FI64023B - CONDENSER FOR FREQUENCY REARING - Google Patents

Abstract

1441803 Dielectric fluids GENERAL ELECTRIC CO 24 July 1973 [16 Aug 1972 12 bune 1973 (2)] 35315/73 Heading C5F [Also in Division H1] An insulating liquid composition for impregnating a wound capacitor having paper, plastics or both as dielectric comprises a liquid aromatic ester having an epoxide additive. The ester may be a phthalate, particularly dioctyl phthalate, a benzoate, a phosphate, e.g. tricresyl phosphate, mixtures of these with each other or with other insulating liquids, e.g. dibutyl sebacate, castor oil, mineral oil, alkyl naphthalenes, polybutenes and dodecylbenzene. The epoxide may constitute 0À01 to 10% by weight of the impregnant, or even more where it can itself function as an impregnant.

Description

Γβΐ ^ ANNOUNCEMENT, .Λλ ^ ®Γα ^ (1) utläggningsskrift 640 2 3 c («); 3 ^ ν ^ (51) Kv.ik? /Tat.a.3 Η 01 G 4/22, Η 01 Β 3/20 FINLAND — FINLAND ai) 21 * 96/73 (22) HakemJiptJvt - AnsOknlnftdftf 09.08.73 ' * (33) Altaipilv »—GiM (h« tadag 09.08.73 (41) Tullut iulkMal - Mlvlt offMCNg ΐγ 02 7l * μ J. r.kiattrih.llltw «« ν · μ-ρ ^ * »« ι * μ · , ρ * _ r | wnt · och r «gl> t * rstyr« lMn AmMun uttagd och utljkrMMn pubUcmd 31.09.83 (32) (33) (31) Pjnrtetty «uollnui — Begird prlorlut 16.08.72 12.06.73, 12.06. 73 USA (US) 281201 *, 369203 369201 * (71) General Electric Company, Schenectady, NY, USA (US) (72) John Walker Eustance, South Glens Falls, New York, USA (US) • (7 ^) Oy The present invention relates to a long-life capacitor impregnated with a stabilized liquid ester impregnating agent and to a method for producing such a capacitor.

The invention uses a dielectric liquid impregnating agent containing an aromatic ester and an epoxide added thereto which is capable of acting on the harmful substances present or formed in the condenser during its use, thereby preventing the decomposition of said aromatic ester.

More specifically, the aromatic ester may be a derivative of phthalic acid, such as the higher reaction product of phthalic acid and 2-ethylhexyl, known as di (2-ethylhexyl) phthalate or more commonly dioctyl phthalate (DPO). In the following, the term DOP is alternatively used with di (2-ethylhexyl) phthalate.

2 64023

AC capacitor tests have shown that DOP is not a better impregnating agent in AC capacitors used under high voltage stresses, despite having certain good properties such as capability in the capacitor, high dielectric constant, and biodegradability. These good properties are overshadowed by the instability under high electrical stresses, resulting in a short service life. An indication of a short service life with a capacitor is a fast rising or high loss factor. The loss factor, which is a measure of the electrical loss of a capacitor, is generally a critical factor for AC capacitors that are exposed to high voltage. Electrical instability leads to early breakthrough or interference, which is critical for long-life capacitors such as current power capacitors impregnated with chlorinated diphenyl.

Stabilization of the impregnating agent usually involves a small addition to the impregnating agent of another agent which will improve the impregnating agent by neutralizing the impurities present in or generated in the condenser which cause decomposition. Usually, the impregnating agent whose properties need to be improved is already a good and effective capacitor impregnating agent and stabilizer additive provides a certain improvement. DOP is a fluid which, when used as an impregnating agent in capacitors exposed to high temperatures and high voltage steel skis, is associated with a rapid increase in the loss factor and subsequent capacitor failure. Primarily for these reasons, the development of DOP as a commercially acceptable impregnating agent for electric capacitors has been abandoned.

However, it has now been found that DOP can be effectively stabilized or modified so that it can be used as the sole main impregnating agent in AC capacitors and under high-voltage steel conditions. More specifically, it has been found that epoxides, previously assumed to be only chlorine (Cl) or chlorine-hydrogen (HCl) detergents, act differently and stabilize the condensation of DOP in the market where hydrogen chloride or chlorine is present. - 64023 3 is not present and is not born.

The features of the invention are set out in the claims.

