US1910068A - Circuit interrupter - Google Patents

Description

May 23, 1933. J sL 1,910,068

CIRCUIT INTERRUPTER Filed April 27, 1929 3 Sheets-Sheet l INVENTOR AITORNEY May 23-, 1933. J. SLEPIAN 1,910,068

CIRCUIT INTERRUPTER Filed April 27, 1929 5 Sheets-Sheet 2 a 2 w j fi MMIH HHHHHHWHIHH I m N a 3 L 3 w 8 a 219 2 lmwfiw --4| "m qi \i u w w T May 23, 1933. J. SLEPIAN CIRCUIT INTERRUPTER Filed April 27, 1929 Fig, 5.

3 Sheets-Sheet 3 INVENTOR Joseph Slepian BY We ATTORNEY Patented May 23, 1933 V urrsn jsraras ATE-NT OFFICE JOSEPH SLEPIAN, OF' PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA CIRCUIT INTERRUPTER Application filed April 27,

My invention relates to circuit breakers and particularly to circuit breakers of the type wherein the are drawn between the oncuit breaker contacts is exposed throughout its length or most of its length to the action of means accelerating the removal of ions,

so that thearc is prevented from reigniting after the current passes through zero value.

An object of 'my invention is to provldc means whereby the various portions of the arc length-are kept under the same electrostatic conditions irrespective of the potentials of the various portions of the arcspace and regardless of theproximity of adJacent grounded apparatus or electrically energlzed members.

A further object of my invention is to provide a circuit breaker of the above-mentioned type having a potential distributing shield associated with the deionizing means wherein means are provided for preventing the creation of electrostatic corona forming stresses in the air-gap between the distributing shield and the deionizingmeans and any auxiliary apparatus which may be contiguous to the deionizing means.

These and other objects that will be made apparent throughout the further description of my invention are obtained by means of the apparatus hereinafter described and illus trated in the accompanying drawings where- 111;

Figure 1 is a longitudinal section through a circuit breaker embodying features of my invention;

Fig. 2 is a development of certain of the tin foil potential distributing shields shown in Fig. 1;

Fig. 3 is an'end view of a complete shield assembly;

Fig. 4 is a longitudinal section through the shield shown in Figs. 1 and 3 showing the contour of the various shielding sheets employed ill my improved circuit breaker con- .Struction.

Figs. 5, 6 and 7 are developed views showing the individual tinfoil sheets which are used in the static shield; and

Fig. 8 is a diagram illustrating the elec- 1929. Serial No. 358,603.

trical relations invention.

In my Patent 1,784,760, issued December 9, 1930, I have disclosed a form of circuit breaker wherein the deionizing plates of P- shape and adapted to provide a recurrent path for the are which is compelled to travel in a circular orbit under the influence of a magnetic field produced by series-connected coils disposed between groups of plates and concentric to the orbit. A potential distributing shield is employed for uniformly distributing the potential difference between successive plates and one feature of my present invention constitutes an improvement in the form of a shield which produces a more perfect potential distribution by means of a simpler mechanical construction in design.

In. the copendin application of Robert C. Dickinson, Serial 0. 317,617, filed November 6, 1928, and assigned to the Westinghouse Electric & Manufacturing Company is disclosed a circuit breaker embodying features of the construction of the circuit breaker disclosed in my above-mentioned copending application wherein an improved form of electromagnetic device is used for creating a magnetic field for moving the are drawn between the circuit breaker contacts int the stack of deionizing plates. This electromagnetic device constitutes an auxiliary of the circuit breaker, the pole pieces of the electromagnet being disposed on opposite sides of the stack of deionizing plates and connected by an iron gprekband that substantially surrounds the The circuit breaker herein illustrated is similar in construction to the circuit breaker illustrated and described in the copending present in the structure of my vapplication of Robert C. Dickinson and the presence of the electromagnet core additionally efi'ects an unequal potential difference going into the particulars of the theories of operation of the circuit breaker as disclosed in the above-noted copending applications.

