US2937251A - Circuit breaker - Google Patents

Description

CIRCUIT BREAKER Filed March 14, 1956 CIRCUIT BREAKER Albert R. Cellerini, Beaver, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 14, 1956, Serial No. 571,534

9 Claims. (Cl. 200-88) This invention'relates to circuit'breakers and more particularly to circuit breakers of the type which are tripped instantaneously on overload currents of predetermined magnitude and after a time delay on lesser overload currents.

An object of the invention is to provide a circuit breaker embodying an iimprovedtrip device which provides a relatively short time delay in tripping the breaker on motor starting currents and instantaneous tripping in response to short circuit currents.

Another object of the invention is to provide a circuit breaker embodying an improved electromagnetic trip device having an armature operable to trip the breaker, in which a thermally responsive element blocks the tripping operation of the armature for a relatively short time delay on motor starting currents and permits instantaneous tripping operation of the armature in response to short circuit currents.

" The inventioii'both as to structure and operation, together with additional objects and advantages thereof, will be best understood from the following detailed description thereof when read in conjunction with the accompanying drawing.

In said drawing:

Fig. 1 is a vertical sectional view through a circuit breaker embodying the principles of the invention.

Fig. 2 is a top plan view with the breaker cover re moved showing the trip device for one of the poles of the breaker.

Fig. 3 is a diagrammatic view of the tripping electromagnet showing the flux paths.

The invention is illustrated as applied to a circuit breaker having an operating and contact mechanism of the typefully disclosed in Patent No. 2,419,125, issued April 15, 1947 to Hiller D. Dorfman and Gerald J. Freese and assigned to the assignee of the instant invention- The circuit'breaker is of the three-pole type and since the poles are the same, only the center pole, in which the operating mechanism is disposed, will be described. The circuit breaker comprises generally a base 11 and cover 13 of molded insulating material, a stationary contact 15, a movable contact 17, an operating mechanism indicated generally at 19 and a trip deviceindicated generally at 21.

The stationary contact 15 is mounted on the inner end of a conducting strip 23 which has a terminal connector 25 at its outer end. The movable contact 17 is mounted on a movable switch arm 27 which is pivoted at 29. The operating mechanism 19 consists of a releaseable member 31 pivoted at 33 and operatively connected to the switch arm 27 by a pair of toggle links 35 and 37. The knee of the toggle 35-37 is connected by means of four overcenter operating springs 39, only two of which are shown, to a pivoted operating handle 41 which is movable between an on position and an off position toefiectmovement of the switch arm 27 to the closed and open positions in'a Well-known manner. When 2,937,251 ,Pe e e ay 17, 1960 the circuit breaker is in the closed position, the toggle 35-37 is in an overset position and holds the switch arm 27 in the closed contact position. When the circuit breaker is in the closed position and the releaseable member 31 is released, it causes collapse of the toggle 3537 and movement of the switch arm 27 to the open position. The mechanism is reset and relatched by movement of the operating handle 41 to the ofi position. Thereafter, the contacts are closed by movement of the handle to the on position.

Only a brief description of the operating mechanism and its operation has been given. For a fuller understanding of the operating mechanism, reference may be had to the previously mentioned Patent No. 2,419,125.

The releasable member 31 is releasably held in its I operative position, as shown, by engagement of the free end thereof with a latch 43, which is mounted on a pivoted trip bar 45 that is common to all of the poles of the breaker and which may be operated by the trip device 21 of any pole of the breaker to effect release of the releasable member 31. The trip device 21 comprises generally an electromagnet 47 and a bimetal element 49. The electromagnet consists of a fixed angular magnet yoke 51 of magnetic material having a fixed core 53 rigidly secured thereto about which is Wound an energizing coil 55. A pole piece 56 is rigidly mounted on the upper end of the fixcd'core 53. The lower end of the coil is connected to a heater element 57 having a reduced section on which is rigidly mounted the lower end of the bimetal element 49. The other end of the heater element 57 is connected, by means of a connector 59 and a flexible conductor 61, to the. movable contact member l7.