The invention will now be described in more detail with reference to the accompanying drawing, in which

Fig. 1 is an example of a capacitor roll with paper as an insulator,

Fig. 2 shows a finished capacitor in a closed housing containing the coil of Fig. 1.

Fig. 3 shows a cross-section of a part of a capacitor coil utilizing a synthetic resin film as an insulator.

Fig. 4 shows a part of a capacitor roll mixed with a synthetic resin film and paper as an insulator,

Fig. 5 shows a cross-section of a part of a capacitor roll with a synthetic resin film in a different type of insulation system, and

Fig. 6 is a greatly reduced view of a power capacitor having a plurality of coils common to large scale correction of a loss factor used in induction heating and high frequency capacitor applications.

DOP is a substance known in the art as a chemical plasticizer for synthetic resins and is commercially available from a number of sources, for example, as "Flexol", which means a product of Union Carbide Company. A description of DDP as a plasticizer can be found in Arthur K. Doolittle's book The Technology of Solvents and Plasticisers, copyright 1954 Union Carbide and Carbon Corp., Properties of Individual Plasticisers, pp.962-964. In addition, U.S. Patent No. 1,923,939 describes this product in more detail.

Typical properties of this product are given in Table I below.

4 s / 1 n o 7

TABLE I U, · U ^ O

Typical properties for DOP fluid.

Di (2-ethylhexyl) phthalate, ^ 24 ^ 38 ^ 4 'm ° le ^ weight = 391

Density 25 ° C _D 0.987 g / cm 3

Refractive index N 20 ° C 1.4859

Boiling point 229 ° C / 5 mm pressure

Lowest running temperature -55 ° C Dielectric constant (DK) 5.25 / 25 ° C

% loss factor 7.7%, 8.5% at 100 ° C / 100 Hz, obtained in a 240 liter drum.

Viscosity 38 ° C: 30 es 99 ° C: 4.2 es When using the invention, OOP has been used as the sole impregnating agent in a) capacitors using only paper material as an insulator, b) capacitors using only synthetic resin as an insulator, and e) capacitors; using a mixture of synthetic resin and paper as insulation.

The capacitor according to the invention typically contains, as a typical example, one or more capacitor rolls which are relatively tightly packed in a shell which is filled with a fluid impregnating agent and sealed. The capacitor chip 1a alternately comprises strips of insulating material and electrode material that can be brought together by different laminating arrangements or structures, as disclosed in U.S. Patent No. 3,363,156.

Figure 1 shows an example of a capacitor roll 10 comprising two electrode foils 11 and 12 and dielectric paper strips 13 and 14. The electrode foils 11 and 12 can also be end-to-end paper strips 11 and 14 or with separate dielectric strips. with strips containing paper and plastics. Suitable connection pins 15 and 16 are used to connect the electrode diffusers 11 and 12 to the capacitor terminals 19 and 18. The roller is placed in the housing 17 in Figure 2 and after suitable drying and evacuation the housing is filled with a liquid impregnating agent 11a and sealed. The terminals 10 and 19 of the housing 5 64023 are connected to the output pins 15 and 16 of the roller 10 to provide an electrical connection.

Each dielectric paper strip 13 and 14 can be replaced with a plurality of paper strips so as to provide a thicker insulation. Each strip 13 and 14 may also be replaced with one or more synthetic resin strips 20 and 21, as shown in Figure 3, or a composite insulator having a paper strip 13 and a resin strip 20, as shown in Figures 4 and 5. Typical structures and embodiments are further shown in U.S. Pat. in Patent Publication 3,363,156.

In these typical embodiments, the dielectric fluid impregnating agent is caused to penetrate, pierce, and fill substantially all of the zones, cavities, and spaces in and between the insulating strips 13 and 14. This type of impregnation, called substantially complete impregnation, is necessary to reduce the generation of harmful corona discharges in AC capacitors and to prevent arcing. Because the impregnating agent is in an electric field between the electrodes, it is exposed to high electrical stresses, certain corona discharges, elevated and fluctuating temperatures, and other adverse environmental factors. For example, in the case of power capacitors, such conditions are not expected to cause a fault for capacitors with an active life of 10 to 20 years.

