US2280616A - Electric circuit breaker - Google Patents

Description

April 2,1, 1942. l

R. J. BASKERVILLE ELECTRIC CIRCUIT BREAKER4 Filed Oct. 22, 1940 Ralph J. Baskerville,

b9 7,1 MW

His ttorneg.

Patented Apr. l21,y 1942 ELECTRIC CIRCUIT BREAKER Ralph J. Baskerville, Yeadon, Pa., assignor to General Electric Company, a

New York corporation ot Application October 22, 1940, Serial No. 362,211

(Cl. 20o-146) 9 Claims.

My invention relates to electric circuit breakers, more particularly to the movable contact structure of air circuit breakers of the magnetic blowout type for example, and has for its principal object the provision vof improved contact structure that is compact and rugged in design and particularly adapted to carry, as Well as to make and break, large power currents with minimum contact deterioration and heating.

The use of main or current carrying, secondary or transfer and tertiary or arcing contacts in the movable contact structure of air circuit breakers has been proposed for the purpose of eliminating all possibility of arcing at the main contacts which separate first; The main contacts are generally faced with a low melting point metal such as silver having'good current carrying characteristics. The arcing proper takes place only at the tertiary contacts which separate last. In such an arrangement, it will be apparent that the various contact elements, coasting biasing springs, et cetera, may require appreciable space for proper functioning. However, in the case of magnetic blowout circuit breakers using a comparatively narrow arc chute, the width and general size o! the movable contact arm are limited by the arc chute design and related factors. It has therefore been diflicult to design contact struc- -ture of the character in question having, for example, suiiiclent contact pressure at the arcing contacts during the' opening and closing operaarate at the entrance to the arc chute. Specifltions due to limitations on the space forsprings Y and associated apparatus.

In accordance with my invention, the contact structure is improved by utilizing to better advantage magnetic forces in the breaker and by providing greater mechanical advantage for the 'biasing springs at comparatively low gradient spring pressure without increasing the overall size of the movable contact arm; also in accordance with my invention, thev secondary and tertiary contacts are provided with auxiliary arc extinguishing means operable in accordance with the breaker opening movement for use in low current interruptions.

Myv invention will be more fully set forth in the following. description referring to the accompanying drawing, land the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this speciiicatlon.

Referring to the drawing, Fig. 1 is an elevational view. partly broken away and in section of a circuit breaker including the contact structure embodying the present invention; Fig. 2

is an enlarged sectional View1 also in elevation of the movable contact arm shown in Fig. 1, and Fig. 3 is a plan view of the arcing end of the Contact arm along the line 3-3 of Fig. 2.

The air circuit breaker-shown by way of example is of the magnetic blowout type employing an arc chute of any suitable form into which the arc is forced by the magnetic blowout iield and extinguished. The power circuit to be interrupted includes relatively movable contacts between which the arc is formed when the contacts sepcally, the contacts comprise nxed contact structure generally indicated at I and coacting movable contact structure'generally indicated at 2. The ixed contact structure is electrically connected to the lower end of a lead-in conductor stud 3 dening one terminal of the breaker, and the movable contact structure comprises an arm electrically connected to and pivotally mounted at l on the conductor stud 5 defining the otherbreaker terminal. The pivoted contact 2 is suitably operated between open and closed circuit positions by an operating rod 6 that is connected through a crank l to the operating mechanism (not shown).

The breaker is shown in the closed circuit position, the coacting main, transfer and'arcing contacts, 8, 9 and i0 respectively, of the movable y contact arm being in engagement with the corresponding main, transfer and arcing contacts Ii, I2 and I3 respectively of the iixed contact structure. As previously indicated, opening of the breaker by counter-clockwise rotation of the breaker arm 2 causes in the sequence named separation oi the main current carrying contacts 8-I|, the transfer contacts 9--I2, and finally the arcing contacts Ill-i3 where the power arc is formed at the entrance of the arc chute i4. The arc chute per se forms no part of the present invention and may be provided with insulating are extinguishing baiilesl I4' of the character` disclosed in an application Serial No. 298,946, filed October 1l, 19'39, by L. J. Linde for Electric air circuit breaker" (Docket No. 63,579).