The upper end of the coil 55 is rigidly secured to the inner end of a conductor 63 at the outer end of which is mounted a terminal connector 65. Mounted on the upwardly extending portion of the yoke 51 is an angular bracket 67 of non-magnetic materialhaving an opening therein in which is pivoted an armature 69 provided with projections 71 and 73. The projection 71 extends downwardly and has an insulating member 75 mounted on the lower end thereof which, upon operation of the armature 69, engages a projection 77 on the trip bar 45 and actuates the latter to effect release of the releaseable member 31. Mounted in the projection 73 of the armature 69 is an adjusting screw 79 which has a latch portion 81 disposed to engage a latch surface 83 on the upper end of the bimetal element 49. The magnetic air gap may be varied by turning an adjusting screw 85 in the horizontal portion of the bracket 67. The screw 85 provides an adjustable stop against which the armature 69 is biased to its unattracted position by a spring 87 tcnsioned between the bracket 67 and a bracket 89 of magnetic material secured to the armature 69.

When the circuit breaker is closed to start a motor, the sudden rise in current, several times normal running current, required to start the motor energizes the electromagnet 47 which immediately attracts the armature 69. Immediate tripping action of the armature, however, is blocked by engagement of the latch portion 81 of the adjusting screw 79 with the latch surface 83 on the free end of the bimetal element 49. The motor starting curirent flowing through the heater element 57 indirectly heats the bimetal element 49 which, when heated a predetermined amount, bends to the left toward the pole piece 56. When the current is reduced to its normal running value, the heating of the bimetal element 49 continues at a reduced rate, but the heating of the bimetal element in response to normal running current is suflicient to maintain the bimetal deflected to a position where it is clear of the latch 81 so that the armature 69 is free to instantaneously trip the breaker in response to overload currents occurring during motor running. Also,

when the current is reduced to its normal running value, the spring 87 returns the armature 69 to its unattracted position without having tripped the circuit breaker. If, however, the overcurrent persists, the bimetal element 49 will continue to deflect and, after a time delay, the bimetal element will release the armature 69 and the member 75 will engage the projection 77 on the trip bar 45 and cause the latter to release the releasable member 31 and effect automatic opening of the circuit breaker.

The trip device responds to overcurrents of short circuit magnitude to instantaneously trip the breaker. In the event of a short circuit current occurring during the motor starting period, the free end of the bimetal element 49 will be attracted toward the pole piece 56 clear of the latch portion 81. The electromagnet 47 has two flux paths indicated at A and B in Fig. 3. The path A is the conventional flux path in magnets of this type while the path B is completed through the bimetal element 49, two air gaps G1 and G2 and the pole piece 56 at the top of the fixed core 53. The bimetal element 49 is flexible so that when the magnet is energized in response to excessive overload currents or short circuit currents of approximately to times rated current, the free end of the bimetal element will be attracted to the end of the pole piece 56. This permits an immediate full stroke of the armature 69 to instantaneously trip the breaker. The air gaps G1 and G2 are such that the bimetal element 49 will not be magnetically deflected on overcurrents below approximately 15 times rated current.

The characteristics of the bimetal element and the heater may be selected so that, should an overcurrent of, for instance, 100% to 150% of normal running current occur, the bimetal element 49 will be heated and will deflect sufliciently to permit magnetic tripping after a short time delay.

The invention provides a circuit breaker for motor starting purposes embodying an electromagnetic trip device which trips the breaker instantaneously on short circuit currents, but which includes thermally responsive means providing a short time delay in the magnetic tripping of the breaker in response to high initial motor starting currents, thereby permitting motor starting without tripping the breaker. The trip device also functions to trip the breaker after a short time delay in response to predetermined overcurrents occurring during normal running of the motor.

