US3555471A

US3555471A - Automatic breaker with coil adjustable to effect current limiting or electrodynamic blowoff compensation

Info

Publication number: US3555471A
Application number: US709101A
Authority: US
Inventors: Gennady Feodosievic Mitskevich; Vladislav Yakovlevich Guschin; Jury Nikolaevich Vorontsov; Vladimir Avramovic Boguslavsky; Anatoly Mikhailovic Bela-Belov; Viktor Izrailevich Rakhlis; Viktor Revoldovich Oktyabrev; Oleg Ivanovich Artsybashev; Fedor Andreevich Vakhomchik
Original assignee: VNI I PK I ELECTR OAPPARATOV
Current assignee: VNI I PK I ELECTR OAPPARATOV; VSESOJUZNY NAUCHNO-ISSLEDOVATELSKY I PROEKTNO-KONSTRUKTORSKY INSTITUT ELECTR OAPPARATOV
Priority date: 1968-02-28
Filing date: 1968-02-28
Publication date: 1971-01-12
Anticipated expiration: 1988-01-12
Also published as: FR1588512A; GB1189948A; DE1763007A1; DE1763007B2; BE726591A

Abstract

AN AUTOMATIC BREAKER INCLUDES A MOVABLE CONTACT SYSTEM AND A STATIONARY CONTACT SYSTEM OPERATIVELY ASSOCIATED WITH ONE ANOTHER. THE STATIONARY CONTACT SYSTEM IS CONSTITUTED AS A SERIES COIL HAVING BOTH A MOVABLE AND STATIONARY MEMBER. THE STATIONARY MEMBER IS ADJUSTABLY SUPPORTED SO THAT IT CAN BE TURNED 180* FROM A FIRST POSITION TO ALTER THE ELECTRODYNAMIC FORCES EXERTED BY THE STATIONARY MEMBER ON THE MOVABLE MEMBER. IN THIS RESPECT THE STATIONARY MEMBER WHEN IN THE FIRST POSITION CONSTITUTES THE SERIES COIL AS A CURRENT LIMITER AND WHEN TURNED 180* THEREFROM CONSTITUTES THE SERIES COIL AS A COMPENSATOR.

Description

Filed Feb. 28, 1968 1971 G. F. MITSKEVICH ETAL 3,555,471

AUTOMATIC BREAKER WITH COIL ADJUSTABLE TO EFFECT CURRENT 1 LIITING 0R ELECTRODYNAMIC BLOWOFF COMPENSATION '4 Sheets-Sheet 1 3,555,471 CT CURRENT ATION Sheets-Sheet 2 Jan. 12, 1971 G. F. MITSKEVICH AUTOMATIC BREAKER WITH COIL- ADJUSTABLE TO EFFE LIMITING OR ELECTRODYNAMIC BLOWOFF COMPENS Filed Feb. 28, 1968 4 FIG. 2 v

H V/A Jan. 12, 1971 rrs v c ETAL 3,555,471

AUTOMATIC BREAKER WITH COIL ADJUSTABLE TO EFFECT CURRENT LIMITING OR ELECTRODYNAMIC BLOWOFF COMPENSATION Filed Feb. 28. 1968 4 Sheets-Sheet 3 Z 22 331735 3536 F/G5 as I 4 Jan. 12, 1971 s v c ETAL 3,555,471

AUTOMATIC BREAKER WITH COIL ADJUSTABLE T0 EFFECT CURRENT LIMITING OR ELEUTRQDYNAMIC BLOWQFF COMPENSATION Filed Feb. 28, 1968 4'Sheets-Sheet 4.

United States Patent AUTOMATIC BREAKER WITH COIL ADJUSTABLE T EFFECT CURRENT LIMITING 0R ELECTRO- DYNAMIC BLOWOFF COMPENSATION Gennady Feodosievich Mitskevich, Vladislav Yakovlevich Guschin, Jury Nikolaevich Vorontsov, Vladimir Avramovich Boguslavsky, Anatoly Mikhailovich Bela- Belov, Viktor Izrailevich Rakhlis, Viktor Revoldovich Oktyabrev, Oleg Ivanovich Artsybashev, and Fedor Andreevich Vakhomchik, Kharkov, U.S.S.R., assignors to Vsesojuzny Nauchno-Issledovatelsky I Proektno- {(JoSnsStrIgktorsky Institut Electroapparatov, Kharkov,

Filed Feb. 28, 1968, Ser. No. 709,101

Int. Cl. H01h 77/10 US. Cl. 335-195 Claims ABSTRACT OF THE DISCLOSURE An automatic breaker includes a movable contact system and a stationary contact system operatively associated with one another. The stationary contact system is constituted as a series coil having both a movable and stationary member. The stationary member is adjustably supported so that it can be turned 180 from a first position to alter the electrodynamic forces exerted by the stationary member on the movable member. In this respect the stationary member when in the first position constitutes the series coil as a current limiter and when turned 180 therefrom constitutes the series coil as a compensator.