Capacitor technology thus places great emphasis on providing materials that are highly pure and combinable, such as paper and chlorinated diphenyl, and high demands are placed on high temperature drying and evacuation methods to remove gases and water vapor. Impurities in the capacitor material and structure may be derived from gases, water vapor, and solid contaminants such as elements and chemical compounds present in other materials, such as paper or polypropylene film. These elements and chemical compounds may be of foreign origin or used in the manufacture of other substances, in which case they are included for that reason. One source of condenser impurity is the catalyst used in the production of polypropylene. A typical catalyst gets. impurities in the form of aluminum and titanium salts. The impregnating agent can cause defects which are not immediately B 6 4 C 2 3 effective. For example, a chlorinated diphenyl impregnating agent is a solvent that dissolves and transports impurities and extracts impurities from the dielectric material that are harmful to the capacitor. The impurities react unfavorably with the impregnating agent or otherwise combine and react with the impregnating agent, resulting in a deterioration which is usually observed in the condenser as a first addition in the loss factor.

Elevated temperature conditions in the operating capacitor and smaller electrical discharges and the presence of Korona activate the contaminants, resulting in a weakening of the capacitor. The main elements known to cause premature capacitor failure are hydrogen and chlorine, which react to form, for example, hydrogen chloride. Chlorine is therefore considered to be an undesirable element in a capacitor impregnation or other capacitor. Unfortunately, for other reasons, it remained a critical component used in significant amounts in the best AC capacitor impregnants available, i. in polychlorinated diphenyl. Due to these considerations, several additives were proposed for chlorinated diphenyl impregnants which would act as eliminators of HCl, chlorine or hydrogen and thus increase the efficiency and service life of the capacitors. These additives included tin tetraphenyl anthraquinone and epoxides.

As previously mentioned, previous attempts to use 00P to impregnate AC capacitors have been severely hampered by the severely high loss factor and rapid degradation properties that such DOP-impregnated AC capacitors suffer from. As DOP does not contain any chlorine components, there was no compelling need to use the proposed additives. Experiments with the DOP-impregnated AC capacitors under Figures 1 and 2 under high-voltage steel conditions show relatively good electrical results from the beginning. However, in accelerated service life tests at elevated temperatures, capacitor failures occurred to an increasing and detrimental extent, mainly reflected in increasing loss coefficients and subsequent electrical failure of the capacitor. The experiments were repeated with a capacitor according to Figures 3 and 4, which differs from the capacitor according to Figure 1 in that the synthetic resin film strips replace the paper clarifiers 13 and 14 of Figure 1. Similar failures occurred in paper-based capacitors. In either case, the study did not show the presence of HCl or chlorine, as would have been expected in a chlorinated diphenyl impregnated capacitor.

Surprisingly, it was found that the addition of an epoxy compound to DOPr effectively stabilized the DOP-impregnated capacitor against premature failure and short life. The repetition of the above and other suitable experiments using epoxy showed a strong reduction in capacitor failures, as shown in the following example. In this example, DOP was purified in a column filtration process using alumina or diatomaceous earth as a filter medium. In addition, the impregnation process generally corresponds to that described in U.S. Patent No. 3,363,156, including drying the capacitors by exposing them to elevated temperatures, which may be above 100 ° C, usually below about 125 ° C, for several hours. At this point, the capacitors were under a pressure of less than 200pmHg. After DOP impregnation at about 70-80 ° C, the capacitors were sealed and allowed to absorb at about 100 ° C for several hours, for example 4-16 hours. The absorption time does not take into account the time taken to reach the desired temperature in the condenser, nor the time taken for the condenser to cool to room temperature, the times indicated refer to the times the condenser was at said temperature.

The invention is further illustrated by the following examples.

Example 1

Two sets of capacitors were assembled, each with 10 capacitors according to Figures 1 and 2. The paper insulating strips 13 and 14 each comprised a pair of paper strips, one 2.54 cm wide and 0.0075 mm thick and the other 2.54 cm wide and o 0087 mm thick. The uncondensed condensates of Figure 2 were placed at 125 ° C and vacuum for several hours. The Group 1 capacitors were then filled with purified OOP and the Group 2 capacitors were filled with the same purified DPO to which 1% by weight of epoxide known as diglycidyl ether of bisphenol A was added (bisphenol A is Dow Epoxy Resin No. 330, Dow Chemical Co. product). The results are shown in the following table.

