RESIN

The subject of the invention is a method for protecting a capacitor winding made of a metallised plastic film with an epoxy resin. An impregnation method, in which a winding is first dried in vacuum at an increased temperature, impregnated with a liquid epoxide and then drained, makes it possible to produce a capacitor, in which the environmental influence is excluded. As a consequence, the capacitor has a stable capacitance and a long life span. The invention belongs to class H01G 4/22 of the International Patent Classification.

A technical problem successfully solved by the present method and the design of the capacitor is an adequate protection of a metal polypropylene capacitor winding in order to protect its thin metallised coating that is sensitive to the presence of oxygen and air moisture from oxidation.

Environmental influences on the capacitor can be done away with by protecting capacitor windings. An adequate agent is used to prevent the thin metallised coating that is sensitive to the presence of oxygen and moisture from oxidation, thus reducing the number of partial discharges and thus a decrease in the capacitance of a capacitor in its life. There are mostly three known types of protecting a metal polypropylene capacitor winding, i.e. with biodegradable plant oil, by gas filling and by coating a capacitor winding with epoxide. A drawback of protection by using biodegradable plant oil is high weight and a possibility of capacitor leakage. A disadvantage of gas filled capacitors is a possibility of gas leakage and a disadvantage of capacitors coated with epoxide is high capacitor's weight.

The present invention relates to low-voltage power capacitors used for the improvement of power factor at low voltage as well as to engine capacitors and capacitors for fluorescence produced in MKP technology.

It is commonly known that capacitors used for these purposes consist of one or several capacitor elements. Each element consists of two top quality biaxially oriented polypropylene films serving as dielectric, onto which a thin layer of aluminium, zinc or a mixture thereof is vaporized under vacuum and serve as capacitor electrodes. Both electrodes are contacted on the front side of a capacitor element via thicker layer, onto which pins are soldered.

It is also common knowledge that there are huge problems with the stability of the thin vaporized capacitor coatings. The main reasons for poor stability are moisture and air. Since the very beginning of the MKP technology much attention has been paid to the elimination of these two main reasons for a poor quality of capacitors and their short life span.

Coating with epoxy filling, plant oil based resin and a use of a neutral N2 insulation gas proved to be of best quality and most practical among the protection technologies used. All these technologies more or less ensure a minimum change in capacitance during the entire life span of a capacitor and a long life of a capacitor.

A possibility of protecting a capacitor winding with a dielectric fluid containing acetoxystearate is disclosed in the US patent specification US 4,609,969. This type of protection of a capacitor winding leaves a possibility of capacitor leakage in case its coating is damaged and consequently leads to capacitor breakdown.

The subject of the invention is a method for protecting a capacitor winding made of a metallised plastic film with epoxy resin, wherein the winding is first dried in vacuum at an increased temperature, impregnated with a liquid epoxide and then drained.

The invention will be described in more detail by way of an embodiment and Figure 1 , which shows a cross-section of the capacitor.

The capacitor, the cross-section of which is shown in Figure 1 , has a housing 1 , in which a lower insulation insert 2 and an upper insulation insert 3 are arranged with a capacitor winding 4 therebetween. An electric connection 5, 6 is soldered between soldering spots 8, 11 and coated with insulation 7. The top of the capacitor is closed by a sealing plate 9. A discharge resistance 10 is connected between the soldering spots 8 and 1 1 .

Capacitor windings 4 are protected by a method for protecting a capacitor winding made of a metallised plastic film with epoxy resin of the invention, in that capacitor windings 4 are first arranged into specially prepared baskets adapted to be inserted into impregnation boilers. The windings so arranged are inserted into boilers and hermetically closed. A boiler must withstand high vacuum and be well sealed.

Then follows a method of drying under vacuum. The windings are dried at an increased temperature from 40 to 120 °C until all moisture is removed from the windings and the boiler, which usually takes from 24 to 48 hours. Vacuuming time depends on the size of the boiler and the number of windings contained therein, of the power of vacuum pumps and the level of moisture. Epoxide coating should be previously prepared in a tank in a way to reach the same temperature as the windings, it should not contain any moisture and other not allowed admixtures.

Epoxide coating thus prepared is slowly poured into the boiler containing the windings, until it reaches approx. 5 cm above the windings. The windings thus immersed are vacuumed for a couple of hours, thereafter air is let into the boiler, the coating is pumped into the tank, the boiler is opened and the basket with impregnated windings lifted and drained for 1 hour.

Polymerisation of the epoxide that remains on the capacitor windings 4 is carried out in ovens at a temperature exceeding 100 ⁰ C until the epoxide hardens.

The capacitor windings 4 thus treated are conventionally hermetically closed. The method for protecting a capacitor winding made of a metallised plastic film with epoxy resin of the invention successfully solves the set technical problem and provides for a possibility to extrude air from the front sides of the winding thus preventing moisture from getting between the windings and oxidation of the thin metallised layer sensitive to the presence of oxygen and moisture. Moreover, the number of partial discharges is smaller, which prevents the capacitor from losing its capacitance in its life span.