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Publication numberUS2306186 A
Publication typeGrant
Publication dateDec 22, 1942
Filing dateJan 27, 1941
Priority dateJan 27, 1941
Publication numberUS 2306186 A, US 2306186A, US-A-2306186, US2306186 A, US2306186A
InventorsRankin William K
Original AssigneeGen Electric
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
High voltage electric circuit breaker
US 2306186 A
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Description  (OCR text may contain errors)

Dec. 22, 1942. w. K. RANKIN 2,306,186

HIGH VLTAGE ELECTRIC CIRCUIT BREAKER Filed Jan. 27, 1941 2 Sheets-Sheet l Inventor Wliam K.Rankin,

g His Attorney.

De@ 22, 1942. w. K. RANK\N 2,306,186

HIGH vVOLTAGE ELECTRIC CIRCUIT BREAKER Filed Jan. 27, 1941 2 Sheets-Sheet 2 Jygmpyalm inventor- \/\/i| lam K. Ranmn,

l-is Attorney.

-cipal object thev provision yblast circuit breaker operable at high transmis- Patented D. .22, i942 William General Electric New York K'. Rankin, Lansdowne, Pa.,

assignor to Company, a corporation of Application January 27, 1941, Serial No. 376,21 8 Claims. (Cl. 20u-148) My invention relates to high voltage lelectricl circuit breakers, more particularly to circuit breakers or the gas blast type having separable contacts between which a blast of gas is directed for extinguishing arcing', and has for its prinof an improved gas sion line voltages and capable of eiciently interrupting and clearing high voltage power circuits.

The interruption of a high voltage power circuit, such as for example a 138 kv'. circuit, by means of a gas blast involves a number of difficult problems due to the limited dielectric strength of gases (such as air) most commonly used. Heretoore, oil circ 't breakers have been almostexclusively used for ,such interrupting duty -since the dielectric strength of oil is many times that of air. Accordingly, when the arc is extinguished at a current zero by the oil circuit breaker, the intervening oil dielectric is much better able to withstand the returning recovery voltage than air. Reestablishment of the arc therefore does not occur and the circuit remains open. Air on the other hand may be so stressed by the recovery voltage across the interrupting gap that breakdown occurs'. The power arc is thereby reignited and failure of the breaker results.

In accordance with my invention, the high voltage range of a gasor air blast circuit breaker is greatly increased by utilizing the increased dielectric strength o gas under pressure, during interruption, so as to minimize the danger of restriklng ofthe arc within the interrupting charnber, without however impairing the arcex tinguishing action of the blast.

It is known that the dielectric strength of agas increases according to pressure increase; also that, in a nozzle, a backpressure in excess of 50% with no appreciable decrease in the velocity of the gas through the nozzle. My invention in combination makes effective use of these phenomena by separating interrupting contacts to draw an arc in a chamber in which a relatively high pressure exists, or is applied co-incident with contact separation. This arc chamber pres- 'sure does not impede the velocity or impair the effectiveness of the interrupting gas blast. An

interrupter constructed in accordance with my invention is found to have the same ability to interrupt current as one using a similar but freely vented nozzle, and in addition is operable at much higher voltages.

of the applied pressure may -be permitted ing structure y cated at 1.

In practicing my invention, the interrupting chamber communicating with the source of blast pressure is provided with a venting or exhaust opening having a suitable cross-sectional area that is related to the interrupting chamber and blast pressure so as to insure effective blast velocity for arc interruption while maintaining the interrupting chamber atmosphere surrounding the interrupting gap at a substantially predetermined related pressure. In order to provide for unusual or variable operating conditions, means are also provided for further increasing the aforesaid cross-sectional area of the exhaust blast opening in accordance with the pressure in 'the interrupting chamber.

My invention will be more fully set forth in the following description referring to the accompanying drawings, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexe to and forming a part of this specification.

Referring to the drawings, Fig. 1 is an elevational, sectional view of a high voltage gas blast circuit breaker ,embodying the present invention in the closed circuit position thereof, Fig. 2 is an elevational View of a single phase double-break outdoor circuit vbreaker of the character shown by Fig. 1 with disconnecting means intermediate the dual interrupting units, and Fig. 3 is a plan viewof Fig. 2 illustrating the operation oi the disconnecting means.

