US1820709A - Circuit breaker - Google Patents

Description

Aug. 25, 1931. K. c. RANDALL CIRCUIT BREAKER Filed NO'v'I 27, 1929 2 SheetsShee INVENTOR Karl 6. Eanaa/l ATTORNEY Patented Aug. 25, 1931 UNITED STATES PATENT OFFICE KARL C. RANDALL, OF EDGEWOOD, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & muraerunme COIPANY, A CORPORATION OF PENNSYLVANIA CIRCUIT BREAKER Application fled llovember 27, 1929. Serial No. 410,113.

My invention relates to circuit breakers responsive portion of the trip mechanism may and particularly to enclosed oil-filled circuit breakers having automatic tripping means for causing such circuit breakers to open under predetermined current conditions.

Heretofore bushing or ring type current transformers could be practically used in conjunction with trip coils to control high-tension circuit breakers only where the current values exceed certain limits and were not practical for overload and short-circuit protection below circuit-breaker ratings of about fifty amperes. It was, therefore, necessary to employ other means for controlling high-tension circuit breakers of relatively low current ratings. For this purpose, wound-primary type transformers are usually employed, but these have the disadvantage of requiring relatively expensive insulations and occupy considerable space exterior of the circuit-breaker housing.

An object of my invention is to provide a control device for high-tension low-current circuit breakers wherein, a current transformer immersed in oil within the circuitbreaker housing is employed toenergize a thermal elementthat is operative, on relatively low currents, for tripping the latch mechanism of the circuit breaker.

Another object of my invention is to probreaker when an objectionable overload has endured for a predetermined time.

A further object of my invention is to provide a circuit breaker wherein the trip mechanism may be energized by a relatively small to current supplied by a current transformer associated with one of the circuit-breaker con- {5 characteristics wherein the trip mechanism may be rotected against destructive forces induced y sudden overload or short-circuit surges.

A further ob ect of my invention is, to pro- 60 vide a circuit breaker wherein the currentbe enclosed within the circuit-breaker housing and which is relatively compact and may be carried upon the bushing of the stationary contact or upon the moving contact.

A further object of my invention is to provide a circuit breaker having a thermal-responsive trip mechanism that will be infiuenced by current proportional to that flowing through the circuit-breaker contacts and which will not be responsive to changes in ambient temperature.

A further object of my invention is to pro vide a circuit breaker with a trip mechanism to be energized by a current transformer and wherein the usual expensive insulation may be dispensed with by placing the transformer in the circuit-breaker housing and immersing it in the usual insulating fluid within the housing.

These and other objects that will be made apparent throughout the further description of my invention are attained by means of the apparatus hereinafter described, and illustrated in the accompanying drawings, wherein Figure 1 is a vertical section through a circuitbreaker embodying features of my invention,

Fig. 2 is a vertical section, on an enlarged scale, showing a detail of the current-responsive trip mechanism shown in Fig. 1.

Fig. 3 is a transverse section through the device shown in Fig. 2, taken on the line IIIIII thereof,

F i 4 is a vertical section through a circuit breaker disclosing a modified form of the thermal-responsive trip mechanism, and

Fig. 5 is a wiring diagram of a modified control circuit.

Referring to the drawings and particularly to Fig. 1, the circuit-breaker apparatus comprises a metal housing 8 containing insulating fluid 9, such as oil, and provided with a metal cover 11 that is fixed to the housing by means of bolts 12. The cover 11 supports a pair of contact bushin s 13 which support stationary contacts 14 aving exteriorly projecting terminals 15 to which the feed conductors 16 are connected.

The stationary contacts 14 are adapted to be connected by a movable bridging contact device 17 that is provided with an operating being connected by a conductive cable 21 that is connected to the terminals 22 of the primary coil 23 of a wound-type transformer24. The transformer 24 is mounted upon the in sulating bar and its purpose will hereinafter appear. 7 p

The nature of the contact between the stationarycontact jaws-14 and the contact blades 19 of the bridging contact 17 is such that,

.when the rod 18 is released, the bridging contact 17 is caused to fall away from the g -contacts 14 under the influence of gravitational force. a

The bridging contact device 17 is retained in closed position by means of a latch bar 25 that engages a notch 26in the operating rod A urpose bf my invention is to provide a simple and inexpensive means for tripping the circuit breaker to open position, inbresponse to an overload condition, after an overload has persisted in the circuit a predetermined time.

