JPS6117228B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing an electric coil, and more particularly, to a method of insulation treatment. As the voltage and capacity of electrical equipment such as rotating machines and transformers have increased, coil insulation has come to be required to have excellent electrical, mechanical, and physical properties. In general, coil insulation treatment methods for high-voltage, large-capacity rotating electric machines can be divided into the following two types. One is to wrap so-called dry mica tape, which uses less adhesive, around an electrical conductor and place it in a tank.
After drying under reduced pressure to remove solvent and moisture, a solvent-free synthetic resin such as an epoxy resin is injected into the voids of the insulating structure under reduced pressure and pressure. Another method is to wrap a so-called prepreg mica tape, which already contains a sufficient amount of resin necessary to form an insulating layer, onto an electrical conductor and then heat mold it. The former requires a resin injection process after winding the mica tape, which requires a long manufacturing period and increases manufacturing costs. Furthermore, in the case of high-voltage, large-capacity rotating machines and transformers, which are produced in small numbers, there may be no opportunity to use the resin repeatedly within the usable life of the injected resin. In such a case, the manufacturing cost becomes even higher. However, it is possible to obtain an electrically, mechanically, and physically excellent insulating layer by selecting the resin to be injected or by selecting an optimal injection process. The latter does not require a resin injection process, so the manufacturing period is short and the manufacturing cost is low. However, volatile substances cannot escape from inside the insulating layer, or voids tend to remain, resulting in poor electrical properties at high temperatures and high voltages. Further, completely solvent-free prepreg mica tapes have been used to improve these properties, but they have various drawbacks such as short pot life, poor flexibility, and the need to heat the electrical conductor during winding. There is a need for a prepreg tape and coil insulation treatment method that uses prepreg mica tape to obtain electrical, mechanical, and physical properties equivalent to or better than the reduced pressure resin injection method. The present invention was made in response to the above-mentioned problems, and the adhesive resin contained in mica tape has been improved to a solvent type that has a long shelf life and is easy to wind on electrical conductors. During the heating and drying process, volatile substances such as solvent and moisture contained in the mica tape and minute voids that occur when it is wound around an electrical conductor are removed, and then the temperature and pressure are appropriately selected to harden the resin. By doing so, it is possible to obtain coil insulation having characteristics equivalent to or superior to those obtained by the reduced pressure resin injection method. The prepreg mica tape used in the present invention and the method of applying it to an electric coil will be specifically described below. The characteristics of the mica tape used in the present invention are that a resin consisting of an epoxy resin and an acid anhydride is used as an adhesive;
In addition, the tape contains an appropriate amount of solvent in order to facilitate the tape winding work around the electrical conductor and to extend the usable life of the tape. Generally, acid anhydride as an epoxy resin curing agent has a slow reaction, so a curing accelerator is used in conjunction with it, but if this is done, the resin will not flow sufficiently during the molding process after coil winding, and the insulating layer voids remain, which adversely affects electrical properties and dielectric strength at high temperatures. As a specific example, in the mica tape adhesive varnish of the present invention, an acid anhydride (for example, methylnadic acid anhydride) is added to a bisphenol A-based epoxy resin (for example, Epikoat 828 or Epikoat 1001 manufactured by Ciel), and then acetone is added. , tan δ-voltage of the insulating layer when no curing accelerator (for example, BF ₃ -piperidine, etc.) is added to the resin with toluene or a solvent such as methyl ethyl ketone, or when 0.1 part or 1 part is added. The characteristics are shown in Figure 1. When the solid resin content is less than 40%, the viscosity of the varnish decreases, and the drying history during normal prepreg mica tape production causes poor adhesion to the backing material and makes it easy to peel off. Furthermore, when the solid resin content exceeds 80%, the flexibility of prepreg mica tape is sensitive to the effects of temperature and residual volatile matter, making it difficult to manufacture and store the tape, and making it extremely difficult to wind it around electrical conductors. It becomes stable. Since alicyclic epoxy resin undergoes a rapid curing reaction with acid anhydride, if it exceeds 30% of bisphenol A epoxy resin, the pot life of the tape will be shortened and the heating and curing reaction required for the curing reaction will be shortened. The amount of heat flowing out of the resin during pressurization is reduced, making it difficult to obtain a dense insulating layer without voids. As a specific example, FIG. 2 shows the amount of heat leaked from an alicyclic epoxy resin (for example, Chitsonox 221, etc.) that is 30% or more of the bisphenol A epoxy resin and when it is 30% or less. In order to maintain appropriate workability and heat flow properties of the resin during coil molding without shortening the pot life of the mica tape, and to ensure that the resulting coil exhibits excellent insulation properties under high temperature and high voltage conditions, the curing agent acid is required. It is preferable to contain at least 40% of anhydrous methyl CD acid (for example, Kayahard MCD manufactured by Nippon Kayaku Co., Ltd.) as an anhydride. As a specific example, FIG. 3 shows the tan δ-voltage characteristics of a sample coil with the resin composition shown in Table 1.

