FI74837B - ELECTRIC CAPACITOR. - Google Patents

Description

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SUOMI FINLAND

(Fl> (21) Patent application - Patentansökning 791510 (22) Application date-Ansökningsdag 11.05-79

National Board of Patents and Registration (23) Start Date-Giltighetsdag 20.02.76

Patent-och registerstyrelson (41) Became public-Biivit offentiig 11.05.79 (44) Date of publication and date of publication. - 30.11.87

Ansökan utlagd och utl.skriften publicerad (86) Kv. Application-Int. ansökan (32) (33) (31) Privilege claimed - Begard priority 28.02.75 USA (US) 554070 (71) General Electric Company, Schenectady, New York, USA (US) (72) John Walker Eustance, South Glens Falls, New York,

Emilie Lucille Carley, Hartford, New York,

Stanley Young Hobbs, Scotia, New York, USA (US) (7 * 0 Oy Koi ster Ab (54) SShcondenser - Electric Capacitor (62) Divided by application 760442 (patent 64534) -Avdelad frän trap 760442 (patent 6453 * 0 The invention relates to an electric capacitor comprising a housing having electrical terminals, one or more rollers housed in the housing, each having at least one strip of rough surface film interposed between a pair of electrodes, and electrical connections between the electrodes and the terminals and impregnated with dielectric fluid.

Polypropylene film has been widely used as a dielectric medium in capacitors used in electrical engineering impregnated with dielectric liquid. In the manufacture of such a capacitor, very thin polypropylene strips are superimposed on the aluminum foil strips and this combination is wound into a dense roll. The rollers are placed in a suitable housing and impregnated with a dielectric liquid absorbent. Alternatively, the aluminum foil strips can be replaced with metal coatings formed on suitable dielectric strips. The polypropylene film made by the well-known pipe blowing and drawing and stretching method 2,74837 usually has a very smooth surface throughout, which causes the surfaces to adhere very tightly to each other or to other nearby surfaces. This results in difficulties in absorbing the film when it is in a densely wound capacitor roll. It is very difficult to make an absorbent such as oil completely penetrate the capacitor roll and especially between the surfaces of the polypropylene strips and the polypropylene and foil strips.

As a result, many attempts have been made in the past to effect the absorption of capacitor rollers by roughening the surfaces of interconnected film strips, foils, and so on, by etching, grooving, grinding, or shaping. The results obtained by these methods have not been entirely satisfactory for a variety of reasons. In particular, many of these roughening methods tend to affect the physical strength of the film as well as its dielectric strength. Also, molding methods that increase the overall thickness of the film, such as corrugation and grooving, increase the overall thickness of the roll and consequently make the final roll too large. The blowpipe method has been found to be able to produce films with slightly rough surfaces. However, this roughness has not been uniform or sporadic, and thus is not already suitable for the film-making process.

The electric capacitor of the present invention is characterized in that the rough surface film strips are of thermoplastic material, that one surface of each rough surface film strip has crater-like recesses such that the total surface roughness is that said rough surface comprises a fabric formed by raised ridges, the ridges overlapping and intertwined and substantially uniformly covering the entire surface.

The invention is explained in more detail in the following and accompanying drawings.

Figure 1 is a schematic diagram of a blown tube or bubble generating process used in the manufacture of a polypropylene film.

3,74837

Figure 2 is a photomicrograph of a smooth surface film.

Figure 3 is a photomicrograph of a portion of a polypropylene film having a surface roughness of 20%.

Figure 4 is a photomicrograph of a polypropylene film having a surface roughness of 30%.

Figure 5 is a photomicrograph of a polypropylene film having a surface roughness of 40%.

Figure 6 shows a capacitor using a film of uneven surface according to the present invention.

Figure 7 shows a capacitor roll using a film of uneven surface according to the present invention.

In the device according to Figure 1, in order to obtain a blown pipe, the polypropylene plastic is fed in the form of granules 11 to a hopper 12 and then to an extruder 13, where it is heated to obtain a very soft or hard polypropylene mass. This mass is extruded from the extruder 13 through the nozzle 14 in a tubular manner, after which it comes into contact with the cooling mandrel 15, where it begins to crystallize in a tubular or tubular form 16. From the cooling mandrel 15 the hose 16 is drawn between two rolls 17 which compress the hose tightly. located in the gap between them. After passing the rollers 17, the cooled and crystallized hose 16 is again heated to its softening temperature by suitable heating means 19, for example radiant heaters, after which it is expanded by introducing pressurized air through the air tube 18. The expansion causes the formation of a bubble of a controlled size, i.e. a wide tube 20, whereby the polypropylene hose stretches approximately six times in both the horizontal and vertical directions, resulting in a biaxially oriented polypropylene film. The bubble 20 is then pressed between two other pairs of press rolls (not shown) and drawn into a strip cutting roll where the bubble is cut into one or more strips which are then wound on a take-up roll. Typical apparatus and methods for making a film by the blow molding method are disclosed in U.S. Patent Nos. 2,720,680 (Gerow), 3,235,632 (Lemmer) and 3,223,764 (Kahn).

