US3406269A - Fluid-blast circuit breakers having means for increasing the density of the fluid during interruption - Google Patents

Description

W. H. FISCHER Oct. 15, 1968 3,406,269 HAVING MEANS FOR INCREASING FLUID'BLAST CIRCUIT BREAKERS THE DENSITY 0? Filed Feb. 26, 1965 THE FLUID DURING INTERRUPTION 3 Sheets-Sheet l INVENTOR William H. Fischer WITNESSES ATTORNEY Oct. 15, 1968 w. H. FISCHER 3,406,269

FLUID-BLAST CIRCUIT BREAKERS HAVING MEANS FOR INCREASING v THE DENSITY OF THE FLUID DURING INTERRUPTION Fil ed Feb. 26, 1965 s Sheets-Sheet 2 Oct. 15, 1968 w. H. FISCHER 3,406,269

FLUID'BLAST CIRCUIT BREAKERS HAVING MEANS FOR INCREASING THE DENSITY OF THE FLUID DURING INTERRUPTION Filed Feb. 26, 1965 5 Sheets-Sheet 5 58 I 54 ss L 47- I 50 F I6 I m l j FIG-5.

' 3,406,269 FLUID-BLAST CIRCUIT BREAKERS HAVIN MEANS FOR INCREASING THE DENSITY F- THE FLUID DURING INTERRUPTION 1 William H. Fischer, Pittsburgh, Pa., assignor to Westingwhouse Electric Corporation, Pittsburgh, Pa., a corpora- .tion of Pennsylvania v H Fil ed Feb. 26, 1965, .Ser. No. 435,563 7 Claims. (Cl. 200-148) ABSTRACTOFYIHE-DISCLOSUREp A gas-blast type of circuit interrupter using an elect'ron'egative arc-extinguishing gas or liquid'increass the densityof the fluid along the established are path by'injector means or piston meaus, andhence the arc voltage at the time ofinterruption.

This invention relates, generally, to circuit breakers, and, more particularly, to circuit breakers utilizing an interrupting medium having an electronegative characteristic. One of the important reasons that sulfur hexafluoride, SP is such a good interrupting medium is its electronegative or electron sponge characteristic; Therefore, an efficie'nt circuit interrupter should have the most dense and un-ionized SP possible along the entire length of the interrupting break. The more molecules ofSF there are present at the arc, the greater will be the capacity of the interrupter to absorb electrons and the faster will be the de-ionization process at current zero. The difference in performance between liquid and gas SF interrupters illustrates this point; The liquid breaker contains SP at a higher density. Because'of this, the size of the interrupter, and hence the breaker, can be made considerably smaller when liquid SP is utilized as the interrupting medium.

An object of this invention is to provide for utilizing a high density electronegative interrupting medium in circuit breakers of a gas, liquid, or gas and liquidtype.

, One of the reasons that pressures greater than 60 p.s.i. at 70? F. have not been extensively used in SP breakers is that the vapor pressure of SE gas is such that at higher pressures it begins to condense out at moderately low temperatures. This results in the need for utilizing resistors to heat the SP Utilizing resistors for this purpose is not desirable because they cannot be utilized at high potential, they use power, they. require control equipment and they are subject to failure.

Accordingly, another object of the invention is to eliminate the need for resistance heaters in high pressure SF breakers. r

A further object of the invention is to provide a circuit breaker having a tank which is small enough in diameter to be exempt from the ASME Boiler and Pressure Vessel Code.

Still another object of the invention is to increase and control thepressure in a circuit breaker containing an electronegative interrupting medium.

-A still further object of the invention is to provide for raising the pressure and the density of the interrupting medium to the required value only at the time of interruption.

Another object of the invention is to utilize the injector principle to improve the performance of circuit breaker interrupters containing an electronegative interrupting medium.

