US1731652A - Electrostatic condenser - Google Patents

Description

-OC- 15 1929 w. DUBILIER 1,731,652.

ELECTROSTTIC CONDENSER Filed OOt. 25. 1922 Paz/yer INVENTOR BY mi@ M, )MAME/w+ LNMW A TTORNE YS Patented Oct. 15, 1929 UNITED STATES PATENT OFFICE WILLIAI DUBILIER, OF NEW YORK, N, Y., ASSIGNOR T DUBILIEB CONDENSEB COB- PORATION, A. CORPORATION OF DELAWARE ELECTROSTATIC CON DEN SER Application filed October 25, 1922. Serial No. 598,719.

bodies to a large degree many of the desirable characteristics heretofore found only in condensers of more expensive construction.

The underlying electrical principles of the present invention are the same as those set forth in my copending application Serial No. 472,105, filed May 24, 1921, wherein is disclosed a condenser consisting of alternate layersl of mica and metal foil, the intermediate layers of foil being isolated one from another by the adjacent sheets of inica. By s such a construction there is produced a oondenser capable of withstanding high potential and in which the tendency toward socalled brush discharge or corona effect is greatly reduced. The brush discharge or corona effect is that discharge which occurs as a result of conduction alon the surfaces and thence across the edges o the sheets of dielectric and is, in effect, a high resistance leakage. Although the breakdown voltage 0f a condenser, as is well known,is approximately proportional to the thickness of the dielectric for any given dielectric material, it does not follow that the brush discharge is 3o likewise proportional. For example, an ordinary condenser comprising alternate layers of metal foil and paper of say .002l thickness may be entirely satisfactory and .may show no appreciable brush discharge with an impressed potential of 1000 volts. By doubling the thickness of the layers of paper the condenser may be capable of withstanding 2000 volts, but in the latter instance an appreciable brush discharge might occur. Likewise, by tripling and-quadrupling the thickness o f the paper the breakdown voltage may be tripled and quadrupled, but in each succeeding case the probability of brush discharge is rapidly increasing. By the provision of intermediate isolated or what may be termed floating metallic plates, the total impressed potential is divided between the several plates so that the potential across any one layer of dielectric is only a fraction of the total. It has been conclusively established by experiment that the brush discharge is thus greatly decreased Without any increase in the amount of dielectric material required for a given capacity and potential, as compared with condensers heretofore known. Another important advantage inherent in this type of condenser arises from the fact that the flow of current therein is transverse to the plane of the metallic plates instead of parallel therewith, as in the former type of high potential condensers, which consisted of a plurality of serially connected condenser units. The effective ohinic resistance of the condenser plates is therefore greatly reduced without increasing their thickness, and the heating effect 'is in consequence correspondingly small.

In high potential condensers of the ordinary type wherein two sets of metallic plates are separated b several layers of paper, it often happens t at one or more of the layers has a defective spot in which excessive heat develops which, in time, burns through or causes the disruption of the other layers of paper, whereupon the condenser breaks down.

condenser of the ordinary type thus broken down is totally useless. Should a breakdown occur through a defective layer of dielectric between a. pair of adjacent metallic plates in a condenser constructed in accordance with this invention, it is not likely to be fatal. The result of such a breakdown would, ordinarily, be merely to proportionately increase the potential across the remaining layers of dielectric, and in view of the fact that condensers are usually designed with a considerable factor of safety, a complete breakdown would not be likely to occur.

In accordance with the previously stated object, the present invention provides a condenser wliich in its preferred embodiment comprises a roll of alternate layers of liexible dielectric material such as paper, and thin sheets of conduct-ing material such as metal foil, in which the intermediate layers, or at least some of the intermediate layers of foil, are isolated. These isolated layers of foil are referred to as Hoating plates, inasmuch as they are not connected to each other and have no connecting terminal. The end or terminal plates of this condenser are preferably made of metal plate of suiiicient thickness and rigidity to permit their being punched or otherwise formed with soldering terminals. These terminal plates are also preferably so proportioned that their edges extend a substantial distance beyond I the ends of the roll of paper and metal foil to provide radiating surfaces for dissipating any-heat which may be generated in the condenser. The roll thus formed, including the terminal plates, is preferably enclosed first within a layer of hard fibre, which in turn is enclosed within a split ring of spring steel or the like, and iinally within an vadjustable clamping band by which pressure may be applied to the roll.

Referring to the drawing which forms adenser pile-up.