Use test

380 volts AC and temperature 100 ° C

Out of order / usage ‘number_hours

Group 1 6-4200

Group 2 (epoxide) 0-4279 550 volts AC and 85 ° C temperature

Group 1 7-1130

Group 2 2-4205

The above values show that in those capacitors that contained epoxy additives, the number of failures was significantly reduced and the service life was extended. In the first service life test, capacitors were tested under the required conditions, with a temperature of 100 ° C and an alternating current of 380 volts. Despite these conditions, none of the capacitors failed in 4279 hours, while 6 of the epoxide-free capacitors failed in 4200 hours. Under even more severe conditions, the improved results in the second service life test were equally surprising. The clear advantage of epoxy addition to the paper insulation capacitor is noteworthy. Normally, the known generation of water vapor from paper and the known hydrolysis of OOP ester to ionizable products would appear to be incompatible. However, a very small amount of epoxide appears to elicit a favorable reaction that would be greater than would be expected based on the stoichiometric ratios of the reactants.

In the following example, the capacitors of Figure 3 with synthetic resin polypropylene films 20 and 21 as insulators were subjected to a similar experiment.

Example 2 In this example, 2 groups, each of 10 uncapped 9,64023 capacitors, were assembled as shown in Figures 1, 2, 3. The insulation was formed from a biaxially oriented isotactic polypropylene strip 47.6 mm wide and 0.0087 mm thick. The capacitors were placed at room temperature under vacuum drying conditions and impregnated at room temperature. Group 2 capacitors contained the same purified DPO but with an additional 1.0 wt% addition of bisphenol A diglycidyl ether. The condensers were vacuum-dried and impregnated at room temperature, then sealed and the impregnating agent was allowed to soak at 100 ° C for 2 hours. The following results were achieved:

Capacitance / power factor at 300 volts AC at 85 ° C Electrical breakdown strength, DC, kV per 0.025 mm 100 ° C 85 ° C polypropylene thickness

Group 1 3.52 / 0.39 3.58 / 0.34 5.49

Group 2 3.54 / 0.28 3.60 / 0.26 5.57 (epoxy)

The same units were subjected to a service life test as follows: Service life test (300 volts AC / 85 ° C)

Hours for betrayal

Group 1 3 remained after 256 hours

Group 2 (epoxide) 7 remained after 256 hours

Example 3 In this experiment, an attempt was made to compare the capacitors according to the invention with the corresponding known capacitors using chlorinated diphenyl as an impregnating agent to which about 0.3% by weight of epoxide has been added. Three groups of capacitors (10 each) were assembled, which had the structure shown in Figure 3. The insulation was made of a polypropylene film having a width of 47.6 mm and a thickness of 0.0-67 mm as in Example 7. The capacitors were dried under vacuum at room temperature for several hours 10 6 4 0 2 3 and then impregnated at room temperature with a given impregnating agent to which 1.0 % by weight of bisphenol A diglycidyl ether. The capacitors were then sealed and the impregnating agent was impregnated for 4 hours at 100 ° C. The service life tests and the results of the electrical penetration resistance determined at an ascent rate of 1B0 V / s at 85 ° C are given below:

Original electrical defective reading / tested through impact strength reading / t 85 ° C-kV average 380V AC / 550V AC

..... 100 ° C current / 65 ° C

Group 1 Pure DOP

no epoxy 1.92 7-10-256 6-9-256

Group 2 Pure DOP

1% epoxide 1.95 6-9-867 7-9-835 (First failure in 394 hours)

Group 3

Chlorinated Diphenyl ♦ Epoxide 1.76 8-9-256 9-9-177 These results show that stabilized DOP according to the invention withstands high temperature life tests better than other capacitors. It should be noted that the first failure in the DOP epoxide capacitor at 380 V AC at 100 ° C occurred only after 394 hours, whereas without stabilization, 7 DOP capacitors failed in 256 hours and 8 chlorinated diphenyl capacitors failed in 256 hours. .

Other capacitor structures were also formed and treated with DPO containing 10% by weight of diglycidyl ether of bisphenol A. For example, a small capacitor having the structure shown in Fig. 5 and said DOP impregnating agent1 was formed according to the present invention, and the results obtained were good.

