CN1243034C - Heat resistant impregnant resin and its preparing method and use - Google Patents

Abstract

A non-styrene type solvent-free insulating impregnation resin, which is a low-viscosity transparent liquid, and its preparation method is 1) heating aromatic diacids and aliphatic polyhydric alcohols to 180-200°C under stirring to undergo esterification reaction, and at the same time Fractionally distill off the water produced by the reaction; 2) Add unsaturated acid anhydride in the temperature range of 140-160°C, heat to reflux, and continue the esterification reaction until the acid value is less than 30; 3) In the temperature range of 120-150°C , add non-styrene type reactive monomer diluent; 4) within the temperature range of 40-80°C, add functional additives. The resin is suitable for impregnating resins for motors; the insulating paint film formed after heating and curing has excellent mechanical properties, high electrical strength, low dielectric loss, chemical resistance, low temperature and fast curing, and thick layers without foaming. It is suitable for impregnation of AC and DC standard motors, large special motors, high voltage motors and distribution transformer windings.

Description

A kind of heat-resistant impregnation resin and its preparation method and application

technical field

The invention relates to a heat-resistant impregnating resin, in particular to a non-styrene solvent-free heat-resistant impregnating resin.

The present invention also relates to a method for preparing the above-mentioned resin.

The present invention also relates to the use of the above-mentioned resins.

Background technique

With the rapid development of the electrical industry, the performance requirements of polymer insulating materials are getting higher and higher; the heat resistance grades of insulating impregnated resins for high and low voltage motors are continuously improved, from B (130°C), F (155°C) to H Grade (180°C) and Grade C (240°C); the impregnation process of impregnating resin has developed from ordinary immersion, continuous immersion, dripping, rolling impregnation to vacuum pressure impregnation; the type of impregnating resin has also changed from solvent type, less solvent type to no solvent direction. With the continuous enhancement of people's awareness of environmental protection, solvent-free impregnation resin has become an important development direction. Solvent-based impregnating resins use a large amount of organic solvents, such as benzene, toluene, xylene, cresol, etc. During use, most of these solvents are either discharged as waste liquid or discharged into the atmosphere as waste gas, causing serious environmental pollution; At the same time, during the baking process of the insulating resin, a large amount of solvent volatilizes and easily produces bubbles, pores, etc., resulting in defects in the insulating structure. With the continuous enhancement of people's awareness of environmental protection, solvent-free impregnation resin has become an important development direction.

Solvent-free impregnating resins mainly include styrene-type unsaturated polyester impregnating resins and epoxy resin-type solvent-free impregnating resins. Epoxy type solvent-free resin has an unpleasant smell due to the use of acid anhydride and/or amine curing agent; in addition, its curing time is long, and the toughness of the cured paint film is poor. Compared with solvent-based impregnating resins, styrene-type solvent-free impregnating resins have certain improvements in environmental protection; since styrene or methylstyrene participates in the cross-linking reaction during the curing process of the resin, volatile organic matter (VOC) emissions have been reduced. However, styrene and methylstyrene have low flash points (31°C and 52°C respectively), and the unsaturated polyester impregnated resin using them as diluents will still have part of the diluent volatilized during the curing process. The volatile amount is as high as 15-25% of the total amount of diluent; therefore, it still has a great impact on environmental pollution and human health. In recent years, industrially developed countries have invested financial, manpower and material resources in this field to develop new low (less) pollution-free impregnating paints;

Hegemann (25 ^th Electrical electronics Insulation Conference & Electrical Manufacturing & Coil Winding, Oct.1999, Ohio, US, P7-13) reported a low volatility solvent-free unsaturated polyester impregnating resin without any diluent Monomer, the heat resistance level can reach 200℃;

The solvent-free unsaturated polyester resin reported by Ron Goetter et al. (Proceding: Electrical Insulation Conference and Electrical Manufacturing & Coil Winding Conference, Oct. 2001, Ohio, US, P16-18), compared with ordinary unsaturated polyester dipping paint, Has a high viscosity, so need to add diluent to reduce the viscosity. In order to reduce the amount of styrene diluent, acrylic acid was used as co-diluent;

Dr. Bardoliwalla (Proceding: Electrical Insulation Conference and Electrical Manufacturing & Coil Winding Conference, Oct.2001, Ohio, US, P61-63) reported a method suitable for immersion and vacuum pressure impregnation (VPI), as well as drip and roll immersion processes. Low volatility, high flash point solvent-free polyester resin, which selects allyl phthalate (DAP) as diluent; and reported a new type of solvent-free polyester resin (EXP) with a VOC of 0.3-0.8%. Thermal rating is 180°C;

Mark Winkeler (Proceding: Electrical Insulation Conference and Electrical Manufacturing & Coil Winding Conference, Oct.2001, Ohio, US, P143-148) compared and analyzed the performance requirements of various motors for impregnated resins, and considered epoxy resin and unsaturated polyester as The two main varieties will develop in the direction of low solvation and no solvation in the future to meet the development needs of new technologies such as motor miniaturization and frequency conversion.

