US3852694A

US3852694A - Overload relay with fast acting bimetal on high current

Info

Publication number: US3852694A
Application number: US00428097A
Authority: US
Inventors: Marco B Di; A Kralik
Original assignee: ITE Imperial Corp
Current assignee: ITE Imperial Corp
Priority date: 1973-12-26
Filing date: 1973-12-26
Publication date: 1974-12-03
Anticipated expiration: 1991-12-03

Abstract

An overload relay having a conventional replaceable heater is provided with an auxiliary bimetal secured to the deflectable end of the main bimetal and arranged to deflect in a direction opposite to deflection of the latter. Tripping results from the net deflection of these bimetals. the main bimetal shields the auxiliary bimetal from direct heat radiating from the heater, so that upon rapid heating of the latter the initial result is that the main bimetal deflects rapidly and there is essentially no reverse deflection of the auxiliary bimetal whereby tripping takes place very rapidly. A contact position-indicating lever is biased to follow the movable contact to its open position. when the contacts are closed, this lever is accessible for manual opening of the overload relay.

Description

United States Patent [191 Di Marco et a1. Y v

[11] 3,852,694 Dec. 3, 1974 OVERLOAD RELAY WITH FAST ACTING BIMETAL ON HIGH CURRENT [73] Assignee: l-T-E Imperial Corporation, Spring House, Pa. 7

[22] Filed: Dec. 26, 1973 [21] App]. No.: 428,097

[52] US. Cl 337/62, 337/59, 337/78,

337/102 [51] Int. Cl. H0lh 71/16, H0lh 61/02 [58] Field of Search 337/62, 77, 78, 79, 82,

5/1966 Kussy et al 337/107 X 3,562,688 2 1971 Kussy et al 337/62 Primary ExaminerArthur T. Grimley Attorney, Agent, or FirmOstrolenk, Faber, Gerb &

Soffen 571 ABSTRACT An overload relay having a conventional replaceable heater is provided with an auxiliary bimetal secured to the deflectable end of the main bimetal and arranged to deflect in a direction opposite to deflection of the latter. Tripping results from the net deflection of these bimetals. the main bimetal shields the auxiliary bimetal from direct heat radiating from the heater, so that upon rapid heating of the latter'the initial result is that the main bimetal deflects rapidly and there is essentially no reverse deflection of the auxiliary bimetal whereby tripping takes place very rapidly.

A contact position-indicating lever is biased to follow the movable contact to its open position. when the contacts are closed, this lever is accessible for manual opening of the overload relay.

5 Claims, 6 Drawing Figures OVERLOAD RELAY WITH FAST ACTING BIMETAL N HIGH CURRENT This invention relates to motor starter overload relays in general and more particularly relates to an improvement of the overload relay disclosed in U.S. Pat.

No. 3,562,688, issued Feb. 9, 1971, to F. W. Kussy et al. for Quick Trip Overload Relayl-leaters.

As noted in the aforesaid U.S. Pat. No. 3,562,688,

conventional overload relays utilizing indirectly heated bimetal tripping elements are satisfactory for opening of the relay contacts under normal fault conditions. However, these conventional overload relays often prove unsatisfactory where extreme faults must be cleared very rapidly in order to prevent irreparable damage to electric motors.

The solution provided by the aforesaid U.S. Pat. No. 3,562,688 is the utilization of a directly heated bimetal as an element of a replaceable heater unit which generates heat for operating the tripping bimetal of the overload relay. Upon heating, the heater bimetal moves to ward the tripping bimetal so that the heat source for the latter is moved closer thereto, bringing about more rapid heating. Upon extremely rapid heating of-the bimetal heater, the latter physically engages and moves the tripping birnetal'toward its tripping position even before the latter has heated sufficiently to deflect to this tripping position. 7

In accordance with the instant invention, a nonbimetal type conventional heater is utilized to furnish heat for the tripping bimetal. The tripping bimetal is a strip having one end fixed and the other end free to demounted on the free end of the tripping bimetal and upon heating thereof moves opposite to the tripping direction. The overload relay trips when the bimetals reach a predetermined deflection obtained by the net movement of the main and auxiliary bimetals'combined. The main bimetal is so positioned between the heater and auxiliary bimetal that the latter is substantially, if not entirely, shielded from radiant energy emanating from the heater. Thus, upon the occurrence of extreme fault conditions, radiant energy from the heater will cause rapid deflection of the main bimetal and essentially zero deflection of the auxiliary bimetal so that the net deflection in the tripping direction is essentially the entire deflection of the main bimetalwhich occurs very rapidly.

In addition to the improved fast acting tripping mechanism, the overload relay of the instant invention is provided with an indicator lever which provides a positive visual indication that the overload relay has tripped. One end of the lever is biased to follow the movable contact arm as it moves from circuit closed to tion to manually open the overload relay contacts.