Referring to Fig. 1, the high voltage circuit breaker comprises essentially separable contacts I and 2 whichvare connected respectively to the breaker terminals 3 and 4. The rod contact I is relatively fixed and is held in position by conduct- 5 and a guide bushing 6 suitably connected to the 'conducting structure as indi- The contact I is mounted within and centrally oi the conducting structure 5 for limited movement, or wipe, as indicated at 8. In the position shown, the contact I is held in contact engagement by means of a biasing spring 9 mounted within the conducting structure 5. Sliding contact structure I0 electrically connects the rod Contact I to the structure 5, which is in turn electrically connected by the conductor Il to the breaker terminal 3.

The coacting or movable rod contact 2 is connected to an operating piston I2 operable within a cylinder I3 for moving the contact 2 into and out of circuit making engagement with the contact I. The contact 2 is electrically connected to the other breaker terminal at 4 through a conducting spring guide and bearing plate I4 carinterconnecting/ange 31" rled by the contact extension i2 (hereinafter.

described), a iiexible conductor I5 and a ilxed conducting spider I6.

-The contacts I and 2 are separable within an interrupting chamber I1 which, in the present instance, is elongated and formed by an insulating tube I 8 composed of mechanically strong insulating material; such as hard fibre. The insulating tube I8, which is capable of withstand-l ing high internal vbursting pressures, is provided with an insulating lining I9 of suitable arc resisting insulating material. The insulating lining I3 forms at 20 substantially at the point of separation of the contacts I and 2 a restricted nozzlelike section in the interrupting chamber. lAccordingly, when gas under pressure is admitted to the lower end of the interrupting chamber, the arc gap formed at the constriction when the gas pressure has elevated the piston I2 causes an arc extinguishing blast longitudinally of. the arc as it is drawn into the upper part of the yinterrupting chamber I1.

The mechanical stresses incident tothe application of the gas blast (which may be introduced at approximately 350 lbs. per sq. in.) require that the interrupting chamber and its insulating structure as well as electrically eiiicient at high voltages. To this end, the insulating tube I8-is secured.` at its lower end, as by a ring-shaped clamping Wedge 2| and clamping flange 22, to a base plate 23 (as indicated at 23') that 24 to the lower terminal structure 3. The base plate 23 is an integral part of the depending contact supporting structure 5 through which a plural'ity of parallel connected gas passages 25 interconnect the lower end of the arc .chamber and fthe gas supply conduit 26. The upper` end of the insulating tube I8 is similarly secured to a top supporting plate 21 .by a clamping ring 28 is in turn bolted at` in the case of air be physically rugged and flange 29 that is bolted at 30 to the top plate.

Between a pair of supporting anges 3I and 32 secured respectively to the top plate 21 and the lower terminal base plate 3 is mounted a high voltage insulator shell 33 surrounding and spaced with respect to the tubel I8. The insulating shell 33 is of the high Voltage outdoor type composed of ceramic material, such as porcelain, and is resiliently connected to the upper plate through a flexible corrugated coupling 34 as illustrated for preventing transmission .of excessive shock to the porcelain insulator. The annular space 35 between the tube I8 and the insulator 33 is preferably lled with a non-iniiammable insulating liquid of high dielectric strength, such as for example a liquid chlorinated hydrocarbon described and claimed in Clark Patent No. 1,931,- 455, granted October 17, 1933, for YDielectric materials for electrical devices.

The top plate 21 forms a base for supporting the piston cylinder I3 and its associated apparatus, the blast exhaust controlling means and the housing 36 therefor. More specifically, the piston cylinder I3 is secured in position through by means of its integral concentric supporting cylinder 431 which seats in an annular recess in the upper face of the supporting plate 21 and is clamped therein by nuts 39 threaded on three evenly spaced studs 38 screwed into the supporting plate 21. Large ports 31' are provided in the supporting cylinder side wall. The cylinder I3 is therefore rigidly secured to the supporting plate 21 and the lower end thereof, which is provided with ports 40 directly communicating with the interrupting l chamber I1, is arranged to admit gas under pressure tothe lower is spring biased toward closed circuitl position.

