US2028589A - Electrical apparatus - Google Patents

Description

Jan. 21, 1936. F; M, A K 2,028,589

ELECTRICAL APPARATUS Filed Dec, 21, 1932 Fig.2.

m L I! y I m m rfl m Fig.3. CLEAR GLASS 2 mar? TIME GLASS F524. A I CLEAR a. GLASS '5 CLEAR cuss E AMBER TIME 0145s w Inventor: 5

AMBER 611139 159 TIME H is Attorneg.

30 wave length, preferably an amber glass, not affect the type of mineral insulating oil in Patented Jan. 21. 1936 2,028,589

llNlTED STATES PATENT OFFICE 2,028,589 ELECTRICAL APPARATUS Frank M. Clark, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York I Application December 21, 1932, Serial No. 648,286

4 Claims. (Cl. 220-82) The present invention relates to encased electo indicate the level of the liquid inside the trical apparatus, such for example as transtank and easing formers, X-ray outfits, high tension bushings, The high voltage bushing I6, as shown in and in general devices which are insulated and greater detail in Fig.2, includes a porcelain shell 5 cooled by liquid dielectric material which is sub- I! which is filled with insulating oil E8 in which ject during use to chemical change, such as is immersed a conductor l9 connecting the bushmineral hydrocarbon oil. i ing terminal 28 with the transformer in the eas- Casings for such apparatus sometimes are ing Ill. The oil I8 extends up into and partially made partly of transparent glass, in order to fills a transparent liquid level gauge M to a '10 permit ascertainment of a condition of the l v l 2- 'Th au e 2 a o e v s a an exin liquid dielectric material, such for example as p s chamber to Permit expansion a 00 1- its level, its fluidity, or the presence or absence traction of the oil 3 in the shell I! due to in it of sludge. Sludge is a semi-solid material p re C which forms during use. It is deleterious to the Transformers are Often used n locations exdielectric properties of oil and renders it less posed to Sunlight, the e D SH being some- 15 m i t as liquid h' medium, times to indirect sunlight but more often being I have discovered that appreciable damage to nt ns di t su t h s n 0. p p .results to liquid dielectric material which is subll, expansion tank I? nd bushing Shell H are ject to acid and sludge formation when exposed formed Q Opaque materials 5 that the insuin such apparatus to the chemical action of light letihg Oil in these parts S.p 0teeted f om out- 20 of relatively short wave length. While no sharp s d l ht- H w v th iqu d l v l au es 5 critical limit of wave length can be designated, d 2| m s e m de of t ansparent material the most deleterious effect appears to be due to in ordel'thet the levels and 22 0f the q d light below about 600 millimicrons of wave may be Visibleus, h Sma l Volume of oil 25 1ength.- In accordance with my invention this n these gauges I d 2| s e s ly exposed 25 harmful effect is obviated while still giving view to any direct indirect lightwhieh eac s to the liquid dielectric material by the use, as the gaugesa part of the casing, of colored transparent ma- I have diSOO'l/eled that light having Wave t -1 1 which is opaque t light of harmful t; lengths greater than about 600 millimicrons does The invention will be more fully explained which electrical lepperetus is Commonly min the following description taken in connecmersed but that light having Substantially m ith th accombanyjng drawing in which shorter wave lengths will cause such oil to de- Fig. 1 is a front elevation view of an encased If this permitted to ppen, the

