A transformer tank is designed to house a transformer electrical core and coils. Conventional tanks are formed in the shape of a rectangular cube and comprise four vertical side walls, a horizontal top wall and a horizontal bottom wall and in the case of a pole-mounted electrical distribution transformer, two pole hangers supporting the tank are fixed at the bottom and back wall. During assembly, five of those walls would be pre-assembled together by welding leaving an opening to permit subsequent insertion of the core and coil assembly.

After the open structure has been leak tested, the transformer core and coil would be placed inside the tank through the open top. Then utilising holes formed in the back plate, the electrical connections are made and the appropriate accessories are installed. The tank will then be filled with oil to the prescribed level. The top wall, substantially flat or domes, is placed on flanges formed by bent-out upper ends of the side panels and welded or bolted in place. The tank will then be coated with a corrosion resistant film.

The corrosion resistant film eventually deteriorates and the transformer tank is at risk of developing a leak, spilling oil on to the area below (in the case of a pole-mounted transformer) and causing the transformer to overheat, catch fire and/or fail. In coastal areas, this can occur in as little as four years and fifteen years in more sheltered inland areas.

OBJECT OF THE INVENTION The invention described herein provides a transformer tank and a method of making same, which will overcome or at least obviate problems in transformer tanks to the present time, or at least to provide the public with a useful choice.

SUMMARY OF THE INVENTION In broad terms the invention may be said to comprise a transformer tank comprising front, bottom and back plates formed integrally by bending a single sheet of a light weight metal (which term including any alloy thereof) and with side plates secured to said front, bottom and back plates and/or a method of forming said transformer tank.

Preferably, a top plate that is adapted to accommodate high- voltage electrical connectors is provided.

Preferably, said top plate accommodates said high-voltage electrical connectors such that they are positioned not on a central axis of said top plate.

Preferably, said front and back plates are bent inwards to form flanges.

Preferably, said side plates are bent outwards near their top edge to form flanges and outwards near their bottom end to form feet.

Preferably, said side plates are adapted to accommodate hanger means to secure a tank to a pole.

Preferably, the hanger means are formed into a required shape.

According to a further aspect of the present invention, a transformer tank is substantially as herein described with reference to the accompanying drawings.

According to a further aspect of the present invention, a method of forming a transformer tank includes providing a single sheet of a light weight metal (which term including any alloy thereof) and bending same so as to form the front, bottom and back plates of the tank, said method further including the fixing to the front, bottom and back plates of side plates.

Preferably, a method of forming a transformer tank as immediately above defined includes forming apertures in said side plates so that said apertures can accommodate low voltage electrical connectors.

Preferably, the method as defined two paragraphs above includes forming a top plate of required dimensions and forming apertures to accommodate high voltage connectors not on a central axis of said top plate.

Preferably, the method as defined three paragraphs above includes aluminium as the metal.

According to a further aspect of the present invention, a method of forming a transformer tank is defined substantially as herein described with reference to the accompanying drawings.

Further aspects of this invention which should be considered in all its novel aspects will become apparent from the following description

given by way of example of possible embodiments thereof and in which reference is made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fiqures 1 a-f : show the basic components of a transformer tank according to one possible embodiment of the invention; Figures 2a & 2b: show rear and front views of a pole hanger for use in one embodiment of the invention; Fiqures 3a-d: show respectively top, rear, left side and front views of a transformer tank according to one possible embodiment of the invention.

BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Referring firstly to Figures 3 of the accompanying drawings, a transformer tank for an oil-filled pole-mounted electrical distribution transformer according to one possible embodiment of the invention is referenced generally by arrow 1. It is shown provided with low voltage connections or bushings 4 secured to the side plates 2 and high voltage connections or bushings 10 secured to the top plate. The pole hanger brackets 5 are shown secured to the side plates 2 and in Figure 3c are shown mounted over a cross-arm 20 of a power pole. As shown particularly in Figure 2, the pole hanger brackets 5 are each in the form of an inverted U-shape, but as seen particularly in Figure 2b, flat sections 21 and 22 may be added so as to spread the load-bearing surface on the cross-arm 20 and at least reduce the biting that would otherwise occur due to the"U"being on its edge and to also retain the ability of the pole

hanger 5 to be bolted to the cross-arm as with some conventional pole hangers. It will be seen that the flat section 21 has an aperture 23 for that purpose. Preferably, the pole hangers 5 are profile-cut from aluminium alloy sheet to eliminate the bending which is required for conventional pole hangers and to avoid the deterioration of the material strength which bending introduces and to also reduce the thickness required to carry the transformer's weight. The material of the pole hanger 5 may preferably be an aluminium alloy so as to be compatible with an aluminium alloy which may be used for the main tank 1 and to avoid electro-chemical or bimetallic problems due to the use of non- compatible materials. The aluminium alloy for the pole hangers 5 will of course be of a strength commensurate with that required for the particular transformer specification and in particular the weight of the transformer.

