US2558075A - Circuit interrupter - Google Patents

Description

ET AL 2,558,075

June 26, 1951 R. c. DICKINSON CIRCUIT INTERRUPTER 3 Sheets-Sheet 1 Filed Feb. 11, 1948 INVENTORS Eoerf 60/07/150 andFuJjel/ Ff I /IK,

WITNESSES: 54. wa 2x1. M

ATTORNEY Pa tented June 26, 1951 CIRCUIT INTERRUPTER Robert C. Dickinson and Russell E. Frink, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 11, 1948, Serial No. 7,678

Claims. 1

This invention relates to circuit interrupters in general, and more particularly to are extin' guishing structures therefor, such as those mounted in grounded metal clad cubicle constructions.

. .It is a general object of our invention to provide an improved circuit interrupter of improved high voltage withstanding ability so that the performance of the interrupter as a whole is considerably increased.

Another object is to provide an improved cir cuit interrupter in which means are provided to evenly grade or distribute the voltage to be interrupted along the arc chute thereof.

Still another object is to provide an improved circuit interrupter in which a transverse magnetic field is employed to cause lateral movement of the arc, and to grade the voltage evenly along the arc chute while at the same time causing the potential of the laterally disposed magnetic pole plates to be substantially midway between the potentials of the arcing horns.

' A further object is to provide an improved circuit interrupter in which the insulation conditions are considerably improved in a simple and inexpensive manner.

- Further objects and advantages will readily become apparent upon reading the following specification taken in conjunction with the drawings, in which:

Fig. l is a side elevational view, partially in vertical section, of an air type circuit interrupter embodying our invention and shown in the closed circuit position;

Fig. 2 is a sectional view taken through the improved arc chute along the line IIEI1 of Fig. 1;

Fig. 3 is an enlarged fragmentary sectional view through an arc horn sub-assembly;

Fig. 4 is a graph depicting the voltage distribution along the arc chute in a conventional type of circuit interrupter;

Fig. 5 is a graph showing the improved voltage distribution along the arc chute resulting from an application of our invention to a conventional type of circuit interrupter;

Fig. 6 is a modified type of arc chute housing;

Fig. 7 is an enlarged sectional view through the arc chute housing of Fig. 6 taken along the line VII--V1I thereof;

Fig. 8 is a modified type of arc chute structure in which a different method, more simple and inexpensive than that of Fig. 2, is employed to effect a raising of the impulse withstanding ability of the interrupter;

Fig. 9 is a diagrammatic view of the arc chute structure of Fig. 8 showing the equivalent resistances and capacitances; and

Fig. 10 is an enlarged fragmentary view of a modified type of arc chute to take the place of that shown in Fig. 8.

Referring to the drawings, and more particularly to Fig. 1 thereof, the reference character I generally designates contact structure operable to draw an arc which moves upwardly into an interrupting chamber generally designated by the reference numeral 2. The are is interrupted within the interrupting chamber 2 to thereby interrupt the circuit controlled by the. interrupter.

More specifically, the contact structure I includes a terminal stud 3 surrounded by a flanged insulating bushing 4, the latter extending through a support plate 5 and secured thereto. At the right hand end of the terminal stud 3 is secured a stationary main contact 6 having a pair of outwardly extending metallic bracket plates 1 secured thereto. A rotatable contact arm 8 is pivotally mounted at 9 between the bracket plates 1, and is caused to move thereabout by the actuation of an insulating operating rod [2.

The operating rod I2 is actuated by suitable mechanism, not shown, which is responsive either to manual operation or to the existence of electrical overload conditions in the circuit controlled by the interrupter.

The operating rod [2 is pivotally connected at l3 between a pair of bracket plates 14, the latter being rigidly secured to and rotatable with the contact arm 8. Also movable with the contact arm 8 is a main contact bridge l5 formed of conducting material and electrically interconnecting the stationary main contact 6 with a second stationary main contact I1. The contact I! is secured to the right hand end of a second terminal stud [8, which is likewise enclosed within a flanged insulating bushing [9. The bushing I9 is secured to and supported by the framework or plate 5.

