US2340957A - Circuit breaker - Google Patents

Description

Feb. 8, 1944. s. e. GRISSINGER CIRCUIT BREAKER Filed Aug. 26, 1942 7 m 3 Q I J. my a M/ 4 1 w. h 7/ I: A,

WITNESSES:

INVENTOR Patented Feb. 8, 1944 cmcmr BREAKER George G. Grissinger, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 26, 1942, Serial No. 456,169

8 Claims.

The invention relates to circuit breakers, and more particularly to overload trip devices for effecting tripping of automatic air circuit breakers.

One object of the present invention is to provide a circuit breaker having an improved thermal trip device wherein the thermal element is heated by eddy currents and hysteretic losses in a solid iron member.

Another object of the invention is the provision of a circuit breaker for controlling heavy alternating currents with an improved trip device having a plurality of bimetal strips secured at one end to an iron member and disposed in intimate contact with each other, said iron member surrounding a conductor and being heated by eddy currents and hysteretic losses caused by alternating current flowing through said conductor.

Another object of the invention is to provide a circuit breaker with an improved trip device operated after a time delay by a thermal element heated by eddy currents and hysteretic losses in an iron core on overloads below a predetermined value and operated instantaneously on overloads above the predetermined Value.

- Another object of the invention is to provide a heavy duty circuit breaker with an improved thermal and electromagnetic trip device capable of efficient operation without current transformers of short-circuited heaters and which operates without damage to the thermal element on short circuits.

Another object of the invention is to provide a circuit breaker with an improved trip device of rugged construction which is simple, reliable in operation and inexpensive to manufacture.

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 description of several embodiments thereof when read in conjunction with the accompanying drawing in which:

Figure 1 is a side elevaticnal view, partly in section, of a circuit breaker embodying the principles of the invention;

Fig. 2, is a fragmentary front elevational view showing the trip device and a part of the operating mechanism of the circuit breaker;

Fig. 3 is a horizontal sectional view taken on line III-III of Fig. 1, and showing a plan View of the trip device.

Referring to Figure 1 of. the drawing, the ref-- erence numeral ll designates a base of strong insulating material which supports the various parts of the circuit breaker. A pair of terminals [3 and I5 are suitably secured to the base and each terminal has one or more terminals l9 secured thereto which extend through the back of the base It and serve to electrically connect the breaker to the circuit which it controls.

The upper terminal l3 has a contact block 2| of rigid conducting material secured thereto; and a rigid contact block 23 secured to the base is electrically connected to the lower terminal l5 through the energizing winding of the trip device of the breaker, which will be hereinafter described.

The specific structures of the contact means and operating means of the circuit breaker are not an important part of the present invention, and these parts, as shown, are of the same construction as the contact means and operating means fully disclosed in Patent No. 2,214,471 issued September lO, 1940, to Leon R. Ludwig and Merle El. Horn, and assigned to the assignee of the present invention. Hence only a brief description of these parts will be given in this application.

The main stationary contacts 25' and 21 are rigidly secured to the contact blocks 2| and 23, respectively; and the auxiliary stationary contacts 29 and 31 are secured to a triangularlyshaped contact, platform 33 of conducting material which is mounted on the upper portion of the block 2| for limited tilting and rocking movement by means of pins 35 projecting from the opposite sides of the platform which engage in slots 31 provided in a pair of side walls 39se-- cured to the block 2 I. The platform 33 is biased outwardly from the base II by a plurality of springs 4i and t3, and outward movement of the platform is limited by the engagement of the pins 35 with the outer ends of the slots 31 and by stop projections 45 carried by the platform adjacent its upper end. The platform 33 and, consequently, the auxiliary contacts 29 and 31f are electrically connected to theterminal l3 -'by means of a flexible shunt conductor 41. j

The movable contact means of the circuit breaker comprises a channel-shaped contact arm 49 of conducting material which is rigidly secured to a pivoted switch member 5| by means of a plurality of screws 53. The contact arm 49 carries a main contact bridging member 55 for bridging the main contacts 25 and 21, and an auxiliary contactmember 51 for engaging the stationary auxiliary contacts 29 and 3|. the

auxiliary contact member 51 being secured to the upper end of the channel-shaped contact arm 49 by a plurality of screws 59.

