US3737727A

US3737727A - Thermal overload device

Info

Publication number: US3737727A
Application number: US00272132A
Authority: US
Inventors: L Mouis
Original assignee: Furnas Electric Co
Current assignee: Siemens Energy and Automation Inc
Priority date: 1972-07-17
Filing date: 1972-07-17
Publication date: 1973-06-05
Anticipated expiration: 1990-06-05
Also published as: CA980391A

Abstract

A polyphase circuit device using solder pot structures each controlling an independently operating actuating lever acting on an associating lever arm carried on rotatable shaft. A lever rotatable with the shaft operates a contact actuator to open a control circuit when a thermal overload occurs in any one conductor of the circuit being protected. A reset actuator is provided to permit reset when the overload has been removed.

Description

United States Patent 1 Mouis [4 1 June 5, 1973 [54] THERMAL ()VERLOAD DEVICE 3,118,990 1/1964 Jansson ..337/l88 3,284,596 11/1966 Barone "337/18! [75] Inventor: Louis Mouis, Aurora, [11.

73 Assi nee: Furnas Electric Com an B tavia, Primary Examiner-James Tramme 1 g m v p a Attorney-McDougall, Hersh & Scott {22] Filed: July 17, 1972 [57] ABSTRACT [21] Appl. No.2 272,132 A polyphase circuit device using solder pot structures each controlling an independently operating actuating lever acting on an associating lever arm carried on [52] US. Cl. ..3l7/40 A, 317/40 A, 317/46, rotatable Shaft A lever rotatable with the Shaft 4 317/54 operates a contact actuator to open a control circuit [51] Int. Cl.....' ..H02h 5/04 when a thermal overload occurs in any one conductor Fleld of Search of the circuit being protected. A reset actuator is pro- 337/189; 317/114, 54, 40 A, 46 vided to permit reset when the overload has been removed. [56] References Cited UNITED STATES PATENTS 7 Claims, 14 Drawing Figures 2,496,020 l/1950 Pepper.....- ..3l7/40 A PATENTEB JUH 51973 sum 1 n7 4 PATENTEBJU" 51915 3, 737, 727

sum u [1F 4 Pics. 10 8 THERMAL OVERLOAD DEVICE BACKGROUND OF THE INVENTION This invention relates generally to improved electrical circuit protective devices. More specifically, it relates to devices for providing thermal overload protection to polyphase electrical circuits.

It is known in the art that thermal overload protection may be provided by the use of so-called solder pots. See for instance the patent to D. Wilcox et al. issued Feb. 7, 1961. Solder pots consist of tubes or cylinders containing a quantity of solder in which is embedded a shaft held from rotation when the solder is in a solid state. Carried on the end of the shaft is a ratchet for rotation with the shaft. A spring pawl engages the ratchet and is effective to prevent the movement of a contact actuator until the solder melts and permits movement of the ratchet. A heating element connected in the electrical circuit to be protected is disposed around the solder pot and, in the event of current flow in excess of that desired, the heat produced by the heating element is effective to melt the solder thereby permitting rotation of the shaft and ratchet carried thereon and consequently release of the switch actuator.

As stated; such devices have been in use for some time for connection to individual conductors in order to protect the same against thermal overload. With the advent of large electrical loads such as bigger motors, it has become increasingly necessary to use polyphase circuits instead of single phase circuits to supply these loads. Inasmuch as thermal overload protecting devices of the type described-possess numerous advantages in particular situations, it would be advantageous to provide such a device for the protection of polyphase circuits.

Therefore, it is an object of this invention to provide a novel thermal overload protection device for a polyphase circuit which utilizes the advantages of the solder pot devices described.

It is another object of this invention to provide a ther- I BRIEF SUMMARY OF THE INVENTION The foregoing and other objects are achieved in one embodiment of the invention by the provision of a circuit controlling switch actuated by a rocker mounted on a shaft which carries a number of lugs equal to the 'number of conductors in the circuit and wherein each lug engages with a separate-pawl normally held from movement by a solder port but which are permitted movement when the solder in any one pot has melted due to excess current flowing in any one conductor so as to permit actuation of the rocker arm thereby permitting operation of the switch.