Referring to the drawings, the circuit breaker apparatus com rises a stationary contact 5 that is moun upon an arc horn 6 consisting of a plurality of spaced metal plates which terminate in a discharge opening 9 provided in the end-plate 11 of the supporting frame. The movable contact 12 is so pivotally mounted at a point not shown in Fig. 1 of the drawings that it may be moved to the right under the influence of a strong tension spring, not shown, when a short circuit condition occurs inthecircuit to which the circuit breaker is connected, when released by an electromagnetic trip mechanism not shown. The circuit breaker is arranged for manual trip so that the movable contact 12 may be moved to open position when desired by an operator. When the movable contact 12 opens, an arc is drawn between the contacts 5 and 12, one end of which is transferred to the arc horn 13 which comprises a plurality of spaced metal plates which terminate in discharge openings 14 provided in the end plate 15 of the circuit breaker frame structure.

Between the end frames 11 and 15, a stack 16 of metal deionizing plates 17 is provided, the plates being insulated from one another by insulating washers 18 and strips 19 which serve to separate the lates about of an inch apart, the plates being aproximately of an inch in thickii'ess. The plates which are of the shape indicated in doted lines in Fig. 3, are provided with entrance slots 21 for receiving the are drawn between the contacts 5 and 12 which is moved into the slots from the arc horns 6 and 13 by the influence of the electromagnetic field produced by the coils 30 of the electromagnet 36 shown in dotted lines in Fig. 1 which is disposed at right angles to the plane of the stack of plates. When the arc reaches the end of the slots in theplates, it is split into a number of short arcs correspondin to the number of plates in the stack and t e short arcs are rapidly moved toward the enlarged end of the plates where they are influenced by series connected coils '22 disposed between groups of the plates as indicated in Fig. 1 and which are wound concentric to the center of the large circular end of the plates. The coils 22 cause the arcs to then move in a circular or recurrent path in the manner specified in my copending application above referred to.

Immediately surrounding the stack of deionizing plates I provide an electrostatic shield 23 that conforms in contour to the edges of the plates and which abuts at one end and is conductively connected to the plate 11 of the circuit breaker frame and extends over and beyond the end plate 15 of the circuit breaker frame as shown in Fig. 1. The assembly of the circuit breaker frame, deionizing plates and intermediate coils 22 is retained by means of a metal-tension bolt- 24 that extends through the central opening of the deionizing plates and end plates 11 and 15 and which is insulated from the frame and plates by insulating bushings 25 and 26, the ends of the bolt being covered with insulat ing caps 27.

The shield 23 is substantially surrounded by the pole pieces of the clectroma et 36 and the connecting core band 20 for t e pole pieces 37 of the electromagnet.

It will be understood that the coils for producing the elctromagnetic field for moving the are from the contacts into the stack of deionizing plates is normally denergized and is energized through the medium of a relay at the time a short circuit occurs and that the coils 22 for producing the radial field for rotating the arc afterit has entered between the plates are connected to deionizing plates disposed on oposite sides of the coil and immediately adjacent thereto. Therefore, the coils of the elctromagnet and the coils for the radial field are energized only while the circuit is being interrupted.

The operation of the circuit breaker, such as disclosed in the above-mentioned copending applications and herein illustrated, is as follows: When the circuit breaker contacts 5 and 12 are separated, the are drawn between them is moved upwardly by the electromagnetic field, the ends of the arc first engaging the arc horns 6 and 13 and the arc subsequently moves into the slots 21 of the plates where it is finally broken into a large number of separate arcs that are caused to travel in a recurrent path at a high velocity until the alternatin current is zero. By reason of the deionizing action of the lates fully set forth in my above-mentioned copending application, the space between the plates becomes deionized in such a way that reignition of the are after current zero is prevented. The are is thus extinguished in less than one-half cycle and does not reignite providing there has been a sufficient number of deionizing plates provided to reduce the voltage between successive plates within the operating limits of the plates, such voltage limit per plate being found to be about 250 volts.

It has been found, however, that when voltage is applied to the end plates of a long uniform stack of plates insulated from one another, the potentialdoes not divide uniformly among the plates, but the potential difference between successive plates at the end of the stack may be many times the potential difference between successive plates in the middle of the stack. This is a consequence of the elementary principles of elec- The presence of auxiliary parts of the circuit breaker such as the core members and band of the electromagnet which surrounds the plates further tends to affect the potential distribution over the plates constituting the deionizing agentsand it is an object of my invention to provide an electrostatlc shield that compensates the unbalancing capacity effect of the auxiliary apparatus and to thereby effect a potential distribution among the plates wherein the potential difl'erence between successive plates is substant1ally umform. i a

