US2428575A - Circuit interrupter - Google Patents

Description

Oct. 7, 1947- L. R. LUDWIG ETAL CIRCUIT INTERRUPTER Filed July 10, 1943 3 Sheets-Sheet l INVENTORS WlTNESSES: Z L XL 3 I77PB0ksr and fie /yerz J. Webb.

ATTO EY Oct. 7,

1 7. L. R. LUDWlG ETAL 2,423,575-

C IRCUIT INTERRUPTER :5 Shets-Sheet 2 Filed July 10, 1943 lNVENTOR5 Leon R. Ludwz 'a; Benjamin PBaker' and f/ar'barf J Webb Patented Oct. 7, 1947 UNITED STATES PATENT OFFICE CIRCUIT INTERRUPTER tion of Pennsylvania Application July10, 1943, Serial No. 494,213

' 7 Claims. 1

This invention relates to improvements incirextinguishers for circuitinterrupters of the gasblast type.

i The main object of our inventionis to provide an improved gas-blast circuit interrupter of improved construction which will interrupt the circuit therethrough in a-very short interval of time.

In United States Patent, 2,313,159, which issued March 9, 1943, to Leon'R." Ludwig and Benjamin P. Baker, and which was assigned to the assignee of the instant application, there is disclosed and claimed a gas-blast type circuit interrupter in which are disposed. two arcing chambers of the orifice type which are bridged by a. single tubular movable arcing contact. The tubular movable arcing contact sequentially :draws .a single arc through the two arcing. chambers, and the compressed gas is forced, radially inwardly, substantially transverselyof the terminal ends of the arc which extends through both arcing chambers. .The radial inward gas-blast changes its direction to one which is substantially parallel with the arc stream, and the gas isejected through the orifice in each arcing chamber and also through a discharge opening provided in'the .movable tubular arcing :contact. After the gas is discharged through the two orifices adjacent the arc stream, the gas is permitted'tofreely vent radially outwardly toithe. atmosphere.

Our present invention improves the construction disclosed in the aforesaid patent in a number of respects. 1 First, our present invention contemplates a simultaneous drawing of two arcs through the two orifices of thepair of arcing chambersinstead of a sequential drawing of a single arc which took place in the aforesaid patent. Consequently, the combined interrupting effectiveness of both arcing chambers is immedi ately used at the same time, and there is no delay in bringing into effect the interrupting performance of one arcing chamber prior-to the drawal of the arc into such arcing chamber as 'took' place in the aforesaid patent.

Another object ofourinvention is to utilize an improved operating .mechanism for actuating simultaneously the two serially connected movable contacts toward each other.

Further objects and .advantages will readily become apparent upon a reading of the following specificationtakenin conjunction with the drawings; in which:

Figure 1 is aside elevational view showing a circuit interrupter of the gas blast type embody- 2 ing our invention and shown in the open circuit position;

Fig. 2 is an enlarged vertical sectional View of the arc extinguishing structure of the circuit interrupter of Fig. 1 taken substantially on the line IIII of Fig. 3 and shown with the movable contacts making engagement with the stationary contacts;

Fig. 3 is a View in section, taken on the line III-III of Fig. 2;

.Fig. 4 is :anenlarged-vertical sectional view through the movable contact taken on the line IVIV of Fig. 2;

Fig. 5 is an enlarged fragmentary vertical sectional view taken on the line V-V of Fig. 4;

Fig. 6 is an enlarged side elevational view of the improved valve shown in' Fig. 2 which controls the operation of the movable contact mechanism;

Fig. '7 isa side view of the valve of Fig. 6;

Fig. 8 is an enlarged fragmentary vertical sectional'view of an arc extinguishing structure embodying a modification of our invention with the movable contact in the full open circuit position; and

Fig. 9 is an enlarged fragmentary vertical sectional view of a portion of the lower arcing chamber of the interrupter of Fig. 2 to show the improved dielectric condition adjacent the orifice as compared with the dielectric condition adjacent the orifice of Fig. 8,

Referring to the drawings and, in particular, to Fig. 1, the reference numeral l designates a suitable framework or base structure which supports tubular insulators 2, 3 at the upper ends of which is supported a metallic casing or housing 4 for the operating mechanism of the interrupter. Supported atthe upper end of the metallic casing 4 are tubular insulating means 5, in this instance assuming the form of a hollow insulator, which supports two serially related arcing chambers, generally designated by the reference numeral-B in Fig. 2. The lower arcing chamber 5 is supported at the upperend of the hollow insulator 5 by means of a clamping member 'l which is secured to the insulator 5 by cement 8. Bolts 9 secure the lower arcing chamber 6 to the clamping member 1.

