comprising a bimetallic latching device controlling the opening movement of the circuit breaker, a bimetallic switch, and a current operated heater for said bimetallic members, said bimetallic switch closing a shunt circuit around a portion of said heater upon the occurrence of a predetermined overload of less magnitude than that required'to operate the latching device.

10. An overload tripping device for circuit breakers comprising a bimetallic latching device controlling the opening movement of the circuit breaker, a bimetallic switch, and a current operated heater for said bimetallic members, said bimetallic switch opening a shunt circuit around a portion of, said heater upon the occurrence of a predetermined overload of less magnitude than that required to operate the latching device.

11. An overload tripping means for a circuit breaker comprising a heat responsive device, means associated with said device for subjecting it to thermal effect of overload current in a circuit, said device being movable to cause tripping of the circuit breaker upon overload, and a current-responsive device movable upon a less overload than said tripping device to vary the thermal effect of the current upon said tripping device.

12. An overload tripping means for a circuit breaker comprising a heat responsive device, means associated with said device for subjecting it to thermal effect of overload current in a circuit, said device being movable to cause tripping of the circuit breaker upon overload, and a current-responsive device movable upon a less overload than said tripping device to decrease the thermal efiect of the current upon said tripping device.

CHARLES H. HODGKINS.