US2724755A - Carbon circuit breaker - Google Patents

Description

Nov. 22, 1955 Filed Dec. 26, 1952 w. F. MORGAN 2,724,755

CARBON CIRCUIT BREAKER 2 Sheets-Sheet l 1 V 0 1.111115 VI/( M W y INVENTOR.

WILLIAM F. MORGAN ATTORNEY Nov. 22, 1955 w. F. MORGAN 2,724,755

CARBON CIRCUIT BREAKER Filed Dec. 26, 1952 2 Sheets-Sheet 2 C53 50V, DC

WILLIAM F. MORGAN ATTORNEY States Patent CARBON CIRCUIT BREAKER William F. Morgan, Johnson City, N. Y., assignor to International Business Machines fiorporation, New York, N. Y., a corporation of New York Application December 26, 1952, Serial No. 327,975

12 Claims. (Cl. 29(l145) This invention relates to circuit interrupting apparatus and more particularly to circuit breakers of the multiple p yp An object of the invention is to provide improved circuit interrupter means.

Another object of the invention is to furnish improved circuit breaker means of the carbon pile type capable of interrupting highly inductive current loads with sharp cut-off characteristics.

Another object is to furnish an improved circuit breaker means of the stacked carbon type capable of interrupting highly inductive direct current loads over a wide range of current values with substantially the same cut-ofi. characteristics.

Still another object of the invention is to provide a stacked disc circuit breaker in which the wear on the discs is evenly distributed throughout the contact surfaces thereof.

A further object of this invention is to produce a carbon pile circuit breaker for highly inductive current loads which exhibits low energy arcing and small induced peak voltages.

A still further object of the instant invention is to furnish a carbon pile circuit breaker which includes one or more metallic contacts associated therewith and which exhibits long wearing characteristics in high speed operation over sustained periods of time.

Another object of this invention is to provide a carbon pile circuit breaker in which wearing of the contact surfaces may be quickly and simply compensated for without removing or replacing the carbon pile.

Still another object of the invention is to provide improved circuit breaker means as aforementioned which is simple in construction and economical in manufacture.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of examples, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

in the drawings:

Fig. l is a side elevation of one embodiment of the present invention;

Fig. 2 is an enlarged sectional view taken on lines 2-2 of Fig. 1;

Fig. 3 is an exploded view of a portion of the embodiment shown in Fig. 1;

Fig. 4 is a side elevation of the carbon pile showing another embodiment thereof including a pair of tungsten contacts;

Fig. 5 is a side elevation of the carbon pile showing still another embodiment thereof including a plurality of pairs of tungsten contacts;

Fig. 6 is a schematic circuit in which the instant invention may be placed to provide efficient circuit break-' ing characteristics;

Fig. 7 is a timing chart for the circuit breakers shown in Fig. 6;

ice

Fig. 8 shows at a a sample current waveform for one operation of the circuit breaker and at b shows the voltage waveform associated therewith; and

Fig. 9 shows at a sample current waveforms for dif ferent current values and at b shows the voltage waveforms associated therewith.

Similar reference characters represent similar parts throughout the several views.

Much difliculty has been encountered in D. C. circuit breakers which carry highly inductive current loads where the current varies over a wide range of values. In breaking a highly inductive circuit peak voltages in the order of eight-hundred volts or more are often encountered and the faster the break is made the higher the peak voltage. In order to preserve the breaker contacts it is desirable to break the circuit as quickly as possible with minimum arcing. It is also desirable to maintain substantially the same cut-off characteristics over a wide range of currents, for example, between Zero and sixty amperes. This is necessary to preserve the timing of the device with which the circuit breaker is used. The present invention overcomes these ditficulties in a manner which will be obvious from the following detailed description.

Referring to Figs. 1, 2 and 3 of the drawings, one embodiment of the circuit breaker forming the instant invention is shown. The circuit breaker includes a frame member It? for holding the circuit interrupting elements. A lip 11 is formed at one corner of the frame, said lip being provided with a tapped aperture for receiving an adjusting screw 12. A hanger or mounting member 13 is slotted as at 14 to receive screws i5 which secure the hanger to the frame member. Adjustment of the frame with respect to the hanger may be made by adjusting screw 12. The hanger is also provided with apertures 16 which may be utilized in mounting the hanger to the device with which the circuit breaker is to be used. A connecting screw 17 is provided on the free end of the hanger, thereby forming a terminal to which one side of the circuit is connected. Both the frame and hanger are constructed of a material having electrical conducting properties.