The lower wall Iii of the upper arcing chamber 6 and'the upper wall I l of the lower arcing chamber 5 have formed therein discharge openings or orifices 12, the contour of which are formed by annular metallic inserts IS. The walls ill and H are of insulating material, and if the inserts l3 were not employed there would be a tendency for the arcs drawn through the orifices to burn the Walls of the orifices and. hence to change their contour. As mentioned previously, the size of the orifice i2 is largely determined by the maximum current to be interrupted, and, any increase in the size above this results in an unnecessary Waste of air. Therefore, it is desirable to prevent an enlargement of the orifice 12 by a burning of the walls thereof. The inserts l3 are, therefore, provided.

Tubular insulating members l4 provide a gas passage between the two arcing chambers S. Spacer sleeves I5 disposed about the tubular members l4 serve to space at the desired distance apertured insulating barrier members l6, which have as a part of their purpose the maintenance of the arcs in a centralized position when drawn through the orifices i2.

Insulating tie rods l9 pass through the lateral wall 20 of the upper arcing chamber 6 and are threadedly secured to the upper end of the lateral wall 28 of the lower arcing chamber 6.

A conduit 22 serves as a passage for the transmission of compressed gas from the tubular member l4 to the valve 24, where the compressed gas initially acts only on an area A, as indicated in Fig. 6. The valve 24 is biased to the left by a compression spring 25 which causes the valve 24 to close the passage 22 with the area A of the valve 24. An opening 25 is provided back of the valve 24 to prevent back pressure retarding the opening movement of the valve 24. An aperture 21, which is uncovered by the rightward movement of the valve 24, is employed to permit the compressed gas passing through the conduit 22 to act upon a piston 28 disposed and movable within a piston chamber 29.

The operating means or motor for the moving contact means disposed between the two arcing chambers 6 comprises the piston 28 movable vertically in the piston chamber 29 and having a link 30 pivoted thereto at 3|. The lower end of the link 30 is pivoted at 32 to a pair of crank arms 33 which are pivotally mounted on a stationary pin 34. The stationary pin 34 is mounted on a vertical metallic support plate 35. The lower end of the support plate 35 rests on an extension I8 of the wall I I, the latter forming the upper wall of the lower arcing chamber 6. The upper end of the support plate 35 is secured, as by welding, to an oifstanding metallic support plate 36 (see Fig. 3) which is secured in position by three of the tie rods 19. Preferably, the piston chamber 29 is secured, as by welding, to both the support plate 35 and the offstanding support plate 36.

An extension 3'! of each crank arm 33 is pivotally secured by a pin 38 to the movable arcing contact 39 having a discharge opening 40 therethrough as more clearly shown in Figs. 4 and 5. It will be noted that the upper end of the movable arcing contact 33 is bifurcated to form two upstanding legs 4| (see Fig. 4) between which is disposed a guide link 42 pivotally mounted on a pin 43 which extends through both legs 4| of the movable arcing contact 39. The guide link 42 is pivotally mounted at its other end to a stationary pin 44. The function of the guide link 42 is to guide the opening movement of the movable arcing contact 39 to prevent the latter from rotating too much about the pin 38 during the opening operation, as indicated by the dotted lines in Fig. 2.

