US3562688A - Quick trip overload relay heaters - Google Patents

Abstract

A NORMAL OVERLOAD RELAY HAVING A BIMETAL TRIPPING MEANS IS PROVIDED WITH A REPLACEABLE QUICK TRIP HEATER FOR THE BIMETAL, SUCH HEATER IS SO CONSTRUCTED THAT THE TRIPPING BIMETAL IS QUICK ACTING UNDER EXTREME FAULT CONDITIONS, YET UNDER NORMAL FAULT CONDITIONS THE TRIPPING BIMETAL ACTS RELATIVELY SLOWLY TO TRIP THE RELAY IN A NORMAL MANNER. THE QUICK TRIP HEATER IS CONSTRUCTED WITH A DIRECTLY HEATED BIMETAL WHICH DEFLECTS VERY RAPIDLY UPON THE OCCURRENCE OF SEVERE FAULT CONDITIONS. IF THE FAULT IS SEVERE ENOUGH THE HEATER BIMETAL PHYSICALLY ENGAGES THE TRIPPING MECHANISM DIRECTLY TO OPERATE THE LATTER MUCH MORE RAPIDLY THAN THE TRIPPING BIMETAL WOULD WHEN DEFLECTING SOLELY AS A RESULT OF HEAT ABSORBED THEREBY.

Description

F. w. KussY ETAL 3,562,688

QUICK TRIP OVERLOAD RELAY HEATERS Feb. 9, 1971 2 Sheets-Sheet l Filed Oct. 28, 1968 F. w. KUSSY ETAL 3,562,688

QUICK TRIP OVERLOAD RELAY HEATERS 2 Sheets-Sheet 2 Feb. 9, 1971 Filed oct. ze, 1968 United States Patent Oiiice 3,562,688 Patented Feb. 9, 1971 U.S. Cl. 337-62 14 Claims ABSTRACT OF THE DISCLOSURE A normal overload relay having a bimetal tripping means is provided with a replaceable quick trip heater for the bimetal, such heater is so constructed that the tripping bimetal is quick acting under extreme fault conditions, yet under normal fault conditions the tripping bimetal acts relatively slowly to trip the relay in a normal manner. The quick trip heater is constructed with a directly heated bimetal which deflects very rapidly upon the occurrence of severe fault conditions. `If the fault is severe enough the heater bimetal physically engages the tripping mechanism directly to operate the latter much more rapidly than the tripping bimetal would when deecting solely as a result of heat absorbed thereby.

This invention relates to switches having automatic tripping means and more particularly relates to an overload relay having a replaceable and interchangeable heater unit provided with a bimetal which physically trips the mechanism under severe fault conditions.

Conventional overload relays of the type having a bimetal tripping element are satisfactory for relatively slow opening of the relay contacts under conditions of normal faults. However, conventional overload relays have proven unsatisfactory under severe fault conditions as may be encountered in the operation of electric motors used in air conditioning, refrigeration, maritime, irrigation, oil well, etc., applcations where extreme faults must be cleared very rapidly in order to prevent irreparable damage to the motors. Thus special quick trip provisions must be provided.

The prior art has provided quick trip motor protection by utilizing a Xed non-moveable precisely located heater that is installed in a form of overcurrent protection device requiring high mechanical tripping force. This solution has proved unsatisfactory in several respects, namely, the necessity of providing a special device to house the heater, the heater is designed only for quick trip protection, the heater must be located very precisely in the device, and diiculties are encountered in attempting to calibrate an overcurrent device depending largely upon force and movement. The prior art has also provided other types of quick trip overcurrent protection devices, but such devices were only quick trip and did not operate under normal fault conditions. Further, such prior art devices did not have provisions for readily changing to a different range of current protection.

The foregoing disadvantages of the prior art are overcome by the device of the instant invention which provides a line or number of interchangeable heater units each designed and calibrated to cover small increments of a wide current range. These quick trip heater units are utilized in standard overload relays having bimetal tripping elements by merely interchanging one of these quick l trip heaters for the conventional bimetal heater. Further the quick trip heater of the instant invention is constructed so that the overload relay incorporating such a quick trip heater acts to give ordinary protection on low or minor faults and upon the occurrence of severe fault quick tripping occurs.