The pistonv biasing means comprises in the present instance the movable spring bearing plate I4 on the end of the piston rod (and contact) extension I2"between which and the upper xed spring bearing plate (or spider) .I6 are mounted biasing springs 4I. The springs 4I are guided on the through bolts 38 which are secured at their upper ends at 42 to the xed plate I6. The plate I6 in turn serves as an anchorage for the upper part of the housing 36 which constitutes a dome-shaped cover member 36'. For the purpose of providing low gradient spring action, the springbearing plates I4 are-provided with socketlike extensions I 4', in which the springs 4I are seated and which are guided for reciprocal vertical movement by .the through bolts 38. Accordingly, when the piston I2 is raised by the blast pressure, the spring bearing plate I4 is correspondingly raised to compress the springs 4I, thereby storing energy for closing the contact 2 upon cut-olf of blast pressure.

- For the purpose of controlling the operation of the contact piston I2 so that there is no appreciable tendency to rebound near the end of the opening stroke, and also so that the breaker cam, ifl desired, be reclosed at the proper speed, the cylinder I3 is provided with valve means for controlling pressure within the cylinder. A by-pass connection 43 between the interrupting chamber I1 and the upper part ofthe cylinder tends to equalize pressure on both sides of the piston near the end of the opening stroke for slowing up the speed thereof. This eliminates shockA and excessive stresses at the end of the opening stroke. ThisI` buffer action can be nicely. regulated and adjusted by a valve 43 connected in the by-pass connection and by an adjustable bleed valve indicated 'at 44 connecting with the upper cyiinder space.

I In case excessive back pressure tends to build up in the upper cylinder space causing rebound of thepiston I2 with possible reestablishment of arcing between the contacts, a spring loaded excess pressure valve 45 controls a port in the cylinder wall for relieving the cylinder pressure when it reaches a predetermined value. Accordingly, the piston I2 is not only provided with buffer means for the opening stroke, but is prevented from rebounding due to excessive buffer action. 1 v In certain cases, it is desirable to reclose the breaker as soon as' possible after it has been opened to clear a fault condition. For such operation, it is necessary that the piston I2 be permitted springs 4I downward to closed circuit position immediately after the opening operation without appreciable retarding effect. For this purpose a non-return 'valve indicated at 46 controls a port in the upper cylinder wall for opening under atmospheric pressure when the piston descends so as to prevent creation of a partial vacuum in the upper cylinder space with resultant retarding effect on` the piston. This valve of course remains closed when the piston is moving up- Ward.

Let it now be assumed that the breaker is closed as illustrated and that an opening operationhas been initiated by the opening of a suitable control valve (not shown) for admitting gas under pressure into the interrupting chamber by way of the supply conduit 26. As `the gas rushes side of the pistoniI2, which ear movement on upward through the chamber, it is throttled at the constriction 20 so that it flows at high velocity past this point and enters the lower` part of the cylinder I3 to act directly on the contact piston I2. It will be noted that as the piston l2 is raised to separate the contacts I and 2, the gas blast is already passing through the nozzle portion 20 so that immediately upon for mation of the arc it is acted upon by an intensive cooling and interrupting blast at the nozzle. This extinguishing action is generally sufficient to interrupt the arc at a current zero before it has been drawn to the maximum length determined by the piston stroke in the chamber I1.

The Contact arrangement with relation to the interrupting chamber and blast pressure also aids current interruption, That is, the movable contact moves away from the nozzle restriction in the direction of the blast to draw the arc into the pressure exhaust chamber Where, from its incaption, it is effectively surrounded for cooling and positioned axially by an insulating hose-like blast of pressure gas. straight and at the end of the stroke has a predetermined length as compared with a looped or bowed arc.

However, the interruption of the arc at a current zero by the intense gas blast at the interrupting nozzle does not necessarily complete the circuit opening operation since, as previously The arc is therefore drawn pointed out, the returning recovery voltage across the breaker terminals may break down the air gap between the contacts I and 2 and so cause restriking of the arc. In order to prevent this, the interrupting chamber I1 at the exhaust side of the interrupting nozzle 20 is so vented that the gas in this part of the chamber is partially entrapped to set up an effective back pressure level sucient appreciably to increase the dielectric strength of the gas during the separation of the contacts. It will therefore be noted that it is necessary to initiate and establish a back pressure in the exhaust chamber beyond the nozzle throat to cause separation of the contacts, so that the arc, from its inception, is encompassed by gas appreciably above atmospheric pressure. In the specific arrangement described, the initial or source blastl pressure is approximately 350A lbs. per sq. in. and the average controlled back pressure is calculated for approximately 120# sq. in. at which the dielectric strength of the air may be several times the value it would be with free venting. Using 350# blast pressure it will be appreciated that even a back pressure as high as 180 lbs. per sq. in. at the exhaust end of the interrupting nozzle 20 has no retarding effect on the interrupting blast velocity since'the back pressure at an orice can be approximately 53% sure without causing decrease of the rate of discharge through the orifice. Also, such control of the back pressure avoids wider and disruptive stress differentials within the device during high current interruptions.