The main contact bridging member 55 is formed of rigid conducting material, and is loosely mounted on the contact arm 49 for limited movement relative to the contact arm toward and away from the main contacts 25 and 21 by means of a pair of studs 5| secured to the contact carrying arm 49, only one stud being shown. The free ends of the studs 5| have a pair of nuts 63 mounted thereon for limiting inward movement of the bridging member 55 toward the main contacts 25 and 21. A pair of coil springs 65 encircle the studs 6|, and are disposed between the contact carrying arm 49 and the bridging member 55 for biasing the bridging member toward the stationary main contacts 25 and 2'! with a predetermined force. The ends of the bridging member 55 are beveled to lie parallel with the beveled edges of the contact blocks 2| and 23', and have a pair of contacts 51 secured thereto for engaging the main stationary contacts 25 and 21.

The auxiliary contact member 51 is formed of rigid conducting material, and has an intermediate contact 59 and an arcing contact H secured thereto for engaging the intermediate and arcing contacts 29 and 3| of the stationary contact means.

,A common flexible shunt conductor 13 electrically connects the auxiliary contact member 51 to the main stationary contact block 23. The flexible conductor 13 has its upper end clamped between the auxiliary contact member 51 and the contact carrying arm 49 by one of the bolts 59. The intermediate portion of the flexible conductor 13 is secured at two points to the bridging member 55 by a pair of screws 15. The lower end ofthe flexible shunt conductor I3 is secured to the lower terminal I5 by means of a bolt "ll.

The switch member 5| has a yoke-shaped lower end which is pivotally mounted between the side walls of a main frame H! by means of the pivot pin 8|. The switch member 5| is movable about its pivot axis to open and closed circuit positions to open and close the contact means of the breaker by means of an operating mechanism indicated generally at 83.

The operating mechanism 83 is supported by the main frame 19 and comprises an actuating lever 85 pivoted on a pin 87 carried by the frame, and is connected to the switch member 5| by a link 89. An operating member 9| is also pivoted on the pin 87 for movement about the same axis as the actuating lever 85. The actuating lever 85 is normally and releasably connected to the operating member 9i for movement thereby by means of a pair of latches 93 and 95, which are pivotally mounted on the lever 85 at 91 and 99, respectively. The latch 93 engages a roller |9| carried by the operating member 9|, and this latch is, in turn, held inlatching position by the auxiliary latch 95. The operating member 9| .is adapted to be releasably held in closed circuit position by means of a main holding latch I93 which releasably engages the roller I I. The auxiliary latch 95 is provided with a curved tailpiece I95 by means of which it is released to cause release of the latch 93 and consequent tripping of the circuit breaker by the release of the actuating lever Bfrom its connection with the operating member 9|. When released theactu-w ating member 85 moves in a counterclockwise direction about the pivot axis 91, causing opening of the movable contact means. During this movement, a cam surface l9! of the lever engages the rounded nose of the main holding latch 33, moving the holding latch to released position to effect release of the operating member 9|. The switch member 5| and the actuating lever 85 are biased to open position by means of a pair of accelerating springs I99 (only one being shown), which are connected at their, upper ends to the switch member 5| and at their lower ends to the sides of the main frame 79.

To close the circuit breaker after it has been tripped open, the operating member 9| is first moved in a counterclockwise direction about the pivot axis 87 to the open position to effect resetting of the latches and reestablishment of the releasable rigid connection between the actuating lever and the operating member 9 I. After the rigid connection is thus established, the operating member 9| is moved in a clockwise direction to closed position by means of its handle H to eifect closing of the contact means of the breaker. When the parts have been moved to closed position, th main holding latch I03 reengages the roller |U| to hold the operating member in closed position. It will be noted that the construction of the operating mechanism is such that the movable contact means is trip-free of the operating member 9|; that is, when the breaker is tripped, the contact means move to open position irrespective of the position of the operating member 9|.

The mounting arrangement of the contact means is such that during opening of the breaker the main bridging member 55 is first separated from the stationary contacts 25 and 21, while the auxiliary contacts remain in engagement by reason of the outward movement of the contact platform 33 under the influence of the biasing springs 4| and'43. After the bridging member 55 has separated a predetermined distance from the main stationary contacts, the intermediate contacts 29 and 69 begin to separate. This takes place as soon as the pins 35 engage the ends of the slots 31. During this time, the arcing contacts 3| and H remain in engagement due to the rocking movement of the contact platform 33. After the intermediate contacts have separated a predetermined distance, the arcing contacts BI and ll begin to separate. During closing, the contacts engage in the reverse order, as'will readily be understood. It will thus be seen that the arc formed during separation of thecontacts is drawn only between the arcing contacts 3| and TI.

