DE1790253A1 - Dielectric system for electrical insulation of an electrical conductor such as an electrical cable - Google Patents

Description

Dielectric system for electrical insulation of a electrical conductor, such as an electrical

cable

The invention relates to dielectrics based on impregnated organic plastics, which have a long service life and high dielectric strength, and in particular on AC capacitors in which such Dielectrics, especially polyolefin based, are used.

Today's electrical devices are getting more and more complicated and more powerful. Therefore, the capacitors in such electrical devices are also subject to ever higher requirements be asked. For example, there is a need for

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capacitors that are able to cope with higher performance j but anyway should be smaller and cheaper than the previously known capacitors. Capacitors, in particular alternating current capacitors with higher breakdown field strengths as well as higher corona ignition and extinguishing voltages are special because of this desirable because such capacitors pose many difficulties in the design and operation of electrical equipment help to overcome and make the operation of existing devices more reliable in many ways.

The aim of the invention is therefore a dielectric based on it of impregnated plastics * that have a high dielectric strength having. The corona ignition and release voltages of this dielectric should be very high. This should continue to be The dielectric has a low loss factor. This dielectric is said to be both an AC insulation material as well as an intermediate layer in AC capacitors.

Another object of the invention is an alternating current capacitor for high voltages, which has a larger capacity per unit volume than previously known capacitors. This The capacitor should have a solid dielectric intermediate layer which is particularly thin, but which is subject to high alternating voltage stresses can withstand. The main component of the dielectric intermediate layer should be a polyolefin film, which is impregnated with a halogenated hydrocarbon. The polyolefin film should be a polypropylene film and the halogenated one The hydrocarbon is said to be trichlorodiphenyl.

It has been found that certain combinations of substances and manufacturing processes lead to a capacitor with a dielectric based on impregnated plastic, which is surprising has favorable electrical properties. According to one embodiment of the invention, a plastic based on polyolefin, such as polypropylene, with a halogenated

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th aromatic compound, such as with trichlorodiphenyl, impregnated and used as a dielectric intermediate layer in a capacitor. It was also found that the just mentioned substances and materials interact and interact in such a way that an impregnation of the Polyolefin comes about, which has the most important electrical properties of a capacitor, such as breakdown field strength, Corona ignition and extinction voltages, life under voltage stress and loss factor, significantly improved.

In the following the invention will be described in detail in conjunction with the drawings.

Fig. 1 is an enlarged cross-section of a practically complete Impregnated dielectric interlayer for capacitors based on plastic.

Fig. 2 is a perspective view of a partially wound Capacitor winding.

Fig. 3 shows a complete capacitor having a winding core according to Fig. 2 and has a housing.

FIG. 1J is a cross-section through part of a capacitor which has an impregnated plastic roller as part of the dielectric intermediate layer. The structure of FIG. ¹ I is called "full sandwich".

Fig. 5 is a cross section through part of another capacitor, which has several impregnated plastic films as part of the dielectric intermediate layer. The structure of Fig. 5 is called an "inverted sandwich".

Fig. 6 is a cross section through part of another Capacitor, the dielectric interlayer of which is a

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having relatively thick impregnated plastic film. The structure of Fig. 6 is called a "half sandwich".

Fig. 7 is a cross-section through a portion of a modified capacitor formed in the manner of a "half sandwich" is constructed and as part of the dielectric interlayer several impregnated plastic films having.

8 is a cross section through part of a capacitor in which the interlayer dielectric is exclusively consists of an impregnated plastic film.

In Fig. 1, a dielectric intermediate layer 10 is shown, which is a preferred embodiment of the invention. This intermediate dielectric layer comprises a piece of one solid material 11 made of a polyolefin, in which a number of small pores, bubbles or openings 12 are present are. These pores or bubbles are a peculiarity of this material. Nevertheless, this material is called "non-porous" described as there are very few, if any, pores or vesicles from one surface to the other Pass the surface of the material through which the impregnating liquid according to the invention from one side to other side of the intermediate layer. The polyolefin is impregnated with a dielectric liquid, which on the one hand penetrates the material itself and on the other hand fills these pores or bubbles. The whole thing then stops continuous, but heterogeneous dielectric system. The type of impregnation as taught by the invention, Together with the special substances used, this leads to a surprising combination effect, through which the dielectric strength or the breakdown field strength of the dielectric intermediate layer is increased. From one point of view the insulation capacity of the plastic is determined by the

^ «Φ € ί 10 9884 / U60

Impregnation of the plastic with one material "with one Dielectric strength greater than the luff in the pores · therefore increased because the impregnation liquid penetrates the plastic. Capacitors other than those described here impregnated intermediate layers, which are, however, also impregnated, - are in the US patents 2,864-98 2 and 2,307 * T88.

If one uses the dielectric interlayer according to FIG. 1, for example used as part of a capacitor, surprisingly good properties and results can be achieved. There are already numerous combinations of fabrics for Use as a dielectric interlayer for capacitors has been described, but it has been shown that it is with the known'Stoffkombinen is not possible to get those properties in a capacitor that are necessary for the today's electrical devices are required. The substances with which the best results are achieved according to the invention are Plastics from the group of polyolefins and in particular polypropylene, polyethylene, 4-methylpentene (l) and polystyrene.

