GB2028003A

GB2028003A - Liquid filled transformers

Info

Publication number: GB2028003A
Application number: GB7929643A
Authority: GB
Original assignee: Brush Transformers Ltd
Current assignee: Brush Transformers Ltd
Priority date: 1978-05-25
Filing date: 1979-08-24
Publication date: 1980-02-27

Abstract

A transformer for operation underwater which is housed within a tank filled with a liquid coolant for cooling the transformer during its operation. The tank 2 has a deformable diaphragm 5 which is deformable and, in use, is engaged on its inner side by the coolant in the tank 2, whereby, when the transformer is positioned for operation underwater, external water pressure acting on the diaphragm 5 will effect compression of the coolant within the tank 2 to a value which will balance the external water pressure acting on the tank 2, thereby to maintain the tank 2 from collapse under the external water pressure. A switch 15 operates if the diaphragm 5 distorts due to oil leakage. In a variation (Figures 6 - 9, not shown) wall portions of the tank are formed from flexible corrugated plates. <IMAGE>

Description

SPECIFICATION Transformer or other electrical apparatus for use underwater The invention relates to a transformer, or other electrical apparatus, (hereinafter called a transformer) to be situated in operation under water and particularly for deep sea operation, where the external water pressure may be ten or more bars or hundreds of p.s.i.

According to the invention, the transformer is housed within a tank which, in use, is filled with a liquid coolant for cooling the transformer during its operation, the tank having at least a wall portion which is deformable and, in use, is engaged on its inner side by the coolant, whereby, when the transformer is positioned for operation under water, external water pressure acting on the deformable wall portion will effect compression of the coolant within the tank to a value which will balance the external water pressure by acting on the tank, whereby to maintain the tank from collapse under the external water pressure.

In one embodiment according to the invention, the deformable wall portion comprises a deformable diaphragm closing an aperture in a wall of the tank.

The diaphragm may be of an inflatable kind and be pre-inflated to effect pre-compression of the coolant.

The diaphragm may be capable of outward deformation, thereby to accommodate expansion of the coolant. Such expansion of the coolant may occur before the tank containing the transformer has been lowered to its underwater location, particularly when the tank containing the transformer is being transported through or is stored in a hot climate, or during use when the transformer is being operated under full-load conditions, even in its underwater location.

The diaphragm may be capable of inward deformation to an extent beyond that which will occur when the tank containing the transformer has been lowered to its underwater location, whereby in the event of leakage of coolant from the tank, the diaphragm will be deformed further inwardly by the external water pressure, thereby to maintain the internal coolant pressure substantially equal to the external water pressure. A warning device operable by the diaphragm when it experiences said further inward deformation by a predetermined extent may be provided to give warning of leakage or coolant.

Alternatively or additionally a thermostaticallyoperated warning device to be effective during use of the transformer may be provided to give warning of overheating.

The diaphragm may be protected during transport or storage by a removable cap which would be removed on site before putting the transformer into service and may be replaced by a non-closing cap containing a filter or labyrinth to permit water to reach the diaphragm but to prevent the entry of sand or debris.

It is envisaged that the tank will normally be filled with coolant in the factory before dispatch of the transformer to the site. To enable cable connections to be made on site without interference with any sealed closure of the tank, an openablejunction box is conveniently provided on the outside of the tank, the junction box having terminals therein which have been pre-connected through a wall of the tank to the transformer windings, sealable ports in a wall of the junction box through which cables are arranged to be passed for connection within the junction box with appropriate terminals and closure means whereby the junction box can be filled with coolant and sealed after the cable connections have been made.

The junction box and the tank may be provided with an interconnecting two-way, normally-closed valve which is arranged to be opened, after the transformer has been lowered to its underwater location, whenever the coolant pressure within the tank and the junction box differ by a predetermined small pressure difference, thereby to maintain the coolant pressure within the tank and the junction box substantially equal.

In another embodiment according to the invention the deformable wall portion, which may be a whole wall of the tank or a plurality of walls thereof, is made of a flexible corrugated form capable of inward and outward distortion to accommodate expansion and contraction of the coolant and variation of the external water pressure.

The coolant will usually be a transformer oil, i.e., an oil of the kind usually used for cooling transformers but may be another type of oil, for example a silicone oil or dielectric fluid or other suitable liquid.

