JPS6259881B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to stationary induction electric appliances such as transformers and reactors, and particularly to a bushing fixing device suitable for rectifier transformers and low-voltage, large-current, short-time rated transformers.

In a conventional stationary induction electric appliance, as shown in FIG. 1, the bushing 1 is attached to the cover 3 or side wall of a tank, which is a container that houses the electric appliance (not shown) and is filled with insulating oil, by means of mounting bolts 2. The cover 3 is mounted on an annular mounting seat 4 fixed to the cover 3 or the side wall thereof. Note that 5 is the center conductor of the bushing 1.

Incidentally, the factors that determine the size of such bushings include insulation class, rated current, and mechanical strength. In particular, mechanical strength is an important factor in bushings used in transformers with low voltage, high current, and short-time ratings. This is because it is the short circuit current that determines the mechanical strength, and it is determined by the following formula.

I _s = I × 100 / V _z × 2.55 (A) ………(1) I _s : Short circuit current I : Rated current V _z : Percentage impedance voltage The magnitude of the rated current and the percentage impedance voltage are determined by the above formula (1). The short-circuit current I _s is determined by this, and is said to be about 10 times the normal rated current.
In addition, the force acting on the bushing can be calculated using the following formula.

F=2.05×k×I ² _s /L×10 ^-8 (Kg/m)
......(2) F: Force acting on the conductor k: Experimental coefficient I _s : Short circuit current L: Center-to-center distance with adjacent phase bushings According to the above equation (2), the force acting on the conductor is the short circuit current I _s
The larger the short circuit current I _s is, the larger the force F acting on the conductor becomes, and the strength of the bushing needs to be increased accordingly. The only way to increase the strength of the bushing alone is to increase the diameter of the center conductor. This is because the strength of the center conductor is determined by the following formula.

σ=M/Z, Z=π/32×D ³ σ: Stress in the conductor M: Bending moment generated in the conductor Z: Section modulus of the conductor D: Diameter of the conductor Because of the above, it is used in short-time rated transformers, etc. Since the size of short-time rated bushings is determined by mechanical strength, the bushing itself cannot help but be large. This means that not only does the bushing itself become expensive, but also that the phase-to-phase distance dimension _L1 of the bushing becomes large.Especially in the case of a three-phase transformer with a split winding, as the number of bushings increases to 6 or 12, the distance on the cover increases. The space becomes larger than necessary, and the size of the tank cannot be determined solely by the transformer itself. This means that the transformer as a whole becomes larger, and with the recent rise in land prices, the space of the entire device becomes wider, which is very disadvantageous from the perspective of capital investment.

SUMMARY OF THE INVENTION An object of the present invention is to provide a stationary induction electric appliance which eliminates the above-mentioned drawbacks of the prior art, and which has a simple structure and can reduce the size and weight of the bushing itself.

In order to achieve this object, the present invention fixes the center conductor of the bushing directly to the container via an insulating fixing member, and transfers the mechanical force generated in each bushing directly to the side metal fittings through the divided insulating fixing member. It is characterized by being made to take charge.

An embodiment of the present invention will be described below with reference to FIG. In FIG. 2, the same reference numerals as in FIG. 1 indicate the same or equivalent components.

In this embodiment, six insulating fixed piece mounting seats 6 and four side fittings 7 that receive the repulsive force of the center conductor 5 are fixed by welding between each bushing phase and at both ends on the inner surface of the tank cover 3. Six insulating fixing pieces 8, each having one end surface forming an arcuate surface along the outer circumferential surface of the center conductor 5 and the other end surface forming a flat surface that abuts the side metal fitting 7, are attached to the insulating fixing piece mounting seat 6 by mounting bolts 9, respectively. It is screwed on.

Therefore, according to this embodiment, each insulating fixing piece 8 directly receives the mechanical force generated between the bushings in the event of a short circuit, and the mechanical force is transmitted to the cover 3 via the side metal fitting 7, so that the size of the bushing is determined. Among the elements, the condition of mechanical strength can be excluded, and the diameter D ₂ of the center conductor 5 can be designed with the diameter of the required current density.

Although it varies depending on the specifications of the transformer, in general, for short-time rated transformers, the short-time rated current can be considered to be about 1/6 to 1/10 when converted to continuous current, and the diameter of the center conductor D ₂ can be set to D ₂ <D ₁ by the amount of decrease in current density compared to the diameter D ₁ of the center conductor of the bushing of the conventional structure shown in FIG.

From the above, the bushing of this embodiment can be made smaller than the bushing of the conventional structure, and the price of the bushing itself can also be reduced. Furthermore, by reducing the size of the bushing, the distance between the bushings can be set to L ₂ <L ₁ , and the size of the transformer tank can be reduced to make the transformer, that is, the entire device, more compact.

Further, the present invention is not limited to short-time rated oil-immersed transformers, but can be widely applied to other stationary induction electric appliances such as dry type transformers and molded transformers.

As explained above, according to the present invention, the bushing itself can be designed to be small, and the space for installing the bushing can also be reduced accordingly. As a result, it becomes possible to reduce the size and weight of the entire electrical appliance. Moreover, the reliability of the mechanical strength of the bushing is not impaired.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the vicinity of the bushing attachment part in a conventional transformer, and FIG. 2 is a sectional view of the vicinity of the bushing attachment part of a transformer according to an embodiment of the present invention. 1...butsuthing, 3...tank cover, 5...
...Center conductor, 6...Mounting seat, 7...Side metal fittings,
8...Insulating fixing piece.

Claims (1)

[Claims] 1. In a case in which a container housing an electrical appliance body and bushings having a center conductor passing through the container are separately attached, the inner surface of the container is provided with a spacer that opposes each bushing at a predetermined distance. A stationary induction electric appliance, characterized in that side metal fittings are fixed to the container, and the center conductor of each bushing is supported via an insulating fixing piece arranged between the side metal fittings and fixed to the container.