EP0671748A1 - Heat exchanger for vessel of an immersed electric transformer - Google Patents

Abstract

A transformer tank includes a heat exchanger which is placed on its lateral wall and consists of longitudinal fins (3) held by transversal rods (2). The fins are hollow and communicate with the tank so that the dielectric liquid which fills the tank can flow into the fins. Each of the corner fins (9) is provided with transversal fins (10,11) attached to both of its surfaces. The additional fins are also hollow and filled with the dielectric liquid in the tank.

Description

The present invention relates to the tanks of immersed electrical transformers.

More specifically, the invention relates to the manufacture of heat exchangers constituting the wall of these tanks or attached to them, and intended to ensure the cooling of the dielectric liquid in which the electrical part of the transformer is immersed within the tank.

Recall that an "immersed" transformer is a transformer whose electrical part (primary and secondary windings, as well as the magnetic circuit) is cooled by immersion in a liquid, with high dielectric properties, generally a mineral oil, contained in a tank watertight whose side walls, provided with hollow fins, serve as a heat exchanger with the external environment.

For this purpose, the walls are now usually formed by wavy panels, each panel forming one side of the tank.

In the case of high power transformers, additional heat exchangers, called radiators, and often formed themselves by corrugated panels, are brought to a distance on the tank. Connection pipes are then provided to allow the circulation of the dielectric liquid between the tank and these external radiators.

In the following, for the sake of simplification, the term "exchanger" will be used to designate both the added radiators and the side walls of tanks with cooling fins.

Conventionally, the corrugated panels constituting immersed transformer exchangers are made in one piece and according to a single operation, from a metal strip (generally steel) which is deformed at regular intervals to form parallel, deep folds. The sides of these folds are joined by their edges, which are then closed by sealed welding to form a wave.

It is these elements, once folded and welded at the edge, that are designated by "wavy panel".

A corrugated panel is therefore a component of the manufacture of submerged transformers essentially constituted by a series of parallel waves, distributed along a common base and which, once mounted on the tank, become hollow fins placed in direct communication with the interior volume of the tank containing the dielectric liquid.

Four corrugated panels mounted end to end at right angles thus form the side wall of a transformer tank. In the case of small transformers, it is a single corrugated panel which, folded in four, can form the complete perimeter of the tank. An external radiator, on the other hand, is conventionally made up of two identical wavy panels attached to one another along a plane, which is the plane of symmetry of the assembly, and assembled in a sealed manner. The radiator, once finished, is mounted remotely on the tank opposite one side thereof. In general, the two long sides of the tank, or even the four sides, are thus provided with radiators.

Each end of a corrugated panel, whatever its destination (radiator or wall exchanger) is, as we understand it, constituted by a wave - or fin - one side of which faces outwards, the other side being look at the penultimate wave.

A problem encountered in the manufacture of transformers of the aforementioned type comes from galvanization. The galvanizing operation, desirable before painting to protect the tank and the radiators, is more and more often required by customers. It consists in immersing the tank and any radiators in a bath of zinc, or zinc alloy, brought to a temperature of 450 ° C and more, then after having extracted them, to let them cool in the open air .

During this cooling, the waves deform and warp. The deformation is permanent after returning to ambient temperature. It seems acquired that the cause is the exceeding of the elastic limit of the metal constituting these panels (in general of low carbon steel) during the immersion in the galvanizing bath.

This phenomenon does not constitute a real handicap on the technical level, although that causes overcapacities of the cooling fluid of the tank, therefore an additional cost.

On the other hand, the wave at the ends of each panel, which is clearly visible, then presents an unattractive warping of its face turned towards the outside, further aggravated by the painting, and which render the tank or the radiator hardly acceptable for delivery to customers.

One could manage to resolve these difficulties by preventing deformation by means of an old technique of modular manufacture of radiators which consists in producing the cooling fins by bringing together identical unit elements juxtaposed, the number of which defines the desired length of radiator.

This standard unit element is produced by shallow stamping with a steel sheet press, which is then paired so that these stampings define two by two of the internal cavities of the element thus produced, in which the fluid can circulate. The corresponding redons on the external surface then probably play a role of stiffening ribs sufficient to prevent the appearance of permanent deformation after galvanization.

However, this manufacturing technique requires specific tools which involve additional investments in current transformer manufacturing lines, and which no doubt explain why it is less and less used.

Here, therefore, it is a question of finding a solution to the problem of the permanent deformation of the end faces of the corrugated panels at the end of the galvanization, and this by an inexpensive means for the manufacturer, easy to implement industrially and which does not significantly affect the cost of manufacturing transformers

With these objectives in view, the invention relates to a method of manufacturing a heat exchanger intended to be gal vanized (or more generally coated by immersion in a bath of molten material at high temperature), constituting exchanger of the wall side of a submerged electric transformer tank, or of an external radiator attached to said wall, and constituted by a wavy panel, characterized in that it consists in replacing the last wave situated at each end of the wavy panel by a constitutive structure itself of a wavy panel on a reduced scale which has a main plane wave parallel to the others waves and provided with daughter waves at least on its outer face.