Because of their electrical properties, polyolefins are considered normal dielectric materials (i.e. not as intermediate layers for capacitors), their good thermal stability and their good mechanical properties because, especially because they are easily mechanical machined and deformed and shaped into thin foils. Because of these favorable properties polyolefins are widely used. On the other hand, polyolefins are only used to a limited extent as a dielectric in capacitors has been used because their breakdown field strengths are relatively small, as their corona ignition and release voltages continue are relatively low and since their lifespan under F> stress load is low. The breakthrough field is a very important variable. It is a measure of the material's ability to withstand tension

T09884 / U60 ORIGINAL BATHROOM

to withstand. The voltage stress here is to be understood as the voltage difference per unit thickness of the material. The corona ignition voltage and the corona extinction voltage are the voltages at which corona discharges occur or extinguish, which can lead to the destruction of the material. Furthermore, both impregnation problems occurred on. In particular, "the extent of the impregnation." and the compatibility of the individual materials with one another. Because of these disadvantages it still was not possible to find an imp ragnation procedure η. with-eggs the electrical properties of polyolefins can be improved.

It has now been found that polyolefins and in particular polypropylenes can be impregnated to an unexpectedly high degree if halogenated aromatic compounds are used for this purpose. The polyolefins and the halogenated compounds then act on one another in such a way that the particularly favorable dielectric interlayers for capacitors according to the invention come about. From the group of polyolefins, a polypropylene is particularly suitable for the invention, specifically a biaxially oriented isotactic polypropylene film. An example of such a film is described in "Applied Plastics", November 1961, pages 35 to 64 and in "Modern Dielectric Materials", Beck, JB, London Heywood and Co., pages 140 to 1/2.

The polyolefins described in these articles can be polymerized as linear head-to-tail polymers of unsaturated hydrocarbons of the general formula CIi_ = CHR be understood. So they are << .- olefins. R means a aliphatic radical, a cyclic aliphatic radical or an aromatic radical. These polyolefins can also be used Copolymers of unsaturated hydrocarbons with one another or copolymers of unsaturated hydrocarbons with a monomer that interacts with the unsaturated hydrocarbons

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substances can be polymerized together. One such polyolefin material can also be called non-porous, as it has practically no pores through which the preferred Impregnating agent according to the invention among those previously known operating conditions prevailing in capacitors from one Go through the surface to the other surface of a film can.

A preferred impregnating agent according to the invention is one halogenated organic compound containing 1 to 5 halogen substituents, such as chlorine, and 1 to 3 aryl groups. Trichlorodiphenyl is particularly suitable, the is sold under the trade name Pyranol II99. With this one Material, the corona ignition and extinguishing voltages are very high.

The combination of trichloro-diphenyl as the dielectric liquid with a non-porous polypropylene film as the impregnated According to the invention, dielectric gives the best results. It has already been noted that these two substances were previously regarded as incompatible with each other, so that they have been avoided for dielectric purposes, since polypropylene in halogenated organic compounds such as for example Pyranol II99, easily goes into solution. aside from that it was believed that the polypropylene film could not be wetted by the impregnation liquid. Farther . It has been shown that the dissolution of polypropylene in a non-polar liquid leads to plasticizing effects such as swelling and loss of tensile strength. However, it has now been found that, apart from high temperatures of about 100 ° C., polypropylene has only limited solubility in halogenated aromatic compounds, and that this is limited Solubility surprisingly reflects the properties of a capacitor not affected. This partial solubility of polyrropylene films in trichloro-diphenyl must be strictly observed Temperature conditions at temperatures below

ΙΟ 9 8 84 / 14-60 BAD CRHMNAl

of about 10O ⁰ C must be regarded as an important feature of the preferred combination of substances according to the invention. This partial solubility occurs, as tests have shown, when the impregnation agent has initially penetrated the foil and supports the migration of the impregnation agent in the foil and into the pores which occurs even if no porous layers are arranged on the two sides of the film.

Samples of polypropylene films were impregnated with pyrolysis and subjected to capacitor tests. It was found that there is a close relationship between the type and extent of the impregnation and the corona ignition voltage. Complete impregnation is therefore an essential feature of the invention. The combination of polypropylene with trichlorodiphenyl is particularly favorable for a type of impregnation which is to be described below as "practically complete" impregnation. If the vesicles and pores in the material are practically completely filled by the impregnating agent, and if the impregnation process comprises both the absorption of impregnating agents in the material and the partial dissolution of the material in the impregnating agent, the material is referred to as "practically completely impregnated". Comparative tests with plastic systems that were impregnated to different degrees have shown that very high and reproducible corona ignition voltages can be achieved, which are close to the measured, calculated or final corona ignition voltages, if the impregnation process was extended or otherwise supported by one to achieve complete impregnation. An impregnation process, which is an example for essentially complete impregnation, is to immerse a polypropylene film at a temperature of about 9O ⁰ C in trichloro-diphenyl. Under these conditions, it will be stable between 6 days and 20 days

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^^^ '-. ■ '■ - BADORICMNAL.

Ratios achieved. Then about 1 percent by weight of polypropylene have dissolved in the trichlorodiphenyl while on the other side of the polypropylene about 11 percent by weight tri-. chloro-diphenyl were added. Type and extent of the impregnation can be measured by the system's corona ignition voltage reaching a maximum value that is the full Indicates impregnation.

