US2300884A - Circuit interrupter - Google Patents

Description

Nov. 3, 1942. s GANQ 2,300,884

CIRCUIT INTERRUPTER Filed March 24, 1941 WITNESSES: INVENTOR Herr/m1 S. 64110.

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Patented Nov. 3, 1942 omomr INTERRUPTEB Harlan S. Gano, Wilkinsburg, Pa, assignor to Westinghouse Electric 4; Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 24, 1941, Serial No. 384,907

14 Claims.

This invention relates to circuit interrupters in general and more particularly relates to circuit breakers of the type which are automatically operated instantaneously on heavy overloads and, after a time delay, on sustained overloads of lesser magnitude.

One object of the invention is the provision of a circuit breaker having an improved time-current operating characteristic.

Another object of the invention is to provide a circuit breaker having an electromagnetic tripping device controllable by a thermally responsive element in response to overload currents of less than a predetermined magnitude.

Another object of the invention resides in the provision of a circuit breaker having a tripping mechanism adapted to be operated by an electromagnet which has a movable core controllable by a thermally responsive element to control the tripping time of the breaker.

Still another object is the provision of a circuit breaker including a current responsive thermal element for varying the reluctance or pull of a trip magnet according to the magnitude of abnormal current conditions to control the tripping time of the breaker.

The novel features that are considered characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to structure and operation, together with additional objects and advantages thereof, will be best understood from the following detailed descriptionthereof when ,read

in conjunction with the accompanying drawing,

in which:

Figure l is a sectional view of a circuit breaker embodying the features of the invention, the breaker being shown in closed circuit position, and

Fig. 2 is a view, partly in section, showing a modified form of the invention.

In general, the illustrative embodiment of thev invention includes a movable contact normally sulating base It provided with side walls H and rent conditions of low magnitude, thus gradually reducing the magnetic reluctance until a predetermined point is reached at which the magnet operates an armature to trip the circuit breaker.

The gradual movement of the core into the magnet winding under the control of thether' mally responsive element provides a time lag in circuit is broken and cannot be reestablished until the thermally responsive element has cooled to a degree which permits said element to withdraw the core from the winding of the magnet,

unless the current has decreased to a point.

where the magnet is not energized sufiiciently to trip the breaker with the core partially within the winding.

The design of the magnet is such that on sudden heavy overloads or short circuits it will immediately attract the armature and trip the breaker before the bimetal has been heated. The circuit breaker includes a cup-shaped in- End walls It and I4 and a suitable cover plate I! complete the enclosure which houses the breaker mechanism. A pair of terminal oonnectors It and I1 secured on the opposite endsof the exterior of the closure project through the held in closed position relative to a stationary contact against the tension of an operating spring by a latch mechanism biased to latching position. The latch is adapted to be tripped by an electromagnet which is unresponsive to normal circuit conditions and to abnormal currents of low magnitude. A movable core is provided for the magnet, which core is normally restrained in a position withdrawn from the winding but which is caused to be moved into the winding under the control of avbimetal element which is thermally responsive to prolonged overload ourend walls l3 and II into the interior 0! the closure. The terminal I! at its inner end carries a stationary contact l8 with which cooperates a movable contact l9 mounted on one end of a floating contact bar 20. The other end of the bar 20 extends upwardly and is shaped to cooperate with a spring pressed latch 2| pivoted at 22. An operating spring 23 is compressed between the base It and the underside of the contact bar 20 at a point intermediate the ends thereof. The spring 23 is received in notches in the bottom of the bar and normally biases the contact bar 20 about the latching point as a fulcrum towards closed contact position. The bar 20 is normally retained in this position by the latch 2 I. When the latch is moved to release the bar, the spring 23 rocks the bar in a clockwise direction to open the contacts. 1

A U-shaped member 24 is disposed to slide inwardly and outwardly in guides provided therefor in the closure. The member 24 is provided with slots 24' and 29 which embrace and guide the floating contact bar 20. The U-shaped member 24 and the bar are pressed firmly together by a spring 25 tensioned between a projection on the member 24 and the bar 20.

