JPH038091B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an oil immersion capacitor using only a plastic film as a dielectric, and an object of the present invention is to provide an oil immersion capacitor with a high composite dielectric constant and extremely low dielectric loss (tan δ). A capacitor element using only plastic film as a dielectric is shown in FIG. In the figure, 1 is an electrode such as aluminum foil, and 2 is a plastic film. Such a capacitor element is impregnated with insulating oil to form an oil-immersed capacitor. Conventionally, in order to improve impregnability and corona discharge characteristics, the surface of a plastic film has been roughened by 10 to 40% of the film thickness, or plastic powder or fibers have been coated on the surface of the plastic film to the same thickness as the film. There are examples (Japanese Patent Publication No. 46-13227, etc.) using a film spread at a thickness of 1/100 to 1 times the thickness of the film. In all of these examples, the effective surface unevenness is less than 50% of the effective film thickness, or the capacitor uses a film that has a surface condition with a peak frequency of 50 or more per cm. This is an example. It is true that the capacitor's impregnability and corona discharge characteristics can be greatly improved by roughening up to 50% of the film thickness, but the present inventors have found that the degree of roughening is even greater. While researching oil-immersed capacitors using plastic film with extremely low peak frequency, we discovered that a capacitor with extremely low dielectric loss (tan δ) and a high composite dielectric constant could be obtained. The plastic film used in the present invention has at least one surface roughened, and the maximum height of the surface roughness of at least one of the surfaces (measured according to JIS B0601) is the withstand voltage of the capacitor. For this reason, 51 to 90% of the film thickness is required, and as for the peak frequency, if the peak frequency is too small, new problems regarding impregnability will arise, so 5 to 49 per cm is required.
In this case, the film thickness shall be measured by the JIS-C2318 micrometer method, and the peak frequency shall be counted as the peak having a height of 1/2 or more of the maximum height of the surface roughness. Further, the plastic film used in the present invention preferably has a thickness of 3 μm to 50 μm. Next, the present invention will be specifically explained using Examples. Example As shown in Figure 2, three polypropylene films 4 with one side roughened were sandwiched and wound between a pair of aluminum foil electrodes 3, and impregnated with various insulating oils shown in Table 1 below. As a result, a capacitor with a capacitance of 2μF (rated voltage 2200V) was obtained. The capacitance C and dielectric loss (tan δ) of these capacitors at 20℃,
It was measured at 2200V and the composite dielectric constant ε was calculated. A Schering bridge was used for this measurement.

[Table] For comparison, the following Table 2 shows the characteristics when a conventional film is used as a comparative example.

【table】

[Table] When comparing capacitors using the same insulating oil, it can be seen that there is a significant difference in tanδ. The composite dielectric constant of the present invention is also excellent. Furthermore, an example of the cross-sectional curve of the film used here is shown in FIGS. 3A to 3D. A is the cross-sectional curve of the film used in sample No. 2, B is the cross-sectional curve of the film used in sample No. 3, C is the cross-sectional curve of the film used in sample No. 5, and D is a comparison of sample No. 11. This is a cross-sectional curve of the conventional film used in the example. FIG. 4 shows the tan δ voltage characteristic (curve A) of the capacitor of sample No. 2 in comparison with the same characteristic (curve B) of the capacitor of sample No. 12. The phenomenon in which the tan δ of a capacitor decreases as the voltage increases is well known as the Galton effect, but the capacitor of the present invention has a structure that makes it easy for this Galton effect to take effect.
It is considered that tan δ is extremely low. In the above example, three polypropylene films with one side roughened to a specified roughness were used, but even polypropylene films with roughened surfaces on both sides can be used as a dielectric. It may be something that has been rotated. Regarding the electrodes, it goes without saying that the pair of electrodes may not have the same width, or may have the electrode ends bent. Furthermore, the plastic film used may be a film of polystyrene, polyethylene, polyethylene terephthalate, polyester, etc. in addition to polypropylene film. As described above, according to the present invention, a capacitor with a small tan δ can be obtained no matter what type of insulating oil is used, and a capacitor structure with a high composite permittivity is provided, which is very useful. .

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of a capacitor element in an oil-immersed capacitor, FIG. 2 is a cross-sectional view of an embodiment of a capacitor element used in an oil-immersed capacitor according to the present invention before winding, and FIG. , B, and C are cross-sectional curve diagrams of the polypropylene film used in the oil-immersed capacitor of the present invention, FIG. 3 D is a cross-sectional curve diagram of the polypropylene film used in the conventional oil-immersed capacitor, and FIG. - It is a voltage characteristic diagram. 3... Electrode, 4... Plastic film (polypropylene film).

Claims (1)

[Claims] 1 At least one surface is roughened, and the maximum height of the surface roughness is 51 to 90% of the film thickness.
An oil-immersed capacitor characterized in that a capacitor element constructed using only plastic film as a dielectric material and having a peak frequency of 5 to 49 per cm is impregnated with insulating oil.