The blast exhaust opening is formed by an annular valve-like control member 41 guided in sleeve-like manner for limited vertical, rectilinthe cylinder I3. The member is biased toward its normal lower position by springs 48 mounted on the through bolts 38 between the cylinder interconnecting ange 31" and offset flanges or legs on the control member 41. The member 41 is held in spaced relation to the supporting plate 21 by nxed lock nuts 49 on the through bolts 38 so as to form an of the source presannular venting opening, the cross-sectional area of which is determined by the spacing A and the circumference 0f the member 41. The lock nuts 49 also provide means for adjusting the position of the member 41 for regulating to a fine degree the venting area.

In the specific interrupter herein described, this pre-set venting area is related both to the opening and closing operations. It is small enough to throttle the interrupting blast so that the arc is drawn and extinguished (usually at an early current Zero) in a region of high pressure air or gas; at the same time being large enough to permit decisive reclosure of the piston contact, under the bias of its return springs, immediately following the blast cut-off. In the present instance optimum results were attained with an initial vent area of 2.79 sq. in. for an interrupting chamber cross-sectional area of 6.75 sq. in., a cross-sectional nozzle area of 1.75 sq. in. and nozzle exhaust and source pressures of lbs. per sq. in. and 350 lbs. per sq. in respectively The ratio of the vent or exhaust area to the nozzle area is therefore approximately 1.6. When the back pressure is restricted' within the proper zone, which may vary in accordance with the character of the extinguishing gas employed, the breaker is capable of successfully interrupting and clearing the circuit at much higher voltages than previously possible.

For example, from tests made on comparable experimental single interrupting units the following comparisons were observed. The nozzle employing the restricted exhaust is capable of interrupting at least 21% more current at 44 kv. and 124% more current at 66 kv. than an equivalent nozzle exhausting to the open air, At 88 kv. the nozzle exhausting to the open air was incapable of interrupting any current at all, While.

the restricted exhaust nozzle interrupted 2280 amperes successfully. This, together with other test data, has permitted the successful manufacture, for commercial use, of the 138 kv. circuit breaker herein described which is rated at 1,500,000 kva. interruptingy capacity.

'Ihe venting control arrangement is also provided withl means for increasing the venting area in case unusual and abnormally high pressures, such as in excess of lbs. per sq. in., are generated within the interrupting chamber, for, as previously described, the member 41 can move upwardly on'the guide bolts 38 against the bias of springs 48, although in usual operation the springs 48 maintain the venting area substantially, xed and uniform. Hence, the use of a biased valve is not essential to practice my invention, for fixed vent openings may be used t0 effect the proper blast and exhaust pressure relationship after the latter has been ascertained for a given breaker.

The hot exhaust gases that flow into the housing 36 are nally vented to atmosphere, after passing through ports 31', at the muffler 50 which is provided with suitable cooling plates or the like 5I for preventing or minimizing flame emission from the breaker.

It is within the scope of my invention to employ other methods than that specifically described for providing a suitable pressure level in the exhaust chamber where the arc is interrupted. For example, two different pressures may be admitted substantially simultaneously to the chambers at opposite sides of the nozzle or the exhaust chamber in such an arrangement might be connected to the main pressure source through a reducing valve. l

The circuit breaker herein described automatically recloses after a complete opening operation, i. e., as defined by closing of the main blast control valve. It is therefore necessary that other means in series with the breaker be provided for disconnecting the breaker with respect to the power circuit after circuit interrup" tion and prior to reclosing of the breaker. Figs. 2 and 3 show one phase of a triple-pole outdoor type circuit breaker of the character herein described, each interrupting unit of which corresponds to that illustrated by Fig. 1. The two units are mounted on high voltage shell-like insulating supports 60 and 6| respectively, which are in turn mounted on a supporting frame 63 composed of structural steel work. The frame 63 also supports in depending relation therefrom a gas supply tank 64 which is adap-ted to supply both breaker units through the conduits at 26, and a suitable operating mechanism 65 for the disconnecting means hereinafter described.

faces for coacting with a movable disconnecting switch blade 66 that is mounted for rotatable movement with respect to the terminals on an insulating support 61 likewise mounted on the frame 63, The disconnecting switch blade 66 when rotated approximately 45 in clockwise direction as viewed in Fig. 3 disconnects both is in connecting position bridging the terminals 3, and the breaker units are closed, the power and its upper terminal 4.

