JPH05135992A - Oil-impregnated capacitor - Google Patents

Abstract

PURPOSE:To improve the properties of an oil-impregnated capacitor wherein a polypropylene film is a dielectric layer. CONSTITUTION:A capacitor element, wherein the dielectric layer is a crosslinked film made by crosslinking roughened biaxial oriented polypropylene film consisting of the copolymer of polypropylene and a nonconjugate diene compound by application of an electron beam, is impregnated with benzil toluene insulating oil. Hereby, long-term stability can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oil filled capacitor.

[0002]

2. Description of the Related Art In an oil-filled capacitor, it has been considered that a biaxially oriented polypropylene film is wound to form a capacitor element, which is impregnated with insulating oil to form an oil-filled capacitor. However, this type of film has a problem in long-term stability of the capacitor because it has a high solubility in, for example, an aromatic insulating oil, is easily swelled, and has a high heat shrinkability.

In order to solve this, it has been attempted to irradiate this kind of film with an electron beam or other actinic rays to crosslink it. However, it cannot be used as a film because it cannot be maintained as a film.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to improve long-term stability characteristics in a capacitor using a biaxially oriented polypropylene film as a dielectric layer.

[0005]

DISCLOSURE OF THE INVENTION The present invention is directed to a capacitor element having a dielectric layer of a roughened biaxially stretched polypropylene film which is made of a copolymer of polypropylene and a non-conjugated diene compound and is crosslinked by electron beam irradiation. In addition, it is characterized by being impregnated with a benzyltoluene-based insulating oil.

[0006]

[Function] A roughened biaxially stretched film made of a copolymer of polypropylene and a non-conjugated diene compound can be crosslinked by irradiation with an electron beam, and this crosslink provides a thermally stable film. .. In addition, it exhibits a characteristic of less swelling with respect to benzyltoluene-based insulating oil used as impregnating oil.

Thermal properties of the film crosslinked as described above (crosslinked film), and benzyltoluene insulating oil (B
Table 1 shows characteristics such as swelling property with respect to T). For comparison, each characteristic of a non-crosslinked film (non-crosslinked film) is also shown. Alkylnaphthalene (A
The swelling amount for N) is also shown for reference. In this table, the amount of swelling is obtained by immersing at 100 ° C. for 24 hours.

[0008]

[Table 1]

The polypropylene used here is at least 95% of isotactic polypropylene.
Those containing more than wt% are preferable. The benzyltoluene-based insulating oil used in the same manner preferably contains benzyltoluene in an amount of 60% by weight or more. This is because this type of benzyltoluene insulating oil has a low viscosity and has little swelling property with respect to the film.

[0010]

Example 1 Surface roughening using a copolymer obtained by copolymerizing polypropylene with a non-conjugated diene compound in an amount of 3 mol% 2
An axially stretched polypropylene film was obtained. This was irradiated with an electron beam of 70 KGy at an accelerating voltage of 200 kV to crosslink.
The obtained film has a gel fraction of 95% and a thickness of 22 μm. A capacitor element having an element width of 200 mm was constructed only from this film.

This capacitor element was impregnated with benzyltoluene insulating oil containing 65% by weight of benzyltoluene and 35% by weight of benzylxylene to obtain an oil-filled capacitor.

Example 2 A capacitor element was constructed under the same conditions as in Example 1, and 62% by weight of benzyltoluene,
A benzyltoluene insulating oil containing 35% by weight of diphenylethane and 3% by weight of others was impregnated to obtain an oil-filled capacitor.

Comparative Example 1 A commercially available roughened biaxially oriented polypropylene film (thickness: 22 μm) was used to construct a capacitor element similar to the above-mentioned example. This was impregnated with alkylnaphthalene to obtain an oil-filled capacitor.

Comparative Example 2 A capacitor element was constructed under the same conditions as in Comparative Example 1 and impregnated with alkyldiphenylethane (aromatic insulating oil) to obtain an oil-filled capacitor.

In the capacitors in the above respective examples, three films are sandwiched between aluminum foil electrodes and wound to form a capacitor element, which is housed in a case and dried under reduced pressure, followed by a predetermined insulating oil. Was impregnated. The capacitance of each capacitor is 10 μF. In addition, tolylene diisocyanate 2 is used to remove water in the insulating oil.
Contains more than weight percent.

1 oil-filled condenser of each of the above examples
Zero units were manufactured, and a test was conducted by applying a voltage 1.6 times the rated voltage at 100 ° C. to obtain the residual rate. The result is shown in FIG.

As is apparent from FIG. 1, none of the capacitors of Examples 1 and 2 broke any capacitors even after 300 days. On the other hand, in Comparative Example 1, 5 units were destroyed in 300 days, and in Comparative Example 2, 3 units were destroyed in 300 days. It can be seen from this that the capacitor according to the present invention has excellent long-term stability.

When the copolymer is crosslinked, ultraviolet rays, γ
Irradiation with rays and electron beams is generally considered. However, in the case of using ultraviolet rays, it is necessary to add a photosensitizer, and this additive lowers the dielectric properties of the film, which is not preferable. The use of γ-rays is not preferable because the dose rate is low and the oxidative deterioration of the polypropylene film is rate-determining rather than the cross-linking and the dielectric properties are deteriorated due to the oxidative deterioration.

On the other hand, in the case of using an electron beam, since the dose rate is high, crosslinking is rate-determining due to oxidative deterioration. Therefore, cross-linking is possible without lowering the dielectric properties of the film. In the present invention, the crosslinking means by electron beam irradiation is selected for this reason.

[0020]

As described above in detail, according to the present invention, it is possible to maintain stability for a long time in an oil-filled capacitor using a roughened biaxially oriented polypropylene film film.

[Brief description of drawings]

FIG. 1 is a test result table showing the remaining rate of a capacitor according to the present invention with respect to the number of heating and charging days.

Claims (1)

[Claims] 1. A benzyltoluene-based insulating oil for a capacitor element having a dielectric layer of a roughened biaxially stretched polypropylene film made of a copolymer of polypropylene and a non-conjugated diene compound and crosslinked by electron beam irradiation. Oil-filled capacitor impregnated with.