By way of example, the arc chute is also illustrated as4 provided with magnetic blowout coils I5, I6 and I1 arranged so as to cause the arc formed between the contacts |0--Il to be blown by the magnetic field into the arc chute. The blowout coils I6 and I1 are normally shunted by the main and secondary contact structure in the closed circuit position but are cut into the circuit by the arcing contacts in a manner wellknown in the art. The blowout coil I5, one

terminal of which is connected to the arcing horn I8 within the arc chute and the other terminal to a conducting extension I8 of the terminal conductor stud 5, is cut in the circuit when the arc is drawn across the entrance of the arc chute and jumps to the arc runner I8. When this occurs, the arc current is shunted around the contact arm 2 through the coil I5 and terminal extension I9.

Referring more particularly to the movable contact 2, the main switch arm comprises a pair of spaced plates 20 interconnected by the pivot pin 4 at opposite sides of the stud 5. The spaced plates 20 are also interconnected by a pin 2| which serves to connect the switch arm to the operating rod 6. Secured to the plates 20, as by welding, is the main current carrying contact 8. 'Ihis element is formed as a block extending between the plates 20 in the manner of a partition as illustrated by Fig. 2. The upper or contact surface of the main contact is preferably coated with silver or other suitable. contact material having low contact resistance.

of insulating bushings 22 and 36 at the pivot pin 22 and tlhe plate 3I respectively, the arcing contact member is insulated from the main switch arm so that the arc current flows directly from the arcing contact I8 to the terminal stud 5 through the plates 30, terminal 3| and flexible conductor 32 as illustrated by Fig. 1. As in the case of the transfer contact, the contact and larcing surface of the contact I is coated with a suitable arc resisting metal, such as tungsten copper alloy.

y For the purpose of biasing the contact IIJ about Also mounted between the plates at the outer ends thereof is the secondary or transfer con- .1,

tact 8. This contact is pivotally mounted on a pin 22 .interconnecting the plates 20 and ls springbiased in a clockwise direction by means of a compression spring 23 seated at one end in a depression 24 in the main contact block 8 and at the other end on a spring guide stem 25 pivotally connected at 26 to an extension arm 21 of the transfer contact. It will be noted that the guide stem 25 serves as a limit stop with respect to counter-clockwise rotation and the extension 28 in combination with the main contact 8 serves as a limit stop in the opposite direction. In Fig. 2,

the contact structure is shown in the same position as Fig. 1, i. e. the transfer and arcing contact springs are stressed, the contacts being in the closed position.' The contact surface of the transfer contact 8 is preferably coated with an arc resisting metal, such as a suitable tungsten and copper alloy.

-The proper function of the arcing contact I0 is very important since the power circuit is initially made and finally broken at these contacts. It is therefore essential that the arcing contacts initially close and remain closed under suitable contact pressure notwithstanding large magnetic forces tending to blow open the contacts upon closing. Weak or insufficient contact pressure like members 30 disposed at opposite sides of the switch arm 2 and co-pivotally mounted with the transfer contact 8 on the pivot pin 22. The platesv 30, which extend generally parallel along the outer sides ofthe plates 20 for an appreciable distance are joined together at the outer extremity by the arcing contact III and at the opposite end by the plate 3| which bridges that end to serve both as a spring seat and as a terminal for directly electrically connecting the arcing contact at 3| to the terminal stud 5. By means the pivot pin 22 in clockwise direction so as to assure adequate contact engagement at the arcing contact surface, a plurality of nested springs 33 are positioned in the space defined by the plates 20 so as to seat between the pin 2I and the plate 3| bridging the extremities lof the side plates 30. The springs 33 are positioned and guided by means of an eyebolt 34 that is connected at its upper end to 'the pin 2l and extends freely through the bridge 3|. As shown, the springs 33 engage at one end a shoulder 35 connected to the eyebolt and at the lower end engage an insulating bushing 36 for insulating the springs with respect to the lplates 30. The lower end of the eyebolt is provided with adjustable lock-nuts 31 which define the amount of contact wipe at the arcing contacts. This adjustment is also particularly adapted to assure uniform opening and closing of three similar switch arms in a polyphase breaker.

In the arrangement shown, it will be apparent that when the operating rod 6 is lowered to open the breaker, the main contacts 8 and I I separate practically at once, subject to limited wipe of the fixed main contact I I as indicated at Il', so that the power current is shunted through the parallel conducting paths defined by the transfer contacts and arcing contacts. No arcing occurs at the main contacts since the transfer contact circuit has low resistance. A's the contact arm continues to open, the spring 23 of the transfer contact maintains this contact in engagement with its coacting contact I2 until the limit stop 28 engages the contact 8. Separation of the transfer contacts then follows, and since the transfer of current to the arcing contact circuit now involves a path of somewhat higher impedance due to the blowout coil I6, slight arcing may occur at the transfer contacts. However, 4this arcing is readily extinguished so that the power current is completely transferred or shunted to the arcing contacts. Y

