GB2050069A - Tanks for use in liquid filled electric apparatus - Google Patents

Abstract

A tank for use in liquid filled transformer or reactor comprises a pair of substantially parallel flat side plates 1a, a pair of substantially semi-circular end plates 1b connected to respective ends of the side walls, and reinforcing members, which may be in the form of gas chambers or beams, having end portions 10 connected to the tank near the joints between the flat side plates and the semi-circular end plates and disposed to be tangential to the end plates. This construction decreases the stress at the joints thus making it possible to decrease the thickness of the tank plate. <IMAGE>

Description

SPECIFICATION Tanks for use in liquid filled electric apparatus This invention relates to oil filled electric apparatus, such as transformers and reactors, more particularly tanks adapted to contain such electric apparatus. Although various insulating liquids such as mineral oil, chlorinated diphenyl, etc., are used, since mineral oil is used in most cases, the term oil is used herein to include all of these known insulating liquids.

In an oil filled electric apparatus, for example a transformer, for the purpose of ensuring high insulating strength it is the usual practice to firstly dry the transformer in air, dispose the transformer thus dried in a tank and then pour oil under vacuum into the tank to completely impregnate the oil into the insulators of the transformer.

In a large capacity transformer, as large bushings and radiators are mounted on the tank, the overall size of the transformer increases, so that aforementioned practice is preferred. Accordingly, reinforcing beams are secured to the side plates of the tank by welding so as to make the tank to withstand against vacuum.

Where nitrogen gas is filled in the space above the oil for preventing deterioration thereof it is necessary to provide a gas chamber for preventing the internal pressure of the tank from exceeding a permissible level caused by the rise in temperature of the transformer itself and of the ambient air. Such gas chamber is generally provided beneath the tank cover, but in a certain case, for the purpose of decreasing the height of the transformer and reinforcing the tank gas chamber or chambers also acting as reinforcing members have been used. This construction not only reduces the gas volume above the oil but also reduces the size of the tank and the volume of the oil contained in the tank. Usually, the tank of this construction is generally elliptical, as shown in Figs. 1 through 3.

Thus, the tank comprises substantially parallel flat side plate la, substantially semi-circular end plates 1, an upper flange 2, a bottom plate 3, rectangular box shaped reinforcing members 6 hermetically secured to the side plates 1 and acting as gas chambers 5, and base beams 4. Each box shaped reinforcing member 6 comprises a rectangular frame 7, a flat plate 8 closing one opening of the frame 7, and a plurality of reinforcing plates 9 with one end secured to the inner surface of the flat plate 8 and the other end spaced a little from the outer surface of the side plate 1 a for defining gas passages. Although not shown, the interior of the reinforcing chamber 6 communicates with the gas chamber at the upper portion of the tank by suitable pipes.

When the tank is evacuated, atmospheric pressure is applied to the tank and the reinforcing members or gas chamber 5 as shown by arrows shown in Figs. 3 and 4. More particularly, the same pressure is applied to the side plates 1 a and the plates 8, whereas at the joints between the side plates 1 a and the semi-circular end plates 1, that is near the side frames 7 of the gas chamber 5, the cross-sectional configuration is subjected to pressure change abruptly. Consequently, a large stress a,, concentrates at these joints as shown in Fig. 5.

Accordingly, in order to construct the tank to have a sufficient strength to withstand such high stress, it is necessary to increase the thickness of the plates near the joints in proportion to the stress if the prior art design is to be maintained. This not only increases the cost of the tank but also its weight.

It is preferable to redesign the tank in order to decrease the maximum stress generated in the tank plates by external pressure applied to the tank thus decreasing the plate thickness, weight and cost of manufacturing the same.

According to this invention there is provided a tank for use in a liquid filled electric apparatus of the type comprising a pair of substantially parallel flat side plates, a pair of substantially semi-circular end plates connected to respective ends of the side plates, and reinforcing members secured to the outer surfaces of the flat side plates, the reinforcing members having end portions at a predetermined angle to the side plates connected to the end plates and extending tangentially thereto at the connection points at or near the joints between the flat side plates and the semi-circular end plates. The reinforcing members may take the form of gas chambers or bars or beams. In one example, the end portions of the reinforcing members form side surfaces of gas chambers.In another example, V shaped reinforcing members extending along the lines of the joints between the side plates and the end plates are provided with one leg of the V forming said end portions.

