US3114816A - Circuit breaker of gas blast type having insulator bushing means for externally locating an impedance means - Google Patents

Description

1963 J. w. BEATTY CIRCUIT BREAKER 0F GAS BLAST TYPE HAVING INSULATOR B MEANS FOR EXTENALLY LOCATING AN IMPEDANCE MEANS Filed Sept. 22, 1960 6 l 1 t 8 8 9 6 4m m Hw h. U t 3 W Inventor: John W. Beatbg, a/Jaw. W

Attorn e5.

Dec. 17, 1963 J. w. BEATTY ,8

CIRCUIT BREAKER OF GAS BLAST TYPE HAVING INSULATOR BUSHING MEANS FOR EXTENALLY LOCATING AN IMPEDANCE MEANS Filed Sept. 22. 1960 2 Sheets-Sheet 2 VJIIIIIIII Yl'llI/lll/i EM m m. T C e e B n mi nn M 1h- 0. J u: b

United States Patent Clll CUlT BREAKER 0F GAS BLAiBT TYPE HAVING INSULATUR BUEEHING MEAN FGR EXTER- NALLY LGCATHNG AN IMPEDANCE MEANS John W. Beatty, Newtown Equare, Pa, asslgnor to General Electric (Iornpany, a corporation of New York Filed Sept. 22, 1960, $92. No. 57,747 9 Claims. (6i. 290 448) This invention relates to an electric circuit breaker of the gas-blast type and more particularly relates to a circuit breaker of this type which has voltage-controlling impedance means connected in shunt with its main contacts.

For controlling the voltage developed across the main contacts of the circuit breaker during a circuit-interrupting operation, it has been customary to shunt these contacts with an impedance through which current is transferred when the main contacts are separated to interrupt the circuit. For interrupting the current through the impedance, there is customarily provided an auxiliary switch which opens within a few cycles after the main contacts have been separated.

A typical gas-blast circuit breaker containing such a voltage-controlling impedance and auxiliary switch is shown and claimed in US. Patent 2,911,546 to Oppel, assigned to the assignee of the present inveniton. In the circuit breaker of that patent, the voltage-controlling impedance is a resistor located within a tank that surrounds both the main contacts of the breaker and the contacts of the auxiliary switch. This tank is filled with pressurized gas that acts to extinguish the arcs drawn at the main contacts and the auxiliary contacts during a circuit-interrupting operation.

Locating the resistor internally of the tank presents certain problems, particularly if the resistor is to be or" a relatively low ohmic value. One such problem is that a low ohmic resistor designed for the high currents involved is quite bulky and therefore difiicult to fit into the tank without necessitating certain design complications, such as a considerably larger tank than would otherwise be required. Another problem is one of dissipating the large amounts of heat generated by the relatively high currents that will flow through a low ohmic resistor during interruption. If the resistor is within the pressurized tank, the large amounts of heat generated will tend to raise the pressure and temperature of the gas within the tank to unduly high levels.

One way of lessening these problems is to locate the resistor outside, rather than inside, the tank. Prior efforts along these lines have not been entirely successful, primarily due to the great expenses that have been involved in providing adequate insulation for the required connections to the externally-located resistor. For example, one eifort along these lines has required two auxiliary high voltage bushings, each adequate to withstand substantially the same voltages as the main terminal bushings of the breaker. Such auxiliary bushings are unduly expensive.

Accordingly, an object of my invention is to construct the connection between an externally located resistor and the usual power circuit through the breaker in such a manner that the connection requires a near-minimum of expensive insulation beyond that otherwise needed in the breaker.

Another object is to construct the connection between the resistor and the main power circuit through the breaker in such a manner that the added insulation used for the connection is required to withstand considerably less voltage than the voltage that the main terminal bushings are required to withstand and is, moreover, required 3,114,816 Patented Dec. 17, 1963 to withstand this lesser value of voltage only during the short interval when current is flowing through the resister.