Each crank arm 33 has integrally formed therewith an oifstanding arm 46 to which is pivotally 4 mounted a link 45 at 41. The left-hand end of the link 45 is pivoted at 48 to a pair of lever cranks 49 which are pivotally mounted on a stationary pin 50. Each lever crank 49 has a portion 5| which is pivotally connected by a pin 52 to a thrust link 53. The upper end of the thrust link 53 is pivotally connected at 54 to a pair of crank arms 55 which are analogous to the crank arms 33 which actuate the movable arcing contact 39 of the lower arcing chamber 6. The crank arms 55 are mounted on a stationary pin 56. The pin 56 and the pin 50 are both mounted on a vertical support plate 51, the lower end of which rests on the annular extension N5 of the insulating plate H. The upper end of the vertical support plate 5'! is secured to an extension 63 of the upper plate l0. Fig. 3 shows the extension 63 more clearly.

Biasing means are provided to bias the two simultaneously movable arcing contacts 39 into engagement with the tubular stationary arcing contacts 60. This biasing means may take the form of a pair of tension springs 59 which have their ends connected to the pins 54 and 58. It will, therefore, be apparent that the tension springs 59 tend to bias the movable contacts 39 into sliding engagement with the tubular stationary arcing contacts 60 against the action of the piston 28. Each tubular stationary arcing contact 60 has an insulating stream-liner 6! disposed at its end to assist in guiding the compressed gas radially inwardly towards the arc. Each tubular stationary arcing contact 60 is slotted at to have the end thereof resilient, and a tension spring 8| encircles the end of the tubular stationary arcing contact 60 to force the latter into engagement with the movable arcing contact 39. A discharge opening 62 is provided through each stationary arcing contact 66 and serves to permit a discharge of compressed gas to atmosphere.

A tubular insulator 65 is supported by the upper arcing chamber 6 and surrounds the upper tubular stationary arcing contact 60. At the upper end of the insulator 65 is a cap member 66 to which is secured a line terminal 61. The cap member 66 prevents gas flowing upwardly in the annular space 68 about the upper tubular stationary arcing contact 60, but permits the discharge of gas through the discharge opening 62 provided in the upper stationary contact 60 to atmosphere. Preferably, a louvered insulating housing 69, as shown more clearly in Fig. 1, is provided about both arcing chambers 6 to prevent rain and snow entering the region between the arcing chambers 6 and hence coming in contact with the operating mechanism. A disconnect switch housing "II is mounted on the metallic casin 4 and encloses the movable disconnect contact, not shown. A stationary disconnect contact 12 is positioned at the upper end of a tubular insulator 14, which may be used to enclose a current transformer or other metering equipment. The line terminal 15 is also positioned at the upper end of the insulator 14. The insulator 14 may be mounted on a framework 16 which may be supported at one side of the base structure I. A tank 11 of compressed gas, in this instance air, is supported by the base structure I, and an electrically actuated valve mechanism, generally designated by the reference numeral 18, may be employed to control the flow of compressed air out of the tank 11.

From the above description it will be apparent that in the closed circuit position of the interr'upter, not shown, the electrical circuit therethrough comprises the" line terminal 61, upper tubular stationary contact 60, upper movable arcing contact 39, crank arm 55, thrust link 53, lever crank 49, link 45, crank arm 33, lower movable arcing contact 39, lower tubular stationary arcing contact 60, movabledisconnect contact, not shown, Stationary disconnect contact 12, current transformer, not shown, to the second line terminal of the interrupter. The levers and pins between the upper contact 39 and the lower contact 39 may for. purposes of conduction be paralleled by a suitable conducting shunt.