In the accompanying drawings: Figure 1 is a plan view showing a prior art tank; Figure 2 is a side view of the tank shown in Fig. 1; Figures 3 and 4 are partial sectional views of the tank showing a pressure distribution thereof; Figure 5 is a partial sectional view similar to Fig. 4 but showing a stress distribution of the tank; Figure 6 is a top plan view of a tank embodying the invention; Figure 7 is a front view of the tank shown in Fig. 6; Figure 8 is a longitudinal sectional view of the tank taken along a line VIII-VIII shown in Fig. 7; Figure 9 is a partial cross-sectional view taken along a line IX-IX shown in Fig. 7 and showing a pressure distribution of the tank; Figure 10 is a partial sectional view similar to Fig. 9 but showing a stress distribution of the tank; Figure ii is a top plan view showing a modification of this invention;; Figure 12 is a front view showing the tank shown in Fig. 11; Figure 13 is a top plan view of another embodiment of this invention; Figures 14 and 15 are top and side views of a modified tank; and Figure 16 is a transverse sectional view similar to Fig. 8 and showing a modified gas chamber.

A preferred embodiment of the tank of this invention is shown in Figs. 6, 7 and 8 in which members corresponding to those shown in Figs. 1, 2 and 3 are designated by the same reference characters. V shaped reinforcing members 10 are provided on both ends of the side plates 1a. Preferably, each reinforcing member 10 has a length substantially equal that of the side plates 1 a and the facing legs of the members are cut away at 12, the cutaway portion having a length equal to the length of the box shaped reinforcing member 1 3. Thus, the box shaped reinforcing member 1 3 is received in the cut-away portion so that the two reinforcing member 10 constitute the two side walls of the box shaped reinforcing member 1 3. The other legs or side walls 14 of the reinforcing member 10 make an angle o with respect to the plate 8 and one end of each side wall 14 is positioned at a portion of the semi-circular end plate 1 b where the peripheral moment is a minimum. The angle of inclination 0 of the side wall 1 4 represents an angle at which the outer surface of the side plate 14 becomes tangent to the semi-circular plates 1 b where the side wall 1 4 is welded to the tank.

Fig. 9 shows the distribution of pressure applied to the tank when it is evacuated. As shown, the same pressure is applied to the opposite surfaces of the side plates 1 a. Since the side wall 1 4 of the reinforcing member 1 3 is tangential to the semi-circular portion 1 b of the end plate 1 the cross-sectional configuration varies relatively gradually thereby greatly alleviating the concentration of the stess at and near the portion where the side wall merges into the semicircular portion.

Thus, the stress distribution of the tank becomes as shown in Fig. 10, the maximum stress a,,' being decreased to be less than a fraction of that o, of the prior art shown by dotted lines. By extending the reinforcing members 10 beyond the upper and lower ends of the gas chamber, the load acting upon the upper flange 2 and the bottom plate 3 would be shared by the reinforcing members, which further alleviates concentration of the stress at the joints between side walls 14 and semi-circular end plates 1.

Accordingly, it is possible to decrease the thickness of the tank plate thus decreasing the cost and weight of the tank.

In a modification shown in Figs. 11 and 1 2 reinforcing members of simpler construction are used. Thus reinforcing members 20 each comprising a V shaped steel plate are provided at four corners of each box shaped reinforcing member or gas chamber 6. One side of each reinforcing plate 20 is welded to one corner of the reinforcing member 6 and the other side is welded the end plate near to the joint between the side plate 1 a and the semi-circular end plate 1 b to be tangential to the end plate at the weld. Even with this simplified construction it is possible to obtain the same advantageous effect as in the first embodiment.

In a still further simplified embodiment of this invention shown in Fig. 1 3 the box shaped reinforcing member 6 defining gas chamber 5 is provided with side walls 21 which are inclined by an angle fl with respect to its longitudinal surface and the other end of each side wall 21 is welded to to the end plate near the joint between the side plate 1 a and semi-circular end plate 1 b.