Returning to Figures 3, it will be seen that the present invention, particularly from Figure 3a, enables the transformer tank 1 to be suspended very close to the power pole and by the reduction of the distance between the centres of gravity, which could be of the order of 25%, an additional safety factor is achieved, especially important where the pole-mounted transformer is positioned in a pedestrian area.

Figure 3a also shows that the high-voltage connectors 10 are now positioned off-centre and this has the particular advantage of eliminating or at least substantially reducing the risk of potential damage to the high- voltage connections 10 during use of the A-frame lifting chains used to install the transformer onto the power pole, including reducing the risk of short circuiting occurring. Referring particularly to Figure 3b, this illustrates the positioning of the low voltage connectors 4 to the side walls 2, allowing the centre of gravity moment to be reduced. Figure 3b also illustrates that the side walls 2 may be bent at their bottom portions to form respective feet 24 which facilitate material handling during

manufacturing and in storage and also substantially reduces or eliminates the potential for direct impact damage to the welds in the tank 1 during transportation and storage.

Figure 3c illustrates the closeness of the cross-arm 20 to the tank in the affixing of the pole hangers 5 directly to the side walls 2 and the use of a spacer plate 15 to assist in keeping the tank 1 in an upright position.

Figure 3d shows in particular the lifting lugs 6 provided for the side plates 2.

Referring now particularly to Figure 1, Figure 1 a shows the front, bottom and back plates, 11, 12,13 being bent from a single plate of the light weight metal or alloy, suitably aluminium, with the ends 14 being bent inwards to form respective flanges and to substantially eliminate those edges as potential leak points. The side plates 2, see Figures 1 b and 1 c, may then be welded as an end cap with an appropriate over hang of the side walls. The provision of an over hang may be beneficial in enlarging the heat sink capacity for welding purposes. The pole hangers 5 may then be welded on the side plates.

The top of each side plate 2,18 is shown bent outwards to form a flange and the bottom of each side plate 2 is shown bent outwards to form supporting feet 24. The lifting lugs 6, see Figure 1f, may then be welded to the side plates2. The spacer bracket 15 may include a notch or the like 26 substantially centrally to allow the transformer tank 1 to slip over the cross arm support bracket and bolt on the power pole during installation. The notch 26 may also act as a guide to centrally position the pole hangers 5 an equal distance on the cross-arm 20 from the power

pole. This can be of substantial advantage for workers who may be installing the transformers in darkness.

As mentioned previously, all the materials used in the construction of the transformer tank 1 including the pole hanger brackets 5 are metallurgically compatible and preferably a particular aluminium alloy may be used for the tank 1 itself and a stronger aluminium alloy may be used for the pole hanger brackets 5 and lifting lugs 6.

An advantage of using a metal such as aluminium as opposed to steel, apart from the major advantage inherent in its light weight nature is in the substantial elimination of eddy currents which are prevalent in steel transformer tanks. Additionally, in using a substantial amount of bending in the construction of the tank 1 a major cost advantage can accrue due to the reduction in the number of welds required.

Furthermore, the present invention, by providing the low-voltage connectors on the side plates inherently provides various advantages facilitating the use of the transformer tank 1 as a pole-mounted transformer including but not limited to reducing the centre of gravity moment.

Additionally, the present invention substantially avoids chemical corrosion due to dust and salt build-ups. Additionally of course, by eliminating the need for a protective coating in using aluminium, there can be considerable cost saving and a three fold increase in thermal conductivity by the use of aluminium as compared to mild steel means that heat can be dissipated more effectively, lowering the operating temperature and increasing the operating life of the electrical insulation.

Furthermore, the elimination of eddy currents means that energy losses

are reduced so as to increase the capitalised value of the transformer to the user.

Where in the foregoing description, reference has been made to specific components or integers of the invention having known equivalents then such equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the scope of the invention as defined in the appended claims.