When it is desired to open the electrical circuit passing through the interrupter, or in response to overload conditions in the circuit controlled by the interrupter; asv indicated by the current transformer enclosed in insulator l4, suitable relay structure may be operated to cause an actuation of the valve mechanism 18 to first permit a now of compressed gas upwardly through the tubular insulator 2 through a conduit, not shown, which connects'the tubular insulator 2 with the insulator 5 and upwardly in the annular space 64 between the insulator 5 and the lower tubular stationary arcing contact 60. Preferably, the tank pressure. is 350 pounds per square inch. This gas underpressure passesupwardly through the annularspace 64, into the lower arcing chamber 6 and to the upper arcing chamber 6 through the tubular members 14. It will be observed that the gas passing upwardly through the tubular member I4 will act through the conduit 22'and against the area A of the valve 24. The compression spring 25'is so selected as to permit the valve 24 to move to the right when the gas pressure adjacent the movable arcing contacts 39 is approximately 300 pounds persquare inch. It will be observed that prior to the opening of the valve 24 the gas pressure acting through the concluit 22 will only act on a surface area A of the valve 24. However, after the valve 24 has once moved to the right, the gas pressure acting through the conduit 22 will now act on the entire area A of the valve 24 to maintain the latter in its open position until a pressure of approximately 200 pounds per square inch adjacent the arcing contact 60 is reached. Thus the valve 24 opens at a relatively high pressure, but closes only at a considerably lower pressure because of the difference in the areas A and A When the pressure adjacent the movable arcing contacts 39 has reached a pressure of approximately 300 pounds per square inch the valve 24 will move to the right to permit gas acting through the conduit 22 to force the piston 28 downwardly within piston chamber 29. This downward movement of the piston 28will cause clockwise rotation of the crank arms 33and also a clockwise rotation of the lever crank 49-. The thrust link 53 will transmit the clockwise rotation of the levercrank 49' to cause a corresponding clockwise rotation of the crank arms 55 to thereby cause an opening movement ofthe upper movable arcing contact 39 at the same time that the lower movable arcing contact 39 is being opened. Consequently, the simultaneous opening movement of both movable arcing contacts 39 through the orifices l2 will cause a simultaneous drawing of two serially related arcs through these two discharge openings '1 2. -When the movable arcing contacts 39 pass through the discharge openings l2; the compressed gas within the arcing chambers 6 is permitted to vent through the discharge openings l2 and radially 6 outwardly to: atmosphere between the two plates l0 and H. The full open circuit position of the movable arcing contacts 39 is shown by the dotted lines in Fig. 2. When the two serially related arcs have been extinguished, compressed gas actuatesthe movable disconnect contact, not shown, to cause a separation of the latter from the stationary 'disconnect contact 12, When the movable disconnect contact, not shown, has been withdrawn from the stationary disconnect contact 12 into the disconnect housing ll, suitable means are provided to permit a lowering of gas pressure withinarcing chambers B. When the gas pressure adjacent the orifice I2 has dropped to 200 pounds per square inch the force exerted by the compression spring 25 overcomes the gas pressureacting throughthe conduit 22 and forces the valve 24 toward the left, as viewed in Fig. 2, to permit the compressed gas on top of the piston 28 to pass through the aperture 21 and out through the opening 26. The force exerted by the two tension springs 59 acts to cause an upward movement of the piston 28 and a consequent closing of the two pairs of arcing contacts. The closing of the arcing contacts, therefore, takes place after the disconnect contacts have opened and an air gap formed in series'with the interrupters. The closing of the arcing contacts 39, 60 removes the potential stress across the'two arcing chambers 6 and thereby causes the disconnect gap to take the entire electrical stress in the open circuit position of the interrupter as shown in Fig. 1. The disconnect gap is of sufficient length to readily assume the entire electrical stress across the breaker and to prevent reignition as a result of V ta e surges passing along the line. After the disconnect contacts have opened suitable means, not shown, are provided to stop the flow of air through the tubular insulators 3 to the disconnect operating mechanism.

When it is desired to close the interrupter, the valve mechanism 18 is actuated by suitable operating means, not shown, to cause a blast of air to'pass through the insulators 3 to thereby eilect a closing of the movable disconnect contact, the arcing contacts 39, Bll'already havin been closed.