Heretofore, high-tension low-current circult breakers have been opened by'trip-coil .devices energized-by transformers mounted exteriorly of the circuit breaker and requiring relatively expensive insulation. In order to reduce the cost of the-trip mechanism,

" through an opening 33 therein and is brought into operative relation to a toglgle link contype is mounted u a transformer 24 of a simple wound-primary within the circuit-breaker tank or casing.

order that the circuit breaker may be tr pped to open position under predetermmed current conditions, I have provided a tri which projects, exteriorly of the cover 11 stituting a part of the trip mec anism heremafter described.

bracket that is mounted upon the cover 11 aiid'is actuated by a bell-crank lever 35 pivotally mounted on the bracket. The lever 35 is loosely connected to a vertical trip rod *3fi slidably mounted in a guide 37, the rod being pivotedvto the knee pivot'38 of a pair to the ends of the links 39 and41, serves 1 of toggle links 39 and 41 that are movably mounted, by slot-and-pin connections 42,

l upon the. bracket" 34.

An over-center spring 43, that is connected to bias the knee .of the pivot toward either an upward position, as shown, or .adown-- ward position into engagement with theiup 26 and to thereby retain the shaft 18 in closed n the movable circuitbreaker contact which is immersed in the oil rod 32, made of'insulating material, 7

32 is of such length that, when the bridging contact member 17 is in closed position, the upper end thereof lies directly beneath the overhanging portion of the toggle link 41, and a slight upward movement thereof will cause the knee pivot 38'0f the toggle to move below the above-noted center line, at which time, the spring 43 will cause the toggle to collapse downwardly until the knee thereof rests upon the end of the resetting pin .44. V

- The enlarged end of the release rod engages the horizontal arm of the bell-crank lever 35' and causes withdrawal of the latch 25 and subsequent opening of the contact member; 17 which falls away from the stationary contacts 19. As the shaft 18 drops, the link 46 causes the toggle to move resetting pin which resets the toggle. \Vhen the contact member 17 is moved to closed position, the spring 47, connected to the lever 35 causes the latch to be moved into the notch ,(position. a

With particular reference to Figs. 1, 2 and 3, it will be seen that the trip rod 32 is mounted upon a pair of flexible diaphragms 48 and 49 that are supported by a "cylindrical casing 51 to serve to so seal the ends thereof that the liquidwithin the circuit breaker housing cannot enter within the casing 51, which is mounted upon the movable bridging contact member 17.

Hbimetal element 52; of U-shape, and hav-' ing a pair of terminals'53 and 54, is mounted in horizontal position within the casing 51,

the terminals 53 and 54 extending through an insulating bushing 55 in the wall of the I f casing, as indicated in Figs. 2 and 3. The The latch 25 1s shdably supported in a terminals are respectively connected to the terminalsof a secondary winding 56 of the transformer 24.' The current induced therein passes through the bimetal element 52 and is substantially proportional to that flowing through the winding 23 and the bridging contact device 17.

A second bimetal element 57 'is mounted ,upon the casing 51 and interiorly thereof and .directly. opposite the bimetal element 52, as-

indicatedjnF 2 and 3. The bimetal element-52 1s so positioned' that the free end thereof is deflected upwardly when heated to a predetermined temperature, while the .bimetal element 57 isso positioned that .a tise nected to the trip rod 32 by means of a yoke 58 pivotally mounted uponthe trip rod and having downwardly extending fingers 59 and 61 that respectively engage the bimetal elements 52 and 57. Since the rod 32 is connected to the diaphragms '48 and 49, which have substantially equal external pressure thereon, the rod 32 is free to move in response bi; movement of the bimetal elements 52 and Since, ordinarily, the free end of the bimetal element 52 moves upwardly the same distance as the free end of the bimetal element 57.moves downwardly in response to a rise in ambient temperature, substantially no movement of the rod 32 will result l'rom variations in the ambient temperature of the control mechanism. However, should an abnormal current flow through the circuit breaker and the bridging contact device ill, a correspondingly increased current will flow through the bimetal element 52 which is connected to the secondary transformer winding 56.

At such time, the free end of the bimetal element 52 will move upwardl while the free end of the bimetal element 5 remains practically stationary, causing a suflicient upward movement of the rod 32 to trip the toggle and thereb release the operating shaft 18 to permit t e circuit-breaker contact device 17 to fall to open position.

The bimetal element 52, preferably, may have inverse time characteristics and may be calibrated to cause the circuit breaker to open 1 when an overload of predetermined proporti'ons has endured for a predetermined time.

7 It will be noted that the current-responsive device is relatively simple in construction and, because of its compact proportions may be carried conveniently upon the bridging contact and immersed in the fluid within the circuit-breaker tank. The control device, being thus enclosed, isprotected from contact with extraneous objects without requiring special coverings, and tampering therewith is recluded.

urrent transformers for high-tension service, such as are usually emplo ed with high-tension low-current circuit reakers, are placed in separate tanks and require special, relatively expensive insulation and are relatively large. By immersin the transformed in the insulatin fluid within the circuit-breaker housing, t e transformer parts may be reduced in size, and no special insulation is required. Consequently, the size and cost of the transformer may be materially reduced.

