IE910846A1 - Transformer - Google Patents

Abstract

In a transformer, especially a distribution transformer, having an oil tank (1) and an oil catchment container (9), the oil catchment container (9) is constructed as an external tank surrounding the oil tank (1), maintaining a free space (6) between the side walls (7, 8), and ventilation and venting devices (17, 18) are provided for the air space (6) enclosed between the two tanks (1, 9).

Description

The invention concerns a transformer, especially a distribution transformer, with an oil tank and an outer oil collecting vessel whose receiving chamber is partly delimited by the tank wall.

The use of transformers which have oil tanks filled with liquid dielectric (transformer oil) for cooling and insulating requires the operator to meet a number of obligations with regard to environmental protection, operating safety and economical aspects. The national regulations governing the installation of transformers contain precise details regarding the design of rooms for transformers or measures for installing transformers in the open. In the case of liquid cooled transformers it is necessary to provide oil collecting vessels, at least from a certain size upwards. These oil collecting vessels up to now are constructed as oil sumps. When the transformer is placed in the oil sump, which is usually open at the top, its receiving chamber is partly delimited by the tank wall.

The holding capacity of the oil sump must be sufficiently large so that in the event of damage in an unfavourable situation the oil escaping from the transformer tank must all be collected. With transformer stations situated at ground level and especially those assembled in rooms, this requirement cannot be met without great difficulties. Also, conventional oil sumps do not provide any protection against explosions.

The oil sump is not to be confused with a compensating vessel, provided in some transformers, which is connected to the filling chamber of the transformer via pipes and which during heating takes up the excess liquid dielectric. A compensating vessel such as this is preferably used in transformers with air or gas cushions above the liquid dielectric. According to the CH-PS 627 874 such a compensating vessel is attached to the lid of the transformer and through drillings is connected with the filling chamber of the transformer, in which the compensating vessel contains a gas-filled balloon which is designed to compensate the thermal changes in the volume of the liquid dielectric. According to the US-PS 4 609 900 on the side of the transformer tank is mounted a cylindrical receiving chamber in which a spring-loaded pressure piston is displaced in accordance with the momentary expansion of the liquid dielectric. In the DE-OS 35 28 698 is disclosed a transformer with a protective gas cushion situated above the liquid dielectric and on the side of a wall of the transformer is mounted a pressure vessel which is similarly filled with a protective gas and via a siphon is connected to the protective gas cushion above the liquid dielectric. This is designed to give additional protection against the ingress of moisture to the liquid dielectric. However, beyond a certain size all these transformers would have to be additionally fitted with an oil collecting vessel.

In the distribution grid of electricity supply companies (EVU) there is usually a large number of mast-held stations in which the transformer is installed directly on a platform between two masts at some height above the ground. The fitting of an oil sump in this case is not easy.

For the installation of compact stations there has already been developed a compact structure for a transformer with an oil tank, the so-called hermetically sealed transformer, which is very compact and is therefore often used in mastheld station. However, also used are transformers of the semi-hermetically sealed construction type with and without air cushion and without compensating vessel, as well as breathing transformers with air cushion.

In distribution transformers within output ratings of up to 2,5 MVA and occasionally above that, in Europe the socalled corrugated tank is used. The elasticity of the appropriately dimensioned corrugated wall of this tank is able to absorb the changes in volume brought about by the expansion of the oil caused by the temperature. In the hermetically sealed construction the cooling and insulating liquid dielectric of the transformer is completely shut off from the atmosphere.

In extreme cases, e.g. during a massive short-circuit, under exceptionally unfortunate circumstances it is possible for the tank to start leaking or even burst open. In the case of hermetically sealed transformers mounted on a mast station, the escaping oil seeps directly into the ground, creating more and more problems for cleaning the oil polluted ground.

It is the object of the invention to provide a transformer, especially a distribution transformer, with oil tanks and oil collecting vessels, which offers improved protection against the escape of oil into the ground, which does not require any additional servicing and which can also be used as a mast-held transformer, in which the cooling of the transformer is not affected in a detrimental way and the function of the oil collecting vessel is not rendered inactive through atmospheric precipitation.

Even though based on oil-filled grid transformers of the completely hermetically sealed or semi-hermetically sealed construction assembled on mast-held stations with a power rating of from 50 to 63 0 KVA and a maximum operating voltage of 36 Kv used over many years, the general object additionally is to achieve with transformers of the aforementioned kind improved operating safety with regard to oil discharge and fire or the danger of explosions.

This object is achieved principally in that the oil collecting vessel is constructed as the outer tank enclosing the oil tank by maintaining a free space between the side walls, forming the receiving chamber.

The free space between the two tanks is protected from the ingress of rain water, wherein the outer tank forms an additional protection for the inner tank on the one hand and on the other hand not only an oil collecting vessel when the oil tank leaks, but in the extreme case also forms a protection against explosion during the bursting of the inner tank. Naturally, steps should be taken to ensure that the transformer heat losses are properly channelled off. To achieve this, the outer tank can be provided with improved heat exchanger surfaces, e.g. cooling fins, for transferring the heat from the inner chamber and thus from the oil tank of the transformer to the surrounding air, in which according to a preferred embodiment the outer tank is constructed as a corrugated tank .

For preventing condensation from forming, the space between the two tanks must be adequately ventilated, so that ventilating means are provided, in which according to a preferred embodiment it is ensured that only part of the transformer heat loss is dissipated to the atmosphere via the outer wall of the outer tank and the other part of this heat loss is conveyed directly by the air passing through the intermediate space. In order to achieve this, it is possible to provide air conduction and fan means in the air space for generating a cooling air stream. A cooling air stream can be produced, e.g. by utilising the heated air of the oil tank, in that on one side of the outer tank from an upper inlet opening one or more insulated pipes are directed towards the base region and on the opposite side of the outer tank are arranged air outlet pipes. The inlets of the air inlet pipes are protected against the ingress of rain water. Another possibility of course consists in providing a forced ventilation of the inner chamber by means of a thermostatically controlled fan or the like.