The carbon pile assembly, illustrated generally by reference numeral 18, comprises a plurality of carbon discs 19 mounted in stacked relation to each other. As used herein, the term carbon is meant to include carbon and graphitic materials or mixtures of other materials in combination therewith. Each of the discs is undercut as at 20, the arrangement of discs being such that the undercut side of one disc is next to the flat side of an adjacent disc. Each disc is provided with a centrally arranged aperture 21 which is adapted to slidably receive a nylon plunger 22. Frame 10 is also apertured as at 23 to slidably receive said plunger. A metallic plate 24 is mounted adjacent the top disc of the carbon pile, said plate being provided with a centrally arranged downwardly extending sleeve 26 which is internally threaded to receive a threaded reduced portion 25 of plunger 22. The shoulder 27 formed by said reduced portion is adapted to abut an insulating Washer 28 which in turn abuts the lower end of sleeve 26 and the bottom surface of the top carbon disc. In this manner the top disc is firmly secured to the metallic plate. A washer type finger spring 29 is apertured to slidably receive said plunger and is mounted between the aforementioned washer and the undercut portion of the disc which is adjacent the top disc. Spring 29 is constructed such that a base portion 30 is formed which abuts the carbon disc. A plurality of spirally arranged fingers 31 extend from said base portion, said fingers having rounded surfaces 31a on the ends thereof adapted to contact said washer.

Between the remaining discs insulating washers 32 and springs 29 are provided, there being one washer and one spring fitted into the undercut portion of each of the discs.

The only difference between washers 32 and washer 28 is the difference in aperture size.

The top of frame It is furnished with a threaded aperture 36 adapted to receive an externally threaded sleeve 41, said sleeve having a flange 42 secured to the lower end thereof. Flange 42 is knurled on the periphery thereof to aid in rotating the sleeve in the frame aperture. An insulating sleeve 43 is mounted inside sleeve 41, said insulating sleeve projecting beyond the upper end of sleeve 41.

A bolt 35 is adapted to be slidably received by sleeve 43, said bolt being provided with spaced head members 33 and 34. A washer type finger spring, illustrated generally by reference numeral 37, is mounted between said head members and plate 24. The purpose of this spring is to compress the carbon pile and to provide a good electrical conductor. Spring 37 has an apertured central por tion 38, which fits between said head members, and a pair of fingers 39, the ends of said fingers being riveted, as at 40, to plate 24. the junction of said fingers with said apertured central portion which add endurance to the spring. An insulating washer 45 is mounted between flange 42 and head member 33.

In securing bolt 35 in place an insulating washer 46 is mounted on the projecting end of sleeve 43 and a nut 47 is threaded on said bolt. The nut may be tightened until the bolt is firmly secured. Bolt 335 performs an additional function of acting as the other terminal of the circuit breaker. An additional nut 48 is provided for securing an electrical lead to the bolt.

From the above detailed description it will be seen that an electric circuit is formed from terminal 17, through hanger 13, frame 10, carbon pile 13, plate 24, spring 39 and bolt 35.

As is well known the resistance of the carbon pile changes with applied pressure. Spring 39 is utilized to compress the carbon pile to provide low resistance to the current flow.

In order to break the circuit it is necessary to relieve the pressure applied to the carbon pile by spring 39. When this occurs springs 29 tend to separate the carbon discs, thereby increasing the resistance to infinity. The pressure is relieved by compressing spring 39 through movement of plunger 22. While the plunger may be moved in a variety of ways the particular structure shown for causing the movement is in the form of a cam and cam follower arrangement. The cam follower, illustrated generally by reference numeral 48, includes a cam follower arm 51 and cam follower rollers 52, said cam follower arm being pivotally mounted by pin 49 on frame bracket 50. The free end of the cam follower arm is bifurcated to receive a guide post 53, said post being utilized to prevent lateral movement of the arm. Rollers 52 are adapted to ride on the cam 54. it will be understood that the instant cam which is shown is only by way of example, the shape thereof being dependent on the timing cycle required. When rollers 52 ride on the low dwell 55 of the cam the circuit is closed and when the rollers ride on the high dwell 56 the circuit is open. That is, movement of the rollers from the low dwell to the high dwell causes the cam follower arm to engage plunger 22 and move it upwardly. As the plunger begins its movement, plate 24 and the upper carbon disc are moved therewith, the movement of the plate relieving the pressure on the carbon pile. At this time springs 29 between the discs tend to separate all of the discs, thereby increasing the resistance in the pile to infinity. The rise in resistance from a very low resistance to infinity, from the instant the plunger begins its movement, is very rapid but not instantaneous, as in the case of conventional circuit breakers.