Referring to Fig. 4, a modified form of con trol mechanism for a circuit breaker similar to that shown in Fig. 1, is illustrated. The trip mechanism, which is entirely immersed in the insulating fluid within the tank, is similar to that shown in Fig. 1, but the trans former and thermal device are mounted upon one of the insulating terminal bushings.

The advantage of this construction resides in the removal of all control mechanism from the bridging contact device, thereby reducing the weight and the inertia of the movable contacts and permitting of high-speed operation. Furthermore, all of the tripping mech- .anism is enclosed within the tank and immersed in the insulating fluid, thereby affording complete protection to such mechanism.

The current transformer 24 for energizing terminal and the contact 14, respectively,

in such manner that all of the current assing through the circuit breaker passes trough the primary winding. The operation of the circuit breaker is substantially the same as that of the breaker shown'in Fig. 1.

In Fig. 5, I have shown a means for protecting the bimetal element against abnormal curthe bimetal element 52 is mounted upon the r rent surges that would be injurious to it,

which comprises a reactor 66 for shunting the bimetal element. Under normal operating conditions, the current is so divided that it flows mainly through the bimetal element but, when a heavy surge is induced in the secondary winding 56 of thetransformer, the core of the reactor becomes saturated and permits the main portion of the current to pass through the coil 67 of the reactor and thus d1- vert destructive currents from the bimetal element.

While I have illustrated several embodiments of my invention, it will be apparent to those skilled in the art that various changes, modifications, substitutions, additions and omissions may be made in the apparatus illustrated without departing. from the spirit and scope of my invention, as set forth in the appended claims.

' claim as my invention:

1. The combination with anenclosed circuit breaker having a casing, a movable contact member within the case and a means carried by the casing for. releasably retaining the said member in closed position, of a current-responsive means for actuating the releasing means in response to predetermined current conditions, carried by the movable contact member, and so movable thereby, that it is placed in operative relation to the said releasing means when the contact member is in closed position.

2. The combination with a circuit breaker having a movable contact member and a means for releasably retaining said member in closed position, of a current-responsive member carried upon said member and operated by current induced by that passing through the contact member for actuating the retaining means.

3. The combination with a circuit breaker havlng a pair of relatively movable contact members and a means for releasably retaining the contact members in engaged position, of a current-responsive member carried upon one of said contact members and operated by current induced by that passing through one of the contact members for actuating the releasing means.

4. The combination with an enclosed circuit breaker having a movable contact member immersed in liquid and a means for releasably retaining said contact member in closed position, of an enclosed current-re- 'sponslve device mounted upon the lmmersed contact member and energized by current "passing through the contact member for actuating the retaining means.

5. The combination with an enclosed circuit breaker having a movable contact member and a releasing member mounted upon the enclosure for releasably retaining the a transformer within the tankand immersed in the insulating fluidfor-energmmg the 52nd current-responsive means.

8. A circuit breaker comprising a tank containing insulating fluid, a pair of relatively. movable contact members within the tank and immersed in the insulating fluid, means for releasably retaining the contact members in closed position, a current-responsive element immersed in the insulating fluid for, releasing the retaining means, and a transformer within the tank for energizing the current-responsive means.

9. A circuit breaker comprlsing a tank containing insulating fluid, a pair of relatively.

movable contact members within the tank and immersed in the insulating fluid, means for releasably retaining the contact members in closed position, a current-responsive element immersed in the insulating fluid for releasably retaining the contact members in 95 closed position, a current-responsive element for releasing the retainin means; and'a transformer within the tan for energizing the said current-responsive means.

In testimony whereof, I have hereunto subscribed my name this 21st day of November, 1929. KARLC. RANDALL.

contact member in closed position, of a current-responsive member carried upon the movable contact member and movable therewith into operative relation to the releasing member when the contact member is moved to closed position.

6. A circuit breaker comprising a housing having a cover, a contact fixed to'the cover,

' a movable contact within the housing for engaging the first contact, means mounted on the cover for releasably retainin the movable contact in closed position, an a currentresponsive means for actuating the releasing means and carried upon the movable contact and operative] associated with the releasing means only w 1811 the movable contact is in closed position.

7. A circuit breaker comprising a tank containing insulating fluid, a pair of relatively movable contact" members within the tank and'immersed in the insulating fluid, means for releasably retaining the contact members in closed position, a current-responsive elen5- ment for releasing the retaining means, and

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