An arc-extinguishing structure, indicated generally at H3, is mounted on the upper portion of the base II for extinguishing thearcs drawn between the arcing contacts 3| and The arcextinguishing structure may be of any suitable type; but is preferably of the type fully described in Patent No., 2,243,038of LeonR. Ludwig, issued May 20, 1941, andqassigned to the assignee of the present invention.

The circuit breaker is adaptedv to be tripped open either manually, or automatically, in response to predetermined overload conditions in the circuit, by means of a trip device indicated generally at H5.

The trip device comprises a trip lever which is pivotally mounted intermediate its ends on- -the frame 19 by means of a pivot-pin H9, and an electromagnet, indicated generally at |2|,

which is operable in response .to the predetermined overload conditions to move the trip lever I I1 to-tripping position to cause automatic opening'of the circuit breaker.

One arm I23 of the trip lever H1 is offset and extends inwardly toward the base II of the circuit breaker, and has its inner end disposted immediately above the electromagnet I2I to be engaged and moved by a plunger of the .electromagnet to effect automatic tripping of the breaker. The arm I23 of the trip lever is provided with a projection I25 which is adapted to engage the curved tailpiece I of the auxiliary latch 95 to move this latch to released position upon movement of the trip lever to tripping position. The other arm of the trip lever II1 forms a handle I21 whereby the trip lever may be manually moved to tripping position to effect manual opening of the circuit breaker. A spring I29 connects the arm I23 of the trip lever II! to an extension of the main holding latch I03 sothat the spring thus serves to bias the main holding latch to latching position and the trip lever to its normal inoperative position, as shown in Fig. 1. s

The electromagnet I2I comprises a stationary solid member I3I of iron or other magnetic material secured to a recessed portion of the base II by means of screws I33 and heat insulated from the conductor I5 by an insulating tube I32 surrounding the conductor between the conductor and the member I3I. The member BI is provided with an opening through which the conductor I5 extends, and is also provided with anair gap I55 (Figs. 2 and 3). The electromagnet 12! is provided with a movable armature I35 normally resting on the bottom portion of av U-shaped frame I31 of non-magnetic material the legs of which are secured by means of screws I39 to a cross member I4I integral with the frame 19. The armature I35 is aflixed to the lower end of a trip rod I43 whose upper end is disposed directly beneath the arm I23 of the lever Ii 1. The armature I35 is guided in its vertical movement by means of a pair of guide rods I45 secured to the core member I3I and extending downwardly therefrom.

The iron member I3I is energized sufiiciently on the occurrence of an overload current above a predetermined magnitude, for instance, 1000% or more of normal rated current or on a short circuit, to attract the armature I35 and thrust the trip rod upwardly to instantaneously trip the breaker.

On overloads below the predetermined value, the trip lever H1 is operated to effect tripping of the breaker by means of a thermal element I41 comprising a plurality of bimetal elements in the form of straight bimetal strips having their left hand ends (Fig. 1) riveted or otherwise suitably secured to the base of the core I3I and being disposed in intimate relationship with each other and with the core member, the other ends of the bimetal strips being free so that they may slide relative to each other. Vertically disposed adjacent the free end of the thermal element I41 is a trip rod I49 which extends through and is guided in its vertical movement by an opening in the cross member I4I. An insulating member I5I' is adjustably secured by means of a nut I53 on the lower end of the rod I49. The upper end of the trip rod I49 is disposed directly beneath the arm I23 of the trip lever II1.

Heat for operating the thermal element I41 is provided by hysteretic losses and eddy currents .in the .solid iron member I3I induced by alternating current flowing through the conductor I 5. The number of bimetal strips I 41 and the mass of the iron member I3Iv are determined for the rated values of the circuit to be controlled by the breaker. The number of bimetal strips may be varied according to the tripping force desired.

Upon the occurrence of an overload below the predetermined value, the molecular friction caused by magnetic hysteresis and eddy current losses in the iron member I3I are translated into heat causing heating of the thermal element I41. When the thermal element I41 is heated a predetermined amount it deflects upwardly. This thrusts the rod I49 upwardly to operate the trip lever H1 and effect tripping of the breaker in the above described mannen By adjusting the trip rod I49 vertically relative to the insulating member I5I the time delay tripping time may be varied. Difierent widths of air gap I55 may be provided depending on the value of the current to be controlled by the breaker.

By the provision of additional bimetal strips I51 and an additional trip rod I59 as indicated by dotted lines (Fig. 3) a greater thermal tripping force may be obtained.