The washer type finger springs between adjacent discs perform a very useful function. When pressure is applied to the stack the fingers are compressed. As the pres- Raised surfaces 44 are provided near sure is removed the fingersmove the adjacent discs axially of the plunger to separate the contacting surfaces.

It will be noted that when springs 29 are compressed, the ends of the fingers thereof are angularly displaced. The friction between the ends of the fingers, the insulatin washers, and the carbon discs, causes the discs to rotate as said angular displacement occurs. The bottom disc adjacent the frame does not rotate due to friction therebetween. A relative motion does exist between all discs. The result of the disc rotation is a smooth contacting surface upon which the wear has been evenly distributed.

Wear on the carbon discs tends to change the timing of the break point. That is, as the discs become thinner, plunger 22 is moved further down towards the cam follower. This causes the break point to advance to some extent, thereby upsetting the timing cycle of the device. A certain amount of the carbon pile wear is compensated for by mechanical wear on the end of the plunger, on the cam follower, and the cam itself. An adjustment may be made simply by loosening screws 15, adjusting screw 12, and then tightening screws 15. It is but necessary to use a feeler gauge between plunger 22 and the cam follower arm to make a precise adjustment which will restore the original timing condition.

The amount of pressure applied to the pile may be varied by rotating knurled flange 42. As the wear on the carbon pile increases over a long period of time the pressure applied thereto decreases. Therefore it is necessary to move flange 4-2 so that the pressure on the pile is increased.

The present invention is particularly useful as a D.-C. impulse circuit breaker, where, for example, the circuit is broken as many as sixty times per second and greater, on highly inductive current loads. As an example, the instant invention may be used in a circuit such as that shownin Fig. 6, a representative cam timing chart of which is shown in Fig. 7. As shown, circuit breakers CB-1 and CB-2 are connected in parallel and circuit breakers CB-3 and CB-4 are also connected in parallel.

Circuit breaker CB-4, in the instant circuit, is the carbon pile circuit breaker, CB3 being used as a shunting circuit breaker. The pairs of circuit breakers are series connccted and act as the switching means between the input D. C. voltage and the inductive load. As shown in the timing chart CB3 makes ahead of CB-4, which in turn makes ahead of the remaining circuit breakers. CB-l and CB-Z are make circuit breakers while CB-4 isthe break circuit breaker. CB-1 and CB-2 close at the same time thereby completing the circuit. After approximately 6 from the time the circuit is closed CB-3 opens. The circuit is broken when CB-4 opens 3 after CB-3 opened. in this manner the full current load passes through the carbon pile only for the 3 duration after CB-3 opens.

Sample wave forms are shown in Figs. 8 and 9 for the circuit shown. Fig. 8 shows at a the current curve 57. The current builds up upon completion of the circuit and comes to a high point which lasts a few degrees. When CB-3 opens the full load of the circuit passes through the carbon pile. Since the resistance of the carbon pile amounts to approximately two-tenths ohms the current drops slightly forming a clip 58 which lasts for approximately 3. At cut-off the current drops sharply to the zero line. The dip below the zero line is due to the capacitor.

The voltage curve shown at b, illustrated by reference numeral 59, shows that when the circuit is broken the voltage across the circuit breaker remains at approximately fifty volts, the D. C. input voltage. As the circuit is made and the current builds up, the voltage across the contacts drops to zero and stays at this level until the circuit is broken. At this time the voltage peaks sharply to approximately one hundred and fifty volts, as at 60, and then drops substantially exponentially to the: fifty volt level. The ability of the carbon pile to continuously increase its resistance as the pressure is relieved prevents an instantaneous interruption of current, thereby decreasing the self-induced peak voltage. Thus, it is possible to prevent the peak voltage from reaching such high values as one thousand volts or greater. The particular wave forms shown were obtained from an oscilloscope connected in the circuit after the circuit had been made and broken over one-half billion times on a six ampere highly inductive load having an R/L ratio of approximately 200 with fifty volts D. C. applied.

In Fig. 9, at a current wave forms 61 and 62 show the current characteristics for a six ampere and a sixty ampere load, respectively. The voltage curves associated with wave forms 61 and 62 are shown at b. It will be noted that cut-oif is made in substantially the same period of time under both current load conditions. This is very advantageous since the timing of the circuit is not upset over varying current loads.