Also supported by the second stationary main contact structure H are a pair of relatively stationary secondary and arcing contacts, respectively designated by the reference characters 24, 25. The secondary contact 24 cooperates with a movable secondary contact 26 carried by the contact arm 8. The construction 'is such that the movable secondary contact 26 separates from the relatively stationary secondary contact 24 after disengagement of the contact bridge l5 from the stationary main contacts 6, ll. How- 3 ever, the secondary contacts 24, '25 separate prior to the separation of the arcing contacts 25, 21. Thus, the are which is finally drawn by operation of the contact structure I is drawn between the arcing contacts 25, 21.

Because of the loop circuit formed by the contact structure I, including the horizontally disposed terminal studs 3, l8 and the movable arm 8, the are which is finally drawn between the arcing contacts 25, 2'1 expands upwardly to there by cause one portion thereof to engage the panel arcing horn 38. The are position at this point of the opening operation is indicated by the dotted line 32, with the movable arcing contact 21- being moved to the position shown in dotted lines in Fi 1.

five have provided a suitable blow-out coil structure generally designated by the reference numeral 33 including a pair of blowout coils 34, 35 (Fig. 2) disposed in electrical parallel relationship. One end of each of the coils 34, 35 is connected to the panel arcing horn 30 by a stud bolt 28, as shown in Fig. 1. The other ends of the coils 34, 35 are connected to a bifurcated strap 36, the bight portion 3| of which is connected by the bolt 31 to the stationary main contact ll. Thus upon transfer of one terminal of the arc 32 to the arcing horn 38, the coil structure 33 will be connected into series circuit and will serve to energize the transverse magnetic field extending between the magnet pole plates 38, 39 more clearly shown in Fig. 2. This transverse magnetic field extending across the interrupting chamber 2 serves to cause upward movement of the arc, now designated by the reference numeral 43, into the arc chute 45 consisting of a plurality of spaced slotted ceramic plates 46.

The portion of the arc 4! indicated in Fig. 1, extending between the stationary arcing horn 25 and the panel arcing horn 30 is moved toward the left into a transfer interrupting stack, generally designated by the reference numeral 41, and consisting of a plurality of spaced slotted ceramic plates 48. The purpose of the transfer stack 41 is to effect interruption of the arc portion 4| so that the blowout coil structure 33 may readily be connected into series circuit. The details of construction of the transfer stack are set forth and claimed in U. S. Patent application filed January 4, 1947, Serial No. 720,166 by Herbert L. Rawlins, Robert C. Dickinson and Russell E. Frink and assigned to the assignee of the instant application.

Referring more particularly to Fig. 2, it will be noted that after the blowout coil structure 33 has been connected into series circuit and the magnetic field set up thereby between the pole plates 38, 38, the arc 43, extending between the arc horns 30, 44 will move upwardly into the arc chute 45. The are chute 45 effects the extinction of the are 43 by forcing it upwardly toward the closed ends of a plurality of slotted insulating ceramic plates 45. The upward movement of the are 43 into the arc chute 45 affects the restriction thereof and also an elongation thereof. The transverse magnetic field extending between the pole plates 38, 39 imparts to the electrons an upward component of velocity. These electrons bombard gas particles and produce an actual blast of gas perpendicular to the arc, which action requires the arc to ionize fresh quantities of gas in considerable quantity. When current zero is reached, this action is continued to effectively deionize the arc and establish dielectric in the arc chute 45. The theory of the interrupting ac tion is more clearly set forth in U. S. patent ap plication filed December 15, 1943, Serial No. 514,362, now U. S. Patent 2,442,199, issued May 25, 1948 to Robert C. Dickinson and Russell E. Frink and assigned to the assignee of the instant application.

