US2999141A - Circuit breaker - Google Patents

Description

Sept. 5, 1961 w. H. NASH ET AL CIRCUIT BREAKER 2 Sheets-Sheet 1 Filed Dec. 17, 1959 AfA/V- SePt- 5, 1961 W. H. NASH ET AL 2,999,141

CIRCUIT BREAKER Filed Dec. 17, 1959 2 Sheets-Sheet 2 52 vtorng/ United States Patent O 2,999,141 ClRCUIT BREAKER William H. Nash and Raymond J. Bronikowski, South Milwaukee, Wis., assignors to McGraw-Edison Company, Milwaukee, Wis., a corporation of Delaware Filed Dec. 17, 1959, Ser. No. 860,214 2 Claims. (Cl. 20G- 116) This invention relates to circuit breakers and, more particularly, to circuit breakers which have particular but not exclusive application to the protection of electrical apparatus such as transformers.

Distribution class transformers are often provided with circuit breakers which open the secondary circuit upon the occurrence of a fault across the secondary leads or when long continued overloads heat the transformer to a point where there is likelihood that its insulation will fail. For this purpose, therefore, circuit breakers of this type are provided with thermal and overcurrent responsive elements adapted to open the circuit breaker contacts upon the occurrence of such overloads.

It has been found desirable, however, in certain applications where continuation of service is imperative that, such circuit interrupters operate only upon the occurrence of a fault.

It is an object of the invention to provide a new and improved circuit breaker for use in oil-immersed transformers which is responsive solely to fault currents in the secondary leads or extreme overloads.

It is another object of the invention to provide for use in an oil-immersed transformer a circuit breaker having a thermal element responsive to the flow of load current wherein means are provided to compensate for variations in ambient oil temperature.

These and other objects of the invention will become apparent from the detailed description of the invention taken in view of the accompanying drawings in which:

FIG. 1 is a vertical elevation view partly in section of the circuit breaker embodying the instant invention;

FIG. 2 is a front view of the circuit breaker shown in FIG. 1;

FIGS. 3, 4 and 5 show the circuit breaker operating mechanism in certain of its positions;

FIG. 6 is a top view of the circuit breakers temperature responsive elements; and

FIG. 7 is a view taken along lines 6-6 of FIG. 5.

In general terms the invention comprises a circuit breaker for protecting electrical apparatus immersed in dielectric oil and having a first thermal-current responsive means operable to open the circuit breaker contacts and disposed beneath the surface of said oil and in circuit with said apparatus whereby it is subjected to the current ilowing in said apparatus and the temperature of said oil. A second thermal-current responsive means, connected to operate in opposition with said irst means, is also disposed beneath the surface of said oil but electrically insulated from said apparatus so that at least a portion of the effect of said oil temperature ou said irst means is cancelled.

The circuit breaker chosen to illustrate the instant invention is a 2-pole automatic trip-free device which is illustrated in detail in copending application Serial No. 831,424, and which is assigned to the assignee of the instant invention.

Referring to FIGS. l and 2, the circuit breaker mechanisrn is shown mounted on a suitable base 10 of moulded insulating material and each pole includes a contact assembly 12 and an overcurrent responsive assembly 14. A common operating and latch assembly 16 holds each of the contact assemblies 12 in closed position and is operable to release said contact assemblies upon the actuation of either of the overcurrent assemblies 14.

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Each of the Contact assemblies 12 includes a movable contact member 22 and a cooperating fixed contact 24 which is mounted on base it). A U-shaped metallic frame member 26 is rigidly secured to the base and has a transverse pivot pin 27 mounted near its lower extremity for pivotally supporting a contact carrier member 2S formed of a suitable molded insulating material and which carries each of the movable contact members 22 in a contact housing 29 disposed at each of the opposite ends of a transverse connecting portion 30 so that the movable contact members 22 are operated in unison.

As seen in FIGS. l, 6 and 7, the overcurrent responsive assemblies 14 each include a pair of parallel bimetallic elements 32 and 33 which are atlixed at one end to the rear of base 10 by rivets 34. The free ends of elements 32 and 33 are each connected to the upper surface of the lower-most portion 36 of an upwardly extending angular insulating link 35 and electrically connected by a conductive bridging member 40.

A second pair of parallel bimetallic elements 32A and 33A are disposed below said first pair' and in opposed relation thereto. rThe rear ends of each of the second pair of elements 32A and 33A are also secured to the base l0 by rivets 34 and are electrically insulated from members 32 and 33 by a cylindrical insulating block 33 disposed between said ends and an insulating sleeve 39 surrounding rivet 34. In addition, the opposite ends of members 32A and 33A are connected to the lower surface of link portion 36 to provide a mechanical connection between the free ends of the opposed pairs of bimetallic elements while electrically insulating them.