The preferred polypropylene film for use in the invention is made from isotactic polypropylene. This is a high molecular weight polypropylene which has a regular crystal structure and which, in addition to this predominant crystal structure, also contains a non-crystalline or amorphous phase. In some commercially available isotactic polypropylenes, the proportion of the amorphous phase is up to 30 %. In order to produce films from such polypropylenes which are useful for the invention, the polypropylene can be rolled, pressed or extruded. However, the films can also be obtained from a solvent or from a melt by casting. In order to improve the mechanical properties of such films, it is customary to give such films a preferred structure by stretching or tempering. It is advantageous if the films are stretched in two mutually perpendicular directions, that is to say in the longitudinal and in the transverse direction, so that the film is biaxially oriented. However, the films can also only be oriented unaxially or else be stretched evenly in two directions.

Polyolefin films, especially polypropylene films, should Contain as little foreign matter as possible that could affect the loss factor of the finished dielectric. The loss factor is a measure of the energy loss within a Materials. Foreign substances or impurities can also be materials adhering to the outside of the foils, which are absorbed during the production of the foils. Also catalyst substances can count among these impurities, these

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Impurities can, for example, be made from the polyolefin eliminates dissolving the polyolefin and impurities precipitates or adsorbs in the solution. Very good results have been obtained with commercially available polypropylenes achieved, for example, by the Hercules Powder Co. under the name Profax 652OF Resin and by sold by Shell under the name 55OOF Resin will.

Capacitors according to the invention, such as, for example, the capacitors according to FIGS. 2 and 3 *, can be constructed in the same way as previously known capacitors. In FIG. 2, a thick capacitor Ik is shown, which has separate foils 15 and 16 as electrodes, which are separated from one another by two dielectric intermediate layers 17 and 18. The connectors 19 and 20 have enlarged surfaces 21 and 22 (not shown) which are in contact with the capacitor pads 15 and 16. The capacitor pads 15 and 16 can be made from a number of different materials. Examples are aluminum, copper or tantalum. The dielectric intermediate layers 17 and 18 can be constructed as a sandwich. They contain at least one impregnated plastic film 11 according to the invention. A dielectric intermediate layer 17 and the two metal foils 15 and 16 together form a main component of a capacitor.

In FIG. 3, a finished capacitor 23 is now shown, into which a capacitor socket according to FIG. 2 is inserted. The entire condenser has a container 2k with a lid 25 hermetically attached. The cover 25 is provided with a filling opening 26 for the dielectric liquid. Furthermore, two connection terminals 27 and 28 are provided, which pass through the capacitor cover 25 and are isolated from it. Within the vessel, 2k, the two terminals 27 and 28 are connected to the two terminals 19 and? 0 in FIG. 2. The capacitor 23 of Fig. 3 contains

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in addition, a dielectric liquid, which fills the space in the re-container 24, which is left over by the capacitor winding is .. This dielectric liquid is impregnated auPordem the dielectric intermediate layers 17 and 18 from Fin. 2.

Methods for impregnating capacitor windings which are inserted into a housing, that is to say for example methods for impregnating the capacitor according to FIG. 3, are known. According to one such method, the capacitors are first dried in a vacuum to remove the residual moisture. The temperature used during drying changes with the drying time. However, it is generally between 60 C and I ¹ JO C. If the drying temperatures are too low, the drying time will be too long. On the other hand, if the drying temperatures are too high, paper components in the dielectric intermediate layer can decompose. During the drying process, the moisture can ^{escape from the housing 2 1} I through the filling opening 26.

The dielectric impregnation liquid is introduced through the filling opening 26 filled into the dried condenser, if possible, while the condenser is still under vacuum stands. It is customary to fill in so much impregnating liquid that the entire capacitor coil is covered in the container. Then the pressure in the container is increased to atmospheric pressure, the condenser is left to stand for a few hours, so that the impregnation liquid penetrate the capacitor winding ,can. After the impregnation, the capacitor is closed. For this purpose, the filling opening 26 can be soldered. V. 'if the impregnating agent is a polymerizable substance, The capacitor is then warmed up to make the impregnator T.ittoi to polymerize and solidify. In addition to Dipr-er methods can also use other methods of impregnation be used ,, die.general with heat and / or -Γ ··.;.? -! ·: Work. For example, a number of

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drive became known, after which several temperature and / or Pressure steps are applied to aid the impregnation process. Heat and pressure can prevent the impregnation process because they influence the relative wettability, the viscosity and relative solubility of the materials can be changed. By warming and through the application of pressure, the individual components expand or contract the system. Also because of this can prevent the liquid from penetrating the solid dielectric get supported. This is especially true when the Filling opening 26 is soldered.

In the invention, particularly good results have been achieved if the dielectric systems, in particular the capacitors after impregnation or sealing, heated again for a certain time in order to improve the impregnation or to achieve complete impregnation if possible. The capacitor winding in the capacitor can, for example, is first made by heating and evacuating the can and impregnated by subsequent filling with impregnation liquid or by immersion in impregnation liquid. The impregnation liquid can be preheated for this purpose or heated immediately afterwards. After this step, the composite and impregnated capacitors are sealed and the sealed capacitors are sealed for a certain amount of time Period of time brought to an elevated temperature.

A preferred heat treatment step in, practice of the invention is to apply temperatures between 65 ⁰ C and 95 ° C for a period between * J and l6 hours. These times can be shortened by changing the impregnation process, applying pressure and adding additives. AC capacitors for high voltages with a dielectric intermediate shoe were made from polypropylene film and paper. Trichlorodiphenyl was used as the impregnating agent. These capacitors

^ * T09884 / U60 ^"9 - ORIGINAL 0AD

were brought to about 16 hours at temperatures between 85 ⁰ G and 95 ° C for 4 and then consistently showed a very high Koronazündspannung.