Since, as clearly indicated by Fig. 2, the springs 33 are effective to maintain the arcing contact in engagement for an appreciable time after initial contact movement, i. e. until the bridge 3I engages the adjusting nuts 31, it will be apparent that the arcing contacts do not separate until after separation of the transfer contacts. this time, the main arc is drawn and the arc interruption 'process takes place in the manner above indicated. By reason of the arcing contact arrangement, it will be seen that high contact pressure can be maintained atthe arcing contacts without using high -pressure gradient springs with the disadvantages incident to the use thereof. By greatly increasing the mechanical advantage of` the arcing contact arm without appreciably increasing the overall dimensions of the main switch arm, low pressure gradient springs may be used and in addition the switch arm as a whole can be more efficiently operated. Furthermore, the switch arm assembly, notwithprising spaced members to which said main co andere standing the compact'andemcient arrangement throughthe exible jumper l2 so as to eliminate resistance at pivot pins, joints. et cetera.

Another factor tending to increase the emciency of the arcing contact lever I is the increased' arcing contact pressure caused by the magnetic forces of the current. It is well known that the magnetic forces of current flowing through a loop tend to expand `the loop. ThereforeJ it will be observed that in the current loop defined by the conductors 3--30-32-5, the expansive forces acting at the right of the xed point `22 are preponderant and urge the lever 30 in a clockwise direction by reason of the greater length oi the current path between pivot 22 and stud 5 as compared with the length between pivot 22 and contact I0. This increase in contact pressure, which supplements the springpressure, increases with the size of the current, thereby greatly decreasing contact heating. Also, this arrangement counteracts the tendency of the contact arcing pressure to decrease as where the magnetic forces urge the switch arm toward open position.

The interruption of low current arcs at moderate voltages, such as 5000 volts, is sometimes attended with difficulty due to the comparatively weak magnetic blowout field. For the purpose of interrupting arcing under all conditions, the movable contact 2 is provided with pneumatic means for directing an arc extinguishing jet oi air across the arcing surfaces of both the transfer and arcing contacts 'in accordance with opening movement of vthe breaker. To this end, the pivot pin 22 of the main contact arm is connected to a piston 40 that is operable in the ilxed cylinder 4I. The connecting piston rod 42 is hollow as indicated and communicates directly with the interior of the cylinder through the pistonr40, and at the opposite end terminates in a coupling member 43 that is connected to the pivot pin 22. The coupling .member 43 is provided with a lateral passage 44 communicating with the hollow piston rod 42 which terminates in a pair of nozzles or the like 45 adjacent to the secondary and arcing contacts. As best illustrated by Fig. 3, jets of air. directed from the nozzles 45 converge on the arcing surfaces of the contacts 9 and I0. l

When the breaker is opened, the piston 40, which is directly connected tothe coupling pin 22, is forced downwardat high speed with the result that air in the lower part of the cylinder 4| is rapidly forced under pressure into the hollow piston rod and through the nozzles 45' to extinguish low current arcs. Contact burning is thereby minimized and the circuit is cleared within a cycle or so of arcing, thereby precluding unnecessarily long arc lengths.

It should be understood that my invention is not limited to specific details of construction and arrangement thereof herein illustrated, and-that changes and modifications may occur to one skilled in the art without departing from the vspirit of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. Electric circuit breaker contact structure including coacting pairs of main, transfer and arcing contacts, and a pivoted lswitch arm for the movable main, transfer and arcing contacts comtact is secured, means for mounting said transfer contact between said members, elongated means carrying at one end said arcing contact Apivotally mounted intermediate its ends on said switch arm adjacent to the extremity of said arm, said elongated means at .the opposite end extending along said switch, arm throughout an appreciable part of the length of said arm, and spring meansmounted on said arm for engaging and biasing said opposite end of said elongated means in a direction to cause engagement of said arcing contacts.

2. Electric circuit breaker contact structure including coacting pairs of main, transfer and arcing contacts, and a pivoted switch army for the said plates for engaging and biasing said opposite end of said elongated means in a direction to cause engagement of said arcing contacts, the

mechanical advantage of saidi elongated means ing means being with respect to its spring bias sufiiciently large to assure high contact pressure at said arcing contacts coincident with a low pressure gradient at said spring means.