Carried at the upper end of insulating link 35 is a rearwardly extending trip bracket 41 for threadably rew ceiving an adjusting trip pin 42 that engages the upper surface of a latch plate 43 pivotally mounted at 44 on frame 26. The latch plate 43 has a depressed central portion 45 which carries an L-shaped latch member 46.

Referring now in particular to FIGS. l, 2, 3, 4 and 5, the operating and latch assembly 16 is shown to include an inverted U-shaped operating member Sti having an oiset transverse connecting portion Si at its upper end and having its lower ends S2 pivotally received in recesses 53 formed in base member i0. A latching mechanism 55 is disposed between the legs of operating member 5() and includes a latch arm 57 which carries a latch tip 58 at one end and which is pivoted at its other end around a fixed axis by means of a transverse pin 6i? extending between the upright portions of frame 26. An arc shaped link 62 is pivotally connected at one end to the latch arm 57 and at its other end to an inverted L-shaped holding element 64 which is pivotally mounted on a transverse pin 65 r'ixed in frame 2e. Holding element 64 is connected to movable contact carrier 23 by a toggle linkage 67 comprising a pair of parallel upper toggle links 68 which are pivotally connected at 69 to the midpoint of said element and a lower toggle link 71 pivotally connected at 72 to movable contact carrier 2S. rihe other ends of these toggle links are pivotally connected together by means of a knee pin 7d. A pair of parallel overcenter springs 76 connect knee pin 74 to the transverse portion 51 of operating member 5?.

The operation of latching mechanism 16 will now be described with regard to FlGS. l, 2, 3, 4 and 5. As shown in FIG. l the arm 73 of an operating crank '79 is rotatable in the plane of the drawing by an operating handle (not shown) disposed in the exterior of the apparatus being protected. Arm 78 is connected to operating member Si) by means of an operating rod Si) and an operating link 82 which threadably receives the lower end of operating rod Si) in one end and which is pivotally connected at its other end to the transverse connecting portion 51 by means of a U-shaped bracket 83 and a pin 84.

FIG. 3 shows the operating mechanism in its uulatched position with the circuit breaker contacts open. In order to close the circuit breaker contacts from this position the operating member 50 must first be rotated in the clockwise direction until the mechanism is latched as shown in FIG. 4 and then rotated in a counter-clockwise direction closing the contacts as shown in FIGS. l and 5.

More specifically, clockwise rotation of arm 78 pivots operating member 50 in a clockwise direction within recesses 53. As member 5t) pivots, its transverse portion 5l. forces holding element 64 to rotate about pin 65 so that its upper end is moved downwardly and to the right as viewed in FIG. 3. A link 62 transmits the movement of holding element 64 to latch arm 57 thereby rotating it in a clockwise direction around pivot pin 60. As latch arm 57 rotates latch tip 58 engages latch 46 to pivot latch plate 42 in a counter-clockwise direction around its pivot points 43. After latch tip 5S has cleared latch 46, the latter is returned to its position shown in FIG. 4 by a biasing spring 86 which extends between upwardly extending arm 87 on latch plate 43 and bracket member 88 rigidly secured to the base 10. The return of latch plate 42 to its initial position secures the latching assembly in its latched position with the contacts open as shown in FIG. 4.

In order to close the contact assembly l2 after the latching assembly has been made rigid, operating arm '78 is rotated in a counter-clockwise direction to pivot operating member Si) in a counter-clockwise direction in recesses 53. As operating member 50 rotates the upper ends of overcenter springs 7S are moved to the left as viewed in FIG. 4 by transverse portion S1, while their lower ends momentarily remain stationary. Because the upper ends of springs 76 are rotating in an arc that is longer than their initial length, they will be extended thereby storing energy for rapidly closing the contacts and separating them rapidly upon tripping.

When the line of action of overcenter springs 76 passes the upper pivot point 69 of toggle link 68, they will become overcentered causing knee pin 74 to snap from its position shown in FIG. 4 to its position shown in FIGS. l and 5. This brings lower link 7l into toggle with upper link 68 thereby snapping the movable contact carrier 23 in a counter-clockwise direction about pivot pin 27 to close movable contact 22'.

The operating sequence during manual opening of the main contacts I2 is the direct opposite of the closing operation just explained. Here the operating arm 7S is pivoted in a clockwise direction thereby Vmoving the upper end of operating member 5@ to the right as viewed in FIG. 1. When the line of action of overcenter springs 76 passes pivot point 69, the toggle will be broken and knee pin 74 will snap from its position shown in FIGS. l and 5 to its position shown in FlG. 4. The latch arm S7, however, will remain latched as shown in FIG. 4.