The configuration of the interrupting structure 2, just described, makes it difficult to insulate for the higher voltages. It will be readily seen that the dielectric field pattern in such a structure is irregular and' difiicult to accurately analyze. However, certain conditions are apparent.

When the interrupter is in the fully open circuit position (not shown) the blowout coils 34, 35 and the panel end are horn 38 are connected to one breaker terminal l8, while the front are horn 44 is connected to the opposite breaker terminal 3, and full open circuit voltage will appear between these points. The magnet pole plates 38, 39 and the yoke portion 48 of the coil structure 33, being made of iron or other magnetic material, are all at the same potential which is normally somewhere between the potentials of the arc horns 38, 44. If the magnet 49, including the pole plates 38, 33 and the yoke 43, is floating, the capacity coupling between the yoke 43 and the blowout coils 34, 35 will place the potential of the magnet 49 and coils 34, 35 closely together, and practically all of the voltage will appear between the arc horn 44 and the right hand ends 50 of the pole plates 38, 39.

It is comparatively easy to place sufiicient solid 7 insulation between these points to prevent breakdown, but due to the high dielectric constant of the insulation materials (certain ceramic insulating materials having an S. I. C. as high as 11) and the small air voids existing between the components of insulation, the surrounding air is highly stressed and corona results with at tendant radio interference and insulation destroying ozone. Also the field distribution. which exists, and is shown approximately by Fig. 4, with the magnet 49 potential indicated, lowers the impulse strength of the arc chute 45 below the desired level. By impulse strength, we mean the ability to withstand surge voltage of very short duration between the arcing horns 44 with the contacts in the open circuit position. Dielectric field configuration is much more important in withstanding impulse voltage than it is in withstanding 60 cycle voltage.

We have discovered that the use of a band of slightly conducting insulating material such as a band of very slightly conducting paint 56 painted completely around the inside of the arc chute jacket or housing 52 and having its opposite ends connected to the arc horns 38, 44 gives considerable improvement in distributing the voltage along the arc chute 45 during the opening operation. Preferably the band of very slightly conducting but highly resistant material 56 is the same vertical height as the magnet pole plates 38, 33 and lies directly beneath it. The backs of the end vent liners 51 are preferably painted with this very slightly conducting paint forming a layer 51a (Fig. 3), which makes contact with the arc horn support screws 58. Contact between this layer 51a of very slightly conducting paint and the band 56 around the inside of the arc chute jacket 52 is made with contact springs 88, as shown in Fig. 3, the contact springs 58 being disposed between spacer strips 8! and the end liners 5?.

Thus, the opposite ends of the internal band 55 of paint are connected to the arcing horns 38,

44. During the opening operation, the use of such an internal band of paint connected electrically to the are home serves to aid interrupting performance by distributing the voltage evenly along the length of the arc chute 45. The explanation for this is as follows: Let it be assumed that there is no layer of semi-conducting compound 56, and the upper terminal l8 of the breaker (to which is connected the blow out coil 33 and arcing horn 35) be grounded. If voltage is applied to the lower terminal 3 of the breaker (to which is connected arc horn 44) a dielectric field will be established. If the gradient of this field is examined along a line from are horn 39 to are horn 44 the gradient of any point along the line will be determined by capacity at that point to surrounding objects. Along most of the line the magnet pole plates 38, 39 are the closest conductors, and they are also much larger than the arc- horns 39, 44. The result is a high gradient close to are horn 44 and a much lower gradient over the remaining distance. This is shown in Fig. 4.

If the conditions described are altered by placing an internal semi-conducting band 56 in the arc chute 45 connected electrically to the arc horns 39, 44, this band 56 will act as a potentiometer and the gradient between the arc horns 3D, 44 measured over the surface of the band 56 will be constant except for minor efiects caused by capacity currents flowing in the band 55. If the gradient along a line connecting the arc horns 3U, 44 is examined under these conditions, it is found that the band 58 acts as a shield from the magnet pole plates 38, 39 and the gradient along this line follows closely the gradient along the band 56. The result is that the maximum gradient is much lower.