BRIEF DESCRIPTION OF THE DRAWINGS An understanding of the structure and mode of operation of the invention may be derived from the detailed description taken in conjunction with the drawings in which:

FIG. 1 is a top plan view of a thermal overload protective device in accordance with the invention; FIG. 1A is a partial exploded view of the device of FIG. 1; FIG. 2 is a front view of the device shown in FIG. 1; FIG. 3 is a side view of the device shown in FIG. 1; FIG. 4 is a bottom view along the lines 44 of FIG.

FIG. 5 is a view along the lines 55 of FIG. 3; FIG. 6 is a view along the lines 66 of FIGS. 1 and 3;

FIG. 7 is a view along the lines 77 of FIG. 2 illustrating the mechanism in a normal or non-actuated position;

FIG. 8 is a view along the lines 8-8 of FIG. 2 illustrating the mechanism in the normal or non-actuated position;

FIG. 9 is a view along the lines 99 of FIG. 2 illustrating the mechanism in the tripped or actuated posi-,

DETAILED DESCRIPTION The switch housing is best shown in FIGS. 1, 3, and 4 wherein the numeral Zindicates the upper body portion of the switch and the numeral 4 indicates the lower body portion of the switch housing which is formed of any suitable plastic or similar insulating material and has a plurality of ledges or supporting surfaces for a set of incoming terminals 8 and a set of outgoing terminals 10. The incoming terminals 8 are electrically con nected by means of conductors 12 to first terminals 14 which are connected in turn to coiled electrically conducting heating elements 16. The other end of each heating element 16 is connected to a terminal 18 which in turn is connected to one of the outgoing terminals 10. Thus in the embodiment illustrated connections are provided for each of three conductors in a polyphase circuit. In such a circuit therefore'any one conductor is connected to an incoming terminal 8 through a conducting element 12 to a terminal 14 through a heater 16, a terminal 18, and to an, outgoing tenninal 10. In this manner a protective device in accordance with the invention may be connected in a load circuit so as to respond to the current flowing therein.

Connections for operating a circuit interrupting device such as a contactor are provided by a terminal 20 which is connected to a fixed contact 22. The circuit is completed from the fixed contact 22 through a movable contact 24 to another fixed contact 26 which is connected to a terminal 28. Thus one end of the operating coil of a contactor may be connected to the terminal 20, fixed contact 22, movable contact 24, fixed contact 26, and to the terminal 28 so as to be energized when the

contacts

22, 24 and 26 are in engagement with each other and be de-energized when these contacts do not engage.

As may best be seen in FIG. 6 the movable contact 24 is mounted in the lower housing 4 in a hollow extension 30 thereof and is urged toward the

fixed contacts

22 and 26 by a coil spring 34 which bears against it and against the wall of the hollow extension. Thus the movable contact normally completes a circuit between

fixed contacts

22 and 26.

The switch actuating mechanism within the housing includes a reset lever 36, a wedge 38 and an actuator 40. As will be described, the mechanism provides for operation of the switch in the event of overload in any one of the conductors being protected. For resetting purposes the actuator 40 is reciprocated in a direction longitudinally of the same and contacts directly with the wedge 38 which has camming engagement with the reset lever 36 causing the lever to rotate and in turn cause rotation of a shaft 42 extending transversely in the bottom of the lower housing 4. As may best be seen in FIGS. 6 and 7, the shaft 42 rotates in a trough 44 provided in the lower housing and is retained therein by a pair of bars 46 held by threaded fasteners 48 in the lower housing and overlying the shaft 42 and trough 44. Extending upwardly from the shaft 42 are spaced lever arms 50, one for each conductor, provided with a camming surface 52. One such lever arm is provided to correspond with each set of input and output terminals.

Disposed adjacent each lever arm 50 is an actuating lever 54 mounted for free rotation on a shaft 56 extending transversely on the bottom of the lower housing substantially parallel to the shaft 42. Each actuating lever is provided with a rearwardly extending projection 58 having a boss 60 formed thereon. Encompassing the boss 60 and extending between it and the base of the lower housing 4 is a coil spring 62 urging its associated actuating lever in the clockwise direction as shown for instance in FIG. 11. Thus, assuming the actuating lever 54 is free to move, its associated spring 62 extends to cause it to rotate in the clockwise direction. As it rotates about the shaft 56 it bears against the camming portion 52 of the lever arm 50 and consequently causes that arm to rotate in the clockwise direction. The rotation of the shaft 42 causes the reset lever 36 to rotate in the clockwise direction whereby its free end camming against the interior surface 64 of the wedge 38 moves the wedge downwardly as shown in FIG. 11. The downward movement of the wedge forces the actuator 40 which bears against the movable contact 24 to move downwardly against the force of the coil spring 34 interrupting the circuit between

fixed contacts

22 and 26.