The importance of maintalning a substantially uniform potential difl'erence between successive plates is apparent when the manner of the reignition of an arc in apparatus of this type is understood. It has been found that when voltage is impressed upon the deionizing plates, which may be considered condenser plates, that it may require a potential of approximately 250 volts on the cathode to break down into an arc. Whlle the normal working voltage of the circuit breaker may be somewhat under 250 volts per plate, at means are not used to take care of it, the d stribution of voltage among the plates Wlll not be at this uniform value but on the end plates a potential considerably higher than its normal working ,potential will be 1mpressed. In operation then, the arcs between these end plates will reignite after the current zero, this will cause the potential imposed upon the intermediate plates to be increased which will cause reignition of the arcs between these plates successively, resulting 1n a failure of the structure to open the circuit.

If the potential diflerences, between successive plates are not uniform and the potential difference between the end plates is considerably higher than that between the centrally located plates, the possibility of the are restriking the end plates is increased.

In the form of circuit breaker herein illustrated, I have 'found it necessary in order to equalize the potential difierence between successive plates to provide an electrostatic shield of irregular shape, the shape being inshield 23 having the contour of the edges of the plates constituting the stack. the shape of the shield being indicated in Figs. 3 and 4. In order to properly distribute the po tential among the plates, I have provided three compensating sheets comprising an inner sheet 29, an intermediate sheet 28, and an outer sheet 33, preferably made of tin foil and embedded in the insulating sheath and separated by insulating material, as indicated in Figs. 1 and 4. The sheets 28 and '29 are illustrated in their relative positions in Fig. 2 and their individual contours are shown in Figs. 5 and 6. The inner sheet 29 provided with terminals 3% that are elec= trically connected to the grounded end of the .185 of deionizing plates. The outer sheet 33 is 1 stack. The inner-sheet 29 and the outer sheet 33 are thus at opposite potentials corresponding to the ends of the stack and the intermediate sheet 28 floats electrostatically at a potential intermediate the potentials of the sheets 29 and The tin foil sheets are found to cause substantially uniform potential difference between successive plates of the stack if their areas and spacings are properly dimensioned as pointed out below.

The necessary requirement to obtain a uniform distribution of potential along the stack is that the charging current flowing between the plates through the stack shall be the same along the whole length of the stack. The plates are all of uniform dimensions along the stack so that the capacity between plates inthe same along the Whole stack. The uniform current flow then gives equal voltage drops across every gap and the desired uniform distribution of potential is obtained. This would not be true without the provision of the static shield since the capacitance of the plates to the grounded parts of the breaker would cause current to leak from the plates to ground at intervals along the stack thus diminishing the amount of current as it flows between the end plates through the stack. This current of different values flowing across the difierent gaps of the stack and the equal capacities across the difierent gaps of the stack, would then cause different voltage drops across the different gaps, or in other words, a non-uniform distribution of the potential along the stack. This is overcome in the structure of this invention by the provision of the tin-foil sheet 29 connected to the ungrounded end of the stack and its associated sheet 28, which together have such potential and capacity with respect to each plate 17 that the flow of current from the sheets 28 and 29 to each of the plate 17 is equal to the flow of current from the plate 17 to the grounded parts represented principally by the outer grounded sheet 33. This flow of current from the sheets 28 and 29 to t the plates 17 counteracts the effect of the leakage from the plates to ground and allows the amount of current flowing through the stack to be uniform along its whole length with consequent equal voltage drops across each gap between the plates.

The method of determining the shape to be given to the sheets 28 and 29 will now be described. Since the sheets 28 and 29 do not entirely surround the plates 17, there will, in general, be a certain electrostatic capacity (1 between any given particular plate and the grounded portions of the circuit breaker structure such as the electroma et core and su porting structure therefor El iot shown) or tlie outer sheet 33 where it is used and this capacity may be calculated or measured, by means well-known to electricians. There will also be a capacity C fixed by the shape'and position of the sheets 28 and 29, between the same plates 17 and the said sheets. These electrical relations are indicatcd in the diagram of Fig. 8 where the intermediate sheet 28 has been omitted for the sake of simplicity since the principles are the same without it. Suppose that, in accordance with the desireddistribution of potential among the plates 17 a straight line distribution being usually preferable as previously stated. the particular plate under discussion should have a potential e relative to the outer sheet 33 or other grounded parts; it will then have a potential (Ee) relative to sheet 29. E being the line potential at any instant relative to ground. The breadth of sheet 29 opposite each plate it covers should then be made such that U e=U (Ee) in order that the current flowing from the sheet 29 to each'plate 17 may equal the current flowing from each plate to the grounded parts. In this equation C is the only unknown quantity and is easily evaluated.