Referring now to FIGS. l, 2 and 6, the electrical current path through each pole of the device is shown to be from a irst conductive member 90 secured to iixed Contact 24; through the fixed and movable contacts 24 and 22; through the second conductive member 9i secured to movable contact 22; through a tlexible conductive member 92 secured at one end to conductive member 91 and at its other end to a third conductive member 93 aiiixed to bimetallic element 32; through conductive member 4t) and bimetallic member 33 and nally to a fourth conductive member 95 connected to the second of the upper bimetallic elements 33. It can be seen, however, that the insulating members 36, 38 and 39 prevent any current ilow in bimetallic elements 32A and 33A.

If the device is used to protect a distribution transformer, it is normally mounted below the surface of dielectric oil 96, as shown in FIG. l, by means of a bracket member 97 secured to the under side of base member 10. As a result, the bimetallic elements 32, 32A, and 33 and 33A, are exposed to the heat of this ambient oil. Also, bimetallic elements 32 and 33 are each subjected to heat produced as a result of their impedance to the flow of load current. However, because bimetallic elements 32A and 33A are electrically insulated from bimetallic elements 32 land 33 they are subjected only to the heat of the oil 96.

Bimetallic elements 32 and 33 are arranged so that upon the occurrence of an overload or the heating of oil 96 they tend to deflect downwardly as viewed in FIG. l. Bimetallic elements 32A and 33A are so arranged, on the other hand, that they will tend to deflect upwardly in opposition to bimetallic elements 32 and 33 when oil 96 becomes heated. It can thus be seen that by suitably proportioning the bimetallic elements, any tendency of bimetallic elements 32 and 33 to deflect downwardly as a. result of an elevated oil temperature, can be cancelled by the corresponding tendency of bimetallic elements 32A and 33A to deflect upwardly. However, because bimetallic elements 32A and 33A are electrically insulated from the load current, the entire assembly will deflect downwardly as a result of the heat developed in elements 32 and 33 caused by the ow of the load current.

As bimetallic elements 32 and 33 detiect downwardly, as viewed in FIG. l, there will be a corresponding downward movement of trip pin 42 to rotate latch plate 43 in a counterclockwise direction around pivot 44. If the load current exceeds the minimum setting of the device this rotation of latch plate 43 will be suliicient to release latch arm 57 so that overcenter springs 76 are free to contract, moving knee pin 74 from itsV position shown in FIGS. l and 5 to its position shown in FIG. 3, thereby breaking the toggle linkage 67. This rotates the movable contact carrier 28 in -a clockwise direction from its closed to its open position shown in FIG. 3 whereby the circuit is interrupted. The movement of knee pin 74 also rotates holding element 64 and latch arm 57 in a clockwise direction. Thus, the tripping action just described returns each of the members of the operating assembly I6 from their positions shown in FIGS. 1 and 5 to their original positions shown in FIG. 3.

It can be seen from the foregoing discussion that regardless of the temperature of oil 96 the latchjng'mechanism can only be tripped upon the occurrence of a fault current. This insures that service will continue during periods of expected overload.

The amount of downward deflection of the bimetallic elements for any given current value, and hence, the magnitude of the overcurrent necessary to trip the device, may be adjusted by varying the initial rotation of latch plate 42 through the agency of the threaded trip pins 40.

While the invention has been described in relation to one particular ytype of circuit interrupter, it will be understood that the'invention has application as well to other types of circuit interrupters utilized to protect oil-immersed electrical apparatus.

1. In a circuit interrupter for protecting an electrical transformer immersed in dielectric oil, the combination of a base, fixed and movable contact means mounted on said base, latch means for holding said movable contact means in closed position, a first bimetallic element in circuit with said transformerV and immersed beneath the surface of said dielectric oil, said first bimetallic element being secured near `one of its ends to said base and having its other end coupled to said latch means and operable upon a predetermined deflection to release said movable contact means, a second bimetallic element secured at one end to said base and disposed beneath the surface of said oil in substantial parallelism with said first bimetallic element and electrically insulated therefrom, electrical insuating means connecting the other ends of each of said bimetallic elements, said first and second bimetallic elements having substantially identical thermal characteristics and being arranged for deflection in opposite directions, whereby the elect of said oil temperature on said rst bimetallic element is substantially cancelled.

2. In a circuit interrupter for protecting an electrical transformer immersed in dielectric oil, the combination of "a base, Xed and movable contact means mounted on said base, latch means for holding said movable contact means in closed position, a first linear bimetallic element in circuit with said transformer and immersed beneath the surface of said dielectric oil, said rst bimetallic element being affixed at one end to said base and having its free end coupled to said latch means and operable upon a predetermined deflection to release said movable contact means, a second linear bimetallic element secured at one end to said base adjacent the xed end of said iirst bimetallic element and disposed beneath the surface of said References Cited in the le of this patent UNITED STATES PATENTS 1,952,040 Frank et al Mar. 30, 1934 2,416,170 Gallo et al Feb. 18, 1947 2,757,360 Dripps July 31, 1956 2,835,766 Few May 20, 1958

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