[Table] As shown in Figure 4, many acid anhydrides evaporate at a temperature of 100°C, so an extra amount that will be reduced by heating during mica tape production and coil molding is added in advance to the varnish formulation and cured. The equivalent ratio of the epoxy group to the acid anhydride is adjusted to 1:0.8 to 1.1. The mica may be peeled mica or laminated mica, and glass cloth or
Use glass fiber or polyethylene terephthalate nonwoven fabric. In the varnish with the above formulation, bisphenol A
Part or all of the epoxy resin may be replaced with novolac resin, but this can be used as a base material with glass cloth or glass fiber on one side of laminated mica foil or peeled mica, and polyethylene terephthalate nonwoven fabric on the other side. , the amount of adhesive is 35-45
% (15 to 20% in the case of peelable mica) and then heated and dried at 100 to 120°C for 1.0 to 1.5 hours to obtain an epoxy prepreg mica tape with a solvent content of 2 to 5%. The characteristics of the method for manufacturing an electric coil according to the present invention are as follows:
By using epoxy prepreg mica tape with the above formulation as coil insulation, volatile substances in the insulation layer are removed by heat drying under reduced pressure, and then a mold heat curing process is performed with appropriately selected temperatures and pressures. The aim is to obtain winding insulation with excellent insulation performance. Next, the method for manufacturing an electric coil according to the present invention will be explained in detail and specifically, and the characteristics of the completed coil will be explained using figures. The epoxy prepreg mica tape according to the present invention is wrapped on top of the electrical conductor in a half-wrap manner with a constant tension so that the backing material glass cloth or glass fiber is on the surface of the coil depending on the voltage class used. A molding iron plate cut to size is placed on top of the mold, and a heat-shrinkable tape (for example, polyethylene terephthalate) is wrapped around it. The electrical conductor made in this way is set in a tank that can be depressurized and pressurized, and then placed under reduced pressure (approximately 3 Torr or less).
Volatile substances such as solvents and moisture that are mixed between the insulation layers are removed through a heating drying process at an appropriate temperature (50 to 130°C) and time (5 to 15 hours) depending on the number of turns. After that, the temperature inside the tank is raised to 150-170℃, at which point the resin in the epoxy prepreg mica tape starts to gel, and a mold pressure treatment is applied to apply a pressure of 5-15 kg/ ^cm2 to the coil surface. Strain, 25~
After heat treatment for 35 hours, the coil insulation is cooled to 60-80°C and then taken out from the tank to obtain coil insulation with excellent properties. The coil insulation thus obtained has superior properties compared to the vacuum impregnation method, and can obtain class F heat resistance. Also, depending on the voltage class, it can be manufactured from low voltage (3300V class) to high voltage (25000V class) with a single heating, drying and curing process.

[Brief explanation of the drawing]

Figure 1 shows the tanδ-voltage characteristic curve, Figure 2 shows the tanδ-voltage characteristic curve.
Figure 3 shows the relationship between heat flow amount and heat treatment conditions.
The figure shows sample coils with resin compositions in Table 1.
Figure 4 shows the relationship between the weight loss rate of acid anhydride and heating temperature. Figures 5 and 6 show the coil insulation obtained by the present invention and reduced pressure. This is a diagram showing a comparison of the characteristics of coil insulation obtained by the impregnation method. Figure 5 is a diagram showing the tan δ - voltage characteristics of coil insulation, and Figure 6 is a diagram showing the tan δ and volume resistivity of coil insulation at 500V. FIG. 7 is a diagram showing the tanδ-voltage characteristics before and after immersion in water. 1...0 parts of curing accelerator, 2...0.1 part of curing accelerator
3... 1 part of curing accelerator, 4... Alicyclic epoxy resin to bisphenol A epoxy resin
30% or more, 5...30% or less of alicyclic epoxy resin to bisphenol A epoxy resin, 6...Sample A, 7...Sample B, 8...After heating for 3 hours at normal pressure, 9...100±10mm/Hg3Hrs After heating, 10... prepreg insulated coil, 11... vacuum pressure impregnation coil, 12... volume resistivity (present invention), 13... volume resistivity (low pressure pressure impregnation method), 14... tan δ (present invention), 15... tanδ (vacuum pressure impregnation method), 16...
Before water immersion, 17...after water immersion.

Claims (1)

[Scope of Claims] 1. A varnish consisting of an epoxy resin selected from the group consisting of bisphenol A-based epoxy resins, alicyclic epoxy resins, and novolac-based epoxy resins, an acid anhydride, and an organic solvent is applied to mica on a backing material. A method for manufacturing an electrical coil, which comprises: winding a prepreg mica tape impregnated with semi-hardened varnish around an electric conductor, drying under reduced pressure by heating to remove volatile substances, and then heat-molding. 2. Claim 1, wherein not more than 30% of the epoxy resin is alicyclic.
A method for manufacturing an electric coil as described in Section 1. 3. The method for manufacturing an electric coil according to claim 1, wherein 40 to 80% of the epoxy resin is solid resin. 4. The method for manufacturing an electric coil according to claim 1, wherein 40% or more of the acid anhydride is methyl CD acid anhydride. 5. The method for manufacturing an electric coil according to claim 1, wherein the mixing ratio of the epoxy resin and the acid anhydride is acid anhydride equivalent/epoxy equivalent = 0.8 to 1.1.