In carrying out my invention in one form, I provide a circuit breaker comprising a tank containing pressurized gas. A pair of separable main contacts are located within the tank, and a main insulating bushing extends through a wall of the tank. The bushing comprises a tubular main conductor electrically connected between one of the main contacts and terminal structure located at the outer end of the bushing. The bushing structure also comprises a housing in which the tubular main conductor is supported. The housing comprises a hollow main insulator disposed externally to the tank and surrounding a portion of the tubular main conductor. Located externally to the tank and bushing is voltage-controlling resistance means. Located internally of the tank are the electrodes of an auxiliary switch. These auxiliary electrodes and the resistor are connected in series with each other and in parallel with the main contacts by conduc tive means comprising an auxiliary conductor providing a connection between one terminal of the resistor and one of said auxiliary electrodes. This auxiliary conductor extends through the bore of the tubular main conductor and is radially spaced therefrom in electrically insulated relationship. A first auxiliary insulator of tubular form surrounds a portion of the auxiliary conductor and is disposed at the outer end of the main insulator for supporting one end of the auxiliary conductor. A second auxiliary insulator of tubular form surrounds another portion of the auxiliary conductor and is disposed at the inner end of the bushing for supporting the other end of the auxiliary conductor.

For a better understanding of my invention reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side elevational view partly in section showing a circuit breaker embodying one form of my inven tion.

FIG. 2 is a cross-sectional view of a portion of the breaker shown in FIG. 1.

FIG. 3 is a diagrammatic view of the circuit breaker shown in its fully-closed position.

FIG. 4 is a diagrammatic view of the circuit breaker of FIG. 1 shown in its fully-open position.

FIG. 5 is a diagrammatic view showing the circuit breaker of FIG. 1 in a partially-open position in which its main contacts are open but its auxiliary contacts are still closed.

Referring now to FIG. 1, the circuit breaker shown therein is of the general type shown and claimed in my Patent 2,783,338 and in Patent No. 2,911,546 to Oppel, both of which are assigned to the assignee of the present invention. This circuit breaker comprises an enclosed interrupting chamber defined, in part, by a metallic tank 10 which is filled with pressurized arc extinguishing gas, preferably air.

Disposed within the tank 10 are two pairs 11 and 1 2 of separable main contacts connected in series-circuit relationship. Each pair of separable main contacts comprises a stationary contact 13 or 14 and a movable contact 15 or 16. The movable contacts 15 and 16 are pivotally mounted on a central metallic housing 17 which is electrically connected to the tank and which provides a conductive path interconnecting the two movable contacts 15 and 16. The movable contacts 15 and 16 are adapted to be simultaneously separated from their respective stationary contacts 13 and 14 by means of an operating mechanism generally indicated at 18 acting through a set of connecting links 19. The details of this operating mechanism form no part of the present invention and are therefore not shown in the drawing. Pref- 9 erably, however, this mechanism is constructed as shown and claimed in my aforementioned patent.

When the main contacts are separated by the operating mechanism 13, an arc is formed across each intercontact gap. This arc is quickly extinguished by flow of pressurized gas from the tank 149 to the exterior of the tank via a path extending through the inter-contact gap and through a nozzle structure 21 formed in the central housing 17. The path of this gas how is indicated by the arrows 2b in FIG. 1. This flow of pressurized gas is controlled by suitable valve means (not shown) internally of the central housing 17 and such valve means interrupts the flow of pressurized gas as soon as the circuit is interrupted. A more detailed description of the interrupting operation will appear hereinafter.

The main stationary contacts 13 and 14 are respectively supported on the inner ends of terminal bushings 25 and 26 extending through aligned openings provided in the wall of tank It). These bushings each comprise centrally-disposed conductive studs for carrying electric power to and from the contacts of the breaker through the openings in the wall of the tank It). The conductive stud of bushing 25 is a tubular metallic member 2'7 connected through metallic adapter structure 3% to the stationary contact 13. The adapter structure comprises a conductive contact-mounting block 32 and an end plate 3 mechanically and electrically connected together by means of circumferentially-spaced metallic rods 35. Each of these metallic rods is Welded or otherwise secured at its opposite ends to the parts 32 and 34, respectively. At the opposite, or outer, end of the stud 27, there is a conductive nut 5t) that forms a terminal for the circuit breaker to which a power line 36 is suitably connected. The stud 27 is thus electrically connected between the terminal structure 5% and the contacts 11 of tie circuit breaker.