Other objects of the invention will be explained fully In accordance with one embodiment of the invention,

2 the injector principle is utilized to maintain high' density un-ionized SP along the entire length of an interrupting break, thereby improving the performance of the interrupter. Also, high densityof the SP is maintained by means of an accumulator connected to the'ta'nk of a breaker containing liquid SP The accumulator prevents an excessive rise in the pressure during an interruption.

Another method utilizes auxiliary means to raise the pressure 'and the density of the SP5 to the required value only at the time of interruption. For a better understanding of the nature and objects of the invention, reference may beh ad to the following detailed description taken in conjunction with the accompanying drawings, in which: i

FIGURES 1, 2, 3 and4are diagrammatic'views of circuit interrupters embodying features of the inveniton for maintaining high density of an interrupting medium, such hereinafter or will be apparent to those skilled in the art;

FIGS. 5 and 6 are diagrammatic views of interrupters having means for maintaining high pressure and density of liquid SP Referring to the drawings, and particularly to FIG. 1, the structure shown diagrammatically therein comprises a generally cylindrical housing or tank 11 having an interrupting chamber 12 disposedinside the tank 11. The tank contains an electronegative interrupting medium, such as sulfur hexafluoride (SF which is normally in a gaseous state. However, as explained hereinbefore, the vapor pressure of SP is such that at pressures above 60 p.s.i. it begins to condense out at moderately low temperatures. Therefore, a collector 13 is provided at the bottom of the tank 11 to collect the liquid SP that condenses from the gaseous SP As shown, a relatively stationary contact member 14 and a movable contact member 15 are disposed inside the interrupting chamber 12 when in their closed position. The movable contact member 15 may be separated from the stationary contact member 14 to draw an are 16 therebetween in the interrupting medium. The contact member 15 may be actuated by a cross member 17 connected between two spaced operating rods 18 which may be moved longitudinally by a suitable operating mechanism (not shown), such as, for example, the one described in-a copending. application, Ser. No. 61,284, filed Oct. 7, 1960, now United States Patent 3,154,658, issued Oct. 27, 1964 to R. G. Colclaser and R. N. Yeckley and assigned to the Westinghouse Electric Corporation.

In order to extinguish the are 16 drawn between the contact members, a putter mechanism 21 is provided to create a blast of the interrupting medium through an orifice 22 in the interrupting chamber 12. The orifice 22 is formed by a liner 23 which is preferably composed of polytetrafiuoroethylene which is sold under the trade name Teflon. The puffer 21 includes a piston 24 which is slidably disposed inside the cylindrical interrupting chamber 12. A bushing 25 surrounds the stationary contact member 14 where it passes through the head of the piston 24. The piston is actuated by the operating rods 18 the ends of which are attached to the piston. Thus, when the contact members are separated, the piston causes the interrupting medium SP to flow through the orifice 22 at a relatively high velocity.

As explained hereinbefore, if a portion of the SE, in the tank 11 has condensed into a liquid, the density of the gas is reduced. As also explained hereinbefore the reduction of the density of the SP lessens its interrupting ability. In order to increase the density of the interrupting medium during the interrupting operation, the well-known injector principle is utilized to introduce some of the liquid SE, in the collector 13 into the interrupting chamber. As shown, openings 26 are provided in the orifice member 23. A tube or pipe 27 having its lower end disposed in the collector 13 is Thus, the high velocity of the gas forced through the orifice 22 by the putter mechanism 21 causes some of the liquid SP to be drawn up from the collector 13 and into the orifice in a manner similar to the operation of an atomizer. In this manner, the density of the interrupting medium along the interrupting break in the chamber 12 is increased, thereby improving the interrupting ability of the medium.

The structure shown in FIG. 2 is in general similar to that shown in FIG. 1. However, a storage tank 28 contains some of the interrupting medium, such as SP at a high pressure. A blast valve 29, which is opened in conjunction with the separation of the contact members, admits high pressure gas from the tank 28 into the interrupting chamber 12. The valve 29 may be operated by a ratchet mechanism 30 which is operated by the operating mechanism for the movable contact member 15. The ratchet mechanism 30 may be of the type described in a copending application Ser. No. 102,176, filed Apr. 11, 1961 now U.S. Patent 3,214,545, issued Oct. 26, 1965 to C. F. Cromer and assigned to the Westinghouse Electric Corporation.