4In particular the instant invention provides an overload relay heater element having a directly heated bimetal as an integral part of the heater element assembly. Under normal operating conditions heat radiating from the heater element is absorbed by the tripping bimetal to cause opening of the overload relay under predetermined fault conditions. In addition under severe fault conditions the heater bimetal deflects very rapidly, coming into contact with the tripping mechanism to physically move the latter and also to increase the rate of heat transfer to the tripping bimetal thereby bringing about extremely rapid opening of the overload relay.

Accordingly, a primary object of the instant invention is to provide an overload relay having novel features for achieving quick trip and normal trip operations.

Another object is to provide an overload relay having an interchangeable quick trip heater unit.

Still another object is to provide an overload relay in which the heating unit for the tripping bimetal includes a directly heated bimetal.

A further object is to provide a novel construction for an overload relay which would trip very rapidly on the occurrence of severe faults and will operate in a normal relatively slow manner under lesser fault conditions.

A still further object is to provide an overload relay heater having a directly heated bimetal which under severe fault conditions deects very rapidly and physically engages the tripping mechanism to exert a mechanical force thereon acting in the tripping direction.

These as well as other objects of this invention will become readily apparent after reading the following description of the accompanying drawings in which:

FIG. l is an exploded perspective of the electrical elements and operating mechanism for an overload relay constructed in accordance with the teachings of the instant invention.

FIG. 2 is an end view of an overload relay constructed in accordance with the teachings of the instant invention.

FIGS. 3 and 4 are side elevations, looking in the direction of arrows 3-3 of FIG. 2, with the side cover of the overload relay removed. In FIG. 3 the control circuit contacts are closed while in FIG. 4 the control circuit contacts are open.

FIGS. 5 and 6 are a perspective and side elevation, respectively, of another embodiment of a quick trip heater utilizable with the overload relay of IFIGS. 1-4.

FIG. 7 is a perspective of still another embodiment of a quick trip heater.

Now referring to the figures and more particularly to FIGS. 1 through 4. Overload relay unit 10 consists of a molded housing divided along line 11 to form base 12 and cover 13 joined by screws 75. In a 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.

As seen in FIGS. 3 and 4, there is a top opening 14 which forms an entrance to main cavity 15 in base 12. Disposed externally of housing at the top thereof are spaced apart main circuit terminals 16, 17, each of which is generally L-shaped. Heater unit 18 is disposedwithin main cavity and is provided with outturned legs 16e, 17e having clearance apertures which receive screws 19 for securing heater 18 to terminals 16, 17. Auxiliary wire connector 17a is mounted to extension 17b of terminal 17.

Disposed within cavity 15 and extending generally parallel to bimetal leg 101 of heater 18 is tripping bimetal element 21. The upper end of element 21 is iixedly secured as by welding to the upper end of main support member 22. Main support 22 extends between the arms 23 at the bifurcated upper end of auxiliary support 24 and is secured to auxiliary support 24 near the free ends of arms 23. The lower ends of supports 22 and 24 are joined together by factory calibration screw 25 extending through slot 26 in auxiliary support 24 and is received in a threaded aperture of main support 22. It is noted that arms 23 have two bends therein and that the crosssectonal areas of both arms 23 is less than the crosssectional area of main support 22. Thus, manipulation of screw 25 the movement of main support member 22 relative to auxiliary support member 24 is accomplished by bending auxiliary support member 24.

At a point intermediate its ends, auxiliary support member 24 is provided with a threaded aperture which receives `field adjustment screw 27 whose enlarged head 28 is disposed externally of housing 12, 13. Bowed leaf springs 28 is disposed within main cavity 115 with the ends thereof bearing against base 12 and the center portion thereof bearing against auxiliary support member 24 at a point thereof near its lower end. The action of spring 28 urges main support member 22 to seat itself against bearing surface 29 internal of base 12. Surface 29 forms a xed point of reference about which bimetal 21 movesupon deflection thereof. Bimetal 21 is so constructed that the lower end thereof, connected to translator bar '31 at notch 31a thereof, is free to deflect to the right with respect to FIG. 3 when bimetal 21 is heated.