Any suitable means may be provided for operating the blade 66, and by way of example an operating rod 68 secured to the blade and ticing this invention One such arrangement is described and claimed in a copending application Serial No. 367,789, iiled November 29, 1940, by Carl Thumim and Alexander C. Boisseau for Circuit breaker operating system.

It should be understood that my invention is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the What I claim as new and desire t secure by Letters Patent of the United States is:

1. A high voltage electric circuit breaker of the gas blast type comprising relatively movable contacts, an elongated are extinguishing chamber having a restricted cross-sectional area at which said contacts are separable to form an arc gap, a source of gas pressure for supplying to said chamber at one side of said restriction an arc extinguishing gas under pressure so that the arc in said restriction is blast,

for further increasmg the cross-sectional area of/said exhaust opening when the pressure in said extinguishing mined amount.

4. high voltage gas blast circuit breaker striction, said fixed contact being disposed in said chamber at the pressure entrance end thereof and said movable contact being disposed at the exhaust end of said chamber, and a piston connected to said movable contact and operable by gas pressure for drawing the power arc at said movable Contact axially into said exhaust chamber in the direction of the gas blast so that said arc is enveloped by said gas blast.

5. A high voltage gas blast circuit breaker comprising an insulating interrupting chamber, contacts separable to form an arc gap in said chamber, said chamber having a constriction through which a gas under pressure is directed to extinguish arcing at said gap, said chamber at the exhaust side of said constriction being of sufficient size substantially to enclose said arc gap, and means for so restraining flow of blast gas from said exhaust chamber that a pressure level is built up in said exhaust chamber sufiicient to increase appreciably the dielectric strength of said gas by the time said contacts separate for preventing restriking of the arc after interruption at a. current zero, said pressure level being related to the gas pressure at the entrance side of said constriction so that the effectiveness of the interrupting gas blast through said constriction is not impaired.

6. A high voltage electric circuit breaker of the gas blast type comprising relativel1 xed and movable rod contacts disposed in vertical aligni ment, a tubular sleeve-like arc extinguishing chamber in which said contacts are separable to form an arc gap, the point of contact separation being at a restricted section of said chamber, a source of gas pressure for supplying an arc extinguishing gas to said chamber, a substantially circular port defining a radial exhaust opening at the upper end of said chamber of such predetermined cross-sectional area with respect to the cross-sectional area of said restricted section that the gas pressure within said chamber is maintained sufficiently high during the gas blast to prevent breakdown of said gap after arc interruption, spring-biased means for further increasing the cross-sectional area of said exhaust opening in accordance Iwith predetermined increase of pressure Within said chamber, and a piston disposed at the upper part of said chamber connected to the movable contact for causing separation of said contacts in response to the admission of gas under pressure to said chamber, said piston and movable contact being mounted for reciprocal movement concentrically with repect to said radial exhaust opening.

7. A high voltage electric circuit breaker of the gas blast type comprising relatively fixed and movable rod contacts disposed in vertical alignment, an insulating tube forming a sleeve-like arc extinguishing chamber in which said contacts are separable,1 the point of contact separation being at a restricted section of said chamber so as to form the initial arc gap in said section, a source of gas pressure for supplying an arc extinguishing gas to the lower part of said chamber, a substantially annular member deiining an exhaust opening at the upper end of said chamber, said opening having a minimum predetermined cross-sectional area with respect to the cross-sectional area of said restricted section so arranged that the gas pressure within said chamber is maintained sufciently high during the gas blast t0 prevent breakdown of said gap after arc interruption, spring means coacting with said annular member opposing the chamber `gas pressure for permitting further increase in the cross-sectional area of said exhaust opening in accordance with predetermined increase of pressure within said chamber, and a. piston disposed at the upper part of said chamber connected to the movable contact for causing separation of said contacts in response to the admission of gas under pressure to said chamber, said piston and movable contact being mounted for reciprocal movement within said springbiased member.