When the main contacts of the circuit breaker are in open position, the tank lltl is at approximately a midpotential with respect to the two conductive studs extending through the bushings 2S and 26. Under these open circuit conditions, the insulation of these bushings and 26 serves to electrically insulate their respective conductive studs from the tank 1b, as will soon be described. Since the bushings 25 and 26 are substantially identical, only one will be described in detail.

Referring now to FIG. 2 which is a detailed cross-sectional view of bushing 25, it can be seen that the bushing comprises a tubular housing iii, 41, 42 surrounding the tubular conductive stud 27. This tubular housing is composed of a plurality of tubular insulating shells as and 41, preferably of porcelain, and a metallic tubular support 42 disposed between the two shells 4d and ill. End plates 34 and 44 are disposed at opposite ends of the housing 4-0, 41, 42, and through these end plates are transmitted forces tending to compress the insulating shells and 41, as will soon be apparent. A portion of the total force acting through the end plates as and to compress the insulating shells 4d and 41 is derived from a spring assembly 46 of Belleville-type compression springs disposed at the outer end of bushing 25. This compression spring assembly bears at one end against the end plate 44 and at its opposite end against force-transmitting structure mounted on the outer end of stud 27. This force-transmitting structure comprises an annular thrust Washer 48 surounding an abutment in the form of a nut 50 threaded onto the outer end of conductive stud 27. This nut 50 has a flange at its outer end carrying a series of jack screws 52 that bear against the annular thrust washer 48. These jack screws 52 can be suitably adjusted to vary the compression of the spring assembly 46. Since the compression spring assembly 46 is disposed between the end plate 44 and the force-transmitting structure 48, 50 attached to the end of conductive stud 27, it Will be apparent that the spring assembly 46, in seeking to expand, tends to force the end plate 34 to the right and the end plate 44 to the left, thus compressing the two insulating shells til and 41 between the end plates 34 and 44 and at the same time loading the conductive stud 27 in tension. The spring assembly 45 serves the desirable purpose of maintaining the insulating shells in compression despite unequal expansion of the main conductor 27 and the housing 40, 41, 42 of the bushing. The spring assembly 46 also serves to force the end plate into sealed relationship with the porcelain shell 41 and to maintain this sealed relationship despite unequal expansion of the main conductor 27 and the housing id, 41 4-2.

Between the housing 4-0, 41, 42 and the stud 27 there is a generally cylindrical chamber 55 that communicates with the pressurized gas in the tank 10 through openings 57 provided in the end plate 34. Thus, the chamber 5'5 contains pressurized gas at the same pressure as the gas in tank 1h. The pressurized gas in chamber 55 acts against a piston 59 suitably clamped to the outer end of stud 27 to urge the piston 53% to the righ This force tends to apply additional compressive forces to the inner insulating shell it A tube 60 of insulating material surrounds the piston 59 and a flange 62 formed on the tubular support 42 to define a cylindrical outer wall for the chamber 55. Suitable seals 63 are provided between the tube 60 and the parts 59 and 62 to prevent pressurized air from leaking axially past the tube 69 into the space surrounding the tube se. The space between the tube at} and the porcelain shell 41 is preferably filled with an insulating gas, such as sulfur hexailuoride, at a considerably lower pressure than the air within chamber 55.

Any suitable means may be used for holding the bushing 25 in place within its opening in wall tank 10, but I prefer to use the fastening means shown and claimed in application SN. 843,589, Oppel, filed September 30, 1959, now Patent No. 3,609,983, and assigned to the assignee of the present invention. This fastening means comprises a radially-split annular locking ring 7t? having an unstressed diameter slightly smaller than the diameter of a groove 72 provided in the outer periphery of the tubular supporting member 42. This locking ring is snapped into the groove '72 and in this position bears against the internal face of a reinforcing ring 73 Welded to the tank wall lltl. The tubular supporting member 42 has a radially outwardly extending flange external to the tank 110, and this flange carries jack screws 7 5 threaded thereinto. When the jack screws are tightened, the reinforcing members '73 of the tank wall is clamped between the locking ring it? and the jack screws '75.