The latch 2| is biased to latching position by a spring 24, the tension of which is adapted to be overcome and the latch tripped by the winding of an electromagnet 21, which under certain current conditions is controlled by a thermally responsive bimetal element 28 (to be later described). When the latch 2| is moved to unlatching position, the bar 20 is released and the a clockwise direction by a spring (not shown).

which spring is o! considerably less strength than the operating spring 22. when the bar 2| is operated by the spring 23, upon release oi said bar by the latch 2|, the U-shaped member .24 is thrust outwardly until its travel is arrested by contact of the cam portion 32 of the handle with the inner surface or the cover plate I.

in order to reset the breaker the handle is rocked clockwise to the limit or its movement. on its clockwise travel the cam portion 82 of the handle engages the outer end of the U-shaped member 24. thrusting said member inwardly until the latching nose oi the bar 2! passes the latching position, whereupon the spring 24 restores the latch 2| to latching position, the movement or the latch being limited by a projection 22 thereon striking a stop stud 84. To close,

the breaker mechanism the handle Iii is then rocked counter-clockwise, permitting the spring 22 to rock the bar 20 about its latching point as a fulcrum to close contacts "-42.

The winding 21 of the magnet and the bimetal element 2!, which comprises a straight strip of bimetallic material, are electrically connected in series relation in the circuit through the contacts of the breaker soas to be traversed by the current flowing in the circuit controlled by the breaker. The circuit extends from the terminal ll, wire I, winding 21 of the magnet, wire ll, bimetal element 2', flexible shunt conductor 31, contact bar 20, contacts I! and I! to the terminal II.

An armature ll plvotally mounted on the magnetic frame 38 of the magnet is normally biased against a stop stud 4ll by a spring 4|. When operated by the magnet the armature 3| strikes the projection ll of the latch 2| and moves the latch to released position, thus tripping th breaker.

The magnet is provided with a movable core 42 in axial alignment with the central opening through the winding 21. At its lower end the core 42 has a reduced portion 43 which engages in a slotin the free end of the bimetal element 2|. Ahead 44 formed on the extreme lower end of .the core 42 provides a convenient means whereby the tension or thebimetal element 28 normally restrains the "core 42 in its lower or withdrawn position against the attraction of the magnet under normal current conditions and by which the core 42 may be positively withdrawn from the winding of the magnet by the bimetal element upon cooling of the element following tripping of the breaker.

The core 42 is guided in its travel by a projection thereof extending through an opening provided therefor in a plate 46. The armature 39 is provided with a. clearance opening for the projection 45. A stop 41 formed on the base In limits the downward travel of the core 42.

For purposes of adjustment, the projection 45 may be a rod and the core 42 may be slidable thereon, being secured in its selected position by a set screw 60, as indicated in Fig. 2, the head 44' is on the rod 45 and the core 42 is adjustable on the rod relative to the head 44'.

. The tripping characteristics of the magnet may also be modified by placing a compression spring (Fig. 1) between the end of the core 42 and an adjusting screw 58 in the end of the central opening of the winding 21.

The parts are preferably so designed and ad- Justed that under normal current conditions and abnormal currents of less than a predetermined magnitude, with the magnet core 42 in its lower position, the force of the magnet is insuillcient to overcome the tension of the spring 4| and attract the armature 39 to trip the breaker. On short circuits and currents in excess of a predetermined magnitude, tor example, currents of more than approximately 10 times rated current, the magnet will immediately operate the armature I9 and interrupt the circuit irrespective of the position of the auxiliary core 42.

The bimetal element 2| normally assumes the position in which it is illustrated-and opposes upward movement of the core 42 under normal circuit conditions by its natural resiliency. A continued abnormal current below the predetermined magnitude however, heats the bimetal element and causes it to flex toward the magnet. During this flexing the bimetal element 24 permits the magnet to gradually draw the core into the magnet winding, thus gradually reducing the magnetic reluctance. At a predetermined point in the upward travel of the core, the reluctance of the magnetic field will be reduced to a point where the magnet pull is sumcient to overcome the tension of the bimetal 25 and the spring 55 and attract its armature I! and trip the latch 2|, causing the contacts "-49 to open and interrupt the circuit as obove described.

When the circuit is opened, the bimetal element 28 cools and gradually resumes its normal position, withdrawing the core 42 from the winding 21.