3. Electric circuit breaker contact structure for interconnecting two breaker terminals including a coacting pair of arcing contacts, and a pivoted switch arm for the movable arcing contact, said terminals and switch arm forming a U-shape loop, an elongated lever icarrying at one end said arcing contact pivotallyf' mounted intermediate its ends on said switch arm adjacent to the extremity of said arm so that said arcing contact coacts with the fixed arcing contact at one of said terminals, the opposite end of said lever extending an appreciable distance toward the other terminal so that the length of the lever extension from its pivot is considerably greater than the length of the lever from said pivot to said arcing contact and being electrically connected independently of said switch arm to said terminal by means of a ilexible conductor connected to the extremity of said opposite end of said lever, the

pivot for mounting said arcing contact lever be-` ing positioned comparatively near the iixed contact terminal whereby the magnetic forces oi the current traversing the loop including said lever tend to r'otate said lever about its pivot to increase the arcing contact pressure, and spring means engaging said arm and lever for biasing said elongated lever in a direction to cause engagement of said arcing contacts.'

4. Electric circuit breaker contact structure inextremity of said'arm, said elongated lever also comprising a pair of spaced platelike members disposed generally parallel to and at opposite sides of said arm, a member interconnecting the extremities of said last-named members, and spring means mounted in said arm between said plates an appreciable distance from said arcing.

contact for engaging said interconnecting member and biasing said elongated lever in a direction to cause engagement of said arcing contacts.v

5. Electric circuit breaker contact structure including coacting pairs of main, transfer and arcing contacts, and aswitch arm for the movable main, transfer and arcing contacts comprising a pair of spaced plate-like members to which said main contactis secured, means for mounting said recting a iet of compressed air across the arcing surfaces vof said contacts in accordance with switch opening movement.

v 6. An electric circuit breaker comprising a pivoted main switch arm having an arcing contact mounted 'at the free extremity thereof, a coacting relatively ilxed arcing contact, means for operatingsaid switch arm between open and closed circuit positions, magnetic blowout means for normaily extinguishing arcing between said arcing contactsA during moderate and heavy current in-V terruptions and pneumatic means for extinguishving low-amperage arcs comprising a relatively fixed cylinder, a piston movable in said cylinder C and' operatively connected to said switch arm, v and air passage means including the connection between said piston and switch arm for directing air under pressure from said cylinder across the arc gap formed upon separation of said arcing contacts when said switch ann is actuated to open circuit position. y

7. An electric circuit breaker comprising a pivoted main. switch arm having an arcing contact mounted at the free extremity thereof, a coacti ing relatively fixed arcing contact, means for operating said switch arm between open and-closed circuit positions. magnetic blowout means for Y normally extinguishing arcing between said arcassumo ing contacts during moderate and heavy current interruptions and pneumatic means for extin guishing low-amperage arcs comprising a relatively fixed cylinder, and a piston movable in said cylinder and operatively connected through a hollow piston rod to said switch arm, said hollow piston rod forming a passsage for directing air under pressure from said cylinder across the arc gap formed upon separation of said arcing contacts when said switch arm is actuated to open circuit position.

8. An electric circuit breaker comprising a pivoted main switch arm having anl arcing contact mounted at the free extremity thereof, a coacting relatively fixed arcing contact, means for operating said switch arm between open and closed circuit positions, magnetic blowout means for normally extinguishing arcing between said arcing contacts during moderate and heavy current interruptions and pneumatic means operatively connected to said switch arm for extinguishing low-ampera-ge arcs comprising a relatively movable piston and cylinder one of which is xed,

air passage means formed by the connection to said switch arm for directing air under pressure from said cylinder when said switch arm is actuated to open circuit position, and a nozzle at the end of said passage means movable with said switch arm and adjacent to said first-named arcing contact for directing a jet of air across the arc gap formed contacts.

9. An electric circuit breaker comprising a pivoted main switch arm, an arcing contact controlled by said switch arm, a coacting relatively xed arcing' contact, means for operating said switch arm between open and closed circuit positions for causing separation and engagement respectively of said arcing contacts, and pneumatic means for extinguishing low-amperage arcs at said arcing contacts comprising a relatively movable piston and cylinder one of which is connected to said switch arm and the other of which is xed, a hollow tube constituting the connection to said switch arm for directing air under pressure from said cylinder due to relative movement of said cylinder and piston when said switch arm is actuated to open-circuit position, and a noa'sle at one end of said hollow tube movable with said switch arm and adjacent to said first-named movable arcingcontact for directing a Jet-of air across the arc gap formed upon separation of said arcing contacts.

RALPH J. BABKERVILLE.

upon separation of said arcing

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