For controlling the voltage developed across the contacts of a high voltage circuit breaker, it is customary to provide resistance means shunting the contacts of the breaker. The principal function of this resistance means is to control the rate of rise and the peak value of the usual recovery voltage transient that appears across the open contacts of the breaker following a current zero during the circuit-interrupting operation.

In the disclosed circuit breaker, the resistor for performing this function is schematically shown at disposed in a location outside the tank 10. This resistor 86 is preferably mounted on suitable conductive structure e32 mechanically connected to the end plate 44 and electrically connected to the terminal nut 5% through a suitable conductor 81. One terminal of the resistor 3% is electrically connected to the conductive structure 81, 32 and the opposite terminal is connected through a conductor S3 to the outer end of a conductive rod 85. This conductive rod, also referred to hereinafter as an auxiliary conductor extends in coaxial relationship through the tubular conductive stud 27 of the bushing into the tank It). This conductive rod is connected at its inner end to one terminal 83 of an auxiliary, or resistor, switch 90 through a suitable conductor 9'7.

The auxiliary switch 9% comprises a pair of electrodes 91 and 92 spaced apart to form an interrupting gap therebetween. The electrode 91 is supported on the central housing 17 by means of an insulator 93 which is capable of electrically isolating the electrode 91 from the central housing when the auxiliary switch is open. The electrode 92 is also supported on the central housing 17 but is electrically connected to the housing. Electrically bridging the two stationary electrodes 91 and 92 is a movable electrode 95 which in its closed position of FIG. 1 abuts against the two stationary electrodes. Thus, it will be seen that when the auxiliary switch 90 is closed, the series combination of the auxiliary switch 90 and the resistor 80 is connected in shunt with the main contacts 11 by means of a shunt circuit which extends through the parts 81, 82, 80, 83, 85, 87, 91, 95, 92 and 17.

The other set of main contacts 12 is shunted by a circuit similar to the shunt circuit described hereinabove around the main contacts 11. Since the parts forming this latter shunt circuit are substantially identical to those forming the first shunt circuit, corresponding parts of the latter circuit have been assigned corresponding reference numerals followed by the suflix a.

The electrodes of the resistor or auxiliary switch may be thought of as being auxiliary contacts or electrodes for the overall circuit breaker and are frequently referred to in the present application as auxiliary contacts or electrodes.

The auxiliary switches 91) and 9dr: are provided with a suitable operating mechanism that is capable of opening the contacts of these two switches substantially simultaneously and within a short time after the main contacts part. This operating mechanism can be of any conventional form but is preferably of the type shown and claimed in the aforementioned Oppel Patent 2,911,456. The details of the operating mechanism form no part of the present invention and have not been shown in the drawing. For the purposes of the present invention, it is sufficient to understand merely that the movable contacts 95 and 95a of the auxiliary switches 9i? and 9921 are con nected together by cross bar 97 of insulating material, and this cross bar is coupled to the movable main contacts 15 and 1 6 through an operating rod h 8. When the movable maincontacts are driven into their open position, the operating rod 98 and the cross bar 97 are driven upward and this lifts the movable auxiliary contacts 95 and 95:: from their respective stationary electrodes. The operating mechanism of the auxiliary switches is so con structed that the contacts of the auxiliary switches part at a precisely timed interval (e.g., 1.2 cycles) after the main contacts part.

For insulating the main power circuit through the breaker from the connection between the resistor 80 and the terminal 88 of the auxiliary switch 98, I provide a pair of cylindrical insulators 1% and 102 located at on posite ends of the terminal bushing 25. As will be apparent from FIG. 2, each of these insulators surrounds the centrally disposed conductive rod 85 and provides a support for one end of the conductive rod. The outer insulator 100 is mounted on the outer end of the terminal bushing 25 and is clamped in compression between the nut 50 and an auxiliary end plate 164 by means including a nut 196 threaded on the end of conductive rod 85. A suitable compression spring assembly 108 disposed'between the nut 106 and the end plate 104 controls the amount of clamping forces provided by the nut 113-6. The spring serves also to hold the insulator 106 in compression despite unequal expansions of the central rod 85 and the surrounding insulators and to maintain a sealed relationship between the end plate 164 at the insulator m despite such unequal expansions.