The present invention relates to automatic breakers intended for short-circuit and overload protection in electrical units, as well as for occasional operational switchings of AC and D-C circuits and, more particularly, to automatic breakers intended for the operation in both current-limiting (quick-action) and selective protection duties. 1

Known in the art are automatic breakers, e.g. triplepole breakers, comprising a control mechanism, a maximum current release gear, and movable and stationary systems of contacts in each of the poles, either of the contact systems being provided with arcing horns arranged under arcing suppressors.

Also known are automatic breakers, e.g. triple-pole selective breakers with electrodynamic compensators, as well as automatic breakers of increased switching capacity with built-in quick-break fuses.

Each of these known automatic breakers has its own designation; correspondingly, they all vary in design, overall and setting dimensions, which fact complicates their manufacture and create difficulty in arranging them in switching devices. Other disadvantages are a low switching capacity, inconvenience in use since after cutting off short-circuit currents, the requirement of a change of burned out fuses, thus leading to time waste in the equipment operation and making impossible the remote control of automatic breakers, and also the provision of a fuse unit increases overall dimensions.

It is an object of the present invention to provide an automatic breaker usable both as a current-limiting and selective switch, requiring only a minor rearrangement of the components of its contact system.

According to this and other objects, in an automatic breaker with a system of movable and stationary contacts in each of the poles, according to the invention, the system of stationary contact is fashioned as at least a double-Wound series coil serving as an electrodynamic device, and consists of a movable part functioning as a stationary contact, and of a stationary part. The point of "ice connection of these parts of the series coil and their shape are selected such as to permit a turn of the stationary part of said coil in relation to its longitudinal axis, provided the position of its movable part insuring normal closure of the contacts remains invariable. The turn of the stationary part of the series coil varies the direction of electrodynamic impact on the movable part of said coil and, depending upon the position of its stationary part, permits the use of the coil both as a current limiter in the current-limiting version of the breaker and as a compensator in its selective version.

The movable and stationary parts of the series coil may be U-shaped, while it is feasible that the point of connection of these parts be between the sides of the U-shaped stationary part of the coil.

It is feasible that the point of connection of the U- shaped stationary and movable parts of the series coil be equidistant from the sides of the U-shaped stationary part.

In order to increase the electrodynamic impact on the movable part of the series coil, one of the sides of the latter may be arranged inside the stationary part of the coil, while the other side is arranged on its exterior.

The movable part of the coil may have an elongated end serving as an arcing horn for the stationary contact.

For the connection of an outer circuit, the stationary part of the series coil may have a lead-out arrangement symmetrically with respect to the sides of said part, one of which sides may support the stationary part within the breaker.

It is feasible to divide the movable part of the series coil, which serves as stationary contact, into at least two longitudinal portions whereon the contacts are secured.

In order to synchronize the motion of the above-said longitudinal portions, it is feasible that they be mechanically interconnected by means of, for example, a roller.

It is feasible that said longitudinal portions be connected to one another with a clearance so as to permit their self-setting when the breaker contacts are closed.

In order to preclude the interwelding of the arcing horns of the stationary contacts when moving towards each other, the surfaces of said horns facing each other, may be provided with projections arranged below the working surface of the horns.

The automatic breaker may be fitted with a device for insuring contact pressure and automatic lowering of the working contacts of the compensator.

It is feasible to make the device for insuring the contact pressure and automatic lowering of the working contacts of the compensator in the form of a spring, a bushing and a rod, the latter passing inside said spring and bushing and having a nut on one of its ends and a head on the other end, and movable inside the bushing secured in the automatic breaker body. It is feasible that the spring of said device be resting against the nut at one of its ends and against the bushing at the other end.