Where. as in the circuit breaker shown here, the spacing between sheet 29 and the edges of the various plates 17 is uniform, the capacity C is proportional to the breadth of sheet 29 opposite the plate in question. so that the breadth of sheet 29 at a point of its length corresponding to each plate 17 is readily determined.

It will be observed that sheet 29 does not extend so far lengthwise of the chamber as to cover all the plates 17. but that the sheet 28, which is spaced further away from the edges of these plates. does cover the remaining ones. It will also be clear that sheet 28 and sheet 29 constitute the plates of a pair of condensers in series between the edges of the remaining plates 17 aforesaid and the ungrounded terminal 15. Thus the total potential difierence between said remaining of current to each of the plates 17.

plates 17 and terminal 15 is subdivided between two condenser dielectrics in series, one that intervenes between sheet 29 and sheet 28, and the other that intervenes between sheet 28 and the remaining plates 17 aforesaid, in accordance with the well-known electrical laws. The capacity of the compound condenser thus constituted is less than that of either of its components separately; and likewise the capacity of this compound condenser is readily calculated. The capacity of that component condenser comprising the dielectric between sheets 28 and 29 is easily calculated once the shape of sheet 29 has been determined as above described. Thejnet capacity'C required for each of the remaining plates 17 being also known from the calculations above described, it is a simple matter to determine the breadth which must be given to sheet 28 opposite each plate 17 not covered by sheet 29. Thus the complete shapes of sheets 28 and 29 are determinable.

From the relations above it is seen that since the plates 17 at the left-hand end of the stack are at a potential only slightly greater than the grounded end plate 11, there will be very little flow of current from the plates at that end to the ground. The intermediate sheet 28 having a very narrow portion at the left-hand end, therefore, provides suflicient capacity, even though the sheet 28 is connected to the plate 15 at the op osite end of the stack only through the con enser formed by the plates 28 and 29, to cause sufficient current to flow to the plates 17 to equal the current flow from the plates to ground. As the plates 17 become further from the grounded end 11, the desired potential of the plates to ground becomes greater, thus increasing the amount of leakage current. The intermediate sheet 28 is, therefore, flared toward the right-hand end to provide the increased eapacitance necessary to give the requires flow t approximately the center of the stack the triangular tip 31 of the intermediate sheet 28 has reached almost the full width of the shield and the inner sheet 29 connected directly to the end plate 15 is then used to get the required increased flow of current to each of the plates 17. Since the inner sheet 29 is at a higher potential than the intermediate sheet 28, and since both the sheets 28 and 29 are effective in causing current to flow to the plates 17 in the right-hand end of thestack, sufiicient current flow to the plates is obtained at the center of the stack with the sheets 28 and 29 of reduced width. The sheets 28 and 29 then increase in width from the center of the stack to right hand end to give the required flow of current to the plates 17 at that end.

The tie bolt- 24 extends through the stack of plates 17 for its whole len h and is insulated from all of the plates; ince the plates trostatically float at a potential half way between line and ground potentials. This means that the tie bolt 24 will be at a higher potential than the plates 17 at the left-hand end of the stack and at a lower potential than the plates 17 at the right-hand end of the stack. Charging current, therefore, flows from the tie rod 24 to the plates atthe lefthand end of the stack, making it unnecessary to have the triangular tip 31 of the intermediate sheet 28 extend all the way to the lefthand end of the stack, as is shown in Fig. 1, since the flow of current from the tie bolt to the plates is as great as the flow of current from the plates to the grounded parts.

At the right-hand end of the stack where the tie bolt is at a potential less than the potential of the plates, the current flow will be from the plates to the tie bolt. This makes it necessary to cause additional current to flow to the plates. at the right-hand end of the stack from the sheets 28 and 29 in order to keep the potential of the plates 17 at the proper value. This is accomplished by the provision of the widened portions or wings 38 on the right-hand end of the inner sheet 29. It is thus seen that provision has been made at each end of the stack to correct the static unbalance which would otherwise occur in opposite directions at each end of the stack due to the tie bolt being electrostatically floated at a potential intermediate the potentials at the opposite ends of the stacks.

