JPS636966B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a prepreg mica tape used for coil insulation treatment of rotating electric machines and the like. 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. Since the latter does not require a resin injection process, 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. The present invention provides a prepreg mica tape that can obtain coil insulation having characteristics equal to or better than those achieved by the reduced pressure resin injection method. The prepreg mica tape and the method of using the same according to the present invention will be specifically explained below. The characteristics of the prepreg mica tape of the present invention are that it uses a resin made of epoxy resin and acid anhydride as an adhesive, makes it easy to wind the tape around an electric conductor, and uses an appropriate amount of solvent to extend the usable life of the tape. The point is that it contains a certain amount. 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. Specific examples include varnish for adhesion of mica tape in the present invention, bisphenol A-based epoxy resin (for example, Epicoat, a trade name manufactured by Ciel Co., Ltd.
828 or Epicote 1001) and an acid anhydride (e.g. methylnadzic anhydride), a curing accelerator (e.g.
FIG. 1 shows the tan δ-voltage characteristics of the insulating layer when no additive (such as BF ₃ -piperidine) is added, or when 0.1 part or 1 part is added. 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 the 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) 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, a curing agent is required. It is preferable to contain at least 40% or more of anhydrous methyl CD acid (for example, Kayard MCD manufactured by Nippon Kayaku Co., Ltd.) as the acid anhydride. As a specific example, the tan δ-voltage characteristics of a sample coil having the resin composition shown in Table 1 are shown in FIG.

[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 using peelable mica), and then heated and dried at 100 to 120°C for 1.0 to 1.5 hours to obtain an epoxy repulg mica tape with a solvent content of 2 to 5%. Since the prepreg mica tape according to the present invention is an epoxy prepreg tape with the above-mentioned formulation, volatile substances in the insulating layer are removed by heat drying under reduced pressure, and then a mold heat curing process is performed with appropriately selected temperatures and pressures. By rubbing, winding insulation with excellent insulation performance can be obtained. Next, the method of using the prepreg mica tape according to the present invention will be explained in detail and concretely, 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 thus prepared is placed in a tank that can be depressurized and pressurized, and then placed under reduced pressure (approx.
3Torr or less) at an appropriate temperature (50~
Volatile substances such as solvents and moisture that are mixed between the insulation layers are removed through a heating drying process (130℃) and time (5 to 15 hours). After that, the temperature inside the tank is raised to 150-170℃, at which point the resin in the epoxy prepreg mica tape begins to gel, and a mold pressure treatment is applied to apply 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 is a diagram showing the tanδ-voltage characteristic curve, Figure 2 is a diagram showing the relationship between heat flow amount and heat treatment conditions, and Figure 3 is a diagram showing the tanδ of the sample coil with the resin composition in Table 1.
- A diagram showing the voltage characteristics, Figure 4 is a diagram showing the relationship between the weight loss rate of acid anhydride and heating temperature, Figures 5 and 6
The figure compares the characteristics of the coil insulation obtained using the prepreg mica tape of the present invention and the coil insulation obtained by the vacuum pressure impregnation method. Figure 5 shows the tanδ-voltage characteristics of the coil insulation. Figure 6 shows the temperature characteristics of coil insulation tanδ and volume resistivity at 500V, Figure 7 shows tanδ before and after immersion in water.
- It is a diagram showing voltage characteristics. 1...O part of curing accelerator, 2...Curing accelerator
0.1 part, 3... 1 part of curing accelerator, 4... 30% or more of alicyclic epoxy resin to bisphenol A epoxy resin, 5... Alicyclic epoxy resin to bisphenol A epoxy resin 30% or less, 6...Sample A, 7...Sample B, 8...
...After heating for 3Hrs under normal pressure, 9...100±10mm/Hg3Hrs
After heating, 10... prepreg insulated coil, 11...
...Vacuum pressure impregnation coil, 12...Volume resistivity (this invention), 13...Volume resistivity (vacuum pressure impregnation method), 14...tanδ (this invention), 15...tanδ (vacuum pressure impregnation method) 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. In the prepreg mica tape impregnated with semi-cured varnish, not more than 30% of the epoxy resin is alicyclic, 40 to 80% of the epoxy resin is solid resin, and acid anhydride. A prepreg mica tape characterized in that 40% or more of it is methyl CD acid anhydride, and the blending ratio of the epoxy resin and acid anhydride is acid anhydride equivalent/epoxy equivalent = 0.8 to 1.1.