In certain cases, outside gas chambers are not used. Even in such a case spaced apart horizontal beam shaped reinforcing members are provided on the outside of the side walls.

With this construction also, on evacuation of the tank, stress concentrates at portions of the tank where both ends of the reinforcing members are connected to the side plates of the tank just in the same manner as shown in Fig.

5. Moreover, when vibrations are applied to the tank in the longitudinal direction (i.e.

parallel to the plates 9) stress peaks appear in the bottom plate near both ends of the beam shaped reinforcing members, whereas when vibrations are applied in the transverse direction, stress peaks appear in the bottom plate 3 near the flat side plates. The maximum stress is inversely proportional to the spacing between the bases 4 (see Figs. 7, 12) and the thickness of the side plate so that even when the acceleration of the vibration is small, when the transformer including mounting means thereof has a natural frequency such that it resonates with the incoming vibration, or when the frequency of the vibrations is high the maximum stress exceeds a permissible value. To withstand against such large stress it is necessary to increase the thickness of the side plates and the bottom plate of the tank.

Figs. 14 and 1 5 show a modification of this invention proposed to solve this problem. As shown in Fig. 15, instead of providing a box shaped reinforcing member (also acting as a gas chamber) as shown in Fig. 7 a plurality of vertically spaced longitudinal (horizontal) reinforcing members 25 (which could be bars but are shown as L shaped beams) are secured to the side plates 1 a of the tank. The reinforcing members 25 have the substantially the same length as the flat side plate. In this embodiment, V shaped reinforcing members 26 are provided at both ends of the reinforcing members 25 with one leg 27 secured to the ends thereof and the other leg 28 inclined by an angle a with respect to the plate 1 a. As before, the outer ends of these legs are welded to the semi-circular end walls 1 to be tangential thereto.

Fig. 1 6 illustrates still another embodiment which is substantially identical to the first embodiment shown in Figs. 6, 7 and 8 except that the upper and lower walls 7a make an angle H2 (rather than 90 as in the case of walls 7) with respect to the wall 1 a. With this construction, the cross-sectional configuration of the gas chamber varies relatively gradually thus alleviating stress concentration.

Claims (7)

1. A tank for use in a liquid filled electric apparatus of the type comprising a pair of substantially parallel flat side plates, a pair of substantially semi-circular end plates connected to respective ends of the side plates, and reinforcing members secured to the outer surfaces of the flat side plates, the reinforcing members having end portions at a predetermined angle to the side plates connected to the end plates and extending tangentially thereto at the connection points at or near the joints between the flat side plates and the semi-circular end plates.

2. The tank according to claim 1 wherein said reinforcing members take the form of rectangular gas tanks, and said tank further comprising V shaped reinforcing members extending along either side of said rectangular gas tanks, one leg of said V shaped reinforcing members being cut away to accommodate said rectangular gas tanks.

3. The tank according to claim 1 wherein said reinforcing members take the form of rectangular gas tanks and said tanks further comprising a plurality of V shaped reinforcing members having a length shorter than the rectangular gas tanks, four of said V shaped reinforcing members being provided at the respective corners of each one of said rectangular gas tanks with one leg secured to the side surfaces of said gas tanks and the other leg connected to said semi-circular end plates to be tangential thereto.

4. The tank according to claim 1 wherein said reinforcing members take the form of substantially rectangular gas tanks with both side walls inclined by said predetermined angle and the ends of said inclined side walls are connected to said semi-circular end plates to be tangential thereto.

5. The tank according to claim 1 wherein said reinforcing members comprises a plurality of laterally spaced bars or beams secured to the outer surfaces of said side plates, and said tank further comprising additional V shaped laterally extending reinforcing members, one leg of said V shaped vertical reinforcing members being secured to the ends of said bars or beams and the other side being inclined with respect to the length of the bars or beams and connected to said semi-circular end plates to be tangential thereto.

6. The tank according to claim 2 wherein upper and lower sides of said gas chamber are inclined by an acute angle with respect to the side plates.

7. The tank according to claim 5 or 6 wherein said V shaped reinforcing members project beyond the upper and lower sides of said gas chamber to reach an upper flange and a bottom plate of the tank.