An additional advantage lies in the saving of insulation obtained due to the use of the two sheets 28 and 29 rather than by making the single sheet 29 of such shape as to give the desired potential distribution. If only a single sheet were used, it would be connected to line potential and would have to extend almost to the grounded end of the stack thus requiring the insulation between the sheet and the plates to be sufficient to Withstand line voltage. An equal thickness is also required between this single sheet and the outer grounded sheet so that the total thickness of insulation required would be that necessary for twice line voltage. By using the intermediate sheet 28 which floats electrostatically approximately half way between line and ground potentials, the sheet 29 at ground potential need extend only half the length of the stack' where the plates 17 are at a potential halfway between line and ground potentials. The insulation between the inner sheet 29 and the plates 17 need then be only one-half that necessary to withstand line potential. The insulation between the sheets 28 and 29 and between the sheets 28 and 33 is each equal that I needed for one-half line potential, so that the total insulation requiredv is only that necessary for one and one-half times line potential rather than twice line potential as is required if only a single sheet is used. This reduction in the thickness of the insulation is particularly important since the magnetic core 20 and its pole pieces which provide the blow-in field are outside the shield 23 so that the length of the air gap between the pole pieces is reduced by the reduction of the thickness of the insulation, thus making it possible to use a fewer number of turns on the blow-in coil.

With a shield such as has been described a high potential difference will exist between each deionizing plate and one or the other tin foil sheet. This potential difference will cause a high gradient in the air space between plate and shield and discharge will take place between the compensating shield and the plates. Similarly there will be a large potential difference between the tin foil and the 'electromagnet core which will cause corona.

Since such a discharge is undesirable because of its disintegrating efl'ect upon the insulation of the compensating shield, I provide means for preventing formation of corona stresses in the air-gaps between the sheets 28 and 29 of the shield and the plates 17 and electromagnet core 20 respectively. For this purpose 1 embed a protecting sheet 33 of tin foil of the shape indicated in Figs. 1, 2, 4: and 7 within the insulating shield exteriorly of the intermediate sheet 28 and this sheet is connected by terminals 34 to the core band 20 of the electromagnet, in order that the sheet 33 is given the same potential as the band and ground. It is thus seen that the outer tin foil sheet 33 serves as means for preventing corona as well as an outer grounded sheet, the capacitance of which to the plates 17 is definitely fixed so that the potential distribution between the plates may-be made uniform by provision of the tin foil sheets 28 and 29.

Parallel insulated strips 35 of tin foil are also embedded in the insulating sheath interiorly of the compensating sheet 29, the strips being arranged circumferentially and insulated from one another. The potential imposed upon the strips is not very much different from that imposed upon the immediately adjacent deionizing plates that are surrounded by the strip due to the fact that strips are so close to the plates 17 that they electrostatically float at a potential not much greater than the potential of the plates. As a consequence of this arrangement, a large part of the potential stresses that would ordinarily exist between the compensating sheets and the electromagnet core andthe deionizing plates respectively is imposed upon the tin foil sheet 33 and the strips 35, the stresses therefor being confined largely within the insulating sheath where no corona can be formed that is detrimental to the insulation. Since substantially the protecting sheet 33 has the same potential as the surrounding electromagnet core and, since the strips 35 have not very different potential imposed thereon than is imposed upon the plates, there is no high "oltage gradient between the respective elements where air-gaps intervene and therefore, in all cases, the sheets are so proportioned with respect to the apparatus that the electric gradient perpendicular to the external surface of the shield is less than 35,000 volts per centimeter, or a oteutial below that at which corona is pr need, no corona occurs in the space between them.

It will be seen from the foregoing that a simple and inexpensive means has been Erovided for distributing the potential di erence between successive plates uniformly and that the efiiciency of the circuit breaker is materially increased. The construction also eliminates the objectionable corona discharges ex erienced in circuit breakers of this type w ich employ a potential distributing shield.

While I have illustrated but one embodiment of my invention, it will be apparent to those skilled in the art that various changes, modifications, substitutions, additions and omissions may be made in the apparatus illustrated without departing from the spirit and scope of my invention as set forth in the appended claims. Where the specification or claims state that one end of the stack or other part of the structure is at ground potential and another part of the structure at line potential, it is understood that the two potenitals may be any two potentials which are different, such as if used on an ungrounded system where neither line terminal of the circuit breaker may be at ground potential.