The other insulator 162 is clamped to the inner end of the bushing 25 by forces acting through an auxiliary end plate 110 bearing against the inner end of the insulator 19:2. This auxiliary end plate 116 is fixed to the conductive rod so that when the conductive rod 85 is forced to the right by tightening of the nut 11% at the opposite end of the conductive rod 85, the end plate 116 is forced to the right into clamping engagement with the auxiliary insulator 102. Thus, the insulators lltltl and H92, are maintained in compression by forces applied to their ends through the conductive rod 35.

For providing insulation between the conductive rod and the main conductor 27 of the bushin the bore of the tubular conductor 27 is radially spaced from the conductive rod 85 throughout the length of the main conductor 27 so as to provide an insulating space 112 between the conductive rod 85 and the main conductor 27.

insulating space 1 12 is filled with pressurized gas at the same pressure as the gas of the tank 1h since an opening 114- is provided in the end plate to afiord communication between the gas in tank 1d and the in sulating space 1 12. Since this gas is at a relatively high pressure, only a small separation between the concentric parts 27 and 595 is needed to withstand a relatively high voltage between these parts. In certain applications, the space between the parts 217 and 85 can be filled with a solid or liquid insulating material instead of the gaseous insulating material shown.

The high pressure gas within auxiliary insulator N2 subjects this insulator to no appreciable stresses since gas at the same pressure is present about the exterior of the auxiliary insulator 102. The other auxiliary insulator Mill is protected from being stressed by the high pres sure gas therein by means of a tubular liner 12h of insulating material spaced from the bore of insulator 1%. This liner 1.243 surrounds suitable flanges formed on the parts 50 and 164 respectively, and suitable seals provided between the flange and the liner prevent the pressurized gas from filling the space between the liner and the percelain shell 1%. The clamping forces applied to the end plate 1% through the nut 1% hold the end plate in sealed relationship with respect to the liner 12% against the gas pressure forces tending to force the end plate 104 to the right.

When the circuit breaker is closed, there is no significant voltage applied across the insulators 1% and 162 since the shunt circuit comprising the resistor 89 and the then closed auxiliary switch 9b is shunted by the closed main contacts 11 of the breaker. This is illustrated in FIG. 3 which is a diagrammatic view of the circuit breaker in closed circuit position.

When the circuit breaker is fully open, as depicted in the diagrammatic view of FIG. 4-, no current is flowing through the resistor fill since the auxiliary switch ht) is open. Thus, during this open circuit interval, conductor 27 is at the same voltage as the conductive structure 83, 85, 87 extending between the resistor as and the auxiliary switch 94 This being the case, no significant voltage would be present across the insulators ltlil or M2 or the gap 112, all of which electrically isolate the conductive structures 27 and 83, 85, $7.