In order to maintain the device in its normal or nontripped position, each actuating lever 54 has attached thereto a leaf spring 66 attached at one end to the lever 54 and having a free end 68 extending beyond the arm and provided with a bent or tooth portion 70. The spring 66 is constructed so that it is biased toward the lever 54. This arrangement constitutes a pawl in which the tooth portion 70 engages with the teeth of a ratchet 72 comprising part of the solder pot construction.

The ratchet is fixed to a shaft 74 which extends within a barrel or solder port 76. The barrel 76 is anchored in the upper housing 2 by means of a U-shaped collar 78 engaging near its bottom on one side of a wall of the housing and a spring washer 80 engaging near its bottom on the other side of that wall. The heating coil 16 surrounds the barrel 76 and as described above is connected into the circuit. As is well known, in solder pot devices the shaft 74 is normally sealed to the barrel 76 by eutectic solder which occupies the space befrom turning and the pawl constituted by the spring 66 and its tooth will be held in its maximum counterclockwise position (see FIG. 10) with the coil spring 62 compressed. However, when an overload condition de velops, the heating coil 16 will melt the eutectic solder releasing shaft 74 and ratchet 72 for rotation. The spring 62 will thereupon cause the actuating lever 54 to rotate and operate the movable contacts 24 in the manner described above.

FIGS. 7 and 8 illustrate the device in the normal or non-tripped position. Thus, in FIG. 7 the spring 66 has its tooth 70 engaged in the ratchet 72 so that the lever 54 is maintained in its maximum counterclockwise position and the coil spring 62 is compressed against the bottom of the lower housing 12. Under these circumstances the force of the coil spring 34 is such as to maintain the movable contact in the upward position, as shown in these figures, completing a circuit between the fixed

contacts

22 and 26. At the same time, the

force of that spring transmitted to the actuator 40 through a pair of legs 41 bearing against the movable contact 24 pushes the wedge 38 upwardly as shown in that figure.

The cooperative movement between the actuator 40 and wedge 38 is achieved in the following manner:

The wedge (see FIG. 10) is provided with a ledge 82 and a beveled apron 84. The actuator 40 has surfaces complimentary to those of the wedge. Thus the actuator is provided with a flat face 86 adapted to have contact with the ledge 82 and a beveled edge 88 adapted to have camming engagement with the apron 84. The flat face 86 and beveled edge 88 are formed on the body of the actuator 40, said actuator being additionally provided with the bifurcated legs 41. The actuator 40 is located between the shoulders 92 formed on the inside of the housing and thus the body of the actuator will at all times have contact with those shoulders. The bifurcated legs 41 have the additional function of accommodating the reset actuator and spring therefor, as will be presently described.

The fixed or stationary contacts of the switch previously identified as 22 and 26 each consists of a member having an exterior portion 94 and an interior depending portion 96 supported on a surface of the housing. It will be observed in FIG. 6 that the fixed contacts are spaced on respective sides of the housing and accordingly the legs 41 of the actuator have a position between the contacts which permits the free movement of those legs. The movable contact 24 is located within a recess 96 provided in the housing and the contact is freely movable in a direction to and from the depending portions of the fixed contacts so as to engage the same and thus control the opening and closing of the electric circuit. The coil spring 34 'yieldingly forces the movable contact 24 in an upward direction as shown in FIG. 6 and thus effects a closing of the circuit unless the contact is maintained in open position by the legs 41 of the ac tuator 40.