I claim as my invention 1. Circuit interrupting means comprising a pair of members between which an arc may be drawn, a plurality of spaced plates of conductingmaterial positioned along the arc path, means to cause a uniform distribution of potential difference between said plates when the arc current is substantially zero and a plurality of narrow strips of conducting material insulated from each other and extending along the edges of said plates for preventing a corona discharge between the said plates and the said distributing means.

2. The combination with a circuit interrupting means comprising a pair of members between which an arc may be drawn, a plurality of spaced plates of conducting material insulated from one another and positioned along the arc path and a grounded auxiliary structure therefor, of an outer conductmg sheet interposed between the plates I and said structure and conductively connected to said grounded structure for definitely fixing the capacitance from the plates to ground and inner conducting means electrically connected to one of said plates and so shaped that the voltage drop between the plates is maintained substantially uniform.

3. The combination with a circuit interrupting means comprising a pair of members between which an arc may be drawn, a plurality of spaced plates of conducting material insulated from one another and positioned along the arc path and an auxiliary structure surrounding the said plates, of an outer sheet of conducting material extending substantially the whole length of said plurality of plates and interposed between the plates and said structure and conductively connected to one of the end plates and an inner sheet of conducting material of such shape in the vicinity of each plate that it counteracts the unbalanced capacitative effect of said outer sheet on the plates, and maintains a substantially uniform difference in potential between successive plates.

4. The combination with a circuit interrupting means comprising a pair of members between which an arc may be drawn, a stack of spaced plates of conducting material in sulated from one another and positioned along the arc path and an auxiliary structure adjacent the said plates, of a sheet of conducting material extending longitudinally of the stack of plates and conductively connected at one end to one of the end plates and being tapered in width for a substantial part of the length thereof toward the other end whereby the unbalanced capacitative effect of the adjacent structure on the plates is compensated and a substantially uniform difference in potential between successive plates is maintained.

5. The combination with a circuit breaker comprising a stack of plates of conducting material insulated from one another and positioned along the arc path of said circuit breaker, an auxiliary structure therefor and an electrostatic potential balancing shield disposed between the structure and the plates comprising an insulating sheath having an outer metal sheet embedded therein and extending substantially the whole length of the stack and electrically connected to one end thereof, of a plurality of narrow metal strips embedded in the sheath and disposed between the said outer sheet and the plates electrostatically floating at potentials near the potentials of the plates, said out sheet and said strips preventing electrostatic corona forming stresses in the air space between the insulating sheath and the structure and plates, respectively. Y

6. The combination with a circuit breaker comprising a stack of plates of conducting material insulated from one another and for intercepting an are drawn between a pair of members, a supporting structure therefor and an electrostatic potential balancing shield disposed between the structure and the plates comprising an insulating I preventmg sheath having a metal sheet electrostaticah ly fixed at one potential embedded therein, of a second metal sheet electrically fixed at another potential and a plurality of electrostatically floating metal strips embedded in the said sheath on opposite sides of the first said sheet and insulated therefrom for electrostatic corona forming stresses in the air space between the insulating sheath and the structure and plates, respectively.

7 The "combination'with a circuit break- 1 er comprising a stack of plates of conducting material insulated from one another and for intercepting an arc drawn between a pair of members an auxiliary structure theresheath surrounding the stack of plates and having a metal stress compensating sheet embedded therein, of a metal sheet embedded in the sheath and disposed 'exteriorly of the compensating sheet and connected to receive potential stresses corresponding to those of the surrounding structure and a plurality of parallel sheet metal strips embedded in the sheath and circumferentially disposed interiorly of the compensating sheet and each strip being positioned to receive potential stresses substantially corresponding to those of the immediately adjacent plates of the stack for preventing corona forming stresses in the air space between the sheath and the structure and plates, respectively,

8. In a circuit interrupter, means for causing an arc, a plurality of members of conducting material positioned along the path 7 of said are and electrically insulated from each other, a pair of capacitative means electrically at two different potentials, and the capacitance between one of said capacitative means and each of said members of conducting material varying according to the position of the member of conducting material so that the product of the potential of said capacitative means and its capacitance to each one of said members of conducting material is approximately equal to the product of the potential of the other capacitative means and its capacitance to the'same one of said members of conducting material.