When this structure is required to interrupt an A. C. are 43 there is an interval of a few microseconds in which this must be accomplished. The current has ceased to flow and transient recovery voltage appears between the arc horns 3B, 44. The gaseous path previously occupied by the are 43 has partially recovered its dielectric strength, more or less uniformly throughout its length and has a definite breakdown strength of volts per unit length. If this is exceeded over any part of the arc length, progressive breakdown will take place and the arc will reignite. When the transient restored voltage appears the impressed gradient will be substantially as described in the aforesaid two paragraphs (altered somewhat by leakage in insulation due to high temperature), and this is the gradient over the path previously occupied by the are 43. It can readily be seen that with the conditions described in the latter of the two mentioned paragraphs a higher transient restored voltage can be impressed between the arc horns 30, 44 without exceeding the breakdown strength of the gas over any part of the path than can be done under the conditions in the first mentioned paragraph. Furthermore, the impulse strength is improved. There results a potentiometer effect with even voltage grading along the arc chute 45. This even voltage distributing eiiect is shown by the graph in Fig. 5, omitting reference to the potential of the magnet 49.

When restored voltage transients appear across the arc chute after an interruption, or a surge is impressed across the open breaker as might be caused by lightning, the maximum potential gradient between the two arc horns 39, 44 is greatly reduced by the flow of current 6 through this band of paint 56, and the maximum interrupting voltage or maximum voltage which may be withstood is thereby increased, as explained above.

In a particular instance, a very slightly conducting paint composed of varnish and a carbonaceous material was used. The carbonaceous material may consist of wood char, coal, bone black, graphite, or coke, and it may be suspended in varnish, gum arabic and ammonia as the vehicle. For an interrupter rated at 15 kv., the resistance between the arcing horns in the open position of the interrupter was 1300 megohms permitting a leakage current of 10 microamperes peak value to flow. The R. M. S. value was '7 microamperes. Our preferred range of resistance values between the arc horns is from 1000 megohms to 5900 megohms. A broader range which will give marked improvement over conventional operation is megohms to 10,000 megohms. There is bound to be wide variation in resistance valves between diiierent units due to the difficulty of applying the paint uniformly and the variation in batches; this is the reason for having the above ranges.

It might be montioned that personnel are not subjected to the hazard of electrical shock by the shuntin resistance band 55 in the open circuit position of the interrupter, since the interrupter is operated in a grounded cubicle construction. When inspection is desired the interrupter is removed completely from the cubicle.

In addition to the marked improvement which may be obtained by the employment of a single internal high resistance band of very slightly conducting paint connected to the arc horns 44, 33, as described above, additional improvement may be obtained, as described below, which, in a particular instance, has doubled the lowest voltage at which corona appears, as well as giving a substantial increase in the voltage impulse level. A band of conducting material, or of a slightly conducting paint 5! is painted completely around the outside of the arc chute jacket or housing 52. This band 5! extends, in a particular instance, wider than the pole plates 32, 39 (extending A" above and below) as more clearly shown in Fig. l. Contact springs 53 of Phosphor bronze sheet are attached to the right hand ends 59 of the pole plates 38, 39, as shown in Fig. 2. Also contact springs 54 are secured by screws 55 to the interior sides of the magnet pole plates 38, 39, as shown in Fig. 2. These contact springs 53, 54 make contact with the semiconducting band 5!. Thisefiectively shorts out the air void between the arc chute jacket 52 and the magnet pole plates 38, 39, by making both sides of the void at practically the same potential. The are chute jacket 52 is then masked in the area where the springs 53, 54 make contact with the layer of semi-conducting paint 5! and the outside of the jacket 52 is painted all over with a good grade of varnish.

