JPH0137818B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a direct current oil bushing with high withstand voltage.

(2) Prior art and its problems Bushings used in high-voltage electrical equipment are
Generally used under AC voltage. The bushing used under this AC voltage is provided with a core 2 in which a potential control conductor is concentrically wound around a center conductor 1, and the outer periphery of the core 2 is surrounded by an insulator tube 3.
It was covered by And this insulator 3
Insulating oil 4 is filled between the core 2 and the core 2 .
The insulator tube 3 is composed of an insulator tube 5 and an insulator tube 6, and a conservator 7 is provided above the insulator tube 5 to cope with expansion and contraction of the insulating oil 4.
On the other hand, a support fitting 8 is provided at the lower part of the oil-submerged insulating tube 6, and a paper insulation shield 9 is provided at the tip thereof for controlling the potential distribution along the oil-submerged insulating tube.

A mounting flange 10 is provided between the submerged insulating pipe 5 and the oil submerged insulating pipe 6, and the bushing is fixed to the wall of the tank 11 filled with insulating oil in a penetrating state by this mounting flange 9. ing.

Bushings with such a configuration have been put into practical use with the shapes of the capacitor core, insulator tube, etc. determined so that they can be used under alternating current voltage. However, in recent years,
As DC power transmission has become more practical, converter transformers and bushings for smoothing reactors have come to be used even under DC.

By the way, in general, AC voltage is distributed according to the inverse ratio of the dielectric constant of the material, whereas DC voltage is distributed according to the resistance ratio of the material. Since the bushing is also an insulating structure having a creeping surface, a difference in potential distribution occurs when it is used under an AC voltage and when it is used under a DC voltage.

For example, when a DC voltage is applied to a conventional bushing, as shown in Figure 2, the insulation resistance of the paper insulation shield 9 is higher than that of the insulating oil, so the paper insulation shield 9 has a potential of 50% or more. There is concentration. As a result, the paper insulation shield 9 cannot exhibit a sufficient insulation effect, and the insulation between the bushing and the tank is reduced.
Further, if the potential is concentrated in only one part of the paper insulation shield 9 as described above, there is a disadvantage that it is not desirable in terms of insulation coordination with other parts. Furthermore, in order to eliminate such drawbacks, attempts have been made to attach and add an insulating material such as a barrier around the shield, and to improve the potential distribution by devising the mounting arrangement. This has the disadvantage that the structure becomes complicated, the assembly work is troublesome, and the size of the lower part of the bushing becomes large.

(3) Purpose of the Invention The present invention was proposed in order to improve the conventional oil bushing as described above. To provide a direct current oil bushing that has a simple structure, is easy to assemble, and is downsized.

(4) Structure of the Invention The present invention will now be specifically explained based on the embodiment shown in FIG.

The structure of the bushing is the same as that of the conventional type, and consists of a center conductor, an insulating tube, an insulated tube, and a conservator, and the bushing is fixed to an insulating oil tank by a mounting flange. A shield 20 is attached to the lower part of the oil-submerged pipe 6 in this bushing via a support fitting 8. The material forming this shield is composed of feldspathic ordinary porcelain, cristobalite porcelain, and alumina-containing porcelain, each having a volume resistivity of about 10 ⁹ to ^{10 13} Ωcm, which is comparable to that of insulating oil. In addition, this shield is not limited to porcelain, but can be made of any material that has the same resistance as insulating oil, such as epoxy resin filled with silicone, epoxy resin mixed with carbon, polyethylene, or carbon paper. It may be configured as follows.

(5) Effects of the invention As described above, since the bushing of the present invention uses a material having a volume resistivity of 10 ⁹ to ^{10 13} Ωcm as a shield, when a paper insulation shield with high insulation and low resistance is used. There is no potential concentration near the shield as shown in Figure 3, and the potential distribution is evenly distributed along the bushing insulator tube as shown by the dotted line in Figure 3. As a result of the potential distribution becoming even,
The insulation effect of the shield is improved, and the insulation coordination is also improved, so that an improvement in DC withstand voltage is achieved. Furthermore, since there is no need to attach or add another insulator, the structure is simple, assembly is easy, and the device can be made smaller.

[Brief explanation of drawings]

Figure 1 is a perspective view of a conventional oil bushing, Figure 2 is a perspective view of a conventional oil bushing.
The figure is an enlarged perspective view of the lower part showing the potential distribution of a conventional oil bushing, and FIG. 3 is an enlarged perspective view of the lower part of the potential distribution of the DC oil bushing of the present invention. 1...Center conductor, 2...Core, 3...Insulator tube, 4
...Insulating oil, 5...Air insulator, 6...Oil insulator,
7...Conservator, 8...Supporting metal fittings, 9...Paper insulation shield, 10...Mounting flange, 11...
Tank, 20...shield.

Claims (1)

[Claims] 1. An oil bushing for direct current, characterized in that a shield made of a material having a volume resistivity of 10 ⁹ to ^{10 13} Ω·cm is provided at the lower part of the oil-filled insulating pipe.