Applying the film manufacturing process described above, it has been found that from time to time certain surface irregularities occur in the film. These irregularities differ considerably from one input used to make the film to another and have not been evenly distributed over the entire surface, i.e., uniform over the entire large surface area of the film. Typically, these uneven surfaces were neither uniform with respect to distribution on the film surface nor were they uniform with respect to the degree of irregularity. In addition, the formation of the pattern of unevenness, i.e., the pattern, was not the same over the entire surface of the film, and the presence or absence of irregularities could not be accurately determined, and their occurrence times were found to be random.

Irregularities in the film made it opaque, a fact that in many cases was found to be less desirable than a clear, smooth film. At that time, it was found that certain such rough films had highly desirable absorption properties. For example, if selected samples of a very rough such film were used to wrap the test capacitor rolls, the film would not adhere to or adhere to itself or adjacent surfaces. In addition, the roughness of the film provides a certain distance between adjacent surfaces so that the absorbent fluid can more easily penetrate this space. As a result, not only did the uniform roughness become a desired feature, but also its pre-creation, adjustment, and uniformity when applied to the film manufacturing process became essential.

It has now been observed that in certain blowpipe methods, temperature control can be used to actually predetermine the presence or absence of irregularities on the film surface. An important observation has also been made that these irregularities can be uniformly applied to the film surface so that the density and amount of irregularities become larger. If the irregularities are of a certain quality and the surface pattern of the irregularities is uniform over the entire surface of the film, and if the degree of elevation of the protrusions is within certain limits and is also uniform over the entire surface of the film, the film is called a rough film according to the present invention.

The amount of surface roughness or irregularity can be expressed as film roughness or degree of roughness. Roughness is determined by measuring the passage of light through a portion of the film, i.e. usually perpendicular to the top and bottom surfaces rather than diagonally. The Gardner Laboratory Haze Meter, available from Gardner Laboratory Corporation, Bethesda, Maryland, catalog # HG1204, was used in the practice of the present invention.

A digital photometric device, catalog # PG5500, was also used. The "Hase Meter" conducts light through the film and measures the intensity of the light as it passes through the film relative to the intensity as the light enters the film. The values obtained are expressed as percent roughness of the film. The methods used were standard methods of the American Society for Testing Materials, Tests ASTM-D1003, ASTM-D1044 and FTMS 406, Method 3022.

Measurements are made with a roughness meter at small distances from the film strips, for example 15 measurements from the film strip with a width of about one meter. The measurements are taken as the average of the 10 largest roughness measurement results and the average is taken from the five smallest readings. The roughness of the whole film is shown as a combination of these two averages, for example 40/20 roughness. When a private roughness number is displayed, e.g., 30% roughness, the private numerical value is obtained with a roughness meter.

A Gardiner Gloss Meter and catalog # GG-9042 were also used, applying ASTM test D2457-70. This device measures the light reflected from the surface of the film, which also gives an image of the surface roughness.

The surface roughness can be adjusted by arranging or adjusting the temperature conditions for a predetermined area of the hose in the apparatus shown in Figure 1, and the adjustment can be accurately performed by heating or cooling a small area of the hose, for example by rapid jet cooling and taking into account bubble roughness differences. The temperature control can be applied, for example, to the hose 16 by using a heating ring 21 in the chamber 22, as shown in Fig. 1. A suitable temperature control medium such as air can be circulated through one or more rings 21, whereby air is sprayed out through suitable openings therein and comes into contact with the hose 16, as a result of which the temperature of the hose 16 rises or falls to a predetermined axial length. Full heating or cooling can be accomplished with a variety of devices known in the art that can raise or lower the temperature of a body passing therethrough by either direct or indirect contact using liquids or gases or radiation as typical examples.