In China, there are also reports on the research on solvent-free unsaturated polyester resin impregnation paint, but most of the reports still use styrene or modified styrene as the diluent monomer. Zhou Jian et al. (Proceedings of the Eighth National Symposium on Insulation Materials and Insulation Technology, October 2002, Kunming, China, No. 11-16) and Dong Zhancai et al. (Proceedings of the Eighth National Symposium on Insulation Materials and Insulation Technology , October 2002, Kunming, China, No. 17-21) reported the performance and application of styrene-type high and low-voltage motor general-purpose F-class solvent-free impregnating varnish and styrene-type H9150 unsaturated polyesterimide solvent-free impregnating resin. Because styrene has a low flash point, low boiling point, high volatility, and is harmful to human health, long-term exposure will have adverse effects on the human heart. Like solvent-based impregnating resins, there are also problems such as a decrease in dielectric strength due to air bubbles, air gaps, etc. during curing. Therefore, both solvent-based impregnating resins and styrene-based solvent-free impregnating resins have environmental pollution problems to varying degrees.

With the gradual enhancement of people's awareness of environmental protection, the research and development of new environmentally friendly, pollution-free solvent-free impregnated resins has become one of the development hotspots in the field of insulating materials.

Contents of the invention

The purpose of the present invention is to disclose a non-styrene solvent-free heat-resistant impregnating resin, which has low volatility, no irritating odor, good storage stability and fast curing speed, and is suitable for insulation systems of various motors.

Another object of the present invention is to disclose a method for preparing the above resin.

In order to achieve the above object, a non-styrene solvent-free heat-resistant impregnating resin disclosed by the present invention has the following main indicators:

Appearance is transparent liquid;

Volume resistivity: ≥1×10 ¹² Ωm under normal conditions, ≥1×10 10 Ωm at 20±5°C for 24 hours, ≥1×10 ¹⁰ Ωm at 155±2°C ≥1×10 ⁸ Ωm;

Dielectric strength: ≥20kV/mm under normal conditions, ≥18kV/mm at 20±5℃ for 24 hours, ≥16kV/mm at 155±2℃;

User application conditions: 120-130℃≤2h;

The effect of resin on enameled wire: the pencil hardness is not softer than 1H;

Adhesive strength (helical coil method): normal ≥ 50N;

Temperature index: 155 (F grade).

See Table 1 for details including the above-mentioned main indicators and other indicators.

The main components of the resin include:

148-286 parts of aromatic diacids, 155-265 parts of aliphatic polybasic acids, 98-164 parts of unsaturated anhydrides, 1500 parts of non-styrene reactive monomer diluents and 0.22 parts of functional additives;

The non-styrene type solvent-free impregnating resin disclosed by the present invention, its preparation method is:

a) heating the aromatic diacid and the aliphatic polyol to 180-200° C. under stirring, an esterification reaction occurs, and the water produced by the reaction is fractionated;

b) In the temperature range of 140-160°C, add unsaturated acid anhydride, heat to reflux, and continue the esterification reaction until the acid value is less than 30;

c) In the temperature range of 120-150°C, add non-styrene reactive monomer diluent.

d) In the temperature range of 40-80°C, functional additives are added to obtain a transparent and uniform solvent-free impregnating resin.

The aromatic diacids described in the present invention refer to 4,4'-biphenyl dicarboxylic acid, 3,3'-biphenyl dicarboxylic acid, 2,2'-biphenyl dicarboxylic acid, 4,4'-diphenylformic acid Ether dicarboxylic acid, 3,3'-biphenyl methyl ether dicarboxylic acid, 2,2'-biphenyl methyl ether dicarboxylic acid, 4,4'-diphenylmethane dicarboxylic acid, 3,3'-diphenylmethane dicarboxylic acid, 2,2'-Diphenylmethanedicarboxylic acid, isophthalic acid, terephthalic acid or phthalic acid.

The unsaturated acid anhydride in the present invention refers to maleic anhydride, norbornene anhydride, 4-methyltetrahydrophthalic anhydride or tetrahydrophthalic anhydride.