By way of example, two transformers in accordance with the invention are now described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a vertical section through the first transformer; Figure 2 is a vertical section in a plane at right angles to Figure 1; Figure 3 is a section on the plane Ill-Ill in Figure 1; Figure 4 is a plan view of the transformer; Figure 5 is a detail view showing the inflatable diaphragm, which is also shown in Figure 2, when fitted with an alternative protective cap for use in the underwater location of the transformer; Figure 6 is a side elevation of the second transformer; Figure 7 is a plan view of the transformer shown in Figure 6;; Figure 8 is a section on the plane VIII-VIII in Figure 7,and Figure 9 is a plan view of the transformer shown in Figures 6 to 8 with its tank cover removed, as described hereinafter.

Referring to Figures 1 to 4, the first transformer 1 itself (that is the core and windings) is mounted within a tank 2. This is made of glass fibre or of other water-resistant material. The tank 2 is filled with liquid coolant, i.e., transformer oil, in the factory and is closed by a top plate 3 which is sealed by a bolted gasket joint. The top plate 3 has lifting lugs 4 (see Figures 2 and 4) by which the transformer can be lowered and raised. The top plate 3 has an aperture therein giving access to an inflatable pressurising diaphragm 5. The aperture is closed by a removable cap 6. In the factory after the tank has been filled with oil and the top plate 3 has been fixed in position, the diaphragm 5 is partially inflated so that the underneath of the diaphragm 5 bears against the coolant in the tank and ensures that the interior of the tank has been completely filled with oil.The top plate 3 has a junction box 7 mounted thereon. The junction box 7 contains terminals 8 which are connected to the windings of the transformer during construction and before the tank has been filled with oil and sealed. The junction box 7 has a wall containing ports 9 through which cables 10, 11 are inserted on site and in which the cables are sealed. The junction box 7 has a removable lid 12 which is sealingly securable to the junction box. The lid 12 contains a closable filter 13 by which coolant, i.e., transformer oil, is introduced into the junction box 7 to fill the latter. There is a two-way, normally-closed, spring biased valve 14(shown only in Figure 1) in the portion of the top plate 3 within the junction box 7, as will hereinafter be explained.A micro-switch 15 is mounted in the tank 1 in a position in which it will be engaged by the diaphragm 5 when the latter has been deformed downwardly to a predetermined extent, as will hereinafter be explained. The microswitch 15 is connected in a circuit to operate an alarm (not shown) at the surface.

As aforesaid, the tank 2 has been filled with oil in thefactory, the top plate 3 fixed and sealed in position, the diaphragm 5 partially inflated and the cap 6 fitted. The junction box 7 is not filled with oil.

The transformer is then taken to the site where it is to be used. If the oil should expand due to a rise in ambient temperature, this will be accompanied by outward deformation ofthe diaphragm 5.

When the transformer has reached the site where it is to be lowered into the water, the junction box 7 is opened and the cables 10, 11 are inserted through the ports 9 and are sealed therein by oil and sea-water resistant seals. The connections of the cables 10, 11 are made to the terminals 8 within the junction box 7, as necessary. The junction box is then closed by the lid 12 and sealed and is then filled with oil through the filler 13. The cap 6 is removed from the diaphragm 5 and the switch 15 is connected to the surface alarm circuit. A replacement cap 17 (shown in Figure 5) is then fitted over the diaphragm in place of the cap 6. The replacement non-closing cap 17 contains a filter or a labyrinth communicating with ports 18 and which will allow free movement of water in to the diaphragm 5; but will prevent sand or debris from entering.The transformer is then lowered to the operating position beneath the surface of the water. The water pressure acting on the diaphragm 5will cause the oil within the tank 2 to be compressed and the internal pressure within the tank 2 will become substantially the same as the surrounding water pressure. In this way, the tank 2 will not be collapsed although the water pressure at the operational depth may be considerable. The oil within the junction box 7 will also prevent the latter from collapse. If the difference in internal pressure between the tank 2 and the junction box 7 should be greater than a predetermined pressure at which the valve 14 is set to open (e.g. 0.35 kg m/cm2 or approximately 5 p.s.i.), the valve will open resulting in equalisation of pressure between the tank 2 and the junction box 7 and re-closure of the valve 14.In this way, the internal pressures within the tank 2 and the junction box 7 will be maintained substantially equal.

If leakage of oil from the tank 2 or the junction box 7 should occur, the water pressure acting on the diaphragm 5 will distort the latter inwardly and maintain the pressure within the tank 2 substantially equal to the ambient water pressure. If the leakage of oil should reach a predetermined amount, the diaphragm 5 will be distorted sufficiently far for the diaphragm 5 to engage the switch 15 and thus to operate the surface alarm.

If under full load, the transformer should overheat, the oil in the tank 2 will expand. This expansion will be accommodated by outward deformation of the diaphragm 5. Athermostatically-operated warning device may be positioned in the tank 2 to give warning of overheating.