In order to reset the switch a reset actuator 98 is provided. The actuator 98 is substantially rectangular in cross-section for approximately its full length and is mounted for reciprocating movement within a passage 100 formed in the housing. The upper portion of the actuator 98 extends above'the housing for convenient access by the operator. The bottom end of the actuator 98 is reduced in size and made circular to form and end portion 102. The end portion provides a first shoulder 104 and above the same a second shoulder 6 is provided on the actuator. The shoulder 104 engages with a coil spring 108 which loosely surrounds the end 102 and is confined between the shoulder 104 and the bottom of the lower housing 4 in a recess 110 provided for that purpose. The spring 104 thus yieldingly forces the actuator 98 upwardly until a third shoulder 1 12 engages an abutment 114 provided on the interior of the upper housing portion 2. The circular end 102 and a part of the coil spring 108 extend between the legs 41 of the actuator wherein the space between these legs is made wide enough so as to receive the structure without interference as respects the movement of either part.

With this understanding of the elements of the switch and their relative disposition, its operation may now be described.

Assuming that the switch contacts are closed by engagement of the movable contact 24 with the depend ing portions of the stationary contacts 22 and 26 (see FIGS. 7 and 8), it will be seen that the actuating levers 54 are held in retracted position against the force of their associated springs 62 by engagement of their respective teeth 70 with their associated ratchet wheels 72. In this position of the actuating levers the wedge 38 and contacts 40 are free but are retained in proper assembled position because the legs 41 of the actuator extend between the shoulders 92 and are biased by the spring 34. The contacts of the switch will thus maintain a closed circuit position until and overload condition exists.

The overload condition will heat the coil 16 and eventually the eutectic solder in the barrel 76 will melt to release the shaft 74. The ratchet 72 is now free to ro-.

tate and such action takes place to release any one of the actuating levers 54 for movement in a clockwise direction (see FIG. 11) as a result of the force asserted by its coil spring 62. The actuating lever 54 upon rotating engages with the camming surface 52 of its associated lever arm 50 to rotate it and thereby the shaft 42 in the counterclockwise direction. With the rotation of the shaft 42 the reset lever 36 rotates in the clockwise direction and causes the wedge 38 to move downwardly (see FIGS. 9 and 11). The ledge 82 bearing against the flat surface 86 of the actuator causes it to move downwardly whereby the legs 41 effect an opening action of the movable contact 34. The switch contacts have now been tripped bythe overload condition existing in any one of the conductors constituting the electrical circuit being protected.

It should be noted at this point that the tripping acbe depressed by an operator for depression of the reset actuator does not interfere with the freedom of the actuator 40 to move.

For resetting purposes the operator depresses the reset actuator moving the same downwardly against the force of the spring 108. When so depressed, the shoulder 106 will contact the body of the actuator 40 since the actuator is now confined between the wedge and the movable contact having a location in its extreme bottom position (see FIG. 9) as the result of which the front of the actuator is in engagement with the shoulders 92. Downward movement of the reset actuator will move the actuator 40 in a downward direction so that the surface 88 of the actuator will cam on the surface tion will occur even through the reset actuator 98 may I 84 of the wedge and cause the wedge to move upwardly as shown in the drawings due to the coaction of the beveled edge 88 with the beveled apron 84. If the overload condition has been relieved, the ratchet 72 will be held against the rotation and relatching of the spring pawl 66 with the ratchet wheel is effected. The actuating lever 54 which had previously been released is thereby again held in a retracted position. However, as long as the reset actuator is held depressed, the switch contacts are maintained in open position and is further noted that should the overload condition still exist, then upon release of the reset actuator the contacts will still be maintained in an opened condition. Thus the switch contacts are permitted to close upon release of the reset actuator only in the event the overload conditions have been corrected.

Obviously various modifications may be made without departing from the scope of the invention and it is intended by the claims appended hereto to claim all such modifications and variations as fall within their scope.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. Apparatus for protecting polyphase circuits against thermal overload comprising: a support structure; a plurality of incoming terminals mounted on said support structure, each for independent connection to a separate conductor forming a part of a polyphase electrical supply system; a plurality of outgoing terminals mounted on said support structure and spaced from said incoming terminals; electrically conducting heating elements each separately connected from one of said incoming terminals to one of said outgoing terminals; a pair of control terminals mounted on said support structure; a movable contact element for connecting one control terminal to the other control terminal; bias means urging said movable contact element in a first direction; a contact actuator movably mounted in said support structure and engaging said movable contact element to cause movement of said movable contact element against the force asserted by said bias means; a plurality of actuating levers, one for each conductor in a circuit to be protected; a spring pawl mounted on each said actuating lever; a ratchet disposed adjacent each of 'said spring pawls; means normally restraining each of said ratchets to prevent movement of its associated spring pawl and actuating lever; and operating means connected between each of said actuating levers and said contact actuator to cause movement of said contact actuator in the event of movement of any of said actuating levers and to cause consequent movement of said movable contact element to interrupt the circuit between said control terminals.