The masking is then removed so the springs 53, 54 can make contact with the semi-conducting paint 5i but the balance of the semi-conducting paint 5!, is protected from sending. Also the varnish has the effect of burying the semi-conducting sheet 5| under the surface which discourages formation of corona at the edges.

The presence of the external band of semi-conducting paint 5! cooperates with the presence of the internal band of very slightly conducting paint 55, previously described, in a manner more fully described below.

When potential is across the breaker terminals 3, IS, the band 56 forms a very high resistance potentiometer of the order of megohnis, which.

distributes the potential evenly between the arc horns 33, i t. The capacity of the inside band 58 to the outside band (which may be made of highly conducting material) tends to bring the outside band 5! to a point midway between the potentials of the arc horns 3Q, 44. Since the magnet i!) is connected electrically to the outside band in by the contact springs 53, 5%, it also is at a potential approximately halfway between the arc horns 38, l l. The potential distribution is now approximately as shown in the graph of Fig. 5 where the ordinates indicate voltage and the abscissae represent horizontal dimensions along the arc chute Q5, and the magnet 49 potential is indicated.

It will be observed that internally within the arc chute 45 the voltage gradient is much more uniform; and, externally, the potential which formerly appeared. around the front of the arc chute housing 52 has been divided evenly between this point and the blowout coils 3Q, 35 to the magnet 49. The semi-conducting paint around the front of the arc chute jacket 52 grades the potential evenly over the surface, while at the panel end of the interrupter the solid insulation is constructed to place the stress internally, and the coils 34, 35 and yoke 48 together constituting a sub-assembly 62 is impregnated to fill up internal voids.

The insulation level of the foregoing circuit interrupter can be raised still further by properly placing sections of foil internally in the arc chute jacket 52 as it is being wound. Such a modified type of arc chute jacket 63 is shown in Figs. 6 and 7. These figures collectively show that while the arc chute jacket or housing 63 is being wound with insulation paper upon a form, not shown, the metal foil pieces t l, 55, El, 88 are placed between the layers of paper. As before, the band of at least slightly conducting paint 5! extends completely around the outside of the arc chute jacket 63. The inside of the arc chute jacket 83 is painted with at least slightly conducting paint only at the ends, as at 35, 58.

Such a construction, when substituted for the arc chute jacket 52 of Figs. 1 and 2 will, by an increase of the capacity coupling between the magnet 33 and the internal segments 62, St, the latter being connected to the arc horns A l, 38, insure that the potential oi the external band El, and hence the magnet it, will be midway between the potentials of the arc horns 33, M.

Furthermore, such a construction will distribute the voltage gradient over the external and in ternal surfaces of the jacket and greatly reduce stress concentration in the air adjacent to these surfaces. This permits operation at a much higher voltage Without the formation of corona. Preferably the capacities between 5! and 8?, between ill and 63, and between 88 and 83 are approximately equal. Then the voltage between El and 83 will divide equally between the layers 5i, El, 68 and as and the maximum voltage that can appear on the external surface between 5! and the projected edge of 87 is somewhat less than oi the total voltage between 5i and 82. If the internal ioils were not present practically all of the voltage between 5! and 89 would appear over this surface. The same conditions hold on the inside surface between 55 and t3, and also at the opposite end of the jacket 63 between 53, E4, 65 and 8%. It might be pointed out that 8 although, as described, the external band 5i and internal sections 68 ard 89 are of at least slightly conducting paint, these items may also be made of foil without impairing the operation. However, if foil is used for these items, it would preferably be buried under the surface in the man-- ner previously described to prevent scuffing, and solid electrical connections brought out to connect external band 51 to the magnet assembly 49 and the internal sections 66, 69 to their respective arc horns 44, 38'.