Other objects and advantages of the present invention will be more apparent from the description of a specific embodiment thereof, reference being had to the appended drawings, wherein:

FIG. 1 shows diagrammatically a general view of the automatic breaker, according to the invention;

FIG. 2 is a series coil of the automatic breaker, which is used as current limiter, side view;

FIG. 3 is a series coil of the automatic breaker, which is used as a compensator, side view;

FIG. 4 is a top view of FIG. 2;

FIG. 5 is a series coil of the automatic breaker, which is used as compensator with a device insuring the contact pressure and automatic lowering of the working contacts, side view;

FIG. 6 shows a joint A in FIG. 5, on an enlarged scale; and

FIG. 7 (a, b and c) is the diagram of the current fiow through the contact systems of the automatic breaker, according to the invention.

Enclosed in a plastic body 1 (FIG. 1) of the automatic breaker are: a breaker-controlling mechanism 2 coupled with a handle 3, a maximum current release gear for switching otf the automatic breaker in case of emergency conditions of a protected circuit, a system 5 of movable contacts and a system 6 of stationary contacts. The systems 5 and 6 are arranged in each pole of the automatic breaker beneath an arcing device consisting of steel plates 7 secured in insulation walls 8 and a fire-extinguishing grid 9.

The system 5 of movable contacts comprises a working contact 10 and a current-conducting contact holder 11 which is coupled with a lead-out busbar 13 by means of a flexible connection 12. The contact holder 11 is provided with an arcing horn 14.

By means of the controlling mechanism 2 the contact holders 11 of each pole of the automatic breaker are coupled with the handle 3 intended for operating the automatic breaker.

The system 6 of stationary contacts is made as a doublewound series coil sewing as an electrodynamic device.

The series coil functioning as a stationary contact consists of movable and

stationary parts

15 and 16 respectively, both U-shaped. The point of connection of said U-shaped movable and stationary parts is arranged between the sides of the stationary part so that one of the U-shaped sides of the movable part 15 of the coil lies within the stationary part 16, whereas the other side is placed on the outer side thereof. This largely increases the electrodynamic impact on the movable part 15 of the coil, as the occurrence of arcing in the contact systems of the automatic breaker results in a current circuit forming an additional coil (FIG. 70). In this case, the point of connection of the movable and the

stationary parts

15 and 16 respectively, of the series coil is equidistant from the sides of the stationary part so that the size g is equal to the size g (FIGS. 2, 3, and 5). Such an embodiment of the movable and

stationary parts

15 and 16 respectively, of the coil and the selection of the point of their connection permit, provided the position of the movable part 15 remains invariable, the turning of the stationary part 16 of the coil by 180 in relation to its longitudinal axis and the use of the series coil as both a current limiter (FIG. 2) and a compensator (FIGS. 3 and 5), as this turn of the stationary part 16 of the series coil changes the direction of electrodynamic impact 'on its movable part 15.

One of the ends of the U-shaped stationary part of the series coil has a lead-out 17 serving as a connection for the outer conductors and is symmetrical or equally spaced from both of its sides so that the distance B is equal to the distance B (FIGS. 2, 3 and 5), while its other end is connected to the movable part 15 of the coil by means of a prop 18 and a current-leading hinge 19.

The symmetrical arrangement of the lead-out 17 in relation to the sides of the stationary part 15 permits a setting of the stationary part 16, after its turn by 180, which insures a permanent and stable contact of the movable part 15 with the working contact 10.

The movable part 15 of the series coil functioning as stationary contact has a working contact 20.

When the series coil is used as a current limiter (the current-limiting version of the automatic breaker, FIG. 2), its stationary part -16 is secured to the body 1 of the automatic breaker with a side having the lead-out 17, in case said series coil is employed as a compensator (the selective version of the automatic breaker), it is fastened with its other side to whose end the prop 18 (FIGS. 3 and 5) is attached. Both sides of the U-shaped stationary part 16 of the series coil are provided with apertures 21 insuring the support of said coil by the automatic breaker body 1 by means of screws 22.

In case the series coil is employed both as a current limiter (FIG. 2) and as a compensator (FIGS. 3 and 5), its movable part 15 remains in a position permitting the normal shortening of the working

contacts

10 and 20.

The movable part 15 of the series coil with its contact 20 is divided into two longitudinal parts, each having an elongated end 23 serving as an arcing horn.

In case the series coil is used as a compensator, its divided movable part 15 reduces the electrodynamic repulsion of the

contacts

10 and 20 owing to a greater number of contact points.