The aliphatic polyhydric alcohol described in the present invention refers to ethylene glycol, propylene glycol, diethylene glycol, propylene glycol, neopentyl glycol, butanediol or pentaerythritol.

The non-styrene reactive monomer diluent of the present invention refers to a low-viscosity liquid organic compound containing reactive carbon-carbon double bonds (-C=C-), including diallyl isophthalate, o- Diallyl phthalate, diallyl diphenyl ether dicarboxylate, triallyl cyanurate, 2-hydroxyethyl methacrylate, hydroxyethyl acrylate, 2-hydroxypropyl methacrylate ester, ethylene glycol dimethacrylate, or ethylene glycol diacrylate.

The functional additives in the present invention refer to organic compounds that can improve the storage stability of the impregnated resin, improve the performance of the resin molding process, promote and accelerate the curing of the resin, and improve the high and low temperature mechanical properties, electrical properties, and storage stability of the cured resin and its components. Mixtures, including methoxyphenol, cobalt naphthenate and mixtures thereof.

The non-styrene type solvent-free impregnating resin of the present invention has the characteristics of excellent mechanical properties, high electric strength, low dielectric loss, chemical resistance, low-temperature fast curing, no foaming in thick layers, and the like.

The non-styrene type solvent-free impregnating resin of the present invention, its main application includes: the impregnation of AC and DC standard motors, large special motors, high-voltage motors and distribution transformer windings; the impregnation methods include ordinary impregnation, roll impregnation, vacuum pressure Dipping etc.