8. A high voltage electric circuit breaker of the gas blast type comprising relatively fixed and movable rod contacts disposed in vertical alignment, an insulating tube forming a sleeve-like arc extinguishing chamber in which said contacts are separable to form an arc gap, the point of contact separation being at a restricted section of said chamber, a high voltage insulating shell surrounding said tube, a source of gas pressure for supplying an arc extinguishing gas to the lower end of said tube, a member normally spaced with respect to said tube dening therewith an exhaust opening at the upper end of said chamber having a predetermined minimum cross-sectional area, said area being about 1.6 times the cross-sectional area of said restricted section whereby the gas pressure within said chamber is maintained sufliciently high during the gas blast to prevent breakdown of said gap after arc interruption, means resiliently biasing said member toward said predetermined minimum spacing so that the cross-sectional area of said exhaust opening can be further increased in accordance with predetermined increase of pressure within said chamber, a piston disposed at the upper part of said chamber connected to the movable contact for causing separation of said contacts in response to the admission of gas under pressure to said chamber, a cylinder for said piston having valve controlled means for regulating the speed of said piston in both directions, a housing for said cylinder and member mounted at the upper end of said insulating shell arranged to receive the arc chamber exhaust gases, and cooling structure in said housing through which said gases are directed to atmosphere.

WILLIAM K. RANKIN.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2439952 *Aug 31, 1944Apr 20, 1948Westinghouse Electric CorpCircuit interrupter
US2440995 *Jun 10, 1944May 4, 1948Gen ElectricElectric circuit breaker
US2444765 *Dec 27, 1944Jul 6, 1948Gen ElectricElectric circuit breaker
US2449208 *Jan 16, 1946Sep 14, 1948Bbc Brown Boveri & CieCircuit breaker
US2449518 *Feb 15, 1943Sep 14, 1948Westinghouse Electric CorpCircuit interrupter
US2459612 *Dec 22, 1944Jan 18, 1949Westinghouse Electric CorpCompressed gas circuit interrupter
US2470628 *May 24, 1944May 17, 1949Westinghouse Electric CorpCircuit interrupter
US2491821 *Dec 13, 1944Dec 20, 1949Allis Chalmers Mfg CoGas blast circuit breaker
US2495156 *Dec 15, 1945Jan 17, 1950Westinghouse Electric CorpCircuit interrupter
US2542798 *Sep 12, 1946Feb 20, 1951Westinghouse Electric CorpElectrical switchgear
US2568381 *Mar 23, 1945Sep 18, 1951Westinghouse Electric CorpCircuit interrupter
US2570769 *Nov 10, 1948Oct 9, 1951Gen ElectricElectric circuit interrupter
US2575949 *Feb 17, 1948Nov 20, 1951Asea AbCompressed air circuit breaker
US2584888 *Jan 23, 1947Feb 5, 1952Andre LatourOperating means for electric switches
US2594075 *Jul 9, 1949Apr 22, 1952Westinghouse Electric CorpMetal enclosed switchgear
US2627005 *Feb 3, 1949Jan 27, 1953Westinghouse Electric CorpInterrupter part of compressed-air breakers
US2658976 *Dec 3, 1948Nov 10, 1953Electrical Eng Equipment CoAir circuit interrupter
US2724751 *Feb 6, 1952Nov 22, 1955Asea AbAir blast circuit breaker
US2999143 *Nov 21, 1956Sep 5, 1961Westinghouse Electric CorpCompressed-gas circuit interrupter
US3473251 *Apr 24, 1968Oct 21, 1969Fedtro IncInsect electrocuting device
US3541220 *Jun 3, 1968Nov 17, 1970Furukawa Electric Co LtdReinforced long porcelain bushing
US4654489 *Sep 27, 1985Mar 31, 1987S&C Electric CompanyInsulating support column with operating member
US5548081 *Nov 30, 1993Aug 20, 1996Kommandidgesellschaft Ritz Messwandler Gmbh & Co.Duct, particularly for high voltages with special electrode holder
Classifications
U.S. Classification218/53, 200/82.00B, 174/179, 218/72, 174/30, 218/66, 218/52, 200/48.00R
International ClassificationH01H33/70
Cooperative ClassificationH01H33/70
European ClassificationH01H33/70