The only time that voltage is present across the auxiliary insulators Hill and 1&2 and the gap 112 is during the short interval (depicted in FIG. 5) when the main contacts 11 and 12 are open but the auxiliary contacts have not yet been open. During this short interval, the voltage applied between the main conductor 27 and the conductive structure 83, 85, 87 is equal to the voltage drop across the resistor 8t). Even under the most extreme transient conditions that could occur while the breaker is in its position of FIG. 5, e.g., those accompanying multiple lightning strokes, to the power line 36, the voltage drop across the resistor 80 is relatively small in comparison to the impulse voltages which the main insulators it) and 41 are required by industry standards to withstand. In this latter connection, the most severe voltage burden imposed on the main insulators 4t and 41 occurs when lightning strikes the power line while both the main contacts 11 and the contacts of auxiliary switch 9% are open. Under these particular conditions, the lightning surge upon reaching the line terminal of the open circuit breaker has its crest value doubled through reflection at the circuit breaker terminal. The resulting voltage peak, which will normally be the maximum encountered by the breaker, is applied across the main insulators 4t and 41 but results in no appreciable voltage across the resistor St? since the auxiliary conductive structure $3, 35, 37 is at substantially the same voltage as the main conductor 27, as explained in connection with FIG. 4. Thus, under the most severe voltage conditions, which are those which govern the design of the main insulators, no appreciable voltage is applied across the resistor till. it will therefore be apparent that the insulators ltltl and 192, which are required to withstand only the voltage applied across the resistor 8t), may be designed for considerably lower impulse voltages than the insulating shells 4i) and 41. For example, in a typical application of my invention, a circuit breaker having a main porcelain shell ll twenty-six inches in length may utilize an auxiliary porcelain insulator 1% only about ten inches long.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects, and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

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

1. An electric circuit breaker comprising a metal tank containing pressurized gas, a pair of separable main contacts located within said tank, a main insulating bushing extending through a Wall of said tank, circuit breaker terminal structure mounted on the outer end of said bushing, said bushing comprising a tubular main conductor electrically connected between one of said main contacts and said terminal structure, said bushing further comprising a housing including a hollow insulator disposed exernally to said tank and surrounding a portion of said tubular main conductor, means for supporting said conductor within said housing, resistance means located externally to said tank and said bushing and having a pair of opposed terminals, an auxiliary switch comprising auxiliary electrodes located within said tank, conductor means for connecting said auxiliary electrodes and said resistance means in series with each other and in parallel with said main contacts, said conductor means comprising an auxiliary conductor providing a connection between one terminal of said resistance means and one of said auxiliary electrodes, said auxiliary conductor extending through the bore of said tubular main conductor and radially-spaced therefrom in electrically insulated relationship to the tubular main conductor, a first auxiliary insulator of tubular form surrounding a portion of said auxiliary conductor and disposed at the outer end of said main insulator outwardly of said circuit breaker terminal structure for supporting one end of said auxiliary conductor, and a second auxiliary insulator of tubular form surrounding a portion of said auxiliary conductor and disposed at the inner end of said bushing for supporting the other end of said auxiliary conductor said conductor means comprising additional conductive structure connected between said circuit breaker terminal structure and the other terminal of said resistance means, said resistance means being located outside said auxiliary insulators.

2. In the circuit breaker of claim 1, means affording communication between the interior of said tank and the space between said tubular main conductor and said auxiliary conductor so that pressurized gas from said tank is present within said space.

3. The circuit breaker of claim 1 in which said second auxiliary insulator is disposed in the pressurized gas within said tank and in which means are provided to afford communication between the interior of said tank and the interior of said second auxiliary insulator so that substantially equal pressures are present internally and externally or" said second auxiliary insulator.

4. The circuit breaker of claim 1 in which said second auxiliary insulator is disposed in the pressurized gas within said tank, in which means is provided to aiford communication between the interior of said tank and the interior of said second auxiliary insulator, and in which means is provided to afford communication between the interior of said second auxiliary insulator and the space between said tubular main conductor and the interior of said second auxiliary insulator so that pressurized gas from the tank is present within said auxiliary insulator and within said space.

S. The circuit breaker of claim 1 in which said auxiliary conductor comprises a conductive rod extending between opposite ends of said auxiliary insulators and in which there is provided means for loading said auxiliary insulators in compression and said conductive rod in tension comprising spring means disposed between one of said auxiliary insulators and said conductive rod.