When the circuit breaker forming the present invention is operated at very high speeds separation occurs between the top two carbon discs before it occurs between the remaining discs. Under very high loads such action causes proportionally more wear on the top two discs.

A study of the action of the carbon pile in breaking the circuit will reveal the reason why the early separation occurs. When plunger 22 is moved axially of the discs its movement is positive. The plunger carries the plate 24 and the top carbon disc with it. The spring action between the discs is not sufficiently strong to overcome the inertia thereof and move as fast as the aforementioned top disc and plate. Therefore, the top disc moves away from the disc adjacent thereto and then the remaining discs separate. Under slower speeds this condition does not prevail to as great an extent since the springs 29 can overcome the inertia of the aforementioned remaining discs as fast as the cam moves the top disc upwardly.

A modification of the present invention proposes to replace the carbon contacting surfaces of the top two carbon discs with a metallic surface. As shown in Fig. 4, the top two discs 63 and 64 have been reduced in size insofar as their carbon thickness is concerned. Metallic rings 65 constructed of a contact material such as tungsten, are welded to the reduced thickness carbon discs, the overall thickness of each tungsten-carbon disc being equal to the thickness of the normal carbon disc 19. The tungsten surfaces are mounted in contacting relation.

' Whenever high speed operation causes the top two discs to separate first, the tungsten is utilized to withstand arcing thereacross. While arcing causes tungsten to wear away faster than carbon in terms of unit weight, the density of tungsten is so much greater that the wear on the surface is less. In this manner the early arcing between the top two discs is taken advantage of by providing contact materials capable of absorbing much more arcing with less wear, thereby saving wear on the remaining discs which are made of carbon only. With a six ampere load having an R/L ratio as previously mentioned, the total wear on the carbon pile of this construction after two-hundred million operations was only seven-thousandths of an inch, with the cam and circuit used this Wear corresponded to a one degree change in timing.

Where the speed of operation is relatively low and the discs all separate quite evenly, the advantages of the abovementioned tungsten contacts may be obtained by additionally compressing the spring tending to separate the tungsten surfaces. This may be accomplished merely by providing a thicker insulating washer between the carbon discs having the tungsten Welded thereto. Thus, the additionally compressed spring tends to separate the tungsten surfaces first permitting a majority of the arcing at this point. It has been found that most wear occurs on the tungsten ring which is positive with respect to the other ring. Advantage is taken of this fact by making the freely rotatable tungsten disc positive in order to distribute the wear evenly over the entire surface. in view of this consideration, it is possible to make the fixed disc of carbon or other softer and cheaper contact materials. Thus, it is necessary to provide only one disc having the tungsten ring.

A further modification is made in Fig. 5, wherein pairs of carbon discs having tungsten rings welded thereto are utilized.- These pairs of discs, illustrated gencombined carbon-tungsten disc.

erally by reference numeral 66, are each similar to the pair of discs having reference numerals 63 and 64 shown in Fig. 4. Each pair of the discs is separated by a carbon disc 67 which is one-half the thickness of the As in the first two forms of the invention insulating washers and springs are provided in the space formed between the pair of discs.

The advantage of using a circuit breaker such as that shown in Fig. 5 is extreme timing stability because the wear is confined solely to the tungsten surfaces. There is a sacrifice in circuit breaking characteristics on high loads, however, due to the decrease in the number of contact gaps. The number of flat carbon discs 67 is determined by thickness and space considerations and they are used to obtain a change in resistance with a variation in pressure.

Overall advantages of the carbon pile forming the present invention are small size in relation to the current which it is capable of interrupting, high speed of operation, ability to dissipate much of the stored energy as heat rather than in destructive arcing, long life, reliability, and ease of adjustment to compensate for wear.

While there have been shown and described and point-- ed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. An electric circuit interrupter comprising a plurality of discs, means for mounting said discs in a freely rotatable stacked relation, at least some of said discs being constructed of a material Whose electrical resistance varies with the pressure applied thereto, means for compressing said discs to establish an electric circuit therethrough, means operating on said compressing means for removing the pressure applied to said discs, and means mounted between at least two of said discs for separating the contacting surfaces thereof and causing relative rotation therebetween.

2. An electric circuit interrupter comprising a plurality of discs, means mounting said discs in stacked relation, at least some of said discs being constructed of carbon, means for applying pressure to said discs to establish an electric circuit therethrough, means operatively connected to the last named means for removing the pressure applied to said discs, and means mounted between certain of said discs for separating the contacting surfaces thereof and causing unidirectional rotational motion of at least one of said certain discs.

