US3021411A - High voltage arc-extinguishing switch - Google Patents

Description

Feb. 13, 1962 J. A. COOLEY HIGH VOLTAGE ARC-EXTINGUISHING SWITCH Filed July 7, 1960 John A. Cooley INV TOR. J KZ ZQJ BY 4%? ATTORNEYS.

i d States Patenta 3,021,411 1 HIGH VOLTAGE ARC-EXTINGUISHING SWITCH John A. Cooley, Chevy Chase, Md.v (6505 Wilmett Road, Bethesda 14, Md.) Filed July 7, 1960, Ser. No. 41,452

- 4 Claims. (Cl. 200-1 (Granted under Title 35, U.S. Code The invention described herein may be manufactured and used by or for the Government for governmental purposes without thepayment of any royalty thereon.

This invention relates generally to electrical switches, and more particularly to switches incorporating means for extinguishing arcs formed during switching.

It is desirable to provide an electrical switch which reduces the amount of arcing occuring when a circuit is broken. One common practice to obtain the desired arcextinguishing characteristics is by immersing the contacts in a liquid having a high dielectric strength such as oil. Oil, as thus used, is a passive extinguisher, that is, it

' extinguishes arcs simply by its dielectric properties and by cooling. While oil does offerexcellent insulating properties, its use does not entirely obviate arcing, and presents additional problems of oil burning and carbonization. Other known means of extinguishing arcs'include those employing water or explosive means. Theseoftentimes present other problems such as securing the desiredinsulating properties and providing sufficient resistance to corrosion. l

Accordingly, it is the object of this invention to provide a more effective arc-extinguishing switch for high voltage switching.

This and various other aspects of the invention will be better understood from the following description taken in connection with the accompanying drawing in which the single figure illustrates a sectional view of a preferred em bodiment of the invention.

Referring to the drawing, a switch is shown which comprises a casing 11 containing within it an insulating liner 12 of suflicient dielectric strength to withstand the maximum voltages to be encountered in the particular use for whichthe switch is intended. One or more so I 1952 see. 266) r. CC

The conducting layer completes the circuit and carries the current flow between the two contacts. When it is desired to break the circuit, the contacts 13 are raised.

As these contacts leave the surface 21 of the conducting layer, they-strike an arc 20. The are heats expansible fluid 17 rapidly, causing it to vaporize violently. The violent'vaporization assists in rupturing the arc, and causes insulating fluid 18 to' rapidly inte'rpose between the contacts and conducting layer 16 extinguishing the arc and preventing it from, reforming. This interposition is abetted by the factthat the vapor of the expansible material condenses almost immediately, leaving behind a vacuum, which is rapidly filled by the insulating fluid, due to pressures in the case caused by the violent vaporization. The expansible fluid used in cooperationwith oil issuperior to oil alone because of its property of violent vaporization, which is in contrast to the slow, non-violent,

vaporization of oil. An oil-water combination is also superior to water alone, due to the insulating powers of the oil which is forced into the arc path. As material vaporized from the expansible layer 17 condenses in the colderoil, it sinks to rejoin the expansible layer. The enclosed area 19 above the liquid 18 in casing 11 serves as a buffer to allow a volume expansion of the liquid contents of switch 10 during the vaporization of expansi- I ble fluid 17. The insulators 14 serve to isolate the circuit from the case, as does also-insulatingliner 12. The enlarged contact areas '15 are a common means used n switches to, minimize-pitting and contact corrosion, and

to provide a lower contact resistance. In summary, the explosive vaporization of the expansible layer, in not only rupturing the are, but also in producing the force (vacuum) to drive an insulating fluid into the arc path,

" provides a means several times superior to conventional techniques for extinguishing arcs.

The thickness of the thin expansible layer is made sufliciently great to provide adequate vaporization and preserve the integrity of the layer for the power load to be encountered. The minimum thickness of the top insulating liquid also variesfor the'power loadinvolved and will be greater for greater loads. As an example, in clrcuit breaking tests involving a fraction of an ampere at movable contacts 13 having enlarged contact areas 15 are insulated from the case 11 and supported by insulators 14. They are adapted to raise and lower into casing 11 through an opening in the insulators. The casing contains a lower layer of either liquid or solid conducting material 16 such as mercury or Phosphor bronze, upon which rests a thin intermediate layer of expansible fluid 17, such as water. The word expansible fluid," as used here, refers to a liquid having the property of changing rapidly into a gaseous form. under the heating action of an are or electric current without substantially altering its chemical composition, this gaseous form occupying at least several times the volume of the original liquid supernatant upon expansible fluid 17 floats a top layer about 15,000 volts, a minimum thickness for the'intermediate layer, using water as the expansible fluid was on the order of M inch, and the thickness of light viscosity hydrocarbon oil used as a top layer was a quarter inch.

This combination proved adequate to quench the resulting are before it reached a length of ,4 inch. This represented at least a ten to one improvement over tests utilizing presently known techniques employing water or oil alone. i

While I have shown aparticular embodiment of my invention,'it will be understood, of course, that I do not of an insulating fluid, such as oil, which is non-expansible,

that is it does not have the expansible property of fluid 17. .All fluids must he immiscible with respect to each 1 other and ascending fluid layersm-ust be of decreasing specific gravity.

The position of the switch at the moment of breaking of the arc is shown in broken lines, while the arc is shown at 20, along with its lower point of termination 21 on the surface of conductor 16. Above the layer of insulating fluid 18 is an enclosed area 19 which serves to absorb shock and pressure changes as will be seen in the following description of the operation of the invention.

In operation, the circuit to be broken is applied to the two contacts 13. When the contacts 13 are driven downwards, they pass'through the insulating layer 18, expansible fluid 17, and contact the conducting layer '16.

lowered through said insulating material and said expansible material to make and break contact ductive contact. p

2. An electrical switch comprising a casing containing with said cona layer of conductive material, a layer of expansible fluid resting upon said conductive layer and a layer of non expansible fluid resting upon said layer of expansible fluid,

at least one movable contact mounted on said casing to "Patented Feb. 13, 1962 reciprocate through said non-expansible layer and said expansible layer to contact said conductive layer.

3. An electrical switch comprising a casing, a layer of conductive material supported within said casing, a layer of water resting upon said conductive layer and a layer of oil resting upon said layer of water, and at least one movable contact supported by said casing and including means to provide passage of said contact through said layer of oil and layer of water to contact said conductive layer.

4. An electrical switch comprising a casing, an insulated liner supported by said casing, a layer of conductive material resting on said liner, a thin layer of water resting upon said conductive material, a layer of oil resting upon said layer of water, a feed-through support insulator mounted on said casing, at least one movable contact supported by said insulator and adapted toreciprocate through said insulator, said oil and said water layers to make and break contact'with said conductive layer.

Rankin Mar. 31, 1925 Hobson Oct. 29, 1935

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