6. An electric circuit breaker comprising a tank containing pressurized gas, a pair of separable main contacts located within said tank, a main insulating bushing extending through a wall of said tank, terminal structure mounted on the outer end of said bushing, said bushing comprising a tubular main conductor electrically connected between one of said main contacts and said terminal structure, said bushing further comprising a housing including a hollow insulator disposed externally to said tank and another hollow insulator disposed internally to said tank, means for mounting said tubular main conductor within said housing with said hollow insulators surrounding said tubular main conductor, an abutment fixed to one end of said tubular main conductor, means for loading said insulators in compression and said tubular main conductor in tension comprising spring means between one of said insulators and said abutment, resistance means located externally to said tank and said bushing, an auxiliary switch comprising auxiliary electrodes located within said tank, conductive means for connecting said auxiliary electrodes and said resistance means in series with each other and in parallel with said main contacts, said conductive means comprising an auxiliary conductor providing a connection between one terminal of said resistor and one of said auxiliary electrodes, said auxiliary conductor extending through the bore of said tubular conductor and radially spaced therefrom in electrically insulated relationship to the tubular conductor, a pair of auxiliary insulators of tubular form mounted at opposite ends of said bushing and surrounding said auxiliary conductor in radially-spaced relationship to said auxiliary conductor, and means located at opposite ends of said auxiliary insulators for mounting said auxiliary conductor on said auxiliary insulators.

7. An electric circuit breaker comprising a tank containing pressurized gas, a pair of separable main contacts located within said tank, a main insulating bushing extending through a wall of said tank, terminal structure mounted on the outer end of said bushing, said bushing comprising a tubular main conductor electrically connected between one of said main contacts and said terminal structure, said bushing further comprising a housing including a hollow insulator disposed externally to said tank and another hollow insulator disposed internally to said tank, means for mounting said tubular main conductor within said housing with said hollow insulator surrounding said tubular main conductor, an abutment fixed to one end of said tubular main conductor, means for loading said insulators in compression and said tubular main conductor in tension comprising spring means between one of said insulators and said abutment, resistance means located externally to said tank and said bushing, an auxiliary switch comprising auxiliary electrodes located within said tank, conductive means for connecting said auxiliary electrodes and said resistance means in series with each other and in parallel with said main contacts, said conductive means comprising an auxiliary conductor providing a connection between one terminal of said resistor and one of said auxiliary electrodes, said auxiliary conductor extending through the bore of said tubular conductor and radially-spaced therefrom in electrically-insulated relationship to the tubular conductor, a first auxiliary insulator of tubular form surrounding a portion of said auxiliary conductor disposed at the outer end of one of said main insulators for supporting one end of said auxiliary conductor, means for mounting said auxiliary insulator in fixed relationship to said abutment, and a second auxiliary insulator of tubular form surrounding a portion of said auxiliary conductor and disposed at the inner end of said bushing for sup porting the other end of said auxiliary conductor.

8. The circuit breaker of claim 6 in which said auxiliary conductor comprises a conductive rod extending between opposite ends of said auxiliary insulators, and in which there is provided means for loading said auxiliary insulators in compression and said conductive rod in tension comprising spring means disposed between one of said auxiliary insulators and said conductive rod.

9. An electric circuit breaker comprising a metal tank, a pair of separable main contacts located within said tank, a main insulating bushing extending through a wall of said tank, circuit breaker terminal structure mounted on the outer end of said bushing, said bushing comprising a tubular main conductor electrically connected between one of said main contacts and said terminal structure, said bushing further comprising a housing including a hollow insulator disposed externally to said tank and surrounding a portion of said tubular main conductor, means for supporting said conductor within said housing, resistance means located externally to said tank and said bushing and having a pair of opposed terminals, an auxiliary switch comprising auxiliary electrodes 10- cated within said tank, conductor means for connecting said auxiliary electrodes and said resistance means in series with each other and in parallel with said main contacts, said conductor means comprising an auxiliary conductor providing a connection between one terminal of said resistance means and one of said auxiliary electrodes, said auxiliary conductor extending through the bore of said tubular main conductor and radially-spaced therefrom in electrically insulated relationship to the tubular main conductor, a pair of auxiliary insulators of tubular form mounted at opposite ends of said bushing and surrounding said auxiliary conductor in radially-spaced relationship, and means located at opposite ends of said auxiliary insulators for mounting said auxiliary conductor on said auxiliary insulators said conductor means further comprising conductive structure connected between said circuit breaker terminal structure and the other terminal of said resistance means, and said resistance means being located outside said auxiliary insulators.