Tripping bimetal 21, upon deflection thereof, acts through translator bar 31 to separate movable contact 32 from stationary Contact 33 in a manner t0 be hereinafter explained. Stationary contact 33 is mounted to one end of conducting strap 34 whose other end constitutes plug-in terminal 35 extending from the bottom of housing 12, 13. Movable contact 32 is mounted to the upper end of contact arm 36 provided with bifurcated sections 37 whose free ends are entered into depressions 38 which constitute pivot points for movable contact arm 36. Depressions 38 are formed in the upper surfaces of spaced projections 41 extending horizontally from conducting strap 39 at a point intermediate the ends thereof. The lower end 40 of strap 39 constitutes a plug-in terminal extending externally of housing 12, 13.

Spring 47, extending through notch 31b in translator bar 31, is connected at its lower end to adjustable screw 48 and is connected at its upper end to contact arm 36. The center line of spring 47 extends to the left of the pivot 38 for movable contact arm 36 as seen in lFIG. 3 to thereby exert a force on the movable contact 32 to the left. However, when the bimetal 21 is heated to cause movement of the translator bar 31, the center line of spring 47 is moved to the right of pivot 38 to thereby exert a force on the movable contact to the right as best seen in FIG. 4.

Spring `47 is secured to the inner end of adjusting screw 48. Screw 48 is threadably mounted to conducting strap 39. Base 12 is provided with aperture 49 through which the slotted end of screw `48 is accessible for adjustment. Adjustment of screw '48 positions the lower end of spring 47 thereby determining the point at which contacts 32, 33 will part as spring 47 is moved to the right by translator bar 31 upon heating of bimetal 21.

Slidably mounted within a suitable guideway of member 12 is reset slide 50. Turned end 51 of V-shaped spring 52 extends into housing window 73 and is received in side notch 53 of slide 50 while the other end 54 bears against an external surface of base 12. The apex of spring 52 is disposed below the head of screw 55 which secures spring 52 to base 12. Spring 52 is partially loaded in a direction such that the arms thereof are urged to separate thereby urging slide 50 to its outward position illustrated in FIG. 3. In this position inclined reset surface 57 at the lower end of slide 50 is so positioned that when translator bar 3-1 moves spring 47 sufficiently to the right of notches 318, with respect to FIG. 3, movable Contact 32 separates from stationary contact 33 by a suflicient distance so that upon cooling of bimetal 21 contacts 32, 33 will not automatically close. This distance is established by the location of base formation 42 having contact arm 36 bearing thereagainst in FIG. 4.

With contacts 32, 33 separated, after reset slide 50 is moved downward with respect to FIG. 3, surface 57 engages the upper end of contact arm 36 driving movable contact arm 36 over center to the left so that spring 47 is effective to move contact 32 into engagement with contact 33.

For automatic resetting, slide 50 is moved inward to a position where notch 61 is in line with locking member 58. Thereafter member 58 is moved to the left with respect to FIG. 3 into notch 61. Locking screw 62, extending through an elongated slot (not shown) of member 58, maintains member 58 in adjusted position.

Factory calibration for bimetal 21 is achieved by manipulating screw 25. As screw 25 is adjusted main support 22 and bimetal 21 are bodily moved as a unit. During this period of time auxiliary support 24 is essentially stationary although the upper portion thereof deforms to permit the aforesaid movement of main support 22. Field adjustment knob 28 is operated to rotate screw 27. This movement brings about the bodily movement of auxiliary support 24, main support 22 and bimetal 21 as a unit with bearing surface 29 acting as a pivot. It is noted that knob 28 is provided with a radial projection 63 which cooperates with base stop 64 to limit rotation of screw 27 to approximately one revolution.

With contacts 32, 33 in engagement a complete electrical path exists between plug-in terminals 35 and 40. This path comprises terminal section 35, conducting strap 34 to stationary contact 33, movable contact 32, movable contact arm 36, and conducting strap 39 to terminal section 40. This series circuit is intended to be connected in series with the operating coil for an electromagnetic contactor (not shown).