The temperature conditions are regulated so that, on the one hand, the polyolefin partially dissolves in the dielectric impregnation liquid and, on the other hand, the impregnation liquid itself dissolves in the polyolefin in order to achieve complete impregnation. The increased penetration of the polypropylene film can be explained by the fact that some of the amorphous and / or low molecular weight components of the polypropylene dissolve in the liquid ^{at temperatures between 85 °} C. and 95 ^{° C.} If the capacitors according to the invention are subjected to the heat treatment described above, more reproducible and higher corona ignition voltages are observed.

The impregnation can be further improved by the physical properties of the components in the impregnated system changes. In particular, the dielectric impregnation liquid can be mixtures of liquid dielectric Contains substances or additives »You can also also treat the solid dielectric material so that the Impregnability gets better. So you can, for example, the Pyranol 1 ^ 99, i.e. the trichloro-diphenyl, up to. 25 percent by weight add to a dielectric liquid sold under the name Pyranol 1475 and mainly consists of trichlorobenzene. Other dielectric fluids, which can be used together with pyranol are for example mineral oil and silicone oil.

The impregnated dielectrics of the invention exhibit certain particularly good dielectric properties »due to those for electrical applications, such as general Iπölatlon ^ are particularly suitable. Come for this electrical cables and transformers in question. For condensate

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The dielectrics according to the invention are also special well suited. In particular, there are three electric ones Properties that are caused by the impregnation, namely increased breakdown field strength, low loss factor and a high corona ignition voltage. Impregnation is particularly important because of the degree of impregnation the corona ignition voltage is determined, which is in the dielectric can get. An increased breakdown field strength is important because this allows for a smaller volume or weight of dielectric material for insulation is required at a given voltage. A low loss factor is important because energy is lost in the dielectric can affect the electrical efficiency and destroy the basic materials of the dielectric, since the lost energy is converted into heat.

These particularly good properties of the dielectrics according to the Invention can be exploited particularly well if you put the dielectrics in AC capacitors for high voltages used. There are AC capacitors have been built with a voltage load of over 50,000 V per mm Dielectric have a long service life and their corona ignition voltage from 750 V to over 3,000 V. The development of alternating current capacitors for high voltages was previously only possible to a limited extent, because of the dielectrics known from ttsher exhibited only a short service life under such high voltage loads. Well-known AC capacitors, that were designed for a long service life could, for example only with tension loads less than about 20 000 V per mm of dielectric are operated, while one these capacitors as pulse capacitors are proportionate short service life only with about JO 000 V per mm of dielectric could burden.

Further examples for capacitor films, in which dielectrics are used according to the invention are shown in FIGS. ¹ to J B

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ro se i pt .. In FIp ₁ . ^{11 shows} a part? 9 of a capacitor in which the dielectric intermediate layer is constructed as a so-called whole sandwich. This capacitor part contains an impregnated plastic film 11 which is placed between two impregnated and porous dielectric sheets 30 and 31. Two metal foils 15 and 16 are then placed on the two dielectric sheets 30 and 31. The sheets 30 and 31 can consist of paper, such as Kraft paper, in a known manner and be impregnated with a liquid dielectric; for this one can use, for example, the dielectric liquid according to the invention. When such a paper is referred to as porous, this is to be understood as the fact that this paper has a number of passages or pores which extend right through the paper so that an impregnating liquid can pass through the paper from one side to the other can. The corona ignition voltages of an impregnated plastic film depend to a large extent on the complete impregnation of the pores and bubbles within the plastic film and on the wetting of the boundary layer between the film and any adjacent materials. The Koronazündspannung of the dielectric shown in FIG. ¹ J, which is constructed as a whole sandwich is ent through the use of an adjacent layer, such as a paper ski increased.

5 shows another embodiment 32 of a capacitor film in which the dielectric intermediate layer is constructed differently. The structure of this intermediate layer is called an inverted sandwich. Here, the interlayer dielectric layer comprises a single sheet of impregnated porous material 30 or 31, the impregnated between two plastic films 11 · ¹ and II is laid. The whole dielectric intermediate also lies between: v.; Ei metal foils 15 and 16. An exemplary embodiment for capacitors of this type uses a porous layer.

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0.016 mm thick paper sandwiched between two 0.012 mm thick polypropylene sheets. This so far difficult to The impregnating system could be impregnated without difficulty and gave a capacitor of 0.9 mF and a corona ignition voltage of more than 2 65O V mean AC voltage.

The joint use of polypropylene and pyranol 1499 allows even tightly wound capacitor windings to be impregnated. With the previously known and for capacitors the combinations of substances used, however, it was necessary use less densely wound capacitor windings to improve the impregnation. A major advantage the material combination polypropylene with pyranol for use in condensers or other devices consists in the fact that the polypropylene is the impregnating agent itself to the Passes on bubbles and pores that are far away from where the impregnation begins. This is especially true for the boundary layer between the film surface and the capacitor slip. Up to now this could only be achieved with great difficulty.

In FIG. 6, part of a capacitor winding 33 is shown, which is constructed similarly to the subject of FIG. This part of the capacitor winding, which is referred to as half a sandwich, differs from the inverted sandwich in that one of the two impregnated plastic films 11 or II ^{1 has been} omitted.

