JPS5850709A - Mold coil - Google Patents

Abstract

PURPOSE:To avoid occurrence of cracks and separation at the time of hardening the molding resin by a coil wherein a bobbin integrally formed by crape insulating paper and the impregnated resin is disposed in the inner side of the coil. CONSTITUTION:The axial direction of a core 1 is coincident with the direction of shrunk folds of a bobbin 2, which includes voids caused by the folds of crape insulating paper. The crape paper is formed of insulating paper endowed with shrunk folds. A wound-up coil 3 using this crape insulating paper as a bobbin is set in a mold such that the shrunk folds of the bobbin 2 extends in the longitudinal direction. After drying and degassing, the coil 3 is impregnated with liquid resin and then molding resin is injected round the coil 3. With this, a mold coil can be attained in which fine portions of the bobbin, coil 3 and main insulating layers are filled with the impregnated resin and coarse portions of them are filled with the molding resin. At this time, since the shrunk folds extends in the longitudinal direction, air bubbles can escape upwardly so that the resin impregnation is made thoroughly. In case of mixing filler powder such as silica or talc, the coil is first impregnated with liquid resin and then is molded with injected resin including such fillers.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in molded coils molded with epoxy resin or the like and used in transformers, current transformers, etc.

For example, small transformers and current transformers with a rated capacity of I KVA or less are often manufactured using resin molds in recent years.

In this case, both the coil and the iron core are generally embedded in resin, but if this is done, the iron core will be subjected to mechanical stress by the resin, which may deteriorate the magnetic properties. To prevent this, it is possible to create a structure in which only the coil is cast and the iron core is attached later. This structure has the advantage that the entire equipment such as the transformer is small and lightweight.

In the case of a transformer in which only the coil is cast, the molded coil is generally made as follows. To explain with reference to FIG. 1, a winding frame 2 is attached to a winding core 1, and a secondary winding 3, a main insulation 4, and a secondary winding 5 are sequentially wound thereon and embedded in a molding resin 6. The winding core 1 is usually a rectangular column made of iron or aluminum, and is extracted from the coils 3 and 5 after the molded resin 6 has hardened.

The iron core will be inserted into this part later. The winding frame 2 is usually made of a molded product of phenol resin, poly, or ester resin, or a breath pod, but these have the following drawbacks. In the case of the winding frame 2 of the molded product, a gap is created between the winding frame 2 and the winding core 1, into which the casting resin 6 flows. If the layer of casting resin 6 is thin, it will peel off during use of the transformer or the like. If this layer is made thicker, it will not peel off, but the equipment itself, such as the transformer, will become larger. In addition, the molded winding frame 2
Since it is hard, stress remains when the casting resin is cured, which may cause peeling or cracking in the vicinity of the winding frame 2.

In the case of presspods, the problem with the inner resin layer is almost the same, and furthermore, this may peel off internally.

The object of the present invention is to eliminate the above-mentioned drawbacks and provide a small, lightweight, and reliable molded coil that does not cause peeling or cracking of the winding frame during curing of the casting resin.

In the present invention, crepe insulating paper is used as a winding frame, and the crepe insulating paper is wound around the winding frame so that the wrinkles are parallel to the axial direction of the coil. This is characterized in that it is constructed such that after impregnating it with a blank resin, it is cast with a resin containing a filler. An embodiment of the present invention will be described below with reference to the drawings. In the twenty-first, 1 is a winding core, and 2 is a winding frame made of crepe insulating paper wound around this winding core. The axial direction of the winding core 1 and the crimp direction of the winding frame 2 are in the same direction. When viewed from the direction of arrow X in Fig. 2, it looks as shown in Fig. 3, and the winding frame 2 contains many voids due to the wrinkles of the crepe insulating paper.The crepe paper has an original thickness of Q, l Im or Q
, 31111 density 0.21! It is preferable to use insulating paper with a thickness of 0.8777 m and wrinkles to give a finished thickness of 0.2111 to 1.0 mm. The coil 3, which is wound with crepe insulating paper as a winding frame, is set in a mold with its axis vertical, that is, so that the wrinkles of the crepe insulating paper in the winding frame 3 are firm, and is pre-dried and vacuum degassed. Impregnate with liquid resin. After that, casting resin is poured around the coil 3 and hardened by heating. In this way, a molded coil is formed in which small parts such as the winding frame 2 and the coil 3 or the main insulating layer are filled with the impregnated resin, and other large parts are hardened with the casting resin. Here, the wrinkles in the crepe insulating paper are firm, allowing the air bubbles to escape upwards, allowing for successful resin impregnation.

However, powders such as silica and talc are mixed in to maintain the proof strength when mixed in large quantities. It is therefore necessary to first impregnate with unfilled liquid resin and then cast with filled casting resin.

The impregnating resin should have a viscosity of 100 centipoise or less during impregnation. The casting resin preferably has a viscosity of 1000 to 500 centipoise during casting. The impregnating resin and the casting resin are preferably of the same type, such as bisphenol A epoxy. The hardening agent should also be the same. However, it is better to adjust the amount of curing accelerator added so that the impregnated resin cures a little faster than the casting resin. If this is not done, problems such as poor curing and residual stress may occur at the boundary layer between the impregnating resin and the casting resin.

It is also possible to use ordinary kraft paper or glass cloth instead of crepe insulating paper as the material for the winding frame 2.
In these cases, a resin flow path in the axial direction of the coil 3 is not formed, so that sufficient impregnation is not achieved. In addition, since the glass cloth and the lepe insulating paper, which also have threads protruding, are further artificially wrinkled, they are intertwined with the casting'#8 fat and are bonded even more firmly. The thermal expansion coefficient of resin-impregnated crepe insulating paper is 2.0 to 3.8 x 10 / 0, which is almost the same as that of casting resin, so it will not crack or peel due to curing shrinkage or heating and cooling during use. .

As described above, in the present invention, a winding frame in which crepe insulating paper and impregnated resin are integrated is used inside the coil, so it is a reliable material that does not cause cracks or peeling even when the casting resin hardens. Moreover, since this winding frame portion can be made quite thin with a thickness of 2 to 3111 mm, a small and lightweight molded coil can be obtained.

[Brief explanation of the drawing]

Figure 1 is a sectional view of a conventional general molded coil, Figure 2 is a cross-sectional view of a conventional general molded coil.
The figure is a front view showing a molded coil according to an embodiment of the present invention, and FIG. 3 is a front view seen from the X direction of FIG. 2.

Claims (1)

[Claims] A winding frame constructed by winding crepe insulating paper around a winding core, a coil wound around this winding frame so that the wrinkle direction of the crepe insulating paper and the coil axis direction are parallel, and this coil and winding. A molded coil made of molded resin that is cast after impregnating the frame with unfilled resin.