JPS59204217A - Transformer - Google Patents

Abstract

PURPOSE:To enhance dielectric strength of a transformer by a method wherein the high-voltage member of the connecting part of a transformer coil and a bushing or a lead-out part from a lead wire is insulatedly constructed completely with oil impregnated paper as not to leave an exposing part. CONSTITUTION:A bushing pocket 2 is expanded on the side of the oil tank 1 of a transformer. A bushing 3 on the air side is fitted thereto, and the inside terminal thereof is connected to a transformer coil arranged in the tank 1 with a high-voltage lead wire 4 covered with an insulator 4'. A high-voltage conductor led in the pocket 2 of the bushing 3 is fixed and insulated by a bushing core 6, and the outside thereof is covered to be insulated with a procelain tube 7 in oil. The under edge of the central high-voltage conductor 5 is connected electrically to the hardware flange of the porcelain tube 7, and moreover a part of the hardware flange is connected to the high-voltage lead wire 4 through a connecting hardware. A shield 12 covered with an insulator is fixed to the hardware flange according to a supporting hardware.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention particularly relates to a transformer for use in DC power transmission equipment with an improved insulation structure.

[Technical background of the invention and its problems] Recently, the development of DC power transmission has been progressing due to its advantages such as low cost of line construction and advantageous for long-distance transmission of long-distance power. This DC power transmission equipment includes a transformer, and conventionally, many DC power transmission transformers have an oil-filled insulated structure. The oil-filled insulated structure is designed based on AC power transmission transformers, while solving the insulation problems unique to DC power transmission transformers.

However, in recent years, there has been an increase in DC transmission voltage and power transmission capacity, and in order to cope with these problems, high-voltage, large-capacity transformers have been developed in DC power transmission transformers. It is being considered. In this case, one of the five major problems that has attracted attention is the problem of DC withstand voltage as the voltage increases.

As is well known, the voltage distribution of DC voltage is determined by the resistance of the material. This results in a large difference in voltage distribution compared to cases where the voltage distribution is determined by the dielectric constant of the material, such as AC side pressure.

In addition, when looking at the strength of materials, oil is extremely weak compared to oil-impregnated paper in the case of DC voltage. On the other hand, in the case of alternating current, the oil and oil-impregnated paper are only about the same, with the oil-impregnated paper showing slightly stronger characteristics. The DC withstand pressure of oil is lower than the AC withstand pressure, and the DC withstand pressure of oil-impregnated paper is several times the AC withstand pressure. For this reason, DC insulation structures that take advantage of the characteristics of insulating materials and potential distribution have been devised and put into practical use.

However, the insulation structure of an AC power transmission transformer, which does not pose any problems, may become a problem in a DC power transmission transformer. This can be seen in the exposed part of the metal system on the high pressure side. For example, it is a connection part between a transformer coil and a bushing, or a lead wire extraction part from a transformer coil.

In these parts, the high-pressure part is usually exposed or nearly exposed. Model tests have shown that poor insulation in these areas is often a problem.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a transformer suitable for direct current power transmission, which has excellent direct current withstand voltage, is highly practical, and has a simple improvement in insulation structure.

[Summary of the Invention] The transformer of the present invention is completely insulated with oil-impregnated paper so that there are no exposed parts of high-voltage members such as the connection part between the transformer coil and the bushing or the lead-out part from the lead wire. It is characterized by:

[Embodiments of the invention]

The present invention will be described below with reference to an embodiment shown in FIG. A bushing pocket 2 is bulged out on the side of an oil tank 1 of the transformer. An air-side bushing 3 is attached to this bushing pocket 2, and its internal terminal is connected to a transformer coil (not shown) disposed inside the tank 1 using a high-voltage lead wire 4 covered with an insulator 4'.

The high voltage conductor 5 led out into the pocket 2 of the bushing 3 is fixed and insulated by a bushing core 6, as shown in FIG. The lower end of the central high voltage conductor 5 is electrically connected to a metal flange 8 of the insulator tube 7, and a part of the metal flange 8 is further connected to the high voltage lead wire 4 via a connecting metal 9. Further, a shield 12 covered with an insulator 12' is attached to the metal flange 8 by means of a supporting metal 10.

The present invention is characterized by the insulating structure of the hardware flange 8, the connection hardware 9, and the support hardware 10.