Accordingly, a primary object of the instant invention is to provide an overload relay having improved means for effecting extremely rapid operation under severe fault conditions.

Another object is to provide an overload relay having novel indicator means.

Still another object is to provide an overload relay having novel means-to effect manual opening thereof.

FIG. 1 is an end view of an overload relay constructed inaccordance with teachings of the instant invention. Y

FIG. 2 is a side elevation looking in the direction of arrows 2-2 of FIG. 1.

FIG. 3 is a side' elevation looking in the direction of arrows 3-3 of FIG. 1, with the casing cover removed.

in the direction of arrows 5 s of FIG. 4.

flectin a tripping direction. An auxiliary bimetal is FIG 6 is an exploded perspective of the'electrical elements and operating mechanism for the 'overload relay of FIGS. l 5.

Now referring to the figures. Overload relay unit 10 includes amolded housing divided along line 11 to form base 12 and cover 13 joined by rivets l4. Ina manner well known to the art, base 12 and cover 13 are provided with internal depressions and protrusions which engage the electrical and active mechanical elements of unit 10 to operatively position these elements.

Opening 15 at the top of housing l1, 12 forms an en 20. The latter is a strip-like member having its upper end 21 welded to the offset upper end of formed stiff resilient support strip 22. Bimetal is interposed between heater'99 and support 22 with the main central portion of support 22 extending generally parallel to heater leg 94. The central portion of support 22 is provided with a threaded aperture that receives the threaded portion of adjusting screw 23 having enlarged head 24 disposed outside of casing 12 at one end thereof. Rotation of adjusting screw 23' is effective to draw the ends of support 22 against casing abutments 26, 27 positioned on opposite sides of adjusting screw clockwise about abutment 27 as a center, thereby moving lower end 31 of main bimetal to the right with respect to FIG. 3.

Reversely bent auxiliary bimetal 35 is secured by rivets 34 to the lower end 31 of main bimetal 20. Free end 36 of auxiliary bimetal 35 is operatively engaged with the right end 42 of translator bar 41 through notch 44 bounded by

bar ends

42, 43. Notch 44 also provides clearance for stationary contact member 45 and main operating spring 46. The latter is operatively engaged by the left end 43 of bar 41.

One end of member 45 extends externally of

housing

12, 13 at the bottom thereof to constitute plug-in stab 47, and the other end of member 45 is reversely bent and mounts stationary contact 51. The latter is engageable by movable contact 52 mounted at the upper end of movable contact arm 50. The lower end of contact arm 50 is bifurcated and is seated in notches 53 in the upper surface of bifurcated extension 54 of conducting element 55. The lower end 48 of element 55 constitutes a plug-in stab positioned externally of casing 12 at the lower end thereof. Main operating spring 46 is a coiled tension member secured at its upper end to contact arm 50 just below movable contact 52. The lower end of spring 46 is secured to extension 56 of member 55, positioned well below the lower end of contact arm 50. It should be obvious to those skilled in the art that main operating spring 46 and movable contact arm 50 are connected and operatively positioned to form an overcenter toggle mechanism for operating and closing cooperating contacts 51, 52 with a snap action.

When contacts 51, 52 are open and reset slide 60 is in its raised or manual position, casing protrusion 59 provides a stop to limit the open circuit position of contact arm 50. When reset slide 60 is held in its depressed or lowered position, cam surface 61 at the lower end thereof limits movement of movable contact 52 to the right with respect to FIG. 3, so that the toggle operating mechanism always stays to the left of its overcenterposition and spring 46 always acts in the closing direction. Reset slide 60 is held in its lowered position by moving end 62 of wire spring 63 upward from MAN" notch 63 to "AUTO notch 64, thereby lowering spring end 65 that isentered into reset slide notch Indicator lever 70 is pivotallymounted in casing 12 on pin 7l.The lower end 72 of lever 70 is biased to the right with respect to FIG. 3 by coiled compression spring 73. Lateral extension 74 of lever 70 is thereby engaged with the left or contact carrying side of movable contact arm 50 so that spring 73 tends to open cooperating contacts 51, 52. However, the force exerted by biasing spring 73 is negligible as compared to the force exerted by-main operating spring 46 so that insofar as bringing about separation of cooperating contacts 51, 52' the force of biasing spring 73 may be ignored. However, when cooperating contacts 51, 52 are open, spring 73 pivots lever 70 counterclockwise with respectto FIG. 3 so that the upper end 77 thereof,

which is visible'externally of

casing

12, 13, moves to the left with respect to FIG. 3 to indicate thatcontacts 51, 52 have separated. To facilitate making this observation, end.77-of indicator lever 70 is of a color that contrasts with the color of housing l2, 13. End 77 is accessible for manual opening of contacts 51, 52.