If the degree of improvement in insulation required for a particular rating is not enough to require the details described above, a considerable improvement can be obtained by dipping the coil and yoke assembly 82 in at least slightly conducting paint (or spraying highly conductive material thereon) and connecting electrically this layer 62a of paint to the magnet pole plates 38, 39, as shown in Fig. 8. Also the potential at the front of the arc chute jacket or housing 18 is graded by employing external and internal bands of at least slightly conducting paint H, F2. The bands ll, l2 may, however, be made of a highly conductive material as foil. The internal band i2 is electrically connected to the arc horn 44 by the spring construction, as previously described in connection with Fig. 2. It will be noted that in this construction, it is not necessary to employ any paint with the end of the jacket ll) associated with the arc horn 38.

As stated previously, in a conventional type of interrupter where the components are allowed to seek their natural potentials, most of the voltage will appear between arc horn 413 and the right hand ends 58 of the pole plates 38, 39. This. causes a high gradient over the external and internal surfaces of the insulating arc chute jacket it between the ends of the pole plates 38, 39. This is greatest at the corners 58 of the pole pieces 38, 39 On the outside and the arc horn support screws 58 on the inside. The maximum gradient at these points can be substantially reduced by the aforesaid construction of Fig. 8 by applying the partial bands of at least slightly conducting paint 7!, l2 around the front of the arc chute jacket l8.

These bands ll, 72 are of the same vertical height as previously described in the construction of Fig. 2, and extend horizontally approximately as shown in Fig. 3. This increases the capacity coupling at the front end of the arc chute, and to prevent too high a gradient between the blowout coils 34, 35 and the yoke 43, the capacity at the panel end or" the arc chute is proportionately increased by applying the coating of at least slightly conducting paint 82a over the coil and yoke assembly 63, and making electrical contact to the magnet pole pieces 38, 39. The schematic electrical circuit is as shown in Fig. 9 when slightly conducting paint is employed for the coatings. The coatings in the Fig. 8 construction could be made of a highly conductive material by spraying conductive material thereon, such as zinc, aluminum, etc.

The capacities between the layers of paint 51a and H and between the layer of paint 62a, coils 35, and yoke Elli cause charging current to flow through the paint which evenly grades the voltage over the surfaces where high voltage stress appears, considerably lowers the maximum gradient which in turn raises the voltage which may be impressed on the apparatus Without the formation of corona. The use of a coating of paint with a relatively high resistance has the advantage over highly conductive coatings produced by spraying, in that the flow of charging currents produces a voltage drop along the high resistance coatings which reduces the potential gradient at critical points, such as between the are born 44 and the immediate adjacent portion 13 of the outer coating ll.

In the construction of Fig. 8, it is not necessary to utilize the spring clips 65, as shown in Fig. 8, to electrically interconnect the arc horn A l with the internal band of paint 72. As shown in Fig. 10, which is a modified form of arc chute utilizing the principles set forth in connection with Fig. 8, no spring clips 60 need be used. The end liner 51, which is preferably of asbestos, serves as a slight conductor to electrically connect the arc horn 44 to the internal band of paint 12. However, the end liner 5'! may be formed of a material with substantially perfect insulation characteristics, such as mica, so as to completely insulate the arc horn 44 fro-m the internal band of paint [2. Even with the use of such a completely insulating construction between the arc horn 44 and the internal band of paint '22, still distinct advantages are achieved in grading the voltage and thereby increasing the interrupting rating of the interrupter as a whole.

From the foregoing description of several embodiments of our invention, it will be apparent that we have improved the operation and voltage withstanding ability of circuit interrupters in a simple and inexpensive manner. By grading the voltage along the arc chute, interruption of the arc is more readily achieved. Also the voltage impulse withstanding ability of the apparatus is raised, and the interrupter is more capable of withstanding voltage surges without consequent breakdown.

Although we have shown and described specific structures, it is to be clearly understood that the same were merely for the purpose of illustration and that changes and modifications may readily be made therein by those skilled in the art without departing from the spirit and scope of the appended claims.