However, temperature control must be provided at a predetermined location or surface of the hose 16. The polypropylene is extruded from the die 14 in a molten state and approaches and moves toward a coaxial mandrel 15 where it continuously cools and crystallizes into a hose 16. As the hose 16 cools, a cylindrical "solidified" zone 16 (a), i.e., an area of about 15 ... 16 cm from the mandrel 14. This area is visible and the crystallization zone indicates the overall surface on which complete crystallization of the polypropylene hose has taken place. The temperature control according to the present invention, which is the usual addition of heat to the hose, must be carried out after the extruder and before the solidification point, and most preferably in the intermediate compartment.

Usually, in a film making process using a blow tube, the cooling temperatures, hose temperatures and solidification point of the mandrel are easy to implement conditions and their ranges are highly controlled. For example, the temperature of the polypropylene exiting the die 14 is about 233 ° C, while the temperature of the solidification point is about 92 ° C. Under these conditions, the crystallization properties of the tube are also easily implemented and the formation of the crystal type is in some way constant.

The rough film of the present invention is produced by providing a surface shape, i.e., a certain type of crystal layer, to the hose in a controlled manner. The shaping of the surface of the hose can be described as a layer of the outer surface of the hose with a point with protrusions of considerably higher density, i.e. spherulites, which are type III polypropylene crystals. The presence of this surface effect in the hose is a factor which, when the hose is diagonally oriented in the bubble, makes the outer surface rough according to the present invention. One explanation associated with type III crystals in terms of roughness is that type III crystals are transformation crystals in the film making process. Experiments have shown that type III polypropylene crystals melt in the preheating process at 19 (Figure 1) just before the cup stretch. The reheating temperatures are in the range of approximately 140 ... 150 ° C. The density of the type III polypropylene crystals in the hose is about 0.8, and when the hose has passed through the reheating device 19, they become type I and II crystals of the order of 0.9. As a result, the elongation of the bubble, together with the change in the density of the crystals, produces a discontinuity, i.e. a crater-like effect, resulting in surface unevenness.

The surface effect which causes the formation of a rough film can be achieved by arranging a certain temperature difference between the polypropylene hose on the surface of the mandrel and the corresponding point on the outer surface of the hose. This temperature difference is also related to the fact that the hose is under tension when it is pressed between the press rolls 17. As a result, additional cooling or heating of the hose changes the tension and tightening state in it. Raising the temperature causes the formation of frictional stresses in the ongoing process and greatly promotes the formation of crystal embryos on the outer surface of the hose, resulting in the formation of crystalline type III protrusions, i.e. spherulites. This increased density of the crystals on the outer surface causes a surface effect, i.e. a surface deformation. One important factor in a rough film is the occurrence of surface deformation on one surface of the hose when the hose is made into the shape of the final film using a certain temperature control. Surface deformation is a physical event and is clearly evident in microscopic images of a portion of the tubing.

According to one embodiment of the present invention, surface shaping occurs by raising the temperature of the outer surface of the hose with the heating means 22 just before the solidification limit very rapidly without significantly disturbing the solidification limit and without disturbing substantially balanced heat flow conditions in the mandrel and hose. Under these conditions, it is believed that the preferred temperature gradient or temperature conditions can be obtained in the tubing, with the conditions then being favorable for the formation of crystal embryos requiring surface formation. In addition, the sudden addition of heat to a particular part of the outer surface of the hose or the rapid prevention of heat transfer therefrom 74837 allows the existing tension to tighten this part of the hose and this stretching or abrasion also promotes the formation of crystal embryos. The use of heat and the resulting frictional stresses at a certain point before and in the vicinity of the solidification limit results in the formation of a rough-surfaced film according to the present invention. The heat flux applied to the hose, taking into account the temperature of its outer surface, is best determined empirically and by visual observations, since the deformation of the surface and the consequent roughness are clearly physical properties that are easily measurable.

Temperature control can be achieved without a separate increase in heat. For example, the temperature distribution, i.e. the gradient from the inner surface of the hose to the outer surface and the higher change temperature at the outer surface are the properties, i.e. the characteristics, which promote the described surface formation. The best results are obtained when the distribution curve is steep and the temperature is considerably higher on the outermost outer surface. For example, according to one embodiment corresponding to the apparatus of Figure 1, the polypropylene resin is isotactic polypropylene commercially available from Dart Industries and extruded at a die temperature of usually about 230 ° C. However, in this example, the temperature was lowered to about 220 ° C. The mandrel / film ratio was that the surface of the film slid with a certain friction in the immediate vicinity of the metal mandrel. The diameter of the membrane was about 15 centimeters, the wall thickness was about 0.4 millimeters, and the axial propagation along the mandrel was about 10 meters per minute. A more uniform hose elongation occurred as a result, and the resulting frictional stresses promoted the formation of crystal embryos. At this point, the cooling of the jacket gradually decreased, resulting in a rise in temperature in the hose without this fact adversely affecting the solidification limit. Cooling may be slightly reduced down to the mandrel or at a particular point, resulting in a higher temperature on the outside of the hose. At this point, the radiation of heat to the environment can also be regulated by suitable shades or heat reflectors located in the control zone 22. In this way, a surface effect is also formed in the hose and a rough film is formed in the bubble. Measurement of the roughness of the film 74837 made according to the example above showed that the roughness was in the range of 20 ... 40% depending on the hose temperature control in step 22.