In case the series coil is used as a current limiter, the division of the movable part 15 insures a more stable magnitude of the operation current of the current limiter. Thus, with current flowing through the coil, its movable part 15 is influenced by the sum of two forces, i.e., the stable force of the electrodynamie circuit induced by the series coil, and the unstable force of the contacts repulsion. The division of the movable part 15 of the series coil helps decrease the unstable component of the sum of the forces and thus decrease the spread of the operation current of the whole series coil circuit. Furthermore, the division of the movable part 15 of the series coil permits a better centering of the arc whose point of bearing tends to travel along a slot dividing the arcing horns 23, as well as improves the conditions of heat emission in the case of prolonged current flow. The division of the movable part 15 of the series coil may occasionally cause irregular distribution of the current in it, which brings about an asynchronous disconnection of the contacts 20. In order to insure the synchronous travel, the divided movable part 15 of the series coil has a connection by means of a roller 24 (FIG. 4) passing through apertures 25. This connection is made with a clearance, thus insuring a selfsetting of the working contacts 20 when the automatic breaker is in ON-position.

In order to prevent the interwelding of the arcing horns 23, and to maintain the clearance therebetween when moving towards each other under the action of the electrodynamic forces emerging when the arc travels along them, the sides of the arcing horns 23 are provided with projections 26, laterally engageable with one another which are below the working surface of the arcing horns 23 along which the are bearing point travels.

Electric contact in the current-leading hinge 19 coupling the movable and

stationary parts

15 and 16 respectively, of the series coil is effected simultaneously in two ways: through the conjugated surfaces of the divided movable part 15 of the series coil and the prop 18, as well as through the surface of a current-conducting axis 27 and the surface of the apertures in the movable parts 15 of the series coil and the prop 18.

When the surfaces of the current-leading axis 27 come into contact with the surfaces of the openings in the movable part 15 of the series coil and the prop 18, the contact pressure is effected by means of a spring 28 (FIGS. 2 and 3), whose one end rests against the movable part 15 and the other end bears againt the stationary part 16 of the series coil.

When the conjugated surfaces of the movable part 15 of the series coil and the prop 18 come into contact, the contact pressure is effected by means of a spring 29 (FIG. 4), whose one end rests against the head of the currentconducting axis 27, and the other rests against the movable part 15 of the series coil.

In order to insure stable contact, the surfaces of the divided movable part 15 of the series coil and the prop 18 carry straps 30 made of a material possessing high conductivity and mechanical strength (for instance, metal ceramics on a sliver basis).

The contact pressure of the working

contacts

10 and 20 of the automatic breaker used as both a current limiter and a compensator (in current limiting or selective variants) is effected by means of a spring 31 (FIGS. 2

and 3), one of whose ends rests against the movable part 15 of the series coil, and the other end rests against a screw 32 screwed into a shoe 33 fastened to the body 1 of the automatic breaker whose turn regulates the contact pressing.

The provision of the series coil as a compensator insures high electrodynamic stability of the contact system of the automatic breaker. However, said electrodynamic stability can be made still higher by lowering of the working contacts so as to compensate the springing effect of the parts of the control mechanism 2, but this reduces the switching capacity of the automatic breaker.

The electrodynamic stability of the working contacts of the automatic breaker may be increased by employing, instead of the spring 31 insuring only contact pressure, a device 34 (FIG. which, in addition to the provision of contact pressure, automatically lowers the working contacts when strong currents flow through the series coil, without affecting the switching capacity of the automatic breaker.

The device 34 comprises a rod 35 (FIG. 6) passing through a Spring 36 insuring contact pressure and a bushing 37. Said bushing 37 is screwed into the shoe 33 secured in the body 1 of the automatic breaker. The rod has, on one of its ends, a head 38 provided inside the bushing 37 and a nut 39 on the other end. By its one end, the spring 36 rests againt said bushing 37, and against the nut 39 by the other end. The extent of compression of the spring 36 conditions the force of contact pressure. By screwing the bushing 37 into the shoe 33 fastened in the body 1 of the automatic breaker, it is possible to adjust a clearance 6 (the normal lowering of the contacts) which is chosen to be smaller than a clearance 5, (FIG. 5) (the lowering of the contacts taken with regard to automatic increase).

The device 34 is an independent unit which can be unscrewed from the body 1 of the automatic breaker and which allows the adjustment of the contact pressure outside the automatic breaker by way of fastening the nut 39 on the rod 35.