11 64023

The previous examples show that epoxy plays a crucial role in the capacitor during its effective life. The epoxy stabilizer is characterized by the ability under these conditions to affect the chemical elements or compounds normally present in or formed in capacitors during use, thereby preventing the degradation or other deterioration of DOP by these compounds. These elements and compounds are those formed in capacitors using a DOP impregnating agent and lacking any substances that would generate HCl. Most known epoxides, which are otherwise useful in a capacitor, appear to provide the desired result to varying degrees. Both water and acids are formed or are already present in the condenser environment. Esters can decompose to form acids and alcohols. The epoxide is expected to react with such acids and thus prevent the acid from adversely affecting the ester or capacitor. The epoxide also appears to minimize the hydrolysis problem because it absorbs water. Epoxy is also assumed to passivate or cover foil scars. In a paper insulating capacitor, the epoxide can react with the cellulose and stabilize the system. The effect of the epoxide appears to be considerably different when only membrane insulation is used, i.e. when paper insulation is not present in Kande ^ aal & Ari. One reason for this is the presence of certain substances in the film. Such substances include stearates and other oxidants not present in the paper. Another reason is the low water content of the film. Thus, the stabilization of a film - only ester - impregnated capacitor can take place through various mechanisms which are not currently fully known.

While the effect of the epoxide on the final result is related to the operating capacitor environment, it also has a significant effect because it is dissolved in the ester. In this environment, the epoxide reacts with ester decomposition products and minimizes the hydrolysis problem. It also combines with impurities present in the ester or which may be introduced into the ester before its use in the condenser, i. during storage, transport and handling.

The epoxide compound of the invention can be generally characterized by the group 1lä 1 2 i I 64023 - c - c - \ / 0 exemplified by glycidyl ethers and ethylene oxide derivatives. Specific examples of these compounds are phenoxypropylene oxide (phenylglycidyl ether), glycidyl allyl ether, benzylethylene oxide, styrene oxide, 1,3-bis (2,3-epoxypropoxy) - * benzene and 4,4-bis (2,3-epoxypropoxy) -diphenyldimethylethane. In addition, there are commercially available epoxide compounds which have proven to be suitable for use in the invention and which are known as EP 107, which is di (2-ethylhexyl) -4,5-, epoxytetrahydrophthalate, under the name E0201, which is 3,4-epoxy-6 -methylcyclohexyl-methyl-3,4-epoxy-6, methylcyclohexanecarboxylate and EP206, which is 1-epoxyethyl-3,4-epoxycyclohexane. Mixtures of any two or more such epoxy compounds may be used if desired. U.S. Patent Nos. 3,362,90S, 3,242,401, 3,242,402, and 3,170,986 describe one or more such epoxides.

Experiments show that the quality of the epoxide is not a critical factor.

Different epoxides or mixtures thereof can be used as long as they are sufficient to provide efficacy. Such an amount depends mainly on the molecular weight, the reaction rate and the solubility in the impregnating agent. It is preferred to use higher molecular weight epoxides in higher amounts than lower molecular weight epoxides. In general, amounts above 0.01% by weight and preferably between 0.01-10% by weight are satisfactory. Epoxides have an effect that is assumed to be common to all epoxides based on their chemical structure. Their reaction time and power are favorable for DOP in a capacitor environment. In the above examples, the results obtained with and without epoxides in particular were compared. According to the invention, the epoxide can be introduced into the capacitor in several ways. It can be added to the dielectric polypropylene material during its manufacture so that it combines with the material, or it can also be added to the flowable OOP before or after it is introduced into the capacitor shell. It is preferred that the epoxide be combined with DPO as a solution and the solution be used to impregnate the capacitor. The primary reason for this is that those esters that include D0P * are sensitive to elevated temperatures and can change strongly with increasing temperatures. The addition of the epoxide to the ester before such heating, especially during impregnation, thus provides stabilization of the ester, completely independent of the stabilization of the condenser environment. OOP has been shown to be compatible with polypropylene film insulation alone or with paper. The preferred method of impregnation is that described in JSA Patent 3,363,156, referred to as “substantially complete impregnation.” In one embodiment, substantially complete impregnation comprises exposing an impregnated capacitor to an elevated temperature, preferably above 85 ° C, for an extended period of time. time (absorption) so that OOP not only penetrates the molecular structure of the polypropylene but also that the polypropylene becomes slightly semipermeable membrane-like with respect to 00P, allowing DOP to pass through the membrane DOP has been shown to penetrate the polypropylene membrane more slowly than chlorinated diphenyl. more intensive evacuation or drying is used 24-hour drying at 130-140 ° C has been effectively used, with D0P penetrating the condenser at about 100 ° C.