That is, after the terminal of the metal flange 8 of the bushing 3 and the high voltage lead wire 4 are connected via the connection part 9, the outer periphery is insulated with an insulator 11 wrapped with oil-impregnated paper, and then the shield support metal piece is connected. It is also insulated with an insulator 12. With this delivery configuration, the hardware 7, the flange 8, the connection 9 and the support hardware 1
The exposed portion of 0 can be completely eliminated. Next, regarding the connection end portion (3) of the bushing 3 to the metal flange 8 of the high voltage conductor 5, it is extremely difficult to eliminate any exposed portion in this portion L3. However, this exposed portion of the connection end portion L3 is solved by forming the cylindrical portion 14 on the oil-impregnated paper insulator 1 and wrapping it a distance 1.

If the high voltage section is insulated with oil-impregnated paper to an appropriate thickness as in the present invention, there will be no problem with DC voltage since the DC withstand voltage of oil-impregnated paper is extremely higher than that of oil. The problem is the high-voltage conductor 5 of the bushing 3, which is extremely difficult to assemble from the viewpoint of assembly technology.
The connection end part should be treated with 13-karat gold or more.

Therefore, Fig. 3 shows the change in the maximum electric field strength of the high voltage conductor exposed portion, determined in order to appropriately determine the insulation of the high voltage conductor exposed portion such as the connection end portion 13, depending on the wrap length ratio 1;/L. . Note that the parameter was t/T. Here, l is the wrap length from bushing flange 8, and L is flange 8.
t is the insulation thickness at the part to be wrapped and insulated, and T is the insulation thickness at the lowest part of the bushing high voltage conductor.

In this way, as shown in Fig. 3, any insulation thickness t/
Also at T, the wrap length t! When B is increased, the maximum electric field strength E in oil at the exposed part is greatly reduced. The thinner the insulation thickness of the wrap portion is, the more practical it is, but the thinner the insulation thickness, the larger the wrap length l needs to be. In this case, the practical insulation thickness is t/T=0.25~t, /'l'=
This figure shows how the electric field strength E changes with respect to l. The question is how to determine the insulation thickness and wrap length.
When the allowable electric field strength E of oil is taken as a reference, the broken line in FIG. 3 shows the allowable electric field strength of this oil. Based on this, the wrap length when t/T=l is approximately 30
Person in charge.

t/T=o, so) case 0) 77 F length C approx. 40%
, t/'1' = 0.25 U), the wrap length is approximately 7
It becomes 0%.

〔Effect of the invention〕

As described above, according to the present invention, by insulating high voltage exposed parts with oil-impregnated paper and providing wrap parts in parts where insulation is technically difficult, It is possible to construct an insulation structure with double the insulation strength.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the bushing pocket portion of the transformer according to the present invention, Fig. 2 is an enlarged sectional view showing the high voltage conductor connection portion of the bushing, and Fig. 3 is the maximum electric field strength at the exposed high voltage conductor portion. FIG. 3 is a characteristic diagram showing the relationship with insulator wrap length. l...Transformer oil tank 2...Bushing pocket 3...Pneumatic bushing 4...High voltage lead wire 5.
...High voltage conductor 6...Bushing core 7...
Oil submerged pipe 8...Bushing hardware flange 9
...Connection hardware 10...Shield support hardware 12...Shield [[...Oil-immersed paper insulator 1]
3... High voltage conductor connection terminal 14... Wrap cylinder part (873
3) Representative patent attorney Yoshiaki Inomata (and one other person)
Figure 1 Figure 2

Claims (1)

[Claims:] A transformer characterized in that the insulation is reinforced by a wrapped cylinder formed of an oil-immersed low-insulating material. (2) At the connection point between the high-voltage conductor of the air bushing installed in the bushing pocket and the insulated high-voltage lead wire led out from the transformer coil, the high-voltage conductor inside the bushing is insulated with a bushing cone and then placed in an oil-submerged insulated pipe. The end of the insulated pipe is connected to the metal fitting 7 flange that closes the insulated pipe, and the terminal of that flange is connected to the high voltage lead wire via the connecting metal fitting. Further, a wrap cylinder portion is formed on the oil-immersed low insulating material on the outer surface of the oil-submerged insulator tube to insulate and reinforce the exposed island voltage portion between the end of the high voltage conductor and the flange of the metal fitting 7. A transformer according to claim 1, characterized in that: (3) The wrap cylinder part that insulates and reinforces the high voltage exposed part is i/
If T=1, l/L≧03 or more t/T=0.5
In the case of l/L≧04 or more t/T=o, in the case of zs, c e
/L 20.7 or more However, t is the insulation thickness of the wrap cylinder part,
The transformer according to claim 2, wherein T is the insulation thickness at the lowest end of the high voltage conductor of the bushing, e is the wrap length from the metal flange, and L is the length of the bushing on the oil side. .