In order to actuate the automatic breaker, the handle 3 (FIG. 1) is transferred into position C. As a result, the control mechanism 2 rapidly shifts the contact holders 11 and instantly closes the working contacts and 20 (FIGS. 2, 3 and 5), said closure being independent of the speed of the travel of the handle 3.

All this results in a closed electric circuit.

The flow of the current through the series coil used as a current limiter causes the emergence of electrodynamic forces which act to turn the movable part of the series coil, fastened to which is the working con- 5 tact 20, toward a pointer F (FIGS. 2 and 7b).

However, the electrodynamic circuit induced by the series coil which is used as a current limiter, as well as means for compressing the spring 31, are selected such that the turn of the movable part 15 takes place only after the current has reached a certain magnitude, i.e. the current of electrodynamic setting. The magnitude of this current is greater than the magnitude of the current causing the operation of the maximum current release gear 4.

The same spring 31 insures contact pressure when the working contacts 10 and (FIG. 2) are closed.

In case of emergence of short-circuit current in a protected circuit, stronger than the current of electromagnetic setting of the series coil used as a current limiter, under the action of electrodynamic forces induced in said coil, the movable part 15 of the series coil begins to turn at a high speed around the axis 27 breaking the contacts 10 and 20 (FIG. 70) before the operation of the control mechanism 2. The emerging arc restricts the growing of the short-circuit current and prevents it from reaching its maximum.

With the arc on the

horns

14 and 23, the current flowing through the latter forms an additional coil largely increasing the electrodynamic effect which results in a higher speed of breaking the

contacts

10 and 20.

As the arc travels along the arcing

horns

14 and 23, it passes into the arcing suppressor to be broken and deionized therein. The flame and glowing gases that appear as a result of the are burning fall into the fiameextinguishing grid 9 wherein they are subject to intensive cooling.

The provision of flame-extinguishing grids largely limits the ionized space beyond the arcing suppressors chambers, which is of primary importance for reducing the dimensions of the distributing devices.

Concurrently with the turn of the movable part 15 of the series coil used as a current limiter, the maximum current release gear 4 becomes operable to actuate the control mechanism 2 which is quick to respond and which, in its turn, withdraws the contact holders 11 keeping them separated so as to ensure a preset clearance between the

contacts

10 and 20.

The handle 3 occupies the position D.

During the operation of the control mechanism 2 the movable part 15 of the series coil used as a current limiter remains in a turned position (FIG. as a result of the current flowing through it, as long as the arc exist. After the suppression of the arc, the movable part 15 of the series coil returns to the initial position under the action of the spring 31, the contact holders 11 being in a withdrawn position (FIG. 1).

In case emergency current is induced in the circuit protected by the automatic breaker, which is weaker than the current of the electrodynamic setting of the series coil used as a current limiter, only the maximum current release gear 4 becomes operable. The movable part 15 of the series coil functions only as a stationary contact. As for the rest, the process of automatic disconnection is similar to that described hereinabove.

Unlike the current-limiting version of the automatic breaker, the selective automatic breaker makes it a condition that its contacts in case of strong currents be closed within a preset time, i.e., prevent an electrodynamic discard caused by the forces of current line narrowings in an area of their convergence in the contact point of the working contacts. This condition is feasible owing to the use of the series coil as a compensator. In addition, the stationary part 16 of said coil should be turned as is shown in FIG. 3. The flow through this coil is strong currents results in the emergence of electrodynamic forces tending to turn the movable part 15 of said coil toward a pointer L (FIGS. 7a and 3), thus biasing the working contacts 20 against the contacts 10 and preventing them from breaking until the preset period of time elapses.

As soon as the preset period of time elapses, the maximum current release gear 4 becomes operable actuating the control mechanism 2 which withdraws the contact holders 11. Further on, the breaking process goes on similar to that described hereinabove.

In case of the employment of the device 34 (FIGS. 5 and 6), the automatic lowering of the working contacts of the automatic breaker without reducing the switching capacity is conditioned by the fact that the flow of strong currents through the series coil used as a compensator, its movable part 15 may turn toward the pointer L until the clearance 6, is fully used up, withdrawing from the rod 35. Simultaneously, the spring 28, in addition to effecting contact pressure on the current-conducting axis 27, returns, with the automatic breaker disconnected, the movable part 15 of the series coil to the initial position, pressing it to the rod 35. The moment created by the spring 28 in relation to the current-conducting axis 27 is far less than the moment created by the spring 36. When the automatic breaker with the device 34 is engaged the control mechanism 2 overcomes the strain of the spring 36 only at a travel length equal to the clearance 5 corresponding to the normal lowering of the working contacts.

