US2313580A - Gas blast electric circuit breaker - Google Patents

Description

March 9,

Figz.

w. K. RANklN l 2,313,580

GAS BLAST ELECTRIC CIRCUIT BREAKER Filed May 14 `1942 pag.1(

20 40 60 60 /00 /ZO TIME SUBSEQUENT 7U CURRENT ZERO IN MICRO-SECONDS Patented Mar. 9, 1943 UNITE-D STATES Gas BLAST ELECTRIC cmciirr 'Bananen William K. Rankin, deceased, late of Lansdowne, Pa., by Jessie M. Rankin, executrix, Lansdowne, Pa., assignor to General Electric Company, a

corporation of New York Application May 14, 1942, Serial No. 442,928

3 Claims.

This invention relates to gas blast electric circuit breakers, more particularly to the gaseous blast medium employed for extinguishing arcing, and has for its principalvobject the provision of an improved gas blast circuit breaker that has 5 increased power interrupting capacity for a given blast pressure, particularly in the high voltage range of modern power transmission systems.

' It has been proposed to use various gases, such as for example carbon dioxide and fluorinated ll0 hydrocarbons in gas blast circuit breakers for interrupting high voltage lpower circuits. These gases have higher dielectric strength than air and are therefore better able to withstand stresses incident to circuit interruption, particularly when high rates of recovery voltage are involved. However, in practice air blast circuit breakers have generally been used due to the ready availability of air and the comparatively low cost of air compressor equipment notwithstanding the fact that increased interrupting capacity may be obtained with gases of higher dielectric strength. Other problems are also involved, such as the possibility of freezing andk jamming of the blast control valves with carbon-` dioxideice when carbon dioxide is used, and the high cost of certain gases, such as dichlorodiiluoromethane where a large number of circuit interruptions are involved. l, 4

In accordance with this invention, the highly 30 desirable practical advantages of the air blast circuit breaker including simplicity, low cost of operation and availability of blast medium are retained, and to these are added the improved arc extinguishing characteristics of a compara-* tively high Idielectric strength gas. It has been found that the interrupting capacity of an air blast circuit breaker can be materially increased 'bysaturating or permeating the air in the storage reservoir with vapor of la liquid having a'greatertio.

moleculary weight than nitrogen (which is the main constituent of air) and that will readily volatilize in air such as for example carbon tetrachloride vapor. A simple method of practicing the invention comprises introducing a com- V45 paratively small amount of carbon tetrachloride liquid or the equivalent [thereof in the air storage clearing high voltage power circuits since by reason of its increased dielectric strength it tendsto prevent ionization and electric breakdown of the arc gap after arc interruption of a current zero.

Arc extinguishing media including carbon tetrachloride in liquid or in liquid spray forms have previously been proposed for arc interruption.

However, in these cases the carbon tetrachloride was in appreciable quantity at the interrupting gap and was primarily relied upon per se to cool the arc stream. Furthermore, 1carbon tetrachloride when used in this manner is injurious to most organic insulating materials and for this reason it has not yfound favor in practice to any known extent. The vapor-containing air blast involving my invention, however, can be safely and widely used since the quantity of carbon tetrachloride for example in the blast is Small and also since the exhaust blast gases are non-inamxmable and non-poisonous.

This invention will be more fully set forth in the following description referring to the accompanying drawing, and the features of novelty which characterize the invention will be pointed out with lparticularity in the claims annexed to and forming a part of this specification.

Referring to the drawing, Fig. 1 thereof is an elevational view, partly in section and partly in diagrammatic form, of a gas blast circuit breaker with its gas storage tank embodying the present invention, and Fig. 2 is a graphical illustration of dielectric characteristics of air, and airlsaturated with carbon tetrachloride vapor.

Fig. 1 illustrates by way of example an air blast circuit breaker arrangement of the cross blast type for practicing rthe present invention.

The circuit breaker per se, however, may be of any suitable type, such as a cross blast breaker of the character disclosed and claimed in Letters Patent No. 2,284,842 issued June 2, 1942, to Prince, Rankin and Skeats for Circuit breaking apparatus. More speciiically, the lcircuit breaker herein shown comprises an insulating arc chute lstructure forming'a slot-like (arc chamber 2in which' the lixed' contact structureS and the movf able contact 4 are arranged to separate to form supply Aconduit 5 so that the arc is driven laterallyagainst the edges of the insulating interrupting barriers 6 which form diverging passages jin the vchute leading from the arc chamber to atmosphere. The trahsverse,'or 'cross blast of the interrupting gas is particularly eiective for interrupting the heavy power currents.

The source of blast pressure comprises a suitable storage tank 1 that is connected to the circuit breaker by the supply conduit which is provided with a blast control valve 8. The control valve 8 is normally biased closed as indicated and is arranged to be opened by suitable means, such as an actuating solenoid 8 in turn controlled in the usual manner by fault responsive relays or the like. When the solenoid 9 is energized to open the valve 8 in accordance with separation of the contacts 3 and 4, air which is stored in the tank I under high pressure flows through the conduit 5 and into the breaker to interrupt arcing. The storage tank 'I can be supplied with air at a predetermined pressure by suitable compressor equipment of Well-known form through the connection indicated at IB.