Polypropylene produced as described above has a high roughness and the roughness is uniformly uniform and similar over the entire surface area of the film. The roughness structure in different cases is shown and compared in Figures 2-6.

Figure 2 is a photomicrograph of a portion of a polypropylene film made without roughening, i.e., prior to the bubble process. This film has a thickness of 0.018 millimeters and a magnification of 75 times. There are a few straight scratch lines and several small curved lines that can be ridges or small cavities or depressions.

Figure 3 is a photomicrograph of a 0.018 mm thick polypropylene film having a surface roughness of about 20% when applied as described above at 70x magnification. The curved lines that delimit the craters, or recesses, are now clearly visible and noticeable. Upward elevations, i.e., fibroids, can rise 2-3 microns larger than the normal thickness of the membrane, and are uniform and continuous. Consistency and continuity means that as the film passes continuously i.e. at least several meters or when the film is on its receiving coil, the structure and density of Fig. 3 are uniformly distributed on one surface of the film.

Figure 4 shows a piece of polypropylene film with a thickness of 0.018 mm at a magnification of 75 times and a roughness of 30%. In this figure, a large number of fibroids, i.e. craters, are intertwined and superimposed on each other and are uniformly and evenly distributed over the entire surface of the membrane. The image appears to be a very compressed mat of thin loose fibers. This surface structure conducts absorbent fluid well, is non-sticky and is a good example of a rough film according to the present invention.

Figure 5 shows a piece of 0.018 mm thick polypropylene film magnified 75 times with a roughness greater than 40%. Namely, a large number of crater-like depressions can be seen in Fig. 5, which can be seen as fiber-like protruding lines which overlap and are intertwined. The appearance is roughly similar to the crack. Figure 5 shows a very good roughness shape according to the present invention.

The rough film of the present invention is credibly proportional to the surface effect described above, i.e., surface deformation and stress-induced crystal embryo formation. The increased roughness can be adjusted by these factors, which now results in the formation of a complete and uniform pattern over the entire surface of the film, i. for the coil from which many capacitor coils can be wound.

Rough films prepared as described above are used for the electrotechnical capacitor structures shown in Figure 6. Figure 6 shows a capacitor 25 using a rough film according to the present invention. Capacitor 25 typically follows the structure and method disclosed in U.S. Patents RE-27,824 (Cox), 3,754,173 (Eustance) and 3,724,043 (Eustance).

In Fig. 6, the capacitor 25 is suitable for use as a high-voltage AC capacitor and mainly as a power factor correction capacitor. The capacitor 25 includes a suitable housing member 26 and a cover 27 with which it is closed. The capacitor 25 is provided with insulators 28 and 29 which isolate the terminals 30 and 31 from the cover 27. The terminals 30 and 31 are electrically connected (not shown) to the pin connectors 32 and 33 of the roller parts 34 in the housing 26. The roller parts 34 are described in more detail in Figure 7.

Figure 7 shows a common example of a rotating coil 34 for use in a capacitor of the absorbed type, which is either a high voltage AC voltage type described above or a capacitor of a smaller type used in a motor. The roll portion 34 usually comprises parallel strips 35, 36 of metal foil and insulating polypropylene film 37 and 38. According to a preferred embodiment of the present invention, the polypropylene strips 37 and 38 are generally less than 0.025 mm thick and the foil strips 35 and 36 are aluminum. . Located near the film strips at suitable locations are rails 32 and 33 used to provide electrical connection to the foil strips 74837 as electrodes, and the rails are suitably connected to terminals 30 and 31. The strips are relatively tightly wrapped in rolls and then flattened to the shape shown.

The absorption of the capacitor 25 is usually effected by introducing the absorbent through one or more small openings in the cover 27, which are then closed by soldering. During absorption, the capacitor 25 is generally immersed in a liquid absorber that fills the housing 26 and absorbs the roller portions 34 therein. Certain pre-evacuation steps, high temperatures, and other process steps are also commonly used.