Automatic opening of contacts 51, 52 is a result of heat generated by current flowing through heater 99. Under many overload conditions heat generated by metal is much less than during normal overload heating 4 heater 99 gradually elevates the temperature within the entire compartment 16 so that the temperatures of main and

auxiliary bimetals

20, 35 rise together by convection heating. Under these circumstances the free end of main bimetal 20 moves to the right with respect to FIG. 3, and simultaneously there is a reverse deflection of auxiliary bimetal 35. However, the net deflection of

bimetals

20, 35 moves translator arm 41 to the right, moving main operating spring 46 to the right until its line of action moves to the right of the toggleknee,

at which point the movable contact arm pivots rapidly in a clockwise direction to open cooperating contacts 51, 52. Under severe fault conditions initial rapid heating of main bimetal 20 is'due to radiation from heater 99, with deflection of bimetal20 being substantial and very rapid. However, during this period there is very little deflection of auxiliary bimetal 35, since main bimetal 20 serves as a shield which prevents heat being radiated from heater 99 from impinging upon auxiliary bimetal 35. Thus, under severe fault conditions, the net deflection of

bimetals

20, 35 is substantially the same as the deflection of bimetal 20, so that opening of cooperating contacts 51, 52 comes about very rapidly.

Although in the foregoing preferred embodiments have been discussed, many variations and. modifications will now become apparent to those skilled in the art, and it is therefore understood that this invention is not limited by the disclosure but only by the appending claims.

The embodiments of the invention .in which an exclusive privilege or property is claimed are defined as follows: i

l. A switch device including cooperating contacts mounted for operation between first and second positions wherein said contacts are engaged and disengaged, respectively; firstmeans operatively connected to said contacts for moving same between said positions, bimetal means which upon predetermined de flection thereof in a first direction operates said first means to move said contacts from one to the other of said positions; said bimetal means including a main himetal and an auxiliary bimetal; said main bimetal upon heating thereof contributing a component of deflection in said first direction to said bimetal means; said auxiliary bimetal upon heating thereof contributing a component of deflection to said bimetal means in a second direction opposite to said first direction; heater means positioned adjacent said bimetal means for heating both the main and auxiliary bimetals by convection during normal overload conditions; said main bimetal being interposed between said heater means and said auxiliary bimetal to substantially shieldthe latter from direct'radiation of heat limited by said heater means whereby upon extremely rapid heating of said heater means said bimetal means undergoes said predetermined deflection during a period of time when deflection of said auxiliary bimetal relative to saidmain biof the bimetal means. I

, 2. A switch device as set forth in claim 1' in which the main bimetal is an elongated strip having a first end that is relatively fixed and asecond end that deflects upon heating of said main bimetal; said auxiliary bimetal being mounted to said main bimetal at its said second end.

3. A switch device as set forth in claim 2 in which the first means includes an overcenter spring-type operating mechanism and a movable second means extending between said mechanism and said auxiliary bimetal to transmit deflection of said bimetal means to said mechanism for operation thereof.

4. A switch device as set forth in claim 3 in which the second means includes an elongated bar mounted for sliding movement parallel to the longitudinal axis thereof.

Claims

1. A switch device including cooperating contacts mounted for operation between first and second positions wherein said contacts are engaged and disengaged, respectively; first means operatively connected to said contacts for moving same between said positions; bimetal means which upon predetermined deflection thereof in a first direction operates said first means to move said contacts from one to the other of said positions; said bimetal means including a main bimetal and an auxiliary bimetal; said main bimetal upon heating thereof contributing a component of deflection in said first direction to said bimetal means; said auxiliary bimetal upon heating thereof contributing a component of deflection to said bimetal means in a second direction opposite to said first direction; heater means positioned adjacent said bimetal means for heating both the main and auxiliary bimetals by convection during normal overload conditions; said main bimetal being interposed between said heater means and said auxiliary bimetal to substantially shield the latter from direct radiation of heat limited by said heater means whereby upon extremely rapid heating of said heater means said bimetal means undergoes said predetermined deflection during a period of time when deflection of said auxiliary bimetal relative to said main bimetal is much less than during normal overload heating of the bimetal means.

2. A switch device as set forth in claim 1 in which the main bimetal is an elongated strip having a first end that is relatively fixed and a second end that deflects upon heating of said main bimetal; said auxiliary bimetal being mounted to said main bimetal at its said second end.

5. A switch device as set forth in claim 4 in which the mechanism includes an operating spring engaged directly by said bar for movement of the spring to an overcenter position by said bimetal means as the latter undergoes said predetermined deflection in said first direction.