With the exception of heater 18 the overload relay construction hereinbefore described is set forth in detail in ULS. Pat. 3,226,510 issued Dec. 28,y 1965 to R. W. Thomas and E. T. Platz for an Electric Overload Switch With Improved Thermal Actuator. In addition to bimetal strip 101, h eater unit 18 includes insulating support spacer 102 for mounting bimetal \101 and terminal member 16e. In particular, insulator 102 is secured by rivets 103 to the longer or free leg 131 of bimetal 101 near its point of intersection with fixed or terminal leg 16C. Rivet 104 secures terminal member l17c to insulator 102. Copper pigtail 105 provides an electrical connection from the lower or free end of bimetal y101 to terminal member 17e. The free end of the bimetal 101 is provided with narrowed projection 107 which, for reasons to be hereinafter explained, extends into notch 31e of translator bar 31 and is engageable with bar 31 upon the occurrence of severe fault conditions to cause opening of contacts 32, 33.

With heater 18 mounted as shown in FIGS. 3 and 4, under minor fault conditions current passing through bimetal 101 generates heat which is radiated to tripping bimetal 21. The latter, upon heating, expands so that the free end 21a thereof deflects to the right with respect to FIG. 3 for operation substantially the same as that of the overload relay described in the aforesaid Pat. 3,226,- 510. However, upon severe fault conditions, that is, when current flow between terminal 16 and 17 rises Very rapidly to a high level, current flowing in heater bimetal 101 causes rapid heating of the latter and rapid deflection of the free end of bimetal 101 to the right with respect to FIG. 3. This moves heater bimetal 101 toward tripping bimetal 21 to increase the rate of heat transferred to the latter. After some lost motion between bimetal 101 and bar 31 resulting from the width of notch 31c, when heater bimetal tip 107 engages translator bar 31, heating bimetal 101 exerts a mechanical force acting on translator bar 31 to aid tripping bimetal 21 in defiecting translator bar 31 to the right with respect to FIG. 3. Forces exerted by heating and tripping bimetals 101, 21 combine to aid in mechanically moving translator 31 to the right to bring about rapid separation of contacts 33, 36.

Under conditions of extremely severe overcurrents tripping forces are provided essentially by said heater bimetal 101.

Heater 18 in FIGS. 1 through 4 may be replaced by heater 118 shown in FIGS. 5 and 6. More particularly heater unit 118 includes L-shaped bimetal 119 whose longer leg 132 for a substantial portion thereof is covered by a layer of insulation 121. Resistance wire 122 wound around insulator 121, to form a coil is electrically connected at its lower end 123 to the free end of heating bimetal 119. The other end of coil 122 is electrically connected to terminal 17e. Heater unit 118 also includes insulating spacer 124 to which both bimetal 119 and terminal 17tare fxedly secured by rivets 125 and 126, respectively.

Since the operation of heater units 18 and 118 are substantially identical no additional explanation of operation will be given herein. However, it is noted that the provision of resistance wire coil 122 wound closely around heating bimetal 119 results in much more rapid heating of bimetal 119 than bimetal 101.

Quick trip heater 200 of FIG. 7 is particularly adapted for low current tripping. Heater 200 includes relatively narrow bimetal strips 201 and 202 in spaced parallel relationship. The upper or fixed ends of strips 201, 202 are oppositely bent to form terminals 16e, 17C, respectively. Strips 201, 202 are connected in electrical series at their lower ends by jumper ,203 having downward extension 204 to engage translator 31.

The narrowness of each strip 201, 202 and the series connection thereof results in a relatively high impedance. Since strips 201, 202 are positioned in a generally cornmon plane and deflect in the same direction upon heating, mechanical forces generated during such heating are combined to produce sufficient force for tripping of the contact operating mechanism.