Having described the invention in accordance with the provisions of the patent statutes, it is to be understood that various changes and modifications may be made in the structural details and combination of elements disclosed without departing from thespirit of the invention.

I claim as my invention:

1. A circuit breaker having relatively movable contact means and operating means operable to effect automatic opening of said contact means, a trip member movable to a tripping position to release said operating means, electromagnetic means having an armature normally disengaged from said trip member and operable to engage and move said trip member to tripping position, a bimetal element having one end supported and the other end free, the free end of said bimetal element being disposed in a position where it is engageable by said armature in a direction longitudinally of said bimetal to normally rigidly block tripping movement of said armature, and said bimetal element deflecting when heated a predetermined amount in response to overload currents to release said armature after a relatively short time delay to permit said armature to engage and actuate said trip member to said tripping position and effect tripping of said breaker, and said magnetic means when energized by excessive currents attracting said bimetal to permit said armature to engage and instantaneously move said trip member to said tripping position to effect tripping of said circuit breaker.

2. A circuit breaker having relatively movable contact means and operating means releasable to effect opening of said contact means, a trip member movable to a tripping position to release said operating means, an electromagnet having a pole piece, an armature normally disengaged from said trip member and operable to engage and move said trip member to tripping position, a bimetal element having one end supported and the other end free, means on said bimetal disposed to be engaged by said armature to normally rigidly block tripping movement of said armature, said bimetal element deflecting when heated a predetermined amount in response to overload currents to move said means and effect release of said armature to permit said armature to engage and move said trip member after a time delay, and said electromagnet when energized by excessive currents attracting said bimetal to said pole piece and moving said means on said bimetal element out of blocking position to per mit said armature to engage and instantaneously move said trip member.

3. A circuit breaker having relatively movable contact means and operating means releasable to effect opening of said contact means, a trip member operable to release said operating means, an electromagnet having a pole piece, an armature movable to said pole piece to engage and positively move said trip member to tripping position, a non-current carrying bimetal element having one end supported and the other end free, a heater element supporting said one end of said bimetal element and heating said bimetal element in response to overload currents, latch means disposed to be engaged by said armature to normally rigidly block tripping movement of said armature, said bimetal element defiecitng when heated a predetermined amount in response to overload currents to actuate said latch means and effect release of said armature to permit said armature to engage and actuate said trip member after a time delay, and said electromagnet when energized by excessive currents attracting said bimetal to said pole piece and moving said latch means out of blocking position to permit said armature to engage and instantaneously actuate said trip member.

4. A circuit breaker having relatively movable contact means and operating means releasable to effect automatic opening of said contact means, a trip member releasably restraining said operating means and operable to release said operating means, an electromagnet having a pole piece, an armature operable to engage and positively operate said trip member to tripping position, a latch element rigid on said armature, a bimetalelement having one end supported and the other end'free, blocking means disposed to be engaged by said latch element on said armature to normally rigidly block tripping movement of said armature, said bimetal element deflecting when heated a predetermined amount in response to overload currents to cause said blocking means to disengage said latch element and permit said armature to actuate said trip member after a time delay, and said electromagnet when ergized by excessive currents attracting said bimetal to said pole piece and moving said blocking means out of blocking position to permit said armature to engage and instantaneously actuate said trip member.

5. A circuit breaker having relatively movable contacts and operating means releasable to effect opening of said contacts, a trip member having latch means thereon engaging and releasably restraining said operating means, a projection on said trip member, an electromagnet having a pole piece, an armature operable to engage said projection on said trip member and positively move said trip member to tripping position, a rigid latch member on said armature, a bimetal element having one end supported and the other end free, the free end of said bimetal element being disposed to be directly engaged in the direction of the length of said bimetal by saidrigid latch member on said armature to prevent tripping operation of said armature, said bimetal element deflecting in re sponse to overload currents after a time delay to dis engage said latch member and permit said armature to engage said projection and actuate said trip member, and the free end of said bimetal element being disposed relative to said electromagnet to be magnetically attracted to said pole piece and deflected to disengage the latch member by said electromagnet when the latter is energized by excessive currents to permit said armature to engage said projection and instantaneously actuate said trip member.