Also, the collector 13 is a closed vessel and a check valve 31 is provided at the entrance to the collector. An additional opening 32 is provided in the orifice member 23 and connected to the collector 13 by means of a tube 33. When the high pressure gas is admitted into the interrupting chamber from the tank 28, some of the gas flows through the tube 33 into the collector 13, thereby increasing the pressure in the collector. The check valve 31 is closed and some of the liquid is forced upward through the .pipe 27 and into the orifice through the openings 26, thereby increasing the density of the interrupting medium.

The interrupter shown in FIG. 3 is of the self-generating type. In addition to the fixed contact member 14 and the movable contact member 15, an intermediate contact member 35 is provided. The member 35 is slidably mounted in a partition 36 in the interrupting chamber 12. The member 35 is biasedupwardly by a compression spring 37.

During the opening operation, the contact member 35 is first separated from the contact member 14, thereby establishing a pressure generating are 38 between these contact members. The heat of the arc 38 vaporizes some of the liquid SP at the bottom of the tank 11 and creates a pressure which causes the vaporized gas to flow through openings 39 in the partition 36 into the upper part of the interrupting chamber 12, where the arc 16 is drawn between the contact member 35 and the contact member 15. The upward travel of the contact member 35 is limited by-a pin or flange 41 which engages the partition 36. A check valve 31 at the entrance to the collector compartment is closed by the increase in pressure in the compartment. The density of the interrupting medium in the interrupting chamber is increased during the interrupting operatiomas previously explained.

The interrupter shown in FIG. 4 is also of the selfgenerating type. In this case, it is assumed that the interrupting medium in the tank 11' remains in a gaseous state under the operating conditions encountered by the breaker. Since the gas forced through the orifice 22 by the pressure generating are 38 is relatively hot and ionized, it is desirable to mix un-ionized gas with the ionized gas in the interrupting chamber. This is accomplished by utilizing the injector principle. As shown, openings 45 are provided in the orifice member 23'. Thus, the velocity of the gas flowing through the orifice past the openings 45 draws un-ionized gas from outside the interrupting chamber 12 through the openings 45 into the chamber where it assists in extinguishing the main are 16. I One of the reasons SP breaker tanks are expensive is the requirement of adhering to the ASME Boiler and Pressure Vessel Codes. The code rules not only add to the initial cost of thebreaker, but for most designs reconnected to the openings'26.

quire a yearly inspection by a qualified inspector. The code does, however, exempt all pressure vessels which are six inches inside diameter and under. Thus, by providing tanks which are six inches or less in diameter and utilizing high pressure, high density liquid SP as the interrupting medium, circuit breakers can be provided which are smaller and cheaper than prior breakers.

The circuit breaker shown in FIG. 5 is of the self-contained type. It comprisesa generally cylindrical interrupti'ng chamber 46 which is of a diameter of six inches or less. The chamber 46 contains liquid SP A stationary contact member 47 enters one end of the chamber through an insulating bushing 48. Likewise, a conductor 49 enters the chamber through a similar bushing 51, which is mounted at the other end of the chamber and at right angles to the bushing 48. The upper end of the conductor 49 is provided with contact fingers 52 which support and engage a movable contact member 53. The contact member 53 may be actuated by any suitable operating means, such as a solenoid having a coil 54 and a core 55, which is attached to one end of the contact member 53 by an insulating member 56. The core 55 is disposed inside an extension 50 of the chamber 46.

A generally cylindrical accumulator 57 has a closed end 58 and an open end which is connected to the interrupting chamber 46 at 59. A floating piston 61 is disposed inside the accumulator 57. Thus, the piston 61 divides the accumulator into two chambers or compartments one of which contains liquid SP and the other of which contains an inert gas, such as nitrogen, at a relatively high pressure, for example 2,000 p.s.i. Thus, the pressure of the nitrogen on the piston 61 increases the pressure and the density of the SP in the interrupting chamber 46. Other compressible means, such as a spring, could be utilized to apply pressure on the piston 61.