Detailed ways

Example 1: Heat 166 parts of isophthalic acid, 190 parts of propylene glycol, and 98 parts of maleic anhydride to 180-220 °C under stirring, and react under reflux until the solution is transparent. After the acid value is less than 50, reduce the pressure Distillation; when the acid value of the reaction liquid is lower than 30, the temperature is lowered to 160° C., and 1500 parts of diallyl phthalate and 0.22 parts of functional additives are added. After uniform stirring, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 2: Heat 166 parts of isophthalic acid, 155 parts of ethylene glycol, and 152 parts of tetrahydrophthalic anhydride to 180-220 °C under stirring, and react under reflux until the solution is transparent, and the acid value is less than 50. Pressure distillation; when the acid value of the reaction liquid is lower than 30, the temperature is lowered to 160°C, and 1500 parts of diallyl phthalate and 0.22 parts of functional additives are added. After uniform stirring, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 3: Heat 166 parts of terephthalic acid, 190 parts of propylene glycol, and 138 parts of 4-methyltetrahydrophthalic anhydride to 180-220°C under stirring, and react under reflux until the solution is transparent and the acid value is less than 50 After vacuum distillation; when the acid value of the reaction solution is lower than 30, cool down to 160°C, add 1500 parts of 50% α-methylstyrene solution of diallyl diphenyl ether dicarboxylate, 0.12 parts of methoxyphenol , 0.1 part of cobalt naphthenate, after stirring evenly, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 4: Heat 166 parts of terephthalic acid, 190 parts of propylene glycol, and 98 parts of maleic anhydride to 180-220°C under stirring, and react under reflux until the solution is transparent, and the acid value is less than 50. Pressure distillation; when the acid value of the reaction solution is lower than 30, cool down to 160°C, add 1500 parts of 30% triallyl cyanurate and α-methylstyrene mixed solution and 0.22 parts of functional additives. After uniform stirring, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 5: Add 148 parts of phthalic anhydride, 190 parts of propylene glycol, and 152 parts of tetrahydrophthalic anhydride, heat to 180-220°C under stirring, and react under reflux until the solution is transparent, and the acid value is less than 50. Pressure distillation; when the acid value of the reaction liquid is lower than 30, the temperature is lowered to 160°C, and 1500 parts of ethylene glycol dimethacrylate and 0.22 parts of functional additives are added. After uniform stirring, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 6: Add 242 parts of 4,4'-biphenyldicarboxylic acid and 260 parts of neopentyl glycol, add 98 parts of maleic anhydride, heat to 180-220°C under stirring, and react until the solution is Transparent state, after the acid value is less than 50, distill under reduced pressure; when the acid value of the reaction solution is lower than 30, cool down to 160°C, add 1500 parts of ethylene glycol diacrylate and 0.22 parts of functional additives. After uniform stirring, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 7: Heat 166 parts of isophthalic acid, 225 parts of butanediol, and 152 parts of tetrahydrophthalic anhydride to 180-220 °C under stirring, and react under reflux until the solution is transparent, and the acid value is less than 50. Pressure distillation; when the acid value of the reaction solution is lower than 30, cool down to 160°C, add 1500 parts of hydroxyethyl acrylate, 0.12 parts of methoxyphenol, and 0.1 part of cobalt naphthenate, and stir to obtain a uniform and transparent impregnating resin.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 8: Add 242 parts of 4,4'-biphenyldicarboxylic acid and 225 parts of butanediol to 138 parts of 4-methyltetrahydrophthalic anhydride, heat to 180-220°C under stirring, and react to a solution under reflux It is in a transparent state, and the acid value is less than 50, then distilled under reduced pressure; when the acid value of the reaction solution is lower than 30, cool down to 160°C, and add 1500 parts of 2-hydroxyethyl methacrylate and 0.22 parts of functional additives. After uniform stirring, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 9: Heat 286 parts of 4,4'-diphenylmethyl ether dicarboxylic acid, 260 parts of neopentyl glycol, and 98 parts of maleic anhydride to 180-220°C under stirring, and react to a solution under reflux It is in a transparent state, and after the acid value is less than 50, it is distilled under reduced pressure; when the acid value of the reaction liquid is lower than 30, the temperature is lowered to 160°C. Add 1500 parts of 50% α-methylstyrene solution of diallyl phthalate, 0.12 parts of methoxyphenol, and 0.1 part of cobalt naphthenate, and stir evenly to obtain a uniform and transparent impregnating resin.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 10: Add 286 parts of 4,4'-diphenylmethyl ether dicarboxylic acid, 265 parts of diethylene glycol, and 152 parts of tetrahydrophthalic anhydride, heat to 180-220°C under stirring, and react under reflux until the solution becomes transparent state, after the acid value is less than 50, distill under reduced pressure; when the acid value of the reaction solution is less than 30, cool down to 160°C, and add 1500 parts of 2-hydroxypropyl methacrylate and 0.22 parts of functional additives. After uniform stirring, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 11: 256 parts of 4,4'-diphenylmethanedicarboxylic acid, 265 parts of diethylene glycol, and 152 parts of tetrahydrophthalic anhydride were heated to 180-220°C under stirring, and reacted under reflux until the solution was transparent. Distill under reduced pressure after the acid value is less than 50; when the acid value of the reaction solution is less than 30, cool down to 160°C, add 1500 parts of 50% alpha-methyl styrene solution of diallyl phthalate and 0.22 parts of functional sexual additives. After uniform stirring, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 12: Heat 286 parts of 4,4'-diphenylmethyl ether dicarboxylic acid, 260 parts of neopentyl glycol, and 152 parts of tetrahydrophthalic anhydride to 180-220°C under stirring, and react until the solution is transparent under reflux state, the acid value is less than 50 and then distilled under reduced pressure; when the acid value of the reaction solution is lower than 30, cool down to 160°C, add 1500 parts of 50% diallyl phthalate α-methylstyrene solution and 0.22 functional additives. After uniform stirring, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 13: 286 parts of 4,4'-diphenylmethyl ether dicarboxylic acid, 190 parts of propylene glycol, and 164 parts of norbornene anhydride were heated to 180-220°C under stirring, and reacted under reflux until the solution was transparent. Distill under reduced pressure after the acid value is less than 50; when the acid value of the reaction solution is less than 30, cool down to 160°C, add 1500 parts of 50% alpha-methyl styrene solution of diallyl phthalate and 0.22 parts of functional sexual additives. After uniform stirring, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 14: Heat 166 parts of terephthalic acid, 190 parts of propylene glycol, and 164 parts of norbornene anhydride to 180-220°C under stirring, and react under reflux until the solution is transparent. After the acid value is less than 50, the pressure is reduced Distillation; when the acid value of the reaction liquid is lower than 30, the temperature is lowered to 160° C., and 1500 parts of 50% diallyl phthalate in α-methylstyrene solution and 0.22 parts of functional additives are added. After uniform stirring, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Example 15: Heat 166 parts of isophthalic acid, 155 parts of ethylene glycol, and 138 parts of 4-methyltetrahydrophthalic anhydride to 180-220°C under stirring, and react under reflux until the solution is transparent, and the acid value Distill under reduced pressure after less than 50; when the acid value of the reaction solution is lower than 30, cool down to 160°C, add 1500 parts of 50% diallyl phthalate α-methylstyrene solution and 0.22 parts of functional additives . After uniform stirring, a uniform and transparent impregnating resin is obtained.

The impregnating resin is used to impregnate the motor windings in a continuous immersion manner, and the impregnated motor windings are obtained by heat treatment at 130°C/1.5 hours.