Another possibility according to the invention for the construction of a capacitor is shown in FIG. In this embodiment a dielectric interlayer 3 ^ is used, referred to as a modified half sandwich target. The dielectric interlayer consists of two impregnated Plastic films 11 and 11 ', which are placed on top of one another. On the film 11 'there is also a sheet 30 made of one porous material. V / ie in the other embodiments

H ^ * 109884/1460

Is this interlayer dielectric on both sides with Metal foils 15 and 16 occupied. The reason why the two plastic films 11 and 11 'are placed on top of one another is there in that dielectric defects should be avoided, the could be present in a single plastic film. If you put two such plastic sheets on top of each other, then ground them possibly existing defects in one film covered by the other film, so that no continuous channels there are more that could cause breakdowns. The construction of a capacitor winding according to FIG. 7 is essential cheaper, because the two plastic films placed on top of each other Have impregnation properties that are in every respect more favorable than the impregnation properties of a single one Foil of equivalent thickness.

8 shows part of a capacitor winding 35 in which two impregnated plastic films 11 and 11 'are placed on top of one another as a dielectric intermediate layer. The two plastic foils are covered with two metal foils I5 and 16. The reason why, instead of a film that is twice as thick, two films 11 and 11. ' are placed on top of one another, is the same as has already been described in connection with FIG. Another important feature of the embodiment of FIG. 8 is the absence of any porous layer 30 or 31 (FIG. U ) which, due to capillary action, can facilitate impregnation.

The embodiments according to FIGS. 4 to 8 can be used in manman -hem be modified. For example, as a condenser

r. ..toreliere instead of the metal foils 15 and 16 shown, the outer surfaces of the dielectric interlayers metallize. Furthermore, the plastic films in the embodiments according to FIGS. 4 to 8 can be used either as self-supporting foils or as a coating or layer on another component of the capacitor winding raise. So, for example, you can use the

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Vrickel capacitor or a porous dielectric layer with Cover plastic. In the capacitors according to FIGS. To 8 there is at least one on one side of the plastic film Relatively non-porous surface applied, such as a metal foil or another plastic film. It is On the one hand, it is very important to sufficiently or even completely impregnate a plastic surface, but on the other hand it is it is very difficult when the surface of the plastic film rests on a surface with few pores. Through the invention this difficulty is greatly reduced. Demzufol-φ ge are capacitor windings, the structure of which is shown in FIGS. * 1 to has been shown, produced according to the invention for the very first time with relatively high corona ignition voltages been.

In order to show the improved properties of the dielectrics of the invention, a number of capacitors have been used constructed and assembled as shown in FIGS. These capacitors became the usual ones Subjected to tests and comparative measurements and Test field tests carried out.

_ It is known that synthetic plastics are extraordinary - have high breakdown field strengths, which is particularly true if only very small areas of plastic are considered. The impregnated polypropylene films according to the invention have an operational breakdown field strength of 50,000 volts per mm and above, although breakdown field strengths of mer; r than 800,000 V per mm can be observed if one

2
based on an area of about 0.065 cm. Impregnated paper, the most widely used dielectric ', ·'. iterial in AC capacitors has an operating breakdown field strength of about 16,000 volts per mm. The extent to which the use of the impregnated plastic films of the invention, with their higher breakdown field strengths, can reduce the amount of dielectric material used in

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the different types of a particular device provided must be, can best be shown by test results in which several similarly impregnated dielectric Interlayers for electrical capacitors are investigated. These types of capacitors, which include paper capacitors, i.e. capacitors in which the dielectric Intermediate layers consist only of paper, with capacitors with a dielectric interlayer made of paper and polypropylene sheets include and capacitors, in which the dielectric interlayer only composed of polypropylene layers are listed in Tables I and II.

Table I.

Description Composition Total Plastic Thickness Part (55)

(mm)

Paper 3 layers of paper - 0.022 " th each 0.007 mm

Whole 0.007mm poly 0.022 sand propylene filament gave way between two

Paper slides of 0.007 mm each

half a 0.011 mm paper 0.022 sand + 0.011 mm polywich propylene film

inverted 0.007 mm paper 0.022 tied between two sand polypropylene fo ■ differed from each 0.007 mm

Plastic - a polypropy- 0.022 material foil of ^ ¹ -> foils 0.022 mm or ·. <■; · two foils of 0.011 mm each;

Breakdown field strength (V / mm)

16,000

26 800 32 000

37 200 48 000

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Table I is for the entire interlayer dielectric each a layer 0.022 mm thick has been used, as some of these intermediate layers consist of three layers are constructed, which can be paper or plastic film and, for practical reasons, the smallest thickness both for paper as well as for plastic films is around 0.007 mm.

The voltage that can be applied to each of these combinations of substances in long-term operation, as listed in Table I, shows the advantages of using polyolefin films either to supplement or replace paper in the previously known dielectric interlayers. The values given can be influenced in the various capacitors by the extent and type of impregnation and by the uniformity of the dielectric properties in the system. The values given are based in part on estimates of the ratio of the electrical constants of impregnated paper and impregnated polypropylene. In particular, a ratio of 3 'x 1 was used here. It should be noted that the strengths in the system, which are based on this assumed ratio of the dielectric constants, lead to a voltage load on the plastic films of about 50,000 V per mm, which corresponds to the operational dielectric strength of polypropylene even for continuous loads.