When the contact members are separated to draw the are 16 in the interrupting medium between thecontact members, the nitrogen in the accumulator may be compressed slightly by the initial interrupting shock. However, the resiliency of the compressed gas continues to force the piston 61 in the direction to maintain high pressure and high density of the interrupting medium in the interrupting chamber, thereby improving the interrupting abilit of the interrupter.

The breaker shown in FIG. 6 is in general similar to the one shown in FIG. 5. The accumulator 57 has a piston 62 therein which is connected to a suitable actuating means (not shown) by a connecting rod 63. The actuating means may be of a type well known in the art such as, for example, a hydraulic mechanism or a spring operated mechanism.

An operating piston 64 is disposed inside a cylinder 65 which is connected to the end of the interrupting chamber 46 opposite the end having the bushing 48 therein. The piston 64 is attached directly to the movable contact member 53. A compression spring 66 is disposed in the cylinder 65 between the piston 64 and the closed end of the cylinder. Other compressible means, such as air or a gas, may be utilized in place of the spring 66.

The contact members are shown in the closed position. When it is desired to open the contact members, the piston 62 in the accumulator 57 is driven to the left by the external actuating mechanism. This forces additional liquid SP into the interrupting chamber, thereby increasing the pressure in the chamber. The increase in pressure forces the piston 64 to the left, thereby opening the contact members. It will be noted that the increase in pressure and density of the SP occurs only at the time of interruption, thereby improving the interrupting ability of the interrupter. When it is desired to close the contact members, the piston 62 is moved to the right by the actuating mechanism, thereby decreasing the pressure in the interrupting chamber 46 and permitting the spring 66 to drive the piston 64 to the right to close the contact mem bers.

In the foregoing structure SP or other media, is utilized at a pressure and density higher than that obtained at room temperature vapor pressure. As an example, the room temperature (70 F.) vapor pressure of SP is 300 p.s.i.g. The density is 12.5 pounds per cu. ft. at this pressure and temperature. In the present case the density is higher than 12.5 pound per cu. ft. for SP Thus, the interrupting medium is utilized at extra high density.

The increased SP density results in higher are voltages. A structure such as that shown in FIG. 6 would have a high arc voltage since arc voltage increases rapidly with pressure. High arc voltage, together with the other outstanding arc interrupting characteristics of SP results in a quick and efiicient arc extinction in an interrupter which is smaller and less expensive than other comparable interrupters. This would find applications in AC circuit breaker interrupters and also DC interrupters and fuses.

The are voltage has the same effect as an increasing series variable resistor. The high arc voltage reduces the magnitude and rate of rise of recovery voltage. This provides more time to recover the needed dielectric strength.

Furthermore, a high are voltage reduces the pressure rise during arc interruption. Calculations have been made of the expected pressure rise of a device similar to that of FIG. 5. The following assumptions have been made: system pressure is 2,000 p.s.i., SP volume is 231 cubic nches, nitrogen volume is 231 cubic inches, arcing time 18 /2 cycle, RMS current at contacts part is 100,000 amperes, current during arcing is 5,000 amperes, system voltage is 500 volts RMS arc voltages 450 volts, and 100% of the heat released is absorbed by the SE, alone. A calculated peak pressure rise is 61 p.-s.i. The pressure will drop rapidly as the heat is absorbed by the metal parts of a pole unit.

Pressure rise is directly proportional to arcing time, current and arc voltage, and inversely proportional to SP and nitrogen volume. As an example, increasing the system voltage to 11.5 kv., the arc voltage to 10.9 kv., the SF volume to 2 gallons, the nitrogen volume to 3 gallons, changing the current at contacts part to 50,000 amperes, current during arcing time to 2,500 amperes, would result in a peak pressure rise of 125 p.s.i.