Table 1 The main technical indicators of non-styrene solvent-free impregnating resin

Appearance: Transparent liquid, no mechanical impurities

Specific gravity (25°C): 1.06-1.20

Viscosity (23±2℃): 15-25s after 4# cup mixing

Acid value ＜9mgKOH/g

Gel time: Test tube method 5-10min/110±2℃

Drying performance: Surface dry 15min/120℃

Thick dry 20min/120℃

Volume resistivity: Normal: ≥1×10 ¹² Ωm

After soaking in water at 20±5℃ for 24 hours: ≥1×10 ¹⁰ Ωm

155±2℃≥1×10 ⁸ Ωm

Dielectric strength: Normal: ≥20kV/mm;

                                                                                                                                                             

                                                                                         

Volatile matter: ≤5%

Storage period: 6 months at 25°C and sealed in groups

Pot life: After the resin is mixed, store it in an open container at 30-35°C for 10 days. After replenishing, part of the solvent will volatilize, and the viscosity increase value will not exceed 50s. It will not gel when stored at room temperature for more than 20 days.

User application conditions: 120-130℃≤2h

Effect of resin on enameled wire: Pencil hardness not softer than 1H

Adhesive strength (screw tube method): Normal ≥ 50N

Temperature index: 155 (Grade F)

Claims (3)

1, a kind of solvent impregnated resin, its leading indicator is:

Outward appearance is a transparent liquid;

Volume specific resistance: under the normality 〉=1 * 10 ¹²Ω m, 20 ± 5 ℃ of immersion 24h 〉=1 * 10 ¹⁰Ω m, 155 ± 2 ℃ 〉=1 * 10 ⁸Ω m;

Dielectric strength: normality: 〉=20kV/mm, 20 ± 5 ℃ of immersion 24h 〉=18kV/mm, 155 ± 2 ℃ 〉=16kV/mm;

User's application conditions: 120-130 ℃≤2h;

Resin is to the effect of enameled wire: pencil hardness is not softer than 1H;

The bonding strength of spiral winding method: normality 〉=50N;

Humidity index: be the F level in the time of 155 ℃;

Major ingredient comprises:

The aliphatics polyprotonic acid of the aromatic diacid of 148-286 part, 155-265 part, the unsaturated acid anhydride of 98-164 part, 1500 parts non-styrene type reactive monomer thinner and 0.22 part functional additive;

Described aromatic diacid is 4,4 '-biphenyl dicarboxylic acid, 3,3 '-biphenyl dicarboxylic acid, 2,2 '-biphenyl dicarboxylic acid, 4,4 '-two methyl-phenoxide dioctyl phthalate, 3,3 '-biphenyl methyl ether dioctyl phthalate, 2,2 '-biphenyl methyl ether dioctyl phthalate, 4,4 '-ditane dioctyl phthalate, 3,3 '-ditane dioctyl phthalate, 2,2 '-ditane dioctyl phthalate, m-phthalic acid, terephthalic acid or phthalic acid;

Described unsaturated acid anhydride is MALEIC ANHYDRIDE, norbornylene acid anhydrides, 4-methyl tetrahydro phthalic anhydride or tetrahydrophthalic anhydride;

Described aliphatic polyol is ethylene glycol, propylene glycol, glycol ether, dipropylene glycol, neopentyl glycol, butyleneglycol or tetramethylolmethane;

Described non-styrene type reactive monomer thinner, refer to contain the low-viscosity (mobile) liquid organic compound of reactive carbon-to-carbon double bond, comprise diallyl isophthalate, Phthalic acid, diallyl ester, phenyl ether dioctyl phthalate diallyl, triallyl cyanurate, 2-hydroxyethyl methacrylate, Hydroxyethyl acrylate, methacrylic acid-2-hydroxypropyl acrylate, Ethylene glycol dimethacrylate or diacrylate one condensed ethandiol ester;

Described functional additive is methoxyphenol, cobalt naphthenate and composition thereof.

2, the described solvent impregnated resin of a kind of claim 1 the preparation method, key step comprises:

A) aromatic diacid, aliphatic polyol under agitation are heated to 180-200 ℃, esterification takes place, fractionate out the moisture content of generation simultaneously;

B) in 140-160 ℃ temperature range, add unsaturated acid anhydride, reflux, proceed esterification to acid number less than 30;

C) in 120-150 ℃ temperature range, add non-styrene type reactive monomer thinner;

D) in 40-80 ℃ the temperature range, add functional additive, obtain transparent, uniform solvent impregnated resin.

3, the described solvent impregnated resin of claim 1 is used to comprise the dipping of AC and DC standard electromotor, large-scale special machines, high-voltage motor and substation transformer winding.