Absorption can be continued after impregnation and condenser closure and is also a significant factor influencing the results. Absorption can occur at temperatures above 85 ° C and are preferred! in the range of 100-120 ° C. Larger capacitors, which are more difficult to impregnate, achieve the best results when multiple absorbers are used after impregnation. The first absorption is carried out, for example, by placing the condensers in an oven and raising the temperature to about 110 ° C. After 8 hours at this temperature the temperature is lowered and the capacitors are allowed to cool to almost room temperature. The temperature in the oven is then raised to 110 ° C and maintained for another 8 hours. Comparative experiments show that the repeated absorption described gives a better result than a single absorption in 16 hours. The most suitable method of making DOP impregnated capacitors using paper comprises a vacuum drying step at a higher temperature, such as 120-140 ° C.

The polypropylene film described in U.S. Patent No. 3,363,156, i. a stereoregular crystalline, biaxially oriented film is preferred and used in all examples. Crystallinity means that a substance has a significant crystal content and crystallinity controls the physical properties of the substance. DOP is not limited to the aforementioned insulating materials, and other members of the poly (poly) group and other carbohydrates, such as poly carbunates, polysulfones and polyesters, are suitable d i e electrically active substances. A significant factor of 14 64023 ηβη is the use of D0P in combination with an epoxy stabilizer.

The stabilized impregnating agent, especially DOP, forms a better impregnating agent for those capacitors that are subjected to high voltage stresses and high temperature conditions. The high-voltage stress condition for the insulator when it consists of a synthetic resin film such as polypropylene is about 750 volts per 0.025 mm thick polypropylene rising to more than 1200 volts per 0.025 mm, with the most critical part of the high voltage range starting at about 900 volts per 0.025 mm and extending to 1400 volts per 0.025 mm. At the same time, the capacitors are subjected to these types of impregnation under these stresses, which is described as substantially complete impregnation in U.S. Patent 3,363,156. Certain results are obtained, e.g., a consistently high initial corona voltage corresponding to the thickness of the insulation. In high-voltage power capacitors in shunt operation, where the total electrical thickness between the electrodes may be of the order of 0.025 mm, the initial corona voltage must be above 2000 volts in general (room temperature) and in many cases will rise above 2500 volts. , the initial corona voltage may be lower The initial corona voltage 1 1 is usually 1 ^ -2i> times the highest voltage stress in the insulator at the operating voltage of the capacitor at room temperature and is stable under varying operating conditions in the capacitor.

OOP is useful for a variety of insulation systems that are a simple type of insulation material, such as paper only, film only, or a combination thereof. An example of a mixed insulation system is shown in Figure 4, where a sheet of paper 13 is right next to the electrode 11. It will be appreciated that other composite insulators may be used, such as that shown in Figure 5, with two sheets of film 20 and 21 interposed between a sheet of paper 13, or conversely there may be two sheets of paper and a sheet of film between them.

Figure 6 shows a high voltage capacitor of the power factor correction type, where a low power factor is essential for its usability. In Figure 6, the capacitor 22 comprises a large 3 shell 23, for example with a volume of 22 dm, in which a large number (10-40) of rollers 10 can be used. The length of these rollers can be 25-64 cm. To be effective, the OOP impregnating agent and additives must have penetrated each roll 10, because failure of one part 10 will cause the entire capacitor to fail. Therefore, these 15 640 2 3 power capacitors 22 are thoroughly dried, for example, by bringing them to a low pressure of less than 200 and a high temperature of 100-150 ° C for 15-30 hours. They are filled with the impregnating agent while still under vacuum and at a certain high temperature Qn it is common for the impregnating agent to be also at a temperature of 70-80 ° C when filling the shells. At this stage, the capacitor is sealed in the usual way and re-exposed to a temperature of about B0-120 ° C for long periods of time. Depending on the size of the capacitor and the dielectric material used, the paper-only dielectric material requires the shortest possible time and no subsequent heating is required. A capacitor made entirely of membrane may require as long as 16-24 hours for absorption.

Example 4

The experiments were performed with other aromatic ester impregnants containing epoxy additives. In one such experiment, which was performed with typical capacitors in the same manner as in the above examples, the insulator was polypropylene and the impregnating agent used was dicapryl phthalate. The epoxide was 1.0% by weight of EP206. These capacitors were tested at 550 volts at 85 ° C under an extremely high film stress of 1570 volts per 0.025 mm thick polypropylene. These capacitors behaved surprisingly after a service life of 9500 hours, as did the reference capacitors using chlorinated diphenyl as an impregnating agent.