It will be observed that we have provided a means for attaining high speed of the movable arcing contact 39' by having a sliding engagement between the movable arcing contact 39 and the upper end of the stationary arcing contact 60 as shown more clearly in the upper arcing chamber 6 of Fig. 2, the distance of sliding engagement between the movable arcing contact 39 and the stationary arcing contact 60 being designated by (D-I! It will be observed that in our improved construction by a simultaneous opening movement of both movable arcing contacts 39, that the interrupting effectiveness of both arcing chambers 6 comes into play immediately to thereby very rapidly causean extinction of the two arcs and consequent rapid'circuit interruption, In other words, each arcing chamber 6 thus performs half the task of effecting the interruption of the electrical circuit through the interrupter. In the interrupter of theaforesaid patent the single arc was drawn sequentially through both arcing chambers and if the interrupting duty was too severe to be handled by the upper orifice alone, it sometimes became choked with ionized gas While waiting for the arc to be drawn in the lower arcing chamber. Thus while waiting for the lower arcing. chamber to become efiective, some of the efiectiveness'of the upper one was lost. Our

improved construction as herein disclosed overcomes this disadvantage by drawing thetwo arcs simultaneously through the two orifices.

We have found that the high pressure gas chamber on the high pressure side of the orifice l2 should be such that the volume of gas contained within an imaginary portion of a sphere on the high pressure side of the orifice with the center of the sphere at the center of the orifice on the high pressure side thereof, and with a radius three times the diameter of the orifice l2 should exceed 100 cubic inches with the contacts in full open circuit position. Should an orifice of smaller area than 1.3 sq, inches be used, the volume of this adjacent gas space may be reduced proportionally. Radius R in Fig. 9 indicates the radius of an imaginary sphere having its center at the center of the orifice l2 on the high pressure side thereof. In computing the volume contained within this imaginary sphere, the volume of the streamliner BI and the volume of the stationary contact '50 should be subtracted. This results since when the movable contact 39 makes engagement with the stationary contact 60 the volume of gas within the contact 60 is not efiective and therefore cannot be included in computing the volume enclosed by the imaginary sphere. We have found that if the radius of the imaginary sphere is increased to a length which is 4 times the diameter of the orifice I 2, the volume included within such a sphere (see R in Fig. 9) on the high pressure side of the orifice l2 should be a least 200 cubic inches. Again the volume of the streamliner 6i and tubular stationary contact 60 is omitted and measurements are to be taken with the contacts in the full open position. We have found that excellent results are achieved if with the radius of the imaginary sphere R equal to 4 /2 times the orifice diameter, the volume enclosed in the sphere exceeds 250 cubic inches.

If the center of the imaginary sphere is taken midway between the upper end of the stationary contact 60 and the high pressure side of the orifice l2 with a radius R which is again three times the orifice diameter, the volume enclosed within such a sphere on the high pressure side of the orifice should exceed 100 times the cylindrical volume between the orifice l2 and the stationary contact 60, indicated by V in Fig. 2, again the measurements being taken with the contacts in the open circuit position. If the radius of such a sphere is increased to four times the orifice diameter as indicated by R in the lower arcing chamber 6 of Fig. 2, then the volume of gas contained within this imaginary sphere on the high pressure side of the orifice should exceed 100 times the volume V. Preferably the volume enclosed by such a sphere having the radius R should exceed 200 times the volume V".

If an imaginary sphere having its center at the center of the stationary contact 60 is used with a radius equal to three times the orifice diameter as indicated :by R in the upper arcing chamber 6 of Fig. 2, then the volume of gas contained within such an imaginary sphere on the high pressure side of the orifice should exceed 100 times the cylindrical volume V between the orifice I2 and the stationary contact 6B. We have also found that if the radius of the sphere is increased to four times the orifice diameter, as indicated by R in the upper arcing chamber 6 of Fig. 2, that the volume of gas contained within such an imaginary sphere should exceed times the cylindrical volume V between the orifice and stationary contact, all measurements being taken with the contacts in the open circuit position. Preferably, the volume within such a sphere having a radius four times the orifice diameter should exceed 200 V".

If a high pressure gas chamber having a relatively large volume and size is provided on the high pressure side of the orifice l2, the dimensions and volume of which may be determined as given above, then we have discovered that the dielectric condition around the streamliner BI and orifice I2 is improved so that the region of maximum voltage gradient is confined to the space directly between the orifice and stationary contact. This dielectric condition may also be improved by having the conducting parts which are electrically connected to the movable contact means, and therefore at the same electrical potential as the movable contact means, disposed above the level of the orifice. The term level of the orifice is more fully understood by an inspection of the lower arcing chamber 5 of Fig, 2 where the orifice level is indicated. More specifically, when the movable contacts 39 separate from the stationary contacts 60 and the arc in one of the arcing chambers 6 is extinguished, the electrical circuit through the interrupter will be broken. At this point the dis connect contacts will still be closed so that the restored voltage will be impressed across the two arcing gaps.