' electric,

The condenser illustrated comprises a core 1, which in this instance is a tube of hard libre or other dielectric material, around which is wound a plurality of layers 2 of alternately interleaved sheets of paper and metal of which the terminal layers of metal are shown in Figs. 3 and 4 respectively, and comprises the outer plate 3 and inner plate 4. The terminal plates 3 and 4 are preferably of sufiicient thickness and rigidity to permit the soldering terminals 3 and 4 being punched integrally therewith, whereas the intermediate plates are preferably of metal foil such as tin foil. These latter constitute what havebeen referred to as the floating plates. Each of these floating plates is supported between the adjacent layers of paper, and is in no way connected with any of the other plates and is not provided with any terminal for outside connection. l

In building up the condenser a sheet of paper, which is preferably impregnated with paraffin or other suitable impregnating diis wound on the core 1, after vwhich plate 4 is slipped on over the layer of paper. Alternate layers of paper and metal foil are then wound about the terminal plate 4, after which the terminal plate 3 is slipped on over the layers of paper and foil. A layer of hard fibre 5 of about 1/64 thickness may then be applied around plate 3.- A split ring 6, which may suitably be of spring steel, is placed over the layer of hard fibre, and a clamping band 7, which may also be of spring steel, encloses the ring 6. The clamping band 7 has a pair of flanges 7a, 7", the former of which is provided with two apertures of suitable siZe to pass the bolt 8, and the latter of which is provided with apertures of -suitable size to lit the libre shouldered bushings 9. By means of the bolts 8 and their nuts 10, the ends of the clamping band 7 may be tightly drawn together, thereby exerting a considerable pressure on the condenser roll comprising the layers of metal and dielectric. The ring 6 and clamping band 7 are preferably insulated from each other by means of a coating of shellac on their adjoining surfaces. The purpose of the insulating bushings 9 is to interrupt the electrical continuity -of the clamping band 7, thereby reducing the possibility of excessive heat being generated therein by hysteresis currents. A bracket 11, shown in Figs. 1 and 2, may be electrically welded to the clamping band 7, and is provided with an aperture 11 for mounting the condenser. The terminal plates 3 and 4 preferably extend beyond the body of the condenser, as is clearlyv shown in Figs. 2 and 5. These outwardly projecting edges of the terminal plates help to dissipate any heat which may be generated within the condenser.

Fig. 5 shows the condenser pile-up in perspective with the terminal plates and sheets of paper laid out flat. The floating plates, which consist of sheets of metal foil, are not shown in Fig. 5, as their dimensions are such that they are hidden from view by the layers of paper.` The schematic diagram of Fig. 6 clearly illustrates the relation between the terminal plates, floating plates, and layers of paper. In this diagram there are shown eleven floating plates of metal foil interposed between the terminal plates and twelve layers of dielectric. The total potential across the terminals of the condenser would therefore be ldivided so that the potential across any one layer of dielectric would be l/12 thereof.

In other words, if a potential of 1200 volts were applied to the terminals 3', 4', the potential across each layer of dielectric would be 100 volts. If the thickness of each sheet of metal foil is .001, the combined thickness thereof would amount to .011. In other words, the amount by which the thickness of the condenser is increased by inserting the floating plates is .011, and the area of the plates is slightly increased to make up the loss of capacity ldue to this slight increase in separation. This slight increase in the amount of material used is, however, more than offset by the freedom from brush discharge which is obtained.

The present invention, however, is not to be construed as limited to condensers having floating plates, as the means here described for applying pressure to the condenser is equally applicable to rolled condensers of the ordinary type.

I claim:

l. In an electrostatic condenser, a roll comprising alternate layers of conducting material and non-conducting material, and adjustable means encircling the roll and directly engaging it over virtually its whole exterior for pressing said layers together over y substantially their entire surface area.

2L In an electrostatic condenser, a roll comprising a plurality of layers of dielectric material and a plurality ot' layers of conducting material alternately interleaved with said layers of dielectric material, certain of said layers of conducting material being adapted for Circuitconnections and the other or others of said layers oi conducting material being conductively isolated, and adjustable means encircling the roll and directly engaging it over substantially its entire eXterior for pressing and firmly holding said layers together.

3. In an electrostatic condenser', a roll comprising a plurality of layers of dielectric material and a plurality ot' layers of conducting material alternately interleaved with said layers of dielectric material, Certain of said layers of conducting material being adapted for circuit connections and the other or others of said layers of conducting material being con-ductively and individually isolated, a resilient split ring enveloping said roll over substantially its entire exterior, and an adjustable clamp encircling the ring to compress it and firmly hold said layers together.

et. In an electrostatic condenser, a roll comprising alternate layers 'of dielectric and conducting material, a resilient split ring, enveloping the roll over substantially its entire exterior, and a clamping band for applying pressure to the exterior of said ring for compressing' said roll.

5. In an electrostatic condenser, a roll comprising alternate layers ot dielectric and conducting material, a protecting layer of relatively stii' non-conducting material around said roll, a resilient split ring substantially surrounding said roll, said layer and said ring enveloping the roll over virtually its entire extent, and a clamping band for applying pressure to the exterior of said ring for compressing said roll.

In testimony whereof I atX mV signature.

WILLIAM DU'BILIER.

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