It will be apparent from the foregoing descrip-,- tion that there is provided a thermal trip device capable of producing ample force to effect trip-.- ping of a large circuit breaker adapted to control large currents of the order of 40,000 amperes or higher. Another advantage of the invention resides in the operation of a heavy duty thermal trip device without the use of current transformers or shunt circuit heaters, thereby permitting efficient operation of the trip device at large values of current mentioned above without damage to the thermal element on short circuits.

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:

1. In a circuit breaker having relatively mov able contacts and operating mechanism therefor, a trip device comprising a conductor in the circuit of the breaker, a member of magnetic material surrounding said conductor and adapted to be heated in response to alternating current traversing said conductor, and a thermal element disposed in heat conducting contact with said magnetic member and having one end secured to said magnetic member, said thermal element being heated by said magnetic member and operable when heated at predetermined amount to effect tripping of the breaker.

2. In a circuit breaker having relatively movable contacts and operating means therefor, a trip device comprising a conductor in the circuit of the breaker, a member of magnetic material surrounding said conductor and adapted to be heated by hysteresis and eddy current losses caused by alternating current flowing in the conductor, a thermal element having a portion disposed in heat conducting contact with said :magnetlcmember, :said thermal element :being adapted to be heated by said magnetic member :and operable when heated a predetermined :amount .byssaid magnetic member to effect tripping vofthe breaker.

.3. A trip device for .a circuit breaker comprising a conductor in the. circuit of the breaker, a

:member of magnetic material surrounding said conductor and insulated from said conductor,

.said magnetic member being adapted to be heat- .ed by hysteresis and eddy .current losses in said member caused by alternating current traversing the .conductor, and a thermal element having a portion .disposed in heat conducting contact with :said member, said thermal element comprising aplurality .of bimetallic strips secured at one end .to the magnetic member, said thermal element being adapted to be heated by said magnetic member and being-operable when heated a predetermined amount to efiect tripping of the breaker.

.4. A trip device for a circuit breaker comprising .a conductor in the circuit of the breaker,

:an electromagnet including a core member of unagnetic material surrounding said conductor,

and an armature operable in response to overlloads above a predetermined value to effect tripping of the breaker, said core member being adapted to be heated by .alternating current traversing said conductor, and a. thermal element secured to said core member and having a portion disposed in contact with said core member so as to be heated thereby, said thermal element being operable when heated a predetermined amount by said core. member in response to overload currents below .said predetermined value to efiect tripping of the breaker.

5. A trip device for acircuit breaker comprising a trip lever operable to effect tripping oi the breaker, a plurality of trip rods each operable to effect operation of said trip lever, a conductor in the circuit of the breaker, electromagnetic means including a core member of magnetic material surrounding said conductor .and an armature operable in response to .overload conditions above a predetermined value to operate one of said trip rods, and a thermal element having a portion of its surface in heat conducting contact with said core vmember and heated by said core member, said thermal element being operable when heated a predetermined amount to operate the other of said trip rods.

6. In a circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a trip lever op- --erable to effect tripping of :the breaker, a plurality :of .trip members'each engageable with said trip ."lever and each operable to effect operation of said lever, a conductor .in the circuit of the :breaker, a core member of magnetic material=surrounding said conductor and an armature operable in response-to overload currents above a predetermined value to operate one of said trip membersito instantaneously trip the breaker, and a. thermal element comprising a stack of bimetal elements secured to said coremember, saidther- :mal element extending incontact with said core member and adapted to be heated thereby, said thermal element being operable when heated a predetermined amount to operate the other of said tripmembers, said core member being heated 'by "hysteretic and eddy current losses caused by alternating currenttraversing the conductor.

.7. In a circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a plurality of trip members each operable toefiect trippingof the breaker, a conductor-in the circuit of the breaker, an electromagnet operable in response to predetermined circuit conditions to operate one of said trip members, said 'magnet including a core rnember surrounding said conductor and heated in response to overload currents, and a thermal element comprising 'a plurality of bimetal strips'secured to said core member, said thermal element being disposed so that at least a portion thereof is in heat conducting contact with said core member and heated thereby, said thermal element being operable when heated a predetermined amount to operate "the other trip member.

7 rent losses caused by overload alternating currents in the circuit of the breaker, and a thermal element disposed along 'itslength in contact with the core memberto be heated by said core member and operable when heated a predetermined amount to 'operate'one of said trip members, said core member being operable in response to an overload current above a predetermined value .to operate the other'trip member to effect instantaneous tripping of the breaker.

GEORGE 'G. GRISSINGER.

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