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Table II

three layers
of 0.025 mm each 0, 075 1200 O, 0215 16 000 0.015 mm film
between two
Layers of paper
of 0.015 mm each 045 1200 0, 033 26th 800

Bezcich- Composition Total- Nominal- Specific breakthrough thick span capacity field strength

(mm) voltage (.uf / ccm) (V / mm)

paper

whole sandwich

half a sandwich

invert
tes
sandwich

Plastic films

0.019 mm foil 0.038

+ 0.019 mm

paper

0.011 mm paper 0.033 between two sheets of 0.011 mm each

1200 0.04

1200 0,

a film of 0.025 mm

0.025 1200 0.055

32,000

37 200

48,000

Table II now lists the same interlayer dielectric layers, along with their thickness, that are used for an operating voltage of 1200 V is required. For this calculation it was assumed that the compound dielectric layers the thickness of the individual foils is the same in each case. In a number of applications, even more favorable arrangements can be achieved if the Paper thickness reduced and slightly thicker plastic films instead used. The results in Table II show that one at a given operating voltage with a lower one "'tight of dielectric material comes from when the proportion of the plastic in the dielectric is increased. Table II also indicates which capacities per volume volume can be achieved with capacitors which have the listed dielectric Use intermediate layers. This information about the

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specific capacities are in the dimension jMicro farad / cmrr Dielectric has been made.

There are both 50 KVA and 150 KVA capacitors according to dor .Invention built and tested over a long period of time. For this belonged many 1000 hours under operating conditions. These Capacitors were designed in such a way that they were charged with 3 voltage that worked in the plastic components of the dielectric Caused field strengths of 50,000 V per mm. The size and the weight of these capacitors now clearly show the improvements listed in Tables I and II £ are really achievable.

For example, a 50 KVA capacitor was produced in 2s , the dielectric intermediate layer of which was constructed as an inverted sandwich of polypropylene and paper. Pyranol 1 * 199, to which an epoxy-based stabilizer was added, was used for impregnation. This capacitor had a volume which was ¹ JO % smaller than the volume of the previously known paper capacitors, that is to say it had a volume which was only slightly more than half the volume of the previously known paper capacitors. If you build a 50 KVA capacitor according to the invention exactly as large as a 50 KVA capacitor according to the prior art, the capacitor according to crfindunprs- W has a significantly higher capacity. A capacitor, the dielectric intermediate layer of which is entirely made of paper, and which has the same spatial size as a 50 KVA transformer with a polyolefin dielectric, has a power loss of around 30 KVA. A corresponding reduction in weight is also achieved.

If you choose a 150 KVA capacitor with a dielectric Compare polypropylene and paper impregnated with pyranol with a 100 KVA capacitor in which the electrical Interlayer consists only of paper soaked in pyranol, r> o shows that the 150 KVA capacitor is smaller and pro KVA weighs only about 10 g. The 100 KVA capacitor with the Paper dielectric, which is a particularly good example of

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Prior art capacitors is v; icgt darcpeη per KVA about 590 to 600 g.

The invention can thus reduce the weight and volume of electrical capacitors of a given capacity and power. It should be noted, however, that in many applications there is an upper limit for the spatial size of an electrical capacitor, so that the invention is able to produce capacitors for these applications which have a larger capacitance or a larger one. · ■ '■' ■ possess performance. In all the above cases the favorable weight and favorable specific capacity of the _Ä capacitors, the use of combinations of materials or Mate ™ be attributed rialkombinationen responsive to a voltage stress in the Polyolcfinkomponcnteführen that amounts to about the upper Betriebsfcldstärke in the plastic layers.

There are areas of application which also include the use of power capacitors for high voltages, in which it is beneficial to reduce the energy loss within the dielectric as much as possible. For such cases, the Dicfcktrika based on impregnated polyolefins according to the invention are particularly favorable. The loss factor of Dielek- ♦ -.Η '"riftch ^ cr ^ rfindunp · liort at the rated voltage in general Λ my between 0.05 and 0.15%, even if the temperatures are well above room temperature. This is a substantial improvement over the previously known impregnated dielectrics in which the loss factors between 0.2 and 0.5%, respectively. As a result, it is also possible, the size of capacitors according to the invention over larger capacitors according to the prior art up to ¹ IO- / S to lower. [

As an example of the lower Energievcrluste in dielectrics on the basis of impregnated polyolefins according to the invention, a 50 KVA capacitor was examined, the interlayer dielectric layer as an inverted sandwich of poly-

'.-M 109884 / U60

, propylene film was built up and impregnated with Pyranol 1499. This capacitor is 40 % smaller than its 50 KVA counterpart with pure impregnated paper dielectric. The size of the energy losses in this capacitor was indicated by the rise in temperature in the dielectric, that is, the size of the temperature rise in the dielectric of the capacitor compared to the ambient temperature Dielektrikutns measured. In the case of a capacitor with a known paper dielectric, however, the temperature of the dielectric was 48 ° C. In a 5,000 hour test between 55 and 70 ° C., the loss factor of the inventive dielectric, which was constructed as an inverted sandwich, was 0.05 % in the known capacitor with paper dielectric, on the other hand, was 0.2 %.