A heat exchanger 16 may be provided to cool the oil or other coolant which the tank contains and has oil passages communicating with the interior of the tank through passageways 19. The heat exchanger also has sea-water passages 20. The heat exchanger is made of a sea-water corrosion resistant material, which also has correct thermal characteristics.

The second transformer constructed in accordance with this invention and shown in Figures 6 and 9 is of simpler construction than that shown in Figures 2 to 5 in that the diaphragm 5 is not provided. Instead side wall portions of the tank are inwardly and outwardly deformable to accommo- date expansion and construction of the coolant and variation of the external water pressure.

Referring to Figures 6 to 9, the transformer 21 itself, that is the core and windings, are enclosed within a tank assembly which comprises a hollow base-plate 22 on which the transformer core and windings are mounted. The base-plate 22 has an aperture through which the transformer core and windings extend upwardly. The aperture is defined within a rectangular plinth 24 on which an inverted box-like cover 23 is fixed and sealed by a water-tight seal. The cover 23 defines a space around the transformer core and windings which together with the base-plate is filled with oil or other suitable coolant through a filler cap 25 at the top of the cover 23. Conductors 27 are connected to the transformer windings and passed through water and oil-tight seals 28 in the base-plate 22 before the tank is filled with oil. The front and back wall of the cover 23 have outwardly-extending wing-like portions 26 which are constructed from flexible corrugated plates which can bulge outwardly or inwardly as the coolant expands or contracts and also to accommo datevanation in the external pressure of the ambient sea-water. In this way the fluid pressure inside and outside the cover 23 and the base-plate 22 will be substantially equal. The material used for the cover and the base-plate are resistant to corrosion by sea water and the oil or other coolant.

Claims

1. A transformer for use under water comprising a tank in which the transforrner is housed and which, in use, is filled with a liquid coolant for cooling the transformer during its operation, the tank having at least a wall portion which is deformable and, in use, is engaged on its inner side by the coolant, whereby, when the transformer is positioned for operation underwater, external water pressure acting on the deformable wall portion will effect compression of the coolant within the tank to a value which will balance the external water pressure acting on the tank, thereby to maintain the tank from collapse under the external water pressure.

2. A transformer as claimed in Claim 1 in which the deformable wall portion comprises a deformable diaphragm closing an aperture in a wall of the tank.

3. A transformer as claimed in Claim 2 in which the diaphragm is of an inflatable kind and is pre-inflated to effect pre-compression of the coolant.

4. Atransformer as claimed in Claim 2 or 3 in which the diaphragm is capable of outward deformation, thereby to accommodate expansion of the coolant.

5. A transformer as claimed in any one of Claims 2 to 4 in which the diaphragm is capable of inward deformation to an extent beyond that which will occur when the tank containing the transformer has been lowered to its underwater location, whereby in the event of leakage of coolant from the tank, the diaphragm will be deformed further inwardly by the external water pressure, thereby to maintain the internal coolant pressure substantially equal to the external water pressure.

6. Atransformer as claimed in Claim 5 in which there is a warning device operable by the diaphragm when it experiences said further inward deformation by a predetermined extent to give warning of leakage or coolant.

7. A transformer as claimed in any one of Claims 2 to 6 in which there is a thermostatically-operated warning device to be effective during use of the transformer to give warning of overheating.

8. A transformer according to any one of Claims 2 to 7 in which the diaphragm is protected during transport or storage by a removable cap to be removed before putting the transformer into service and to be replaced by a non-closing cap containing a filter or labyrinth to permit water to reach the diaphragm but to prevent the entry of sand or debris.

9. Atransformer as claimed in any preceding claim including an openable junction box having terminals therein which have been pre-connected through a wall of the junction box to the transformer windings, sealable ports in a wall of the junction box through which cables are arranged to be passed for connection within the junction box with appropriate terminals and closure means whereby the junction box can be filled with coolant and sealed after the cable connections have been made.

10. Atransformer as claimed in Claim 9 in which the junction box and the tank are provided with an interconnecting two-way, normally-closed valve which is arranged to be opened, after the transformer has been lowered to its underwater location, whenever the coolant pressure within the tank and the junction box differ by a predetermined small pressure difference, thereby to maintain the coolant pressure within the tank and the junction box substantially equal.

11. A transformer as claimed in Claim 1 in which the deformable wall portion is made of a flexible corrugated form capable of inward and outward distortion to accommodate expansion and contraction of the coolant and variation of the external water pressure.

12. Atransformerfor operation underwater constructed and arranged substantially as described herein and shown in Figures 1 to 5 or 6 to 9 of the accompanying drawings.