Figs. 8 and 9 show the contrast between having the lateral wall '20 of arcing chamber 6 composed of insulating material with a considerable volume enclosed thereby on the high pressure side of the orifice l2 as compared to the construction in Fig. 8 where the lateral wall 9| of the arcing chamber 6 is composed of conducting material which is at the same electrical potential as the movable contact 39 in Fig. 8. A portion of plate H in Fig. 8 has been made of conducting material so that the lateral wall BI is at the same potential as movable contact 39. In Figs. 8 and 9, on the right half of each view, are shown the electrostatic lines of force forming the electrical field at a time when the recovery voltage is impressed thereacross, and, of course, at a time when the arcs have been extinguished and when the disconnect contacts are still closed. The lines of electrostatic force have been drawn in Figs. 8 and 9 to show the contrast of electrical stress resulting form the two constructions. The density of the electrostatic flux lines at any point is equal to the potential gradient at that point. If at any point this gradient is greater than the dielectric strength of the insulation (the air in this case) there will be ionizing potentials and breakdown. Since the electrostatic flux density at any point in air will then be equal to the po tential gradient in volts per centimeter, it is apparent that in the construction shown in Fig. 8 the potential gradient at many points along the stationary tubular arcing contact 60 is much greater than in Fig. 9, where the lateral wall 20 is composed of insulating material and the conducting parts at the same potential as the movable contact 39 are disposed above the orifice level. Consequently, by positioning the electrical parts, which are at the same potential as the movable arcing contact 39, above the orifice level a much better distribution of electrostatic fiux lines is obtained and therefore the potential gradient along the stationary tubular arcing contact 60 is considerably reduced.

From the above description it will be apparent that we have provided a novel gas-blast interrupter having two arcingohambers (i disposed in spaced relation and having arcs simultaneously drawn in the two arcing chambers to utilize at the same time their combined interrupting effectiveness. The arcs are only drawn when-the pressure-adjacent the orifice l 2 is sufficiently high to insureinterruption and the contacts are biased to the closed position following a predetermined pressure drop after opening of the disconnect contactsto result in removing the electrical stress across the two arcing chambers and to place this electrical stress across the separated disconnect contacts. It will be observed that we have improved the flow of compressed gas through the orifice l2 by having the arcing chambers 6 constitute high pressure gas chambers adjacent the orifice, and this construction not only improves the dielectric condition adjacent the stationary arcing contacts but also cooperates with the positioning of the conducting parts of the interrupter which are at the same potential as the movable contact means above the orifice level, to thereby improve the electrical conditions adjacent the orifice. Also by increased contact speed and by a discharge of ionized gas through the contacts themselves, we have minimized the accumulation of ionized gas adjacent the orifice prior to the withdrawal of the movable arcing contact 39 through the orifice l2. It will be observed that the clamping means 1 which secures the lower arcing chamber 6 to the tubular insulating means are not at the same potential as the movable contact means 39. The direction of the gas fiow is indicated in Figs. 2, 4 and 5, although Fig. 2 shows the contacts in the closed position.

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

We claim as our invention:

1. In a gas-blast circuit interrupter, a pair of arcing chambers disposed in spaced relation with respect to each other, an arcing contact disposed in each chamber, the two adjacent walls of the arcing chambers having discharge openings therethrough disposed in alignment with the arcing contacts, a pair of movable arcing contacts movable toward each other completely through the discharge openings, a crank arm associated with each movable arcing contact to cause the actuation thereof, link means interconnecting the two crank arms to insure their simultaneous operation, and piston means operated by compressed gas to actuate the crank arms to move the movable arcing contacts toward each other during the opening operation.