The advantages of high density SE; in combination with the high arc voltages that will result when it is used are apparent. An interrupting medium is inserted between the contacts which as they part and arcing is initiated will have a very high resistance, and once the current passes through zero (or reaches the point of instability in the case of a DC interrupter) will have the capacity to rapidly recover its dielectric strength, and the medium will have a high dielectric strength. The interrupter is so constructed and applied that a low amount of heat energy is released during a fault interruption. SP is referred to and described is referred to and described herein because of its excellent properties, but other media such as selenium hexafluoride SeF or trifluoromethyl sulfur pentafiuoride CF SF perfiuoro propane C F perfluoro butane C 1 sulfur monofiuoride S F sulfurylfiuoride SO F perchlorylfluoride ClO F, perfiuorobromomethane CF Br, could be utilized.

Since numerous changes may be made in the abovedescribed construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all subject matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In a circuit breaker, in combination, an interrupting chamber, separable contact members disposed within the interrupting chamber, a tank surrounding the interrupting chamber, a collector disposed at the bottom of the tank, an electronegative gaseous interrupting medium surrounding the separable contact members, the pressure and temperature conditions within the tank being such as to cause a liquefaction of a portion of said gaseous medium into said collector (13), said contact members being separable to draw an arc in the gaseous interrupting medium, means for creating a blast of the gaseous medium through the interrupting chamber and for introducing a quantity of the liquefied medium from the collector into the interrupting chamber to increase the density of the medium in the interrupting chamber and to extinguish the arc.

2. The circuit breaker combination of claim 1, wherein the arc is drawn through an insulating orifice member, and the blast of gaseous medium occurs through said insulating orifice member.

3. The circuit breaker combination of claim 1, wherein the blast-creating means includes a storage tank (28) containing the eleotronegative gaseous interrupting medium at high-pressure and controlled by a blast valve (29) to force said gaseous interrupting medium at high pressure through the arc.

4. The combination of claim 2, wherein the blastcreatin g means includes a storage tank (28) containing the electronegative gaseous interrupting medium at highpressure and controlled by a blast valve (29) to force said gaseous interrupting medium at high pressure through the arc.

5. The circuit breaker combination of claim 1, wherein the blast-creating means includes a piston (24) operable within a cylinder and responsive to the contact separation.

6. The combination of claim 2, wherein a pipe (27) leads from the collector (13) into the insulating orifice member, and openings (26) in the orifice member feed liquid medium into the arcing space.

7. The combination of claim 3, wherein a pipe (33) leads from the down-stream region of the blast valve (29) into the collector (13), and an additional pipe (27) leads from the collector '(13) into the region adjacent the arcing space.

8. The combination of claim 7, wherein an orifice member (23) is provided and the pipe (27) feeds fluid into said orifice member and through additional openings (26) into the arcing space.

9. The combination of claim 1, wherein the electronegative gaseous interrupting medium is selected from the group consisting of SF SeF SO F CF SF ClO F, C3F3, S2F2, C4F10 and CF3BI'.

10. In a circuit breaker, in combination, a metallic cylindrical interrupting chamber of 6 inches or less containing only a liquid electronegative interrupting medium, separable contact members disposed inside the chamber, terminal bushings for supporting the separable contact members, an accumulator connected to the chamber and containing the same kind of liquid, a piston (62) inside the accumulator, means (63) acting on the piston (62) to force liquid from the accumulator into the chamber to increase the pressure and the density of the liquid in the chamber, and piston means (64) for separating the contact members to draw an arc in the interrupting medium.

References Cited UNITED STATES PATENTS 2,757,261 6/ 1956 Lingal et a1 200148 3,150,245 9/1964 Leeds et al 200148 3,257,533 9/1966 Leeds 200148 FOREIGN PATENTS 638,145 11/1936 Germany.

679,327 8/ 1939 Germany.

703,744 3 1941 Germany.

475,370 11/ 1937 Great Britain.

609,589 10/ 1948 Great Britain.

ROBERT S. MACON, Primary Examiner.

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