One of the major manufacturing difficulties encountered in the manufacture of absorbed capacitors, especially roller capacitors, is the difficulty in achieving substantially complete roll absorption. For example, if a high voltage (greater than about 600 volts) AC power factor correction capacitor is to be provided, substantially all of the air spaces or cavities between the electrodes must be filled by substantially complete absorption; or in an insulating material.

In the twisted roll section shown in Figures 6 and 7, the absorbent must move axially along the roll to reach its innermost parts. If the insulating material is porous or otherwise absorbs and allows or conducts the absorbent material to pass under the impregnation conditions, the absorbent material may not only pass rapidly axially through the roll but may also pass transversely through adjacent insulating strips. The rough film of the present invention, when in the vicinity of another rough surface or foil surface or film surface, forms certain openings, openings and passageways due to its irregular surface which facilitate the penetration and transport of the absorbent to the interior of the roll.

According to an embodiment of the present invention, the capacitors were prepared as described in connection with Figure 7 using strips made of rough polypropylene and other identical capacitors were made using smooth polypropylene insulating strips 12,74837. The results were as follows: TABLE 1

Number of defects / 5500 hour test Service life V-AC / ° C Smooth film Rough film 775/70 ° C 6/10 2/10 660/85 ° C 4/10 0/10

Capacitors made using 50 gauge polypropylene were used in the following experiments and the results in 2 Uf 540V-AC units were as follows: TABLE 2 Service life test Smooth film Rough film

Total number of defects / test time 500 hours 17/70 2/25 The rough film of the present invention may have an electrically conductive coating on either its rough surface or another surface. Metallic coatings such as Aluminum do not adhere as tightly as would be desired to a smooth polypropylene surface. The quality of the irregularity and the pattern of the irregular surface in the rough film of the present invention provide a better bond between the metal layer and the film as well as a good bond. When the metal coating is on the smooth surface of the film, a better combination is formed, i. electrode, secretory membrane and rough surface. These metallized strips have an important use in capacitors, eliminating the need for separate electrode foils.

The film of the present invention provides the considerable advantage of facilitating absorption. Since the roughness is uniform over the entire surface area of the film, the impregnation step can be programmed to take this advantage into account. Due to the remarkably high degree of roughness, the penetration of the liquid between the rough surface of the polypropylene strip and its adjacent surface, be it either rough polypropylene or other substances, is facilitated.

The method described above can be applied to crystallizable thermoplastic materials, the manufacturing properties of which generally correspond to those of isotactic polypropylene. These materials include polypropylene grades such as synthetactic polypropylene and copolymers and copolymers of polypropylene, as well as blends of polypropylene with other synthetic plastics. They also include other crystallizable polyolefins.

The rough film of the present invention can be advantageously used as electrical insulating materials and products, especially in the case of working steps using winding and unwinding or requiring impregnation or drying steps. The rough surface not only facilitates winding and winding on the roll, as it is not sticky in its properties, but it also forms passageways for the removal of vapors during the drying step.

Claims (6)

74837 14 An electric capacitor (25) comprising a housing (26) having electrical terminals (30, 31), one or more rollers (34) disposed in the housing, each having at least one strip (37, 38) of rough surface film disposed in a pair of electrodes ( 35, 36) and electrical connections between the electrodes (35, 36) and the terminals (30, 31) and in which the interior of the housing (26) is impregnated with a dielectric liquid, characterized in that the rough-surfaced film strips (37, 38) are of thermoplastic material, that the other surface of each rough-surfaced film strip has crater-like recesses such that the total surface roughness measured at least 20%, expressed as a proportion of the light intensity transmitted to the film as a proportion of the light intensity entering the film, and said rough surface comprising raised ridges; the ridges overlap and are intertwined and cover the entire surface substantially uniformly. Electric capacitor according to Claim 1, characterized in that the rough-surfaced film strips (37, 38) in the rolls are arranged against one another so that the rough surfaces of the film strips are always outwards. Electric capacitor according to Claim 1 or 2, characterized in that the electrodes consist of metal coatings on rough-surfaced film strips which are on surfaces opposite to the rough surfaces of the strips. Electric capacitor according to Claim 3, characterized in that the electrodes are made of aluminum foil. Electric capacitor according to Claim 2, characterized in that two rough-surfaced film strips are arranged between the electrodes, so that the rough surface of each strip is located against the electrodes. Electric capacitor according to Claim 1, characterized in that the total surface roughness is 20 to 40%.