2. In a circuit interrupter of the compressed gas type, a pair of arcing chambers disposed in spaced relation with respect to each other, the two adjacent walls of the arcing chambers having discharge orifices provided therein, means including a movable contact movable completely through each discharge orifice to establish arcs therethrough, the pair of movable contacts being movable toward each other, means for forcing a blast of compressed gas through each discharge orifice to cause the extinction of the arc established therethrough, a crank arm operatively connected to each movable contact to cause the actuation thereof. and means interconnecting the two crank arms to cause their simultaneous operation.

3 Th mbmatign i a, circuit interrupter of the compressed gas type of a pair of spaced wall members, each wall member having a discharge orifice provided therein, means for forcing a blast of compressed gas through each discharge orifice toward the other wall member, two movable contacts movable toward each other completely through the discharge orifices to establish two serially related arcs therethrough, a, crank arm connected 7 to each movable contact, and link means disposed between the two wall members for causingthe simultaneous operation of the two crank arms.

4. The combination in a circuit interrupter of the compressed gas type of a pair of spaced wall members, each wall member having a discharge orifice provided therein, means for forcing a blast of compressed gas through each discharge orifice toward the other wall member, two movable contacts movable toward each other completely through the discharge orifices to establish two serially related arcs therethrough, a crank arm connected to each movable contact, link means disposed between the two wall members for causing the simultaneous operation of the two crank arms, and a fluid motor also disposed between thetwo wall members for actuating the two crank arms.

5. In a circuit interrupter of the compressed gas type, a pair of arcing chambers disposed in spaced relation with respect to each other, the two adjacent walls of the arcing chambers having discharge orifices provided therein, means including a movable contact movable completely through each discharge orifice to establish arcs therethrough, the pair of movable contacts being movable toward each other, means for forcing a blast of compressed gas through each discharge orifice to cause the extinction of the arc established therethrough, a, crank arm operatively con nected to each movable contact to cause the actuation thereof, means interconnecting the two crank arms to cause their simultaneous operation, and all metallic parts at the same potential as the movable contacts being above the level of the orifice in each arcing chamber.

6. The combination in a circuit interrupter of the compressed gas type of a pair of spaced wall members, each wall member having a discharge orifice provided therein, means for forcing a blast of compressed gas through each discharge orifice toward the other wall-member, two movable contacts movable toward each other completely through the discharge orifices to establish two serially related arcs therethrough, a crank arm connected to each movable contact, and link means disposed between the two wall members for causing the simultaneous operation of the two crank arms and all metallic parts at the same potential as the movable contacts being above the level of the orifice for each wall member.

'7. In a circuit interrupter of the compressed gas type, a pair of spaced arcing chambers, the adjacent wall members of the arcing chambers having discharge orifices therethrough, a pair of movable contacts movable toward each other through the discharge orifices to draw two serially related arcs therethrough, means for sending a blast of compressed gas through the discharge orifices to effect extinction of the arcs drawn therethrough, and all metallic parts at the same 11 potential as the movable contacts being above the Number level of the orifice for each arcing chamber. 2,125,525 LEON R. LUDWIG. 716,475 HERBERT J. WEBB. 1,904,577 BENJAMIN P. BAKER. 5 1,898,900 1,794,682 REFERENCES CITED 1,873,388 The following references are of record in the 1,920,894 file of this patent: 2,048,496 10 2,156,663 UNITED STATES PATENTS 2,313159 Number Name Date 2,232,154 1,367,847 Kelman July 19, 1932 2,255,198 1,039,395 Hewlett Sept. 24, 1912 2,262,516 1,885,101 Ainsworth NOV. 1, 1932; 15 2,275,885

12 Name Date Thommen Aug. 2, 1938 Read Dec. 23, 1902 Uebermuth Apr. 18, 1933 Ruppel Feb. 21, 1933 Greenwood Mar. 3, 1931 Greenwood Aug, 23, 1932 Ruppel Aug. 1, 1933 Ehrenberg July 21, 1936 Cole May 2, 1939 Ludwig Mar. 9, 1943 Bakken May 5, 1942 Thommen Sept. 9, 1941 Prince Nov. 11, 1941 Bartlett Mar. 10, 1942

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