Example 5

Capacitors were fabricated using the structure of Figures 2 and 5.

The insulation was a strip of 0.013 mm paper with a width of 9.2 mm and two strips of 0.0175 mm polypropylene with a width of 9.2 mm. The capacitance was about 0.5 μF. The capacitors were vacuum dried at 130-140 ° C for 24 hours and then impregnated at 100 ° C. Here were two groups of capacitors. The second group contained 1.0% by weight of epoxide in the DPOP impregnating agent and the second group contained 80% by weight of OOP: · β and 20% by weight of dodecylbenzone in the impregnating agent. To this mixture was added 1.0% by weight of ΕΡ2Π6 epoxy. The capacitors were then sealed and impregnated at about 100 ° C for 8 hours. Capacitors 16 64023 were subjected to the Korona initial voltage test and were further absorbed for Θ hours. The capacitors were again placed in a corona voltage test. This latter test showed a significant increase in corona start voltage. The latter test showed that the initial Korona voltage increased significantly due to the second impregnation treatment, which is necessary to bring the capacitors to a satisfactory Korona level and was higher with the DOP dodecylbenzene impregnant than with the DOP impregnant alone.

Not all dielectric fluids are satisfactory capacitor impregnants. The dielectric liquid must have the general characteristics of being in a purified or purifiable form and must have a boiling and freezing point outside the operating temperature range and a flash point above 175 ° C. In addition, the vapor pressure of the liquid should be below atmospheric pressure up to a temperature of about 20 ° C and its dielectric constant should be greater than 2, especially for synthetic resin insulators such as polypropylene, and preferably greater than 4 for paper insulation. In addition, the liquid should have a relatively low viscosity, less than about 1,000 es at 25 ° C, and should be fluid up to -40 ° C.

The loss factor is an extremely relevant characteristic of a capacitor, especially an AC power correction capacitor lie, because it is usually useful at high temperatures and is usually exposed to high temperatures during its manufacturing process. The loss factor tends to increase rapidly with temperature. The loss factor for the self-purified impregnating agent should be considerably less than 10% and preferably less than 5% determined at 100 ° C at a frequency of 100 Hz so that the resulting power factor in the final capacitor can be reduced to less than about 1%. The low loss factor must be maintained over a long service life of several years.

In addition, the impregnating agent must be compatible with other substances in the capacitor and must be able to withstand fluctuating capacitor operating temperatures under high voltage stress conditions. Ease of handling and impregnation and other physical properties are desirable. In addition, it is highly desirable that the impregnating agent has a high biodegradability compared to chlorinated diphenyl as well as low toxicity.

17 64023

The aromatic esters best suited for the purposes of the invention meet the above requirements and are preferred in the invention. Preferred esters that otherwise meet the appropriate dielectric tests are the reaction products of aromatic acid and alcohol. A typical formula would be r C - 0 - R 'il

R - O X

V J

wherein represents an aromatic substituent or an acid residue such as pyromellitic, terephthalic, phthalic trimellitic, trimesic acid, etc., or one of trimesyl, phenyl, naphthyl, biphenyl, tolyl, etc., and wherein R 'may be an alkyl or aryl group such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl, etc. These are straight chain alkyl groups. Alkyl groups with branched chains are also possible. These may include, for example, 2-ethylhexyl, isopropyl, isobutyl, isooctyl, etc. Examples of aromatic phthalic acid esters that may also be suitable for use in the invention include dimethyl, diethyl, dipropyl, etc. series. One example of a benzoic acid ester is butyl benzoate.

In addition to organic acids, the esters used in the invention comprise the reaction products of other acids, in particular the reaction product of phosphoric acid and the abovementioned alcohols. A specific example is tricresyl phosphate and triphenyl phosphate. They are also sensitive to degradation by hydrolysis or oxidation and the presence of epoxides is beneficial. The aromatic esters used in the invention are unique in that the reaction properties are known to be similar in advance, especially with phthalate esters, so that when the second component is a good condenser impregnating agent, a combination of aromatic ester and epoxide is useful.