In practicing the invention, but a comparatively small amount of liquid carbon tetrachloride, or equivalent liquid, is necessary in the air storage tank 'I. The method of introducing the liquid into the tank is obviously subject to many variations, and there is shown one such method merely by way of example. A casing II containing liquid carbon tetrachloride I2 is suitably mounted above the storage tank 1 so that the proper supply of liquid can be admitted from time to time to the storage tank. The casing II is normally closed off and communicates with two pipes I3 and I4 arranged to connect the interior of the casing II with the lower part of the storage tank '1. The pipe I3 is provided with a control valve I3' and the pipe I4 is similarly provided Iwith a control valve I4', both of which are closed when the casing II is to be supplied with more liquid, as indicated by the gauge I5. For this filling operation, the filler cap I6 is simply removed and liquid is added. 1n cases where it is necessary to vent air at the upper part of the casing during the filling process a valve controlled atmospheric vent I'I is provided.

When liquid is to be admitted to the tank 1, the cap I6 is tightly closed to seal it, the valve Il is closed and the valves I3 and I4 are opened. Since the pressure is equalized in the" casing II by the pipe extension I3, liquid flows by gravity through the pipe I4 into the bottom of the tank. When the liquid in the tank rises to a level indicated at I8 so that it closes the lower ends of the pipes I3 and I4, further flow automatically ceases according to wellknown hydraulic principles. When the level of be seen that the cooling effect of a liquid spray is not relied upon for arc interruption, since otherwise a comparatively large amount of liquid would be involved, but on the contrary the increased dielectric strength of the fortified air blast is relied upon.

This will become apparent by reference to Fig. 2 which represents the dielectric strength of different gas blasts in a cross blast circuit breaker under varying conditions. The curves are plotted with coordinates representing breakdown voltage in kilovolts and time subsequent to current zero in microseconds. Curve a represents an air (alone) blast at the throat of the circuit breaker, i. e. at the interrupting chamber 2, with a pressure of 3 lbs. per sq. in. The air blast at this throat pressure therefore cannot be expected to interrupt power circuits in the cross blast type breaker at voltages in excess of 40 kv. Curve b represents the interrupting ability of an air (alone) bla-st having a mulch greater throat pressure, i. e. 2O lbs. per sq. in. It will be appreciated of course that this represents very much higher tank pressure, and although the chart indicates that circuits at voltage around 90 kv. may be interrupted, the increased pressures introduce important mechanical problems.

Curve c represents an air blast fortified with carbon tetrachloride vapor at a throat pressure of 3 lbs. per sq. in., and it will be readily appreciated by comparing curves a and c that the voltage range of an air blast circuit breaker embodying the present invention can be appreciably extended. Not only have the advantages of high dielectric strength represented by curve b been substantially retained, but also the mechanical advantages of low operating pressure represented by curve a. In practice it has been found that air saturated with carbon tetrachloride vapor can interrupt a circuit at approximately double the voltage as compared with the air blast alone.

Although there is speciiically described the use of carbon tetrachloride vapor, it shall be understood that the invention is not limited thereto and that the air blast can be permeated or saturated with other vapors having suitable electrical the carbon tetrachloride Within the storage tank drops due to evaporation to a point below pipes I3 and I4, an additional supply of liquid iiows from the casing II.

Experiments were conducted at a normal arnbient temperature of approximately 25 C. and a tank or storage space pressure of r15 lb. sq. in. absolute, i. e. 5 atmospheres. Expressed in m. m. of mercury this pressure is 5 760=3800 m. m. A vapor pressure table for carbon tetrachloride indicates a pressure of 114 m. m. of mercury at 25 C. Hence the compressed vapor and other characteristics without departingfrom the spirit of the invention. For example, halogenated hydrocarbons, such as dichlordiiiuormethane (CClzFz) would be suitable. Non-inflammable liquids such as trichlorethylene (CzHCla) and tetrachlorethylene (C2014) could be used to advantage.

It shall also be understood that the invention comprehends the addition of azeotropic substances intended to cut down the amount of carbon tetrachloride, or equivalent, used in the blast. That is, these additions do not necessarily improve the electrical performance of the breaker but they do permit economy in the use of the dielectric fortifying vapor since the amount thereof taken up by the air is obviously less. By way of example, a variety of alcohol substances can be used for this purpose.

It should be understood that the 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 spirit of the invention.

What is claimed as new and desired to secure by Letters Patent of the United States is:

l. A gas blast circuit breaker comprising relatively movable contacts separable to form an arc gap, a storage tank containing air under pressure,

blast control means interconnecting said tank and arc gap for directing a gas blast through said gap for extinguishing arcing, and a supply of carbon tetrachloride liquid in said tank for permeating the air therein with carbon tetrachloride vapor prior to operation of the gas blast whereby the dielectric strength of said gas blast is materially increased.

2. A gas blast circuit breaker comprising relatively movable contacts separable to form an arc gap, a gas storage tank having means for directing a gas blast through said gap for extinguishing arcing, said storage tank containing an arc extinguishing gas under pressure, and carbon tetrachloride liquid in said tank, the carbon tetrachloride Vapor being in saturating relation to the gas under pressure in said tank prior to operation of the gas blast for materially increasing the dielectric strength of the gas blast and increasing the interrupting capacity of said circuit breaker.

3. A gas blast circuit breaker comprising relatively movable contacts separable to form an arc gap, a gas storage tank having means for directing a gas blast through said gap for extinguishing arcing, said storage tank containing air under pressure, a vaporizable liquid in said tank, said 1iquid having a molecular weight greater than the molecular Weight of nitrogen so that the vapor thereof in permeating relation to the air in said tank materially increases the dielectric strength of the air blast, and an azeotropic substance in said tank for limiting the amount of vapor taken up by said air under pressure.

JESSIE M. RANKIN, Eecutr of the Estate of William K. Rankin,

Deceased.

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