While the heater bimetal has been described and illustrated as directly engaging the translator bar of the tripping mechanism, it should now be apparent to those skilled in the art that mechanical forces resulting from deflection of the heater bimetal may be utilized by applying such forces directly to the tripping bimetal by having a lateral extension at the heater bimetal defiectable and physically engageable with the tripping bimetal. It is also noted that quick trip heaters of the type provided by this invention may be utilized in ambient compensated switch units. For example, the U-shaped compensating bimetal shown and arranged generally as in copending U.S. application Ser. No. 581,246, now U.S. Pat. 3,417,358, filed Sept. 22, 1966 entitled Ambient Temperature Compensated Overload Relay with B. Di Marco as inventor, and assigned to the assignee of the instant invention, may be used as the operative connection between the main contact spring and the translator bar.

Although there has been described a preferred ernbodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the 6 art. Therefore, this invention is to be limited, not only by the specific disclosure herein, but only by the appending claims.

What is claimed is:

1. A switch device including cooperating contacts mounted for operation between first and second positions wherein said contacts are engaged and disengaged, respectively; a mechanism operatively connected to said contacts for moving said contacts between said positions; a first bimetal which upon predetermined deflection thereof in a first direction operates said mechanism to move said contacts from one to the other of said positions; a heating unit mounted in close proximity to said first bimetal for transfer of heat from said heating unit to said first bimetal to cause deflection of the latter in said first direction; said heating unit including a second bimetal which defiects in said first direction and toward said first bimetal upon heating of said heating unit to increase rate of heat transfer from said heating unit to said bimetal during periods of rapid rise in temperature of said heating unit.

2. A switch unit as set forth in claim 1 in which said second bimetal upon predetermined deflection thereof operating said mechanism to move said contacts from said one to said other of said positions, said second bimetal being constructed so that said predetermined deflection thereof during rapid rise in temperature of said heating unit provides essentially all physical forces required to operate said mechanism causing said contacts to operate from said one to said other of said positions.

3. A switch as set forth in claim 1 in which said heating unit is positioned and operatively engageable with the first bimetal to physically move said first bimetal in said first direction during periods of rapid rise in ternperature of said heating unit.

4. A switch as set forth in claim 3 in which under conditions of gradual temperature rise of said heating unit deflection of said first bimetal in said first direction is due solely to a rise in temperature of said first bimetal.

5. A switch unit as set forth in claim 1 in which said heating unit is connected in a circuit Iwith electric current passing through said second bimetal.

6. A switch unit as set forth in claim 5 in which said first bimetal is a non-current carrying element.

7. A switch as set forth in claim 1 in which said heating unit also includes a heater wire adjacent to said second bimetal and connected in a circuit with current passing through said heater wire.

8. A switch as set forth in claim 7 in which the heater wire is connected in series circuit with said second bimetal and current also passes through said second bimetal.

9. A switch as set forth in claim 7 in which said heater wire is wound around said second bimetal.

10. A switch as set forth in claim 1 in which each of said bimetals includes a strip-like portion fixed at one end and free at the other end; said strip-like portions extending generally parallel to one another and when positioned so that said one end of said first bimetal is positioned above said other end thereof, said one end of said second bimetal is positioned above the other end thereof.

11. A switch as set forth in claim 1 in which the heater unit is removable and replaceable.

12. A switch as set forth in claim 11 in which there is a housing wherein said cooperating contacts, said mechanism, said first bimetal, and said heater unit are disposed, means engageable externally of said housing for removal and replacement of said heater unit.

13. A switch as set forth in claim 1 in which said second bimetal comprises a plurality of electrically connected bimetal strips disposed generally in a common plane with all of said strips positioned to deflect out of said plane in the same direction upon heating thereof.

14. A switch as set forth in claim r1 in which said second bimetal is fixed at one end thereof and free at the other end, said second bimetal comprising first and second References Cited UNITED STATES PATENTS Hodgkins 337-78 Rich 337-105 Parks 337-360 Howard 337-62 Thomas et al. 337-57 Ramsey et al 337-99X Ashworth et al 337-100 5 BERNARD A. GILHEANY, Primary Examiner D. M. MORGAN, Assistant Examiner Hallerberg et a1. 337-104 10 337-102, 336

U.S. C1. X.R.

Images