We claim as our invention:

1. A circuit interrupter including a housing, a pair of conductors disposed interiorly within the housing adjacent opposite ends thereof, a layer of highly resistant material extending at least halfway around the inside wall of the housing, means connecting the pair of conductors to the ends of said layer, a portion of at least semi-conducting material on the outside wall of the housing, a blowout coil, means connecting the blow out coil to one of the conductors, a U -shaped magnet threading the blowout coil and having the legs thereof disposed on opposite sides of the housing, the legs of the magnet being electrically connected to said outside portion, and the capacity coupling between the magnet and the internal layer of highly resistant material bringing the potential of the magnet substantially midway between the potentials of the conductors following the extinction process.

2. A circuit interrupter including means for establishing an arc, an adjacently disposed arc chute including a housing, a pair of arc horns disposed at opposite ends of the housing, a layer of highly resistant material extending at least partway around the interior of the housing, means electrically comiecting the arc horns to the ends of said layer, another layer of at least semi-conducting material on the outside of the housing, a blowout coil for moving the established are within the are chute with the terminals thereof at the arc horns, means connecting the blowout coil to one of the arc horns, a U-shaped magnet threading the blowout coil and having the legs thereof disposed on opposite sides of the arc chute housing, the legs of the magnet being electrically connected to the outside layer of at least semi-conducting material, and thecapacity coupling between the magnet and the internal layer of highly resistant material bringing the potential of the magnet substantially midway between the potentials of the arc horns following the extinction process.

3. A circuit interrupter including means for establishing an arc, an adjacently disposed arc chute including a housing therefor, a pair of arc horns associated with the arc chute and disposed interiorly adjacent opposite ends of the arc chute housing, a highly resistant layer of paint extending entirelyaround the inside wall of the housing, a layer of at least semi-conducting material on the outside wall of the housing, a blowout coil for moving the are within the arc chute with the terminals thereof moving along the arc horns, means connecting the blowout coil to one of the arc horns, a U-shaped magnet threading the blowout coil and having the legs thereof disposed on opposite sides of the arc chute housing, the legs of the magnet being electrically connected to the outside layer of at least semiconducting material, means electrically connecting the arc horns to the internal layer of paint, and the capacity coupling between the magnet and the internal layer of paint bringing the potential of the magnet substantially midway between the potentials of the arc horns following the extinction process.

4. A circuit interrupter including a U-shaped blowout magnet and an arc chute disposed between the legs thereof, a pair of spaced conductors within the arc chute, means for establishing an are between the pair of conductors, a capacity layer of highly resistant material extending between the spaced conductors, and the capacity coupling between the magnet and the capacity layer bringing the potential of the blowout magnet substantially midway between the potentials of the conductors following the extinction process.

5. A circuit interrupter including an arc chute housing, a pair of conductors disposed interiorly within the housing adjacent opposite ends thereof, a pair of spaced layers of at least slightly conducting material disposed along the inside wall of the arc chute housing, means electrically connecting the pair of conductors to the spaced layers, one or more pairs of substantially U-shaped spaced foil sections disposed interiorly within the material constituting the arc chute housing, a layer of at least slightly conducting material extending along at least a portion of the outside wall of the arc chute housing, a blowout coil, means connecting the blowout coil to one of the conductors, a U-shaped magnet threading the blowout coil and having the legs thereof disposed on opposite sides of the arc chute housing, the legs of the magnet being electrically connected to the outside layer of at least slightly conducting material, and the capacity coupling between the magnet and the internal spaced layers bringing the potential of the magnet substantially midway between the potentials of the conductors following the extinction process.