35 liquid insulated transformer with a high voltage" depreeietedieil will radually d fiuse and mix 5 bushing of .th 114mm type; Fig 2 is an with the good 011 with which it is in communilarged View of t upper end of t e high t cation in the main casing l0 and in the bushage bushing with parts broken away to indicate ihg Shell I the structure more clearly, and Figs. 3, 4, and 5 The effect of the light of the shorter We've are graphs indicating the relative efiect on oil lengths is to Cause chemical changes in he 011, 40 of clear and amber glass as a container material. and acids and Sludge are Produced- These Like reference characters indicate similar parts duce the dielectric strength of the attack in Figs. 1 and 2 of the drawing. solid material (resins, pitch and the like) used Th tran former casing 10 shown in Fig 1 as insulation in the electrical apparatus imthedrawing isin communication through a pipe mersed in the oil and the sludge is deposited on 45 II with an expansion tank I2 to permit expansion the apparatusso that it is weakened electrically and contraction due to temperature changes of d, h p d during i Opera ion is less mineral oil or such liquid dielectric material as efllcien ly dissip may be employed in the casing Ill. The tank Some of the effects of light passing through Ill, pipe II and expansion tank I: are filled; ordinary c e r l ss a made v d t by thee0 with such liquid to a level l3 in the expansion graphs shown in Figs. 3, 4, and 5. The absence tank and the space above the liquid is in c0mof effe t O the Oil y light passing g munication with the outside air through a amber glass also is indicated. In Figs. 3 and 4 breather M. The expansion tank I2 is prois indicated the progressive change in color and vlded with a transparent liquid level gauge is acidity due to exposure of oil to light passing 2 aoasisse by amber glass no appreciable color or acidity change could be noted'for the same period of time. i

The formation of sludge under the influence of light is even more marked than the color change and acid formation. As shown in Fig. 5,

a rapid increase of potential sludge occurs in the oil. Sludge when first formed in mineral oil tends to be held in suspension or solution, but, of course, accumulates, and eventually becomes precipitated. The sludging produced by exposure to light transmitted by clear glass over a period of about ten weeks (as indicated by the legend Sludge in Fig. 5) and referred to above as potential sludge can be made evident by the socalled bomb test. In accordance with it, samples of oil to be tested are subjected in a bomb at a temperature of 140 C. for about 24 hours to oxygen gas at a pressure of about 250 pounds to the square inch. Any sludge formed under these conditions is centrifugally separated and observed, and measured. As made evident by Fig. 5 oil subjected under the test conditions only to light transmitted by amber glass showed hardly an appreciable tendency to sludge as shown by the bomb test.

In order to prevent or reduce these undesirable results, the liquid level gauges l5 and 2| are formed of material, which is opaque to light rays having wave lengths shorter than about 600 millimicrons. While amber glass is preferred, red glass or glass of other color cutting ofi the 1 short wave lengths of light may be employed.

Harmful light is thus prevented from reaching the oil and light of the visible spectrum having wave lengths substantially longer than 600 millimicrons clearly discloses the level of the oil but does not harm the oil.

The invention has been explained in connection with a particular. application thereof but it will be apparent that other applications and changes may bemade without departing from the spirit of the invention and the scope of the appended claims.

For example, parts of the casing of a fluidcooled electrical device other than a level indicator or gauge may be made of glass having a 'coloradapted to intercept the undesirably actinic short wave lengths. A varnish or other coating of suitable color on a clear glass may be employed within the scope of my invention.

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

1. In'electrical apparatus, a casing, an electrical conductor in said casing, a body of mineral insulating oil in said casing for insulating said conductor, oil level indicating means comprising a portion of said casing, said portion having the capacity to transmit light, said oil being exposed to light passing through said light transmitting portion, and means for substantially restricting transmission of light through said portion to wave lengths in excess of 600 millimicrons to reduce the depreciation .of the insulating value of said oil.

2. In electrical apparatus, a casing, an electrical conductor in said casing, a body of mineral insulating oil in said casing for insulating said conductor, an oil level indicating means comprising a portion of said casing having the capacity .to transmit light, said oil being exposed to light passing through the said light transmitting portion, and means including an amber glass member for preventing the passage through said portion of wave lengths of light having a depreciating effect on the insulating value of said oil.

' 3. In'electrical apparatus, a casing, an electrical conductor in said casing, efibody of mineral oil in said casing for insulating said conductor,

an oil-level indicating means comprising a portion of said casing having the capacity to transmit light, said oil being exposed to light passing through said light transmitting portion, and

means including ared glass member for preventing the passage through said portion of wavelengths of light having a depreciating effect on the insulating value of said oil. 4. A high tension electrical transformer bushing comprising a casing, an electrical conductor in said casing, a-' body of mineral oil in said casing 'for insulating said conductor, a liquid level gauge glass in the wall of said casing, said gauge glass'being composed of amber glass whereby wavelengths of light having a'depreciating effect on the insulating value of said oil are substantially excluded from said casing.

FRANK M. CLARK. I

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