The device is particularly effective if the lowering of the breaker contacts becomes smaller in the course of its operation, say, at the expense of the wear of the working

contacts

10 and 20, as well as the Wear of the parts of the control mechanism 2. Consequently, the provision of the device 34 increases the dependability and prolongs the service life of the automatic breaker.

The switching position of said automatic breaker is determined by adjusting the handle 3 (FIG. 1).

When the automatic breaker is in ON-position, the handle 3 occupies the position C; if said breaker is disconnected manually, the handle is in the position K. The position D indicates the automatic disconnection of the breaker.

In order to engage the automatic breaker after it has been automatically disconnected, it is necessary first to withdraw the handle 3 to the position K, wind up the control mechanism 2 and then transfer the handle to the position C.

Thus, the proposed automatic breaker has small overall dimension and can be manufactured from analogous members both in the current-limiting and selective versions.

In the current-limiting version said automatic breaker insures quick and reliable action while in the selective version its advantage is high electrodynamic stability of the working contacts.

The present automatic breaker insures reliable protection against overloads and short circuits in powerful electric circuits (grids), permitting direct manual and remote control and is prepared for repeated engagement after disconnecting short-circuit currents.

All this indicates essential advantages in the course of manufacturing these automatic breakers and the use thereof.

We claim:

1. An automatic breaker comprising movable contact means and stationary contact means operatively associated with one another, said stationary contact means being constituted as a series coil including a plurality of turns and serving as electrodynamic means and further including a movable and a stationary member, said stationary member acting to exert electrodynamic forces on said movable member, said stationary member being adjustably supported to be selectively turned from a first position to a second position 180 from said first position, whereby the extent of said electro-dynamic forces exerted by said stationary member on said movable member is selectively altered, said stationary member when in said first position acting to constitute said series coil as a current limiter and when in said second position acting to constitute said series coil as a compensator.

2. An automatic breaker as claimed in claim 1, wherein the movable and stationary members of the series coil are U-shaped and interconnected, such that the point of connection is between the sides of the U-shaped stationary member of the coil.

3. An automatic breaker as claimed in claim 2, wherein the point of connection of the U-shaped movable and stationary members of the series coil is equidistant from the sides of the U-shaped stationary member.

4. An automatic breaker as claimed in claim 1, wherein to increase the electrodynamic impact on the movable member of the series coil, one of the sides of the latter is arranged inside the stationary member of the series coil, while the other is extended outwardly therefrom.

5. An automatic breaker as claimed in claim 1, wherein the movable member of the series coil includes an elongated end portion constituting an arcing horn.

'6. An automatic breaker as claimed in claim 1, wherein the stationary member of the coil includes a lead-out portion symmetrical to its sides, and adapted for being fastened in the breaker.

7. An automatic breaker as claimed in claim 1, wherein the movable member of the series coil includes at least two spaced longitudinal portions and a contact element connected to each of said spaced longitudinal portrons.

-8. An automatic breaker as claimed in claim 7, wherein said spaced longitudinal portions are mechanically interconnected by means of a roller.

9. An automatic breaker as claimed in claim 7, including an arcing horn connected to each said spaced longitudinal portions and wherein to preclude the interwelding of the arcing horns when moving towards each other, said horns include projections arranged below the working surfaces of the horns to be engageable with one another.

10. An automatic breaker as claimed in claim 1 including adjustable means for adjusting the contact pressure between said movable contact means and said stationary contact means, said adjustable means comprising a bushing secured to said breaker, a rod including opposite end portions, one of which is a head shiftably extending into said bushing, a nut adjustably secured to the other end portion of said rod, and a spring engaging said nut and said bushing, said other end portion of said rod being engageable with said movable member of said stationary contact means.

References Cited UNITED STATES PATENTS 3,092,699 6/1963 Latour 335'195 3,127,488 3/1964 Bodenschatz 335- 16 3,277,407 10/1966 Kobayasi 200-147X 3,420,971 1/1969 Aupetit 20 0-147X FOREIGN PATENTS 534,048 12/1954 Belgium 335147 1,259,118 3/1961 France 33516 46,194 1960 Poland 335--16 ROBERT K. SCHAEFER, Primary Examiner R. A. VANDERHYE, Assistant Examiner U.S. Cl. X.R. 200-147; 335-16