9. In a circuit interrupter, means for causing an arc, a plurality of members of .conducting material positioned along the path of said arc and electrically insulated from each other, a pair of capacitative means electrically at two different potentials each positioned substantially uniformly from each of said members of conducting material, and thecapacitance from one of said capacitative means to each of said members of conducting material increasing along said plurality of members of conducting material.

10. In a circuit interrupter, means for causing an arc, a plurality of members of conducting material positioned along the path of said are and electrically insulated from each other, a pair of capacitative means electrically at two different potentials each positioned substantially uniformly from each of said members of conducting material, and the capacitance from one of said capacitative means to each of said members of conducting material increasing along said plurality of members of conducting material, and the capacitance from the other of said capacitative means to each of said members of conducting material being substantially constant along said plurality of members.

ll." In a circuit interrupter, means for causing an arc, a plurality of members of conducting material positioned along the path of said are and electrically insulated from each other, a pair of capacitative means electrically at two diderent potentials each positioned substantially uniformly from each of said members of conducting material, and the capacitance from one of said capacitative means to each of said members of conducting material increasing along said plurality of members of conducting material, and the capacitance from the other of said capacitative means to each of said members of conducting material being substantially constant along said plurality of members, and said other capacitative means substantially enclosing'said plurality of members of conducting material on two sides or more for the whole length thereof and being grounded to parts of the circuit breaker.

12. lbs a circuit interrupter, means for causing an arc, a stack of plates of conducting material positioned along the arc path and electrically insulated from each other, a sheet of conducting material positioned along said stack of plates and electrically connected to one of said plates and being tapered in width along a portion of the length of said stack,

13. lln a circuit interrupter, means for causing an arc, a stack of plates of conducting material positioned along the arc path and electrically insulated from each other, a sheet of conducting material positioned along said stack of plates and electrically connected to one of said plates and being tapered in width along a portion of the length of said stack, and a second sheet of conducting material positioned along said stack in capacitative relation to the first aforesaid sheet of conducting material, and said second sheet being tapered in Width along a portion of the length of said stack, a part of which length is different from the part along which said first sheet of conducting material is tapered in width.

14. In a circuit interrupter, means for causing an arc, a stack of plates of conducting material positioned along the arc path and electrically insulated from each other, a sheet of conducting material positioned along said stack of plates and electrically connected to one of said plates and being tapered in width along a portion of the length of said stack, and a. second sheet of conducting material positioned along said stack in capacitative relation to the first aforesaid sheet of conducting material, and said second sheet being tapered in width along a portion of the length of said stack, a part of which length is different from the part along which said first sheet of conducting material is tapered in width, and an outer sheet of conducting material extending along substantially the whole length and width of said stack of plates.

15. In a circuit interrupter, means for causing an are, a stack of plates of conducting material positioned along the arc vpath and electrically insulated from each other, a sheetof conducting material positioned along said stack of plates and electrically connected toone of said plates and beingtapered in width along a portion of the length of said stack, and a second sheet of conducting material positioned along said stack in capacitative relation to the first aforesaid sheet of conducting material, and said second sheet being tapered in width along a portion of the length of said stack, a part of which length is different from the part along which said first sheet of conducting material is tapered in width, and an outer sheet of conducting material extending along substantially the whole length and width of said stack of plates, and'a plurality of strips of conducting material Insulated from each other and extending adjacent the edges of said plates, said strips andsaid sheets of conducting material being embedded in a sheath of insulating material.

16. In a circuit interrupter, means for causing an are, a stack of plates of conducting material positioned along the arc path and electrically insulated from each other, a sheet of conducting material positioned along said stack of plates and electrically connected to one of said plates and being tapered in width along a portion of the length of said stack, and a second sheet of conducting material positioned along said stack in capacitative relation to the first aforesaid sheet of conductbedded in a sheath of insulating material.

17 In a circuit interrupter, means for causing an are, a stack of plates of conducting material positioned along the are path and electrically insulated from each other, a sheet of conducting material positioned along said stack of lates and electrically connected to one of said plates, the capacitance between said sheet of conducting material and each of said lates increasing along the length of the stac with the position of the plate in .the stack, a rod extending along said stack

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