To show that the loss factors in a polypropylene dielectric, which is soaked with Pyranol 1499, constant electrical capacitors were investigated, the dielectric intermediate layer of which consists of a polypropylene film 0.012 mm thick, on which a sheet of 0.01 mm Kraft paper was placed. The dielectric was with pyranol Impregnated in 1499, one percent by weight of 1-epoxyethyl-3,4-epoxyeyclohexane “These capacitors were tested and aged at different temperatures. The following measurement results for the loss factors were obtained at the nominal voltage of the capacitors, which are used in 460 V, 60 Hz AC.

Tabel III 25 ° C 65 ° C '* '.,. \ '■ - ■■■ Time Loss factor 0.143 0.113 -. a * ~ r ■ %. " _: (Hours) 0.120 0.091 ^; 85 ° C 0 0.119 0.094 0.119 519 0.113 0.084 0.096 1524 0.093 5008 0.090

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- ■ 25 -

These results show that the loss factors in the present invention Dielectrics in a temperature range between 25 ° and 85 ° C and even after more than 5,000 hours of operation are constant.

Since it is important to prevent corona discharge in a solid dielectric to impregnate the dielectric, provide the impregnation properties of the dielectric Systems according to the invention are an important consideration. In some areas of application, such as power capacitors for high voltages, corona ignition voltages are used of more than 2,000 V required. Albeit in the impregnation ability the dielectrics according to the invention have many physical properties of the polyolefins and of the possible impregnating agent the ability of the liquid to penetrate the polyolefin depends on the solubility of the polyolefin in ~ depending on the impregnation liquid. This connection was demonstrated in an experiment in which a lot of pyranol 1499 in a bag or container made of a non-porous Polypropylene was filled in as used in the invention. This container was then placed in an oven at 75 ° C brought. The penetration of pyranol 1 * 199 through the soil of the container was observed by the fact that the bottom of the Container continuously passed over a microscopic cover slip. If the Pyranol 1 * 199 * so the dielectric Liquid that has penetrated the polypropylene container, a greasy one forms on the cover slip coating. Using this experiment, it has been shown that a polypropylene film even after at room temperature Pyranol 1 * 199 does not penetrate for many hours. if however, you can raise the temperature to 75 ° C or higher penetration can be observed after a few hours.

If during the impregnation in addition to the temperature another pressure is applied, for example by the fact that the pressure is increased from the outside or by going through

.109884 / U60 &**> 0F? I «/ _NAL

If the internal pressure is increased by heating, it is also very difficult to impregnate objects practically completely, which is noticeable in corona ignition voltages which were consistently above 2,500 V. In the case of a tightly curved capacitor winding, in which the dielectric intermediate layer is directly adjacent to a material with few pores, such as, for example, a metal foil, it is very difficult for the dielectric liquid to penetrate through the interfaces into the dielectric. This is the reason why it is It is better to use pressure in addition to the temperature in order to achieve an optimal impregnation. It is noticeable that both in the penetration tests with the bag and in the capacitor impregnation tests with pyranol 99 the effect of the dielectric liquid on the prit / olefin film at room temperature is a significantly different than at temperatures between 75 and 85 ^Ö C.

To the reproducibility of high Koronazündspannungen to show, three ¹ IO KVA Wickelkondensatorcn prepared according to the invention. These capacitors were constructed as an inverted sandwich. Each capacitor contained a sheet of paper, 0.008 mm thick, sandwiched between two polypropylene sheets, each 0.012 mm thick. Pyran oil 1 * 199, to which a small amount of an epoxy-based stabilizer was added, was used for impregnation. These capacitors were 2? cm wide and initially had a corona ignition voltage between 750 V and 1050 V AC. The capacitors were then heated at 100 ° C. for a few hours. In doing so, practically complete impregnation was achieved, which was concluded from corona ignition voltages of more than 3,000 V, and the corona ignition voltages were checked again as part of the investigation of the other electrical properties of these capacitors. The results of these tests are shown in Table IV.

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Table IV

Corona ignition voltage

Condenser at the beginning after several hours after the end number heating the experiments

1 1050 V '. ^ 3100 V> 3100 V

2 750 V> 3050 V> 3100 V

3 950 V ^ 3100 V > 3100 V ■

The extraordinarily high corona voltage of these capacitors can be combined with the reproducibility of this corona ignition voltage be assessed as an indication that practically complete impregnation has been achieved. As another indication of the achievement of a full Impregnation run; can reflect the fact that the measured values the corona ignition voltages approach the theoretically calculated voltages.

Polypropylene paper dielectric impregnated with Pyranol 1 ^ 99 are much more resistant to corona discharges than the known dielectrics, which are made of impregnated Made of paper. Capacitors constructed according to FIG. 5 were exposed for 30 seconds to a voltage which was three times higher than their nominal voltage. It showed found that only relatively minor corona damage occurred, while the loss factors actually improved became. These capacitors contained a dielectric that consisted of polypropylene paper and impregnated with Pyranol 1 ^ 99 was. For comparison, known capacitors were subjected to the same test, their dielectric made of paper or paper synthetic resin duration. These capacitors showed noticeable corona damage and an increased dissipation factor. The corona damage were determined in both series of tests by the fact that the Disassembled capacitors and visually inspected the dielectrics.