3. An electric circuit interrupter comprising a stack of carbon discs, at least some of said discs being mounted for unlimited rotation, means engaging said stack of discs for applying a pressure thereto so as to establish an electric circuit therethrough, actuating means connected to said last named means for removing the pressure applied to said stack, and means engaging at least some of said discs for separating the contacting surfaces thereof and causing relative rotation therebetween.

4. A circuit breaker of the carbon pile type comprising a plurality of carbon discs, at least one of said discs having a metallic contacting surface, means mounting said discs in stacked relation, means engaging the stack of said discs for resiliently applying a pressure thereto to establish an electric circuit therethrough, means endiscs, said spring means applying a pressure to said stack.

of discs for establishing a circuit therethrough, means for relieving the pressure onsaid carbonpile, and means mounted between said discs for separating the contacting surfaces thereof to break the'circuit, said last. named means causing relative rotation between the contacting.

surfaces. of said. discs after said discs. have been. separated.

6. A carbon pile circuit breaker comprising a plurality of carbon discs mounted in stacked relation, spring means for applying a pressure to the: stack of said discs and causing relative rotation between two of said discs, and actuating means operatively associated withsaid last named means for removing the pressure from said discs and separatingthe contacting surfaces of the aforementioned discs having relativerotation.

7. A carbon pile circuit breaker comprising a plurality of carbon discs mounted in stacked relation, means for applying a pressure to the stack of said discs and causing relative rotation between two of said discs, and actuating means operatively associated with said last named means for removing the pressure from said discs and separating the contacting surfaces of the aforementioned discs havingrelative rotation, at least one of saiddiscs havingv relativev rotation being constructed to have a metallic contact surface.

8.. A carbon pile circuit breaker comprising-a: plurality of freely rotatable discs mounted in stacked relation, at least some of said discs being constructed of carbon, means for applying a pressure to. the stackof said discs and causing" relative rotation between two of said discs, and actuating means operatively associated with said last named means for removing the pressure from. said discs and separating the contacting surfaces of the aforementioned discs having. relative rotation.

9. A carbon'pile circuit breaker comprising a plurality of discs at least some of which-are constructed of carbon, said discs being mounted in stacked relation, means operatively engaging the stack of said discs for applying: a.

pressure thereto, and means for removing the. pressure from said discs, one of said discs being connected to one of said. means to cause separation betweensaid one disc and the remaining discs after said pressure isremoved,

and means between a plurality of the remaining discs for causing separation between the contacting surfaces thereof after separation between. said onev disc and the remaining discs.

10. A carbon pile circuit breaker comprising a plurality of discs at least some of which are constructed of. carbon, said discs being mounted in. stacked relation, means operatively engaging the stack of said discs for applying a pressure. thereto, and means for removingthe pressure from said discs, one of said discs being related to the last named means to cause separation between said one:

disc and the remaining discs after said pressure is removed, at least one of the separating surfaces between said one disc and said remaining discs being of ametallic contact material, and means between a plurality of the remaining discs for causing separation between the contacting surfaces thereof after separation between said. one disc and the remaining discs.

11. A carbon pile circuit breaker'comprising a plurality of carbon discs mounted in stacked relation,.rneansopera-- tively engaging the stack of said discs for applying apressure thereto so that the contacting surfaces thereof are in engagement, means for removing the pressure from said stack of discs, at least one pair of said. discs having tungsten welded thereto to form the only contacting surfaces therebetween.

12. A carbon pile circuit breaker comprising a plurality of carbon discs mounted in stacked relation, means operatively engaging the stack of said discsfor applying a pressure thereto,-..means for removing the pressure from saidstack of discs, at least one pair ofv said discs having tungsten welded thereto to form the contacting surfaces therebetween, and. means operatively engaging said pair of discs for separating the contacting surfaces thereof and causing. relative rotation therebetweenafter said separation occurs so that different portions of the contacting surfaces are moved into engagement when. engagement again occurs.

References Cited in the file of this patent UNITED STATES PATENTS 1,216,386 Williams et al Feb; 20, 1917 1,817,155 Leece Aug. 4, 1931' 1,839,629 Williams Jan. 5', 1932 1,873,499 Steinmayer Aug. 23', 1932 1,900,236 Hall Mar. 7 1933' 1,984,947 Schweibold Dec. 18, 1934 2,026,405 Thompson Dec. 31, 1935 2,406,449 'Whittaker Aug. 27, I946 FOREIGN PATENTS 470,875 Great Britain Ang.124, 1937

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