According to a further development, as already known, the oil tank in the form of a hermetically sealed corrugated tank is connected via at least one pressure relief valve to the air chamber between the tanks, in which the pressure relief valve is designed to prevent the inner tank from bursting when the pressure increases by an unacceptable amount and on the other hand environmental damage is prevented by oil escaping into the air gap between the two tanks.

From a constructional point of view, an embodiment is recommended in which the two tanks are provided with one common lid. For ease of manufacture and servicing, the oil tank can be connected to the outer tank via releasable holding means in the base region.

Further details and advantages of the object of the invention are disclosed in the following description of the invention.

The drawing shows the object of the invention by way of an example. It shows Fig. 1 a front view of the transformer according to the invention represented purely schematically, Fig. 2 a side view of Fig. 1, Fig. 3 a plan view of Fig. 1 and Fig. 4 an enlarged partial section through two oppositely arranged wall portions of the oil tank and outer tank.

The construction of the hermetically sealed transformer should correspond to the standard specification, e.g. according to DIN 42500. The active part of the transformer, comprising an iron core and windings, is contained inside an oil tank 1 which is in the form of a corrugated tank. The liquid dielectric consisting of transformer oil is contained within this oil tank 1 hermetically sealed from the surrounding air. All switches and gauges which are necessary for manipulating and monitoring the oil are attached to the oil tank. Of these are shown a thermometer holder 2, a filler pipe 3 with level indicator, a main oil outlet 4 and a pressure relief valve 5.

The oil tank 1 is enclosed by an outer tank 9 with a free space 6 between the corrugated walls 7 and 8, the outer tank 9 also being constructed as a corrugated tank. Both tanks 1 and 9 are provided with one common closure lid 10 on which are also constructed the high and low voltage bushing 11, 12. Lifting lugs 13 are fixed to the lid 10. The tank 1 is releasably connected to the outer tank 9 via releasable holding means in the base region. Also attached to the outer tank 9 is a carriage 14 and traction and stay rings for pulling the transformer or for lashing it down to the mast-held station. Since the inner tank is releasably connected with the outer tank and the lashing and support elements are provided on the outer tank 9, transporting can be easily accomplished. Instead of a carriage 14, skids or other means can also be provided. In order to be able to maintain the usual distance of the runners 14 of the carriage 14, the outer tank 9 is bevelled towards the ground in the base region.

The heat loss of the transformer is dissipated through the corrugated walls 7 of the oil tank 1 to the air in the intermediate space 6 and from this to the outer tank 9, partly through convection, and from there to the surrounding air. A small portion of the heat transfer also takes place by radiation from tank 1 to tank 9. When dimensioning the surface area of the oil tank 1, the effect of the intermediate cooling circuit above the intermediate space 6 has to be considered, as this is governed by a different temperature drop than the direct transfer of heat from the oil tank to the free surrounding air. With regard to its heat absorption or transfer surfaces, the outer tank is so dimensioned as to keep within the permissible temperature limits of the transformer. Also, the outer tank 9 must naturally be able to collect all the oil of the oil tank 1 in the case of a rupture. A further condition stipulates that in the event of the inner tank 1 bursting, the outer tank 9 must be able to absorb the kinetic energy thus produced or released without itself bursting. Atmospheric precipitation is kept out of the inner space 6.

In order to prevent condensation from forming in the inner space 6, a through-ventilation is provided. For this purpose a pipe, preferably heat-insulated, via devices not shown, e.g. an elbow open at the bottom for protecting the air inlet from the ingress of rain water, leads from air inlet 17 in one corner of the outer tank 9 to the base region, and in the region of the diagonally opposite corner is provided an air outlet 18. For control purposes the outer tank 9 is also provided with an outlet 19.

The outlet of the pressure relief valve 5 leads into the intermediate space 6, which ensures that no oil can escape into the open when the valve is operated. It is also possible to construct the pressure relief valve as a sensor for a safety switch of the transformer.

Compared to conventional oil transformers or hermetically sealed transformers, because of the outer tank, this results in larger overall dimensions. However, these are still substantially smaller than the corresponding dimensions of dry and cast-resin transformers for the same output in one housing.

Claims (7)

1. Patent Claims:

1. Transformer, especially distribution transformer, with oil tank (1) and outer oil collecting vessel (9) whose receiving chamber (6) is partly delimited by the tank wall, characterised in that the oil collecting vessel is constructed as the outer tank (9) enclosing the oil tank (1) by maintaining a free space (6) between the side walls (7, 8), forming the receiving chamber.

2. Transformer according to claim 1, characterised in that the outer tank (9) is provided with heat exchange surfaces (8) e.g. cooling fins, for improving the heat transfer from the inner chamber (6) to the surrounding air.

3. . Transformer according to claims 1 and 2, characterised in that the outer tank (9) is adapted to be a corrugated tank.

4. Transformer according to one of the claims 1 to 3, characterised in that free space (6) enclosed between the two tanks is provided with air supply and ventilating devices (17, 18).

5. Transformer according to one of the claims 1 to 4, characterised in that air conducting or circulating means for producing a cooling air stream are provided in the free space (6) .

6. Transformer according to one of the claims 1 to 5, characterised in that the oil tank (1) is adapted to be a hermetically sealed corrugated tank and is connected via at least one pressure relief valve (5) with the free space (6) between the tanks (1, 9). -9

7. A transformer according to claim 1, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.