JPS6160523B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the insulation structure of a molded bushing used in the so-called medium voltage class of 3 to 30 KV class.

Molded bushings cover the core conductor with an insulating material such as epoxy resin or phenolic resin, and a mounting part is provided in the center of the insulator, and this mounting part is used to attach and support electrical equipment or install it through walls, etc. Used for wire insulation. Since this type of insulation structure has a typical rear creeping insulation configuration, there is a problem that the withstand voltage characteristics, partial discharge characteristics, etc. are lower than that of general insulation supports. Therefore, as shown in FIG. 1, an intermediate electrode 4 for mitigating the electric field is provided between the core conductor 1, the insulator 2, and the mounting ground portion 3 to solve the above-mentioned problem.

However, this method of providing the intermediate electrode 4 has the following problems in the manufacturing process. In other words, since the intermediate electrode 4 is provided in the intermediate layer of the insulating material, when manufactured by casting, the center of the intermediate electrode 4 tends to run out.To prevent this, the intermediate electrode 4 is cast in advance and then the main body is formed. Casting, that is, two-stage casting, is performed, but since the casting process requires a long curing time before being removed from the mold, workability is poor in two-stage casting. On the other hand, when manufacturing by molding, a sheet-like material impregnated with insulating resin is wrapped around a core conductor and molded by heating and pressure, so the curing time is significantly shortened compared to the above-mentioned casting method. Workability improves, but
The adhesive strength at the interface between the intermediate electrode and the resin is weak, and if used in areas where mechanical impact is applied, such as in the bushing of a heat exchanger, partial peeling may occur, resulting in the occurrence of partial discharge. It may also be the cause. As described above, the methods of providing the intermediate electrode 4 in the insulating layer for both cast and molded products have their advantages and disadvantages.

In addition, both epoxy resins and phenolic resins are organic insulators whose main component is carbon, so if they are used in a dirty or humid environment, tracking will deteriorate due to leakage current flowing through the surface (carbonized conductivity due to heat). ) may occur, leading to dielectric breakdown.

The object of the present invention is to provide a bushing with a rear creeping insulation structure cast using epoxy resin, phenolic resin, etc., without providing an intermediate electrode for mitigating the electric field in the insulation layer, and to improve withstand voltage and partial discharge characteristics. In addition, the present invention provides a bushing with improved anti-tracking and anti-fouling properties.

The present invention will be explained below based on an embodiment shown in FIG. In FIG. 2, the core conductor 1 and the insulator 2 are the same as those of the conventional one described above, but in the present invention, the surface of the insulator 2 is coated with a semiconductor resistance paint 5 for mitigating the electric field. It has a structure that covers a water-repellent heat-shrinkable insulating tube 6. The semiconductor resistance paint 5 used was a mixture of oil-based varnish as a main component, to which silicon and carbide were added, in a weight ratio of about 6:4. This weight ratio mixture has excellent adhesion to epoxy resin, etc., and its surface resistivity is 10 ⁸ ~
It was found that the value is in the range of 10 ¹⁰ Ω-cm, which is a preferable value for the structure of the present invention.

In other words, the surface resistivity of epoxy resin etc. is 10 ¹⁵ Ω−
Because it is so high (more than cm), a charge remains on the surface and causes disturbances in the electric field. Particularly in the rear creeping structure, the capacitance of the insulating layer is large, so it is easily affected by this surface charge. However, when the semiconductor resistance paint 5 is applied to the surface as in the present invention, the surface resistance is reduced, so that the electric field in the length direction is shared by the resistance, and local electric field concentration is alleviated. Furthermore, if the resistance value of the semiconductor resistive paint 5 is too low, leakage current will flow at the normal operating voltage, causing problems such as tracking deterioration. Therefore, a resistance value in the range of 10 ⁸ to ^{10 10} Ω-cm is preferable for normal ground voltage, and when a surge overvoltage is applied, its resistance characteristics become nonlinear because it is a semiconductor resistance paint. Since the electric field is further reduced, the electric field in the length direction exhibits resistance sharing characteristics, and the withstand voltage is improved as shown by curve A in FIG. Note that the B curve is the characteristic when the semiconductor resistance paint 5 is not applied. According to the present invention, the creepage distance can be significantly reduced relative to the target withstand voltage.

If the creepage distance is reduced as described above, the resistance value will be much lower than that of the semiconductor resistive paint 5 when used in special environments where it is subject to contamination and moisture. If the tube is coated with a heat-shrinkable insulating tube 6 (for example, Futsuso-based resin) that exhibits a heat-shrinkable insulation tube 6, it will exhibit strong water repellency even when exposed to dirt and moisture, so water droplets will be separated and a conductive film will not be formed due to dirt and moisture. . As shown in FIG. 4, this result shows that the property of the present invention is A compared to the conventional stain resistance property B.
The results showed marked improvement as shown in the curve.

With the insulating structure of the present invention described above, there is no intermediate electrode for mitigating the electric field in the insulating layer, so the withstand voltage and partial discharge characteristics are improved, and the insulation dimensions on the rear creeping surface are reduced, resulting in miniaturization. Not only can it improve tracking resistance and stain resistance voltage characteristics, which are disadvantages of organic insulators, but it can also improve mechanical strength, making it possible to provide bushings with excellent properties.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a bushing made of a conventional cast product and a molded product, Fig. 2 is a cross-sectional view of an embodiment according to the present invention, and Fig. 3 is a comparative characteristic of withstand voltage with respect to creepage distance between the present invention and the conventional one. 4 are comparative characteristic diagrams of the contamination withstand voltage with respect to the amount of contamination deposited between the present invention and the conventional method. 1... Core conductor, 2... Insulator, 3... Mounting grounding part, 4... Intermediate electrode, 5... Semiconductor resistance paint,
6... Water-repellent insulating tube, A... Characteristics according to the present invention, B... Conventional characteristics.

Claims (1)

[Claims] 1. A rear creeping insulation bushing in which a core conductor is molded with an insulator, characterized in that a semiconductor resistance paint is applied to the surface of the insulator, and the surface is further coated with a water-repellent heat-shrinkable insulating tube. Butsing.