The extent and rate of movement of the core 42 is determined by the magnitude and duration of the abnormal current condition. On light overloads the bimetal 28 takes a relatively long time to heat up and cause movement of the core 42 into the winding 21. As the intensity of the overload increases, however, the time required to heat the bimetal decreases. This decrease in time is augmented by the increased pull of the magnet on the core. The several parts are so designed and calibrated that the point at which the magnet will trip the breaker may be accurately predetermined.

The circuit may be interrupted manually by operation or the handle 30 as set forth above. With the breaker in closed circuit position, the handle 20 is rocked clockwise to open the contacts, at which movement the portion 32 cams the member 24 inwardly, rocking the contact bar 20 clockwise about its latching point as a pivot a distance sufllcient to separate the contact I! from the contact IS. The flat end surface of 32 engages the outer face of the U-shaped member 24 to retain the bar 20 in open circuit position. Movement of the handle to the position in which it is shown causes the contacts to close under the action of the operating spring 2 In the modified form of the invention illustrated in Fig, 2 of the drawing, the armature l8 and the latch 49 may be made integral or may be su tably secured together to operate as a unit. In this form the armature l8 and latch 49 are pivoted at 50 on the magnet frame 38 and are intermediate the bimetal 28 and the core 42.

This lever is pivotally supported on brackets 54 (only one of which is shown) secured to the base ll. One end of the lever 53 is bifurcated to straddle the free end of the bimetal and the opposite end is slotted to'operatively engage an annular groove formed by the lower end of the core I! and the head 44' of the rod II. The bimetal, in this form of the invention, is arranged to flex downwardly when heated. The purpose of the lever 53 is to multiply the movement of the bimetal 2| as transmitted to the core 42, thus to increase the extent and rate of movement of the core. In this manner the time lag may be altered to change the time of tripping the breaker,

Longitudinal adjustment of the core 42 on the rod 45 may be made to vary the time at which the magnet becomes eflective to trip the breaker. Obviously if the core 42 is adjusted upwardly, the magnetic reluctance will, as the bimetal flexes in response to abnormalcurrents, be reduced more rapidly to the point where the magnet operates to trip the breaker.

The remaining structure of the breaker shown in Fig. 2 is identical to that shown in Fig. 1 and corresponding parts have been indicated by the same reference numerals in the two figures.

While the invention'has been disclosed in accordance with the provisions of the patent statutes, it is to be understood that various changes in the structural details thereof may be made without departing from some of the essential features of the invention. It is desired, therefore, that the language of the appended claims be given the broadest reasonable interpretation permissible in the light of the prior art.

I claim as my'invention: I

1. A circuit breaker including relatively movable contacts, operating mechanism for the contacts including a trip member movable to cause automatic opening of the contacts, an electroresponsive to overload currents below said pre-- determined magnitude to cause movement of the core to render the electromagnet operable to cause automatic opening of contacts, said thermally responsive means normally acting to oppose movement of the core.

3. A circuit breaker including relatively movable contacts,- releasable operating mechanism for automatically opening the contacts, means normally restraining the operating mechanism in closed circuit position, an electromagnet having an armature for releasing the operating mechanism, said magnet being operable to release the operatingmechanism in response to overload currents above a predetermined magnitude and normally inoperable to release said mechanism in response to overload currents below said predetermined magnitude, a magnet core normally withdrawn from the magnet, and a bimetal element normally, restraining said core in withdrawn position and operable in response to overload currents below the predetermined magnitude for causing movement of the core into the magnet a distance determined by the magnitude and duration of the overload current'traversing said bimetal element to render-the magnet operable to release said mechanism in response to overload currents below the predetermined magnitude.

l 4. A circuit breaker including contact operating mechanism, an electromagnet having an armagnet, an armature operable by the magnet to .an armature operable in response to overload currents above a predetermined magnitude to cause movement of said member toopen the contacts, said electromagnet being normally inoperable in response to overload currents below said predetermined magnitude, 9. core movable relatively to the electromagnet, and means thermally ing operable in response to overload currents for causing movement of the auxiliary magnetic means to reduce the reluctance to a point where the magnet will operate the armature, said bimetal element moving free of said auxiliary magnetic means during at least a part of the operation.