6. A, circuit breaker having relatively movable contacts and operating means releasable to effect automatic opening of said contacts, a trip member movable to a tripping position to release said operating means, electromagnetic means having an armature operable when said electromagnet is energized by abnormal current to engage and move said trip member to said tripping position, a. bimetal element having one end supported and the other end free, the free end of said bimetal when said bimetal is cool being disposed in a position to be directly engaged by said armature in the direction of the length of said bimetal element to block tripping movement of said armature, said bimetal element deflecting when heated in response to currents of predetermined magnitude out of blocking position with said armature with a relatively long time delay and deflecting when heated in response to currents in excess of said predetermined magnitude out of blocking relation with said armature with a relatively short time delay to permit said armature to engage and actuate said trip member, and said magnetic means when energized by excessive currents attracting fsaid bimetal to permit said armature to engage and instantaneously actuate said trip member.

7. A circuit breaker having separable contact means and means releasable to effect automatic separation of said contact means, a trip member movable to a tripping position to release said releasable means, electromagnetic means having a pole piece, an armature operable to engage and move said trip member to said tripping position, means disposed in blocking relation with said armature rigidly blocking tripping movement of said armature, a fixedly mounted bimetal element heated by the current of the circuit and when heated a predetermined amount deflecting in a direction to move said blocking means out of blocking position and permit said armature to engage and move said trip member after a time delay, said electromagnet having a first flux path for actuating said armature, and a second flux path including said bimetal element operative when said electromagnet is energized in response to excessive currents to bend said bimetal element toward said pole piece and cause said bimetal element to move said blocking means out of blocking position to thereby permit said armature to engage and instantaneously move said trip member.

8. A circuit breaker having separable contact means and means releasable to effect opening of said contact means, a trip member movable to a tripping position to release said releasable means, electromagnetic means having a pole piece, an armature operable to engage and move said trip member to said tripping position, a bi metal element having one end supported and the other end free, the free end of said bimetal element being disposed in blocking relation with said armature to normally rigidly block tripping movement of said armature, said bimetal element being heated by the current of the circuit and when heated a predetermined amount deflecting to release said armature after a time delay, said electromagnet having a first flux path for operating said armature, and a second flux path including said bimetal element operative when said electromagnet is energized in response to excessive currents bending said bimetal element and moving the free end of said bimetal element toward said pole piece and out of blocking position to permit said armature to engage and instantaneously move said trip member.

9. In a circuit breaker having separable contact means and means releasable to elfect separation of said contacts, a trip member movable to a tripping position to release said releasable means, an electromagnet for engaging and moving said trip member to said tripping position, said electromagnet comprising a core member having a pole piece, an energizing winding, a magnet yoke and an armature operable to engage and move said trip member, said core member, said magnet yoke and said armature forming a magnetic flux path for operating said armature, a fixedly mounted bimetal element disposed adjacent said electromagnet and in blocking position with said armature, said bimetal deflecting when heated out of blocking position to permit said armature to engage and move said trip member after a time delay, and a second flux path including said bimetal element operative when said electromagnet is energized in response to excessive currents to instantaneously bend said bimetal element toward said pole piece and out of blocking position to permit said armature to engage and instantaneously move said trip member.

References Cited in the file of this patent UNITED STATES PATENTS 2,072,163 Frank et al. Mar. 2, 1937 2,114,845 Kubik Apr. 19, 1938 2,331,740 Smith et a1. Oct. 12, 1943 2,376,759 Dyer et al. May 22, 1945 2,425,983 Bingenheimer Aug. 19, 1947 2,608,629 Dorfman Aug. 26, 1952 FOREIGN PATENTS 569,971 Great Britain June 15, 1945

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