JPS585580B2 - Denki Makisenno Shinkougan Shinhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vacuum impregnation method for electrical machine windings, in which a container housing the windings is evacuated to impregnate the windings with an impregnating resin.

A method of this kind is described, for example, in West German Patent Publication No. 113 381.
No. 2 and No. 1613441.

In this method, the winding is dried under vacuum at high temperature and then impregnated with an impregnating resin under vacuum to obtain complete impregnation of the winding.

At this time, the degree of vacuum is generally kept below 0.2 Torr to minimize the amount of air bubbles remaining within the windings.

Despite such a high degree of vacuum, bubbles remaining in the winding volume at normal pressure concentrate in the insulation at the center of the conductor, causing poor impregnation.

Furthermore, under such a high vacuum, there is a risk that the curing agent contained in the impregnating resin when poured during the impregnation process will begin to boil, and the resulting steam will interfere with the impregnation.

A particular difficulty with such residual air bubbles arises when the insulation thickness is greater than 8 mm.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a vacuum impregnation method that significantly reduces the danger of air bubbles remaining in the windings.

Therefore, according to the present invention, the container in which the winding is housed is evacuated, the impregnated resin is filled with carbon dioxide gas, and then the container is evacuated again to impregnate the impregnated resin.

According to this method, air bubbles remaining in the winding are replaced by carbon dioxide gas absorbed by the impregnated resin.

Therefore, impregnation is carried out almost independently of the volume and thickness of the winding.

In order to prevent the impregnating resin from boiling during impregnation, the impregnating pressure with carbon dioxide gas is preferably set to be higher than the boiling point of the impregnating resin.

Next, an example of the impregnation method of the present invention will be described.

The windings to be impregnated are first placed in a container and dried under vacuum and heat in a conventional manner.

Subsequently, the container is filled with carbon dioxide (CO2), which is absorbed by the impregnated resin, at normal pressure.

The introduced carbon dioxide gas mixes with the air bubbles remaining in the winding depending on the pressure state.

If the container is evacuated to, for example, 0.1 Torr and filled with carbon dioxide gas at normal pressure, a 1:7600 bubble to carbon dioxide mixture is obtained within the winding.

The container is then evacuated again and the remaining air bubbles are further reduced or replaced by carbon dioxide gas.

If the volume is very large and there are too many residual bubbles, repeat the above steps again.

However, in order to avoid boiling of the impregnating resin, as is the case with conventional high vacuums, the vessel filled with carbon dioxide gas is further evacuated to a pressure above the boiling point of the impregnating resin.

This boiling point is often determined by the curing agent as the most boiling component of the impregnating resin.

In the above embodiment, the boiling point of the curing agent is 0.4 Torr at about 80° C., so boiling can be reliably avoided by setting the carbon dioxide pressure to 0.7 Torr.

During the subsequent impregnation of the winding wire with the impregnating resin, the carbon dioxide present in the winding wire is absorbed by the impregnating resin, so the impregnating resin completely penetrates the winding wire, leaving a non-impregnated void volume due to residual air bubbles. Nothing happens.

According to the impregnation method of the present invention, bubble-free impregnation was achieved even in a vacuum of 1 Torr or less.

Claims (1)

[Claims] 1. A method for vacuum impregnating electrical windings, which comprises evacuating a container in which the windings are housed, filling the impregnating resin with carbon dioxide gas, and then evacuating it again to impregnate the impregnating resin.