The ester used in the invention may be an ester mixture or a mixture between the ester and another otherwise satisfactory impregnating agent. It is most preferred that the final impregnating agents comprise the ester as the major or predominant component. An example is a mixture of DOP and dibutyl phthalate or a mixture of DOP and didodecyl phthalate. The mixture may also comprise an ester of the invention with an aliphatic ester, such as dibutyl sebacate or 1 640 2 3 castor oil. The mixture may further comprise an ester with a hydrocarbon such as mineral oil, alkylnaphthalenes, polybutenes and the like. Specific examples of these mixtures include DOP and mineral oil and DOP and dodecyl gasoline. The mixtures may also comprise other esters such as phosphates, for example tricresyl phosphate and triphenyl phosphate. The compositions are also used to impart to the final impregnating agent properties that differ from the ester of the invention. Such a property is an increased dielectric autumn constant. The added substance can also be used in the form of a diluent or as an excipient for an impregnating agent, i.e. as a wetting agent. An example of a substance that acts in several ways is dodecylbenzene, which acts as a wetting agent and impregnating agent and can therefore be used in relatively large amounts. While it is preferred that the ester of the invention be the main component of the mixture in terms of electrical properties, the idea of the invention is that smaller amounts of ester may be used. For example, the ester of the invention can be added to 10-40% by weight of other impregnating agents to alter their properties. In connection with the compositions of the invention, the composition may comprise larger amounts of a suitable epoxide, where the epoxide serves both purposes, i. as a stabilizer and impregnant.

The use of the invention, especially with aromatic esters, has achieved significantly improved results. An epoxy-stabilized aromatic ester, such as DOP, provides an impregnating agent that is surprisingly as good and in some cases better than the best impregnating agent currently in use, which is chlorinated diphenyl.

Claims (7)

64023 1 9 A long-life capacitor comprising a sealed shell and an impregnated roll enclosed within at least one shell, consisting of electrodes wound on a roll and an intervening dielectric material consisting of polypropylene or polypropylene and paper, characterized in that said roll is impregnated in a shell a non-halogenated impregnating agent containing a liquid aromatic ester and an epoxy additive which affects the impurities in or generated in the capacitor so as to prevent electrical deterioration of the capacitor, said dielectric material being substantially completely impregnated and subjected to a load in the range of n00. more than 47000 V / mm in the thickness direction of the material. Capacitor according to claim 1, characterized in that the electrode pair comprises a strip-like body of synthetic resin with a metal surface. Capacitor according to claim 1 or 2, characterized in that said aromatic ester is dioctyl phthalate. Capacitor according to one of Claims 1 to 3, characterized in that the aromatic ester is an ester of 2-ethylhexylalkoxy. Capacitor according to any one of claims 1 to 4, characterized in that said epoxide is a derivative of glycidyl ether. Capacitor according to one of Claims 1 to 5, characterized in that the epoxide is a diglycidyl ether of bisphenol A. A method of manufacturing a capacitor according to claim 1, characterized in that a) the shell and the roll placed inside the shell, consisting of electrodes wound on the roll and a dielectric material between them, consisting of polypropylene or polypropylene and paper, are evacuated and raised b) the shell is filled with a non-halogenated impregnating agent containing a liquid aromatic ester and an epoxide, c) the shell is brought to an elevated temperature where it is maintained until the dielectric material has become substantially completely impregnated, d) the condenser is brought to room temperature e) closing the shell, which can be done before or after step c). A method according to claim 7, characterized in that the shell and roll are dried by keeping them evacuated for at least about 8 hours at a temperature between about 100-140 ° C, that the shell evacuated and at an elevated temperature is filled with an ester-containing impregnating agent having dissolved in more than 0.01% by weight of the epoxy compound, and that the impregnating agent is heat-absorbed into the dielectric material by maintaining the shell for at least about 4 hours at a temperature between about 85-140 ° C to achieve substantially complete impregnation. Method according to Claim 7 or 8, characterized in that paper is used in the capacitor as part of the dielectric system and in that the drying process takes at least 24 hours. A method according to claim Θ, characterized in that after the heat absorption of the impregnating agent by heat, the condenser is cooled, after which the heat absorption is repeated. Process according to Claim 8, characterized in that an impregnating agent is used, the aromatic ester of which has been purified by column refining from substantially all foreign matter and in which at least 1.0% by weight of epoxide has been dissolved in the aromatic ester. 6. G 2 3 21 PATEIMTKRAV