6. A circuit interrupter including means for establishing an are, an adjacently disposed arc chute including a rectangularly-shaped arc chute housing, a pair of arc horns associated with the arc chute and disposed interiorly adjacent opposite ends of the arc chute housing, a pair of spaced internal sections of at least slightly conducting material disposed adjacent opposite interiorends of the arc chute housing, one or more spaced substantially U-shaped foil sections disposed interiorly within the material constituting the arc chute housing, a band of at least slightly conducting material extending along the outside wall of the arc chute housing, means electrically connecting the arc horns to the spaced internal sections, a blowout coil for moving the are within the arc chute with the terminals thereof at the arc horns, means connecting the blowout coil to one of the arc horns, a U-shaped magnet threading the blowout coil and having the legsthereof disposed on opposite sides of the arc chute housing, the legs of the magnet being electrically connected to the outside band of at least slightly conducting material, and the capacity coupling between the magnet and the internal sections bringing the potential of the.

magnet substantially midway between the potentials of the arc horns following the extinction process.

7. A circuit interrupter including a U-shaped blowout magnet, a blowout coil around the bight portionof the magnet, a layer of at least slightly conducting material around the bight portion and the coil and in electrical contact with the legs of the blowout magnet, an arc chute disposed between the legs of the blowout magnet, a

pair of spaced conductors disposed interiorly adjacent opposite ends of the arc chute, means for establishing an arc between the conductors, insulating means disposed within the arc chute to effect extinction of the are therein, a pair of spaced magnet pole plates on opposite sides of the arc chute for causing the motion of the arc, internal and external spaced layers of at least slightly conducting material associated with the end of the arc chute adjacent the open end of the blowout magnet, and the legs of the blowout magnet being electrically connected to the external layer.

8. A circuit interrupter including a U-shaped blowout magnet, a blowout coil around the bight portion of the magnet, a layer of at least slightly conducting material around the bight portion and the coil and in electrical contact with the legs of the blowout magnet, an arc chute disposed between the legs of the blowout magnet, a pair of spaced conductors disposed interiorly adjacent opposite ends of the arc chute, means for establishing an are between the conductors, insulating means disposed within the arc chute to efiect extinction of the arc therein, a pair of spaced magnet pole plates on opposite sides of the arc chute for causing the motion of the arc, internal and external spaced layersaof at least slightly conducting material associated with the end of the arc chute adjacent the open end of the blowout magnet, the legs of the blowout magnet being electrically connected to the external layer, and means at least slightly electrically connecting the conductor adjacent the open end of the arc chute to the internal layer.

9. A circuit interrupter including an arc chute, a pair of spaced conductors within the arc chute, means for establishing an are between the conductors, a blowout coil for moving the established are within the arc chute, a U-shaped magnet threading the blowout coil and having the legs thereof disposed on opposite sides of the arc chute, a layer of slightly conducting insulating material of appreciable area extending along the wall of the arc chute and having its ends electrically connected to the pair of conductors to grade the distribution of voltage along the arc chute, and the capacity coupling between the magnet and the slightly conducting layer bringing the potential of the magnet more nearly halfway between the potentials of the conductors following the extinction process.

10. A circuit interrupter including an arc chute, a pair of arc horns disposed at opposite ends of the arc chute, means for establishing an are between the arc horns, a blowout coil for moving the established arc within the arc chute, a U-shaped magnet threading the 'blowout coil and having the legs thereof disposed on opposite sides of the arc chute, a layer of slightly conducting insulating material of appreciable area extending along the wall of the arc chute and havin its ends electrically connected to the pair of are horns to grade the distribution of voltage along the arc chute, and the capacity coupling between the magnet and the slightly conducting layer bringing the potential of the magnet more nearly half-way between the potentials of the arc horns following the extinction process.

ROBERT C. DICKINSON. RUSSELL E FRINK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,819,207 Slepian Aug. 18, 1931 1,927,888 Dickinson Sept. 26, 1933 2,215,797 Sauer Sept. 24, 1940 2,284,856 Bennett June 2, 1942 2,336,316 Thomm-en Dec. 7, 1943 2,446,859 Traver et a1 Aug. 10, 1948 2,447,674 Strom t al. Aug. 24, 1948

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