5. In a trip device for a circuit breaker, an I electromagnet having an armature biased to an unattracted position, said electromagnet having auxiliary movable magnetic means, a bimetal element having a lost motion connection with said auxiliary magnetic means and normally restraining said auxiliary magnetic means in one position, said bimetal element being thermally responsive to overload currents for causing the auxiliary ma netic means to be moved relative to the electromagnet an extent determined by the magnitude and duration of the overload current and by said lost motion connection to change the magnetic characteristics of the magnet.

6. A trip device for a circuit breaker including an electromagnet having a movable armature operable instantaneously in response to overload currents above a predetermined magnitude, auxiliary magnetic means movable relatively to the electromagnet to vary the magnetic pullof the electromagnet, a thermally responsive element operatively connected to the auxiliary magnetic means for causing movement of said auxiliary magnetic means a distance commensurate to the magnitude and duration of the overload cur- 5 rent, the thermally responsive element acting to restrain the auxiliary magnetic means against the magnetic pull.

7. In a trip device for a circuit breaker, the combination of a magnet winding, an armature movable to trip the breaker, a movable magnet core, and a bimetal element for positively moving the core in opposite directions.

8. A trip device for a circuit breaker including, in combination, a magnet, a winding ior said magnet, an armature cooperating with said magnet and movable to trip the breaker, a movable magnet core associated with said magnet, and a current responsive bimetal element operatively related to said core for moving the core in opposite directions.

ing, in combination, a magnet including a winding, an armature, adapted to be operated by the magnet to trip the breaker, a bimetal element thermally responsive to the current of the circuit, and means comprising a magnet core movable relative to the winding by the bimetal element according to current conditions for varying the magnetic reluctance to determine the tripping time of the breaker, said core being adjustable relative to the bimetal element to vary the operating characteristics of said device.

' 10. A circuit breaker including operating means including a trip member movable to cause automatic operation of .the circuit breaker, magnetic means operable in response to overload currents above a predetermined magnitude for operating the trip member, a thermally responsive element, auxiliary magnetic means controllable by the thermally responsive element to cause the magnetic means to operate the trip member on overload currents below the predetermined magnitude, and resilient means biasing the auxiliary magnetic means against movement adjustable to vary the operating characteristic of the magnetic means.

11. A circuit breaker including releasable operating mechanism to cause automatic operation of the breaker, a latch member movable to release the operating mechanism, an electromagnet operable in response to overload currents above a predetermined magnitude for operating the latch member, a bimetal element thermally responsive to overload currents below the predetermined magnitude, auxiliary magnetic means movable under the control of the blmetal element during only a portion of the movement of the bimetal element to cause the electromagnet to operate the latch member, and spring means biasing the auxiliary magnetic means against movement, said spring means being adjustable to vary the operating characteristics of the electromagnet.

12, In a circuit breaker, the combination of a magnet winding, an armature movable to hip the breaker, a magnet core movable toward and away from the winding, and an element thermally rel5 sponsive to the current of the circuit and having 9. A trip device for a circuit breaker includa lost motion connection with the core for controlling the movement of said core to determine the tripping time of the breaker, said core being adjustable relative to the thermal element to determine the extent of the lost motion connection.

13. In a circuit breaker, the combination or releasable operating mechanism to cause automatic operation of the circuit breaker, a magnet gs including a latch operable on overload currents above a predetermined magnitude to release the operating mechanism, a core movable within an opening in the magnet, a bimetal element thermally responsive to overload currents below a predetermined magnitude, and a lever operated by the bimetal element for causing movement of the core an extent commensurate to the magnitude and duration of the overload current to cause release of the operating mechanism.

14. In a circuit breaker, the combination of a magnet winding, an armature including a latch movable to trip the breaker, a magnet core including a rod extending axially through an opening in the winding, and time delay current responsive means including a lever intermediate the current responsive means and the core for moving the core toward and away from the winding under predetermined circuit conditions to cause the winding to attract the armature and trip the latch, the core being adjustably secured to the rod for adjusting the tripping time o! the winding. HARLAN S. GANO.

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