References Cited in the file of this patent UNITED STATES PATENTS 1,957,982 Smith May 8, 1934 1,969,911 Smith Aug. 4, 1934 2,349,095 Henley May 16, 1944 2,729,721 Forwald Jan. 3, 1956 2,786,117 Forwald Mar. 19, 1957 2,866,173 Newcombe Dec. 23, 1958 2,911,546 Oppel Nov. 3, 1959 2,921,168 Forwald Jan. 12, 1960 3,009,983 Oppel Nov. 21, 1961 FOREIGN PATENTS 933,819 Germany Oct. 6, 1955 1,062,788 Germany H Aug. 6, 1959 1,218,276 France Dec. 14, 1959

Claims (1)

1. AN ELECTRIC CIRCUIT BREAKER COMPRISING A METAL TANK CONTAINING PRESSURIZED GAS, A PAIR OF SEPARABLE MAIN CONTACTS LOCATED WITHIN SAID TANK, A MAIN INSULATING BUSHING EXTENDING THROUGH A WALL OF SAID TANK, CIRCUIT BREAKER TERMINAL STRUCTURE MOUNTED ON THE OUTER END OF SAID BUSHING, SAID BUSHING COMPRISING A TUBULAR MAIN CONDUCTOR ELECTRICALLY CONNECTED BETWEEN ONE OF SAID MAIN CONTACTS AND SAID TERMINAL STRUCTURE, SAID BUSHING FURTHER COMPRISING A HOUSING INCLUDING A HOLLOW INSULATOR DISPOSED EXTERNALLY TO SAID TANK AND SURROUNDING A PORTION OF SAID TUBULAR MAIN CONDUCTOR, MEANS FOR SUPPORTING SAID CONDUCTOR WITHIN SAID HOUSING, RESISTANCE MEANS LOCATED EXTERNALLY TO SAID TANK AND SAID BUSHING AND HAVING A PAIR OF OPPOSED TERMINALS, AN AUXILIARY SWITCH COMPRISING AUXILIARY ELECTRODES LOCATED WITHIN SAID TANK, CONDUCTOR MEANS FOR CONNECTING SAID AUXILIARY ELECTRODES AND SAID RESISTANCE MEANS IN SERIES WITH EACH OTHER AND IN PARALLEL WITH SAID MAIN CONTACTS, SAID CONDUCTOR MEANS COMPRISING AN AUXILIARY CONDUCTOR PROVIDING A CONNECTION BETWEEN ONE TERMINAL OF SAID RESISTANCE MEANS AND ONE OF SAID AUXILIARY ELECTRODES, SAID AUXILIARY CONDUCTOR EXTENDING THROUGH THE BORE OF SAID TUBULAR MAIN CONDUCTOR AND RADIALLY-SPACED THEREFROM IN ELECTRICALLY INSULATED RELATIONSHIP TO THE TUBULAR MAIN CONDUCTOR, A FIRST AUXILIARY INSULATOR OF TUBULAR FORM SURROUNDING A PORTION OF SAID AUXILIARY CONDUCTOR AND DISPOSED AT THE OUTER END OF SAID MAIN INSULATOR OUTWARDLY OF SAID CIRCUIT BREAKER TERMINAL STRUCTURE FOR SUPPORTING ONE END OF SAID AUXILIARY CONDUCTOR, AND A SECOND AUXILIARY INSULATOR OF TUBULAR FORM SURROUNDING A PORTION OF SAID AUXILIARY CONDUCTOR AND DISPOSED AT THE INNER END OF SAID BUSHING FOR SUPPORTING THE OTHER END OF SAID AUXILIARY CONDUCTOR SAID CONDUCTOR MEANS COMPRISING ADDITIONAL CONDUCTIVE STRUCTURE CONNECTED BETWEEN SAID CIRCUIT BREAKER TERMINAL STRUCTURE AND THE OTHER TERMINAL OF SAID RESISTANCE MEANS, SAID RESISTANCE MEANS BEING LOCATED OUTSIDE SAID AUXILIARY INSULATORS.

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