The dielectric systems according to the invention can also solid dielectric material and electrical fluid

-'109.884 / 14-60 BAD ORiQiNAL

contain numerous other components. In particular is it is often beneficial to add one to the impregnated dielectric Adds component that acts as a stabilizer. The effect of such stabilizers is in the dielectric System to neutralize certain impurities or foreign materials that are present or formed in the system .be able to. Such impurities can leave residues of Be catalysts or catalytic activators or neutralizing substances, which are left behind during the polymerization of the polyolefins. Other impurities can arise from decomposition products caused by chemical reactions within of the system, which either run automatically or are triggered by overvoltages. These impurities and foreign products affect the dissipation factor of the impregnated dielectric. Stabilizers have proven to be great proven suitable to stabilize the dissipation factor of an impregnated dielectric based on plastic.

Examples of stabilizers are dipentene dioxide and 1-epoxyethyl-3 »^ - epoxycyclohexane. These stabilizers are described in detail in US Pat. Nos. 3,212,12 and 3,342,402. In the present invention, 1-epoxyethyl-3,4-epoxycyclohexane was used added to the dielectric liquids in amounts ranging between 0.00i and 8 percent by weight. A preferred range for use with polypropylene film and pyranol is between 0.35 and 1 percent by weight.

Certain inorganic materials such as aluminum oxide can also be used as stabilizers. The effect of this Material consists in long-term changes in the loss factor to counteract this and to increase the service life of the capacitor and its impregnation. This is another Position has already been proposed.

Another component that is frequently used in impregnated dielectrics according to the invention is a porous dielectric yoke layer, which is placed on a plastic film and acts like a wick or a sponge. This porous layer

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^ BATH ORIGINAL

Due to its capillary action, the impregnation liquid enters the interface between it and the thin plastic film. In the case of a dielectric which has a plastic film with a very large surface area, it is advantageous to provide at least one such porous layer in order to facilitate the impregnation. This is especially true for relatively large wound capacitors, of which very high corona ignition voltages are required, which must therefore be completely impregnated. Kraft paper, the thickness of which does not exceed 0.025 mm, is preferably used as the porous material. It is particularly favorable to use kraft paper, the thickness of which is approximately 0.008 mm. Such a paper has a dielectric strength which is relatively good compared to other dielectrics, even if it is noticeably lower than the breakdown strengths of most solid plastics. In addition, the Kraft paper has a relatively high dielectric constant so that the voltage distribution in a composite dielectric becomes more favorable in the sense that a greater proportion of the voltage drop occurs on the plastics which have a higher breakdown field strength. Other synthetic plastics or glass fiber fabrics can also be used as porous layers in the invention. By modifying the physical properties of the dielectric impregnation liquid, the type and extent of the impregnation can be improved. This was investigated on capacitors whose dielectric consisted of two polypropylene foils 0.008 mm thick and impregnated with Pyranol 1 ^ 99 with the addition of epoxy. Other capacitors were impregnated with the same impregnation liquid to which another impregnation liquid, namely Pyranol 1 * 178, had been added. ^{About one part of Pyranol I 1} ITS was used for 3 parts of Pyranol 1 * 199. Pyranol 1478 is a commercially available dielectric liquid mainly composed of trichlorobenzene. While the corona ignition voltages of the paper capacitors impregnated with Pyranol 1 ^ 99 alone were between 100 and 1,000 V AC, the capacitors impregnated with the mixed impregnation liquid had corona ignition voltages of more than 1,500 V AC.

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From this one can conclude that the extent of the impregnation was noticeably larger.

In the above description, as an example of a Polyolefin which can be used in the invention, polypropylene has been specified. For the dielectrics according to the invention but other polyolefins are also well suited, in particular polyethylene and ^ -Methyl-pentene-l. Tests have shown that these materials can be impregnated with a dielectric liquid in the same way as polypropylene, however different results are achieved. For example, a film made of high density polyethylene was after impregnated with pyranol using a method similar to that described for polypropylene. An impregnation zv / ischcn 85 and 100 ° C over 16 hours resulted in a noticeably increased corona ignition voltage.

Impregnations with other dielectric liquids have also been carried out, especially those used in ' in the description were only mentioned as an addition to pyranol, i.e. with mineral oil, silicone oil and also with other pyranol qualities. It was found that the liquids can serve as impregnating agents on their own, or at least the main component of the impregnating agent. To other oils which are used to a limited extent according to the invention can include cottonseed oil.

Other combinations of substances are also available for certain applications possible. Crosslinked polyethylene or paper which is impregnated with the polyolefin according to the invention may be mentioned here. Man can, for example, impregnate a paper with a melt or a solution that contains polypropylene and the resulting Impregnate the material with pyranol.

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Claims (3)

- .51 - claims 1. ^! Electrical system for electrical insulation of a electrical conductor, such as an electrical Cable, with a polyolefin insulator adjacent to the conductor and an impregnating agent in the form of a dielectric Liquid in the polyolefin to increase its dielectric strength Dielectric strength, which means that the impregnating agent is a contains halogenated aromatic diphenyl compound and the polyolefin (11) is essentially completely impregnated with the impregnating agent, 2, dielectric system according to claim 1, characterized in that the polyolefin (H) is biaxially oriented. 3. Dielectric system according to claim 1 and / or 2, characterized in that the impregnating agent a chlorinated diphenyl such as e.g. B. is trichlorodiphenyl. i}. Dielectric system according to one or more of the claims 1 to 3, d a d u r c h g e k en η ζ e i c h η e t, that the impregnation of the polyolefin (11) is sufficient, to a corona ignition voltage (CSV) of more than 750 V and an operating voltage field strength of 28 to 47 V / -u result. 109884/1460 Le e rs e i f e