US 1621058 A
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ELECTRIC CONDENSER Filed Feb. 10, 1925 March 15 1927.
IIIIIII INVENTOR Oszua/a Burger BY ATTORNEY"- Patented Mar. 15, 1927.
UNITED. STATES 1,621,058 PATENT OFFICE.
OSWALD BURGER, OF BERLIN-CHARLOTTENBURG, GERMANY, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING- COMPANY, OF NEW YORK, N. Y., A CORPORA- TION.
Application filed February 10, 1925, Serial No. 8,276, and in Germany February 12, 1824.
My invention relates to improvements in electric condensers.
It is well known that the capacity of a condenser is the greater the thinner its dielectric layer. Attempts have therefore been made to keep this layer as thin as possible. These attempts soon reached their limit' owing to the difliculties which arose in producing and finishing the dielectric materials. If the layer is very thin a defective place will naturally form a relatively considerable part of its thickness. Such a weakened place will not be able to sustain the total voltage of the condenser and a puncture will occur which destroys the dielectric layer and thereby the entire condenser. To avoid the danger just mentioned it has hitherto been necessary to make the dielectric layer thicker than was desirable for the capacity of the condenser.
According to my invention this disadvantags is avoided by arranging between the conducting layer and the dielectric layer of the condenser a protective layer of semiconductin material. When the dielectric is in fault ess condition the resistance which the protective layer oflers to the discharge current is relatively low and consequently also the voltage loss caused by it. When, however, there is a defective place in the dielectric which reduces -its resistance, the resistance of the protective layer becomes of considerably greater importance in comparison with the diminished resistance of the dielectric. v p
The improved condenser is illustrated in the accompanying drawing, the single figure of which is a sectional view through a portion of a condenser embodying my invention. The eflect of the protective layer will be clear from the following description and explanation. In the illustration, d-is the dielectric layer, s the protective layer according to my invention and m the metal foil or conductive layer. When the dielectric is in perfectly faultless condition only that resistance of the protective layer comes into lay which it offers to. a current travers ing it at right angles to its surface. Since the resistance is not great, the voltage drop in the protective layer is small. We assume now that at a there is a defective lace in the dielectric d. The current which sows from the oint a, across this place a through the die ectric towards the point a finds a resistance in the protective lever a which is in proportion to the thickness of the protective layer and the area of the defectlve place. The resistance is owing to the small extent of the defective zone. If the current were to flow into the defective place a from other places, such as 72, 6 it would be obliged to pass obliquely through the protective layer in order to reach the defective place a. The length of the path of the current and therefore also the resistance which it encounters would thus become greater. The current intensity at the weakened lace does not therefore, become essentia 1y greater than in other parts of the dielectric so that no temperature rise and no destruction of the dielectric need be feared. From this it follows that when the dielectric is undamaged the resistance of the protective layer and consequently the voltage losses are practically negligible. When, however, the dielectric has become damaged, the protectlve layer comes into full operation. t is therefore possible to make the dielectric thinner than has been permissible heretofore, whereby dielectric material is saved on the one hand while, on the other hand the capacity of the condenser is increase without the danger of short-circuits.
The thickness of the protective layer depends-upon the circumstances, and in articular upon its conductivity in comparison with that of the dielectric. In many cases it is advisable to choose for the protective layer, a material which is not too poor 8. condoctor, and to make it of considerably greater thickness than the dielectric. The protective layer may be disposed at one side of the dielectric only, as shown in the illustration, or at both sides.
What I claim as my invention is 1.. In an electric condenser, the combination of a dielectric layer, conducting layers at both sides of said dielectric layer and a layer of semi-conducting protective material between said dielectric and one of said conducting layers, said layer of protective material being of considerably greater thick ness than said dielectric layer.
2. A condenser comprising two conducting sheets separated by a dielectric, at least one of said sheets comprising a layer of good conductivity capable of carrying currents in considerable,
a direction parallel to its surface and a sec- 0nd layer of such material as to greatly oppose substantially all currents except those owing into the dielectric at approximately right angles to the surface thereof. I
3. A composite plate for an'electric discharge device comprising a layer of good conductivity capable of carrying currents in a direction parallel to its surface and a second layer on one or both of its sides, said second'layer being of such material as to greatly oppose the flow of discharge currents in a direction substantially parallel to its surface, while permitting a relativel easy passage of currents to orfrom sai first-' mentioned layer in a direction normal to its surface;
4. In an electric condenserg the combination of a dielectric layer, conducting layers at both sides of said dielectric layer and a layer of semi-conducting protective material between said dielectric and at least one of,
direction substantially parallel to its surface,
while permitting a relatively easy passage of currents to or from said dielectric in a direction normal to its surface.
In testimony whereof I affix my signature.
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