2. The apparatus of claim 1 including: a reset actuator comprising a plunger having a portion extending outwardly of said support structure and a portion within said support structure engageable with said contact actuator; bias means urging said reset actuator outwardly, said reset actuator when depressed against said bias means engaging said contact actuator to move it and cause movement of said operating means and consequent movement of any one of said actuating levers which may have been released for movement by the existence of an overload in its associated conductor.

3. The apparatus of claim 1 wherein said operating means comprises a rotatable shaft mounted in said support structure; a plurality of lever arms spaced along said shaft for rotation therewith, one disposed adjacent each of said actuating levers for engagement therewith; a reset lever mounted on said shaft for rotation therewith; and a movable hollow wedge mounted over said reset lever and engaging said contact actuator.

4. The apparatus of claim 1 wherein said means normally restraining each of said ratchets comprises a hollow tube, a shaft extending into said tube supporting a ratchet on an end thereof, and a quantity of hardened solder interposed between said shaft and said tube to prevent said shaft from rotating in said tube,

5. The apparatus of claim 4 wherein each tube is encompassed by one of said electrically conducting heating elements so as to melt the solder to free said shaft for rotation in the event of an overload in the circuit to be protected.

6. The apparatus of claim 5 including: a reset actuator comprising a plunger having a portion extending outwardly of said support structure and a portion within said support structure engageable with said contact actuator; bias means urging said reset actuator outwardly, said reset actuator when depressed against said bias means engaging said contact actuator to move it and cause movement of said operating means and consequent movement of any one of said actuating levers which may have been released for movement by the existence of an overload in its associated conductor.

7. The apparatus of claim 6 wherein said operating means comprises a rotatable shaft mounted in said support structure; a plurality oflever arms spaced along said shaft for rotation therewith, one disposed adjacent each of said actuating levers for engagement therewith; a reset lever mounted on said shaft for rotation therewith; and a movable hollow wedge mounted over said' reset lever and engaging said contact actuator.

Claims

1. Apparatus for protecting polyphase circuits against thermal overload comprising: a support structure; a plurality of incoming terminals mounted on said support structure, each for independent connection to a separate conductor forming a part of a polyphase electrical supply system; a plurality of outgoing terminals mounted on said support structure and spaced from said incoming terminals; electrically conducting heating elements each separately connected from one of said incoming terminals to one of said outgoing terminals; a pair of control terminals mounted on said support structure; a movable contact element for connecting one control terminal to the other control terminal; bias means urging said movable contact element in a first direction; a contact actuator movably mounted in said support structure and engaging said movable contact element to cause movement of said movable contact element against the force asserted by said bias means; a plurality of actuating levers, one for each conductor in a circuit to be Protected; a spring pawl mounted on each said actuating lever; a ratchet disposed adjacent each of said spring pawls; means normally restraining each of said ratchets to prevent movement of its associated spring pawl and actuating lever; and operating means connected between each of said actuating levers and said contact actuator to cause movement of said contact actuator in the event of movement of any of said actuating levers and to cause consequent movement of said movable contact element to interrupt the circuit between said control terminals.

4. The apparatus of claim 1 wherein said means normally restraining each of said ratchets comprises a hollow tube, a shaft extending into said tube supporting a ratchet on an end thereof, and a quantity of hardened solder interposed between said shaft and said tube to prevent said shaft from rotating in said tube.

7. The apparatus of claim 6 wherein said operating means comprises a rotatable shaft mounted in said support structure; a plurality of lever arms spaced along said shaft for rotation therewith, one disposed adjacent each of said actuating levers for engagement therewith; a reset lever mounted on said shaft for rotation therewith; and a movable hollow wedge mounted over said reset lever and engaging said contact actuator.