Preferably, daughter waves are present on both sides of the main wave.

The invention also relates to a corrugated panel thus produced, as well as any associated transformer or external radiator tank which is made of it.

Being produced by folding, in the same way as the other waves of the panel and at the same time on the machine folding of waves of the workshop, these waves-girls fulfill two functions:

Above all, they form stiffeners which reduce the range of the faces of the wave which carries them and thus prevent its later warping after cooling at the outlet of the galvanizing tank.

Being hollow, they also have the function of being able to receive dielectric fluid, whereby they contribute to increasing the cooling efficiency by increasing the overall heat exchange surface.

• la figure 1 est une vue en perspective d'une cuve vide de transformateur de type connu habituel;
• la figure 2 est une vue analogue à celle de la figure 1, mais d'une cuve selon l'invention;
• la figure 3 est un schéma représentant une extrémité d'un panneau ondé conforme à l'invention à un stade intermédiaire de fabrication;
• la figure 4 représente le panneau ondé de la figure 3 une fois achevé;
• la figure 5 est une vue partielle de la paroi latérale d'une cuve de transformateur selon une variante de réalisation de l'invention;
• et la figure 6 montre schématiquement un coin de cuve selon une mise en oeuvre particulière de cette variante de réalisation.

The invention will be well understood and other aspects and advantages will appear more clearly in the light of the description which follows, given with reference to the accompanying drawing plates in which:

• Figure 1 is a perspective view of an empty transformer tank of the usual known type;
• Figure 2 is a view similar to that of Figure 1, but of a tank according to the invention;
• Figure 3 is a diagram showing one end of a corrugated panel according to the invention at an intermediate stage of manufacture;
• Figure 4 shows the corrugated panel of Figure 3 when completed;
• Figure 5 is a partial view of the side wall of a transformer tank according to an alternative embodiment of the invention;
• and FIG. 6 schematically shows a corner of the tank according to a particular implementation of this alternative embodiment.

In the figures, the same elements are designated by identical references.

As can be seen in FIG. 1, a traditional submerged transformer tank has on its side wall 1 longitudinal cooling fins 3, the mechanical retention of which is ensured by transverse connecting rods 2.

It will be recalled that these fins have the essential role of ensuring the thermal equilibrium of the transformer in operation at a given temperature level.

To improve the cooling efficiency, these fins are hollow and their internal volume 4 is in direct communication with the enclosure 5 of the tank so as to receive the dielectric liquid with which the latter is filled after the active part has been put in place - not shown- of the transformer (electrical windings and magnetic circuit).

These hollow fins are advantageously obtained by making each of the sides of the side wall 1 by a wavy panel. They are then called "waves".

It is recalled that such a panel is made from a steel strip 12, the width of which defines the height of the waves (fins), and that it is folded at close intervals - conventionally every 4 to 8 cm approximately. -to form parallel and deep folds. After sealing their edges 6 tightly by welding, these folds form the waves which will become the desired hollow cooling fins, once the corrugated panel is mounted on the tank.

The proper technique for manufacturing these corrugated panels is not part of the present invention. If necessary, a more detailed description can be found, for example in document FR-A-92.13299.

The invention, on the other hand, relates specifically to a new design of the terminal waves of such panels intended to become the end fins 7 on the sides of the side wall 1 of the tank and therefore exposed to the outside much more than the central fins 3.

As already explained, under the effect of thermo-mechanical constraints generated by the galvanizing operation after painting, the waves lose their flatness, which creates aesthetic defects which are clearly visible, especially on the faces 8 of the end waves 7 facing towards outside.

To remedy this, the invention consists, as clearly shown in FIG. 2, of endowing the external face at least with end waves, referenced 9 in this figure, daughter waves 10. Preferably, daughter waves 11 are also provided on the internal face turned opposite the central waves 3.

These daughter waves 10 (or 11) are arranged longitudinally on their mother wave 9 and spaced one from the next by 3 to 6 cm approximately, without this being critical for the conservation of flatness. Their width is also not a critical parameter. It can be chosen for example between 3 and 6 cm approximately.

The only constraints are possibly those related to the dimensions of congestion: the extent of the external daughter waves 10 must possibly respect the initial size of the tank, while the internal daughter waves 11 must if necessary take into account the proximity of the neighboring 3 waves.

These daughter waves are advantageously hollow, too, as already explained. In this way, their internal volume is placed in communication with the internal volume of their mother wave 9, and therefore with the enclosure of the tank, which contributes to increasing the cooling efficiency by increasing the overall surface of heat exchange with the outside environment

A preferred embodiment of the corrugated panels according to the invention is illustrated by FIGS. 3 and 4 taken successively in this order:

We start from a wavy panel in the completion phase, of which only the end wave has not yet been formed. Figure 3 shows only the terminal portion of this panel, seen in profile, in a very schematic representation showing the shapes of the elements only.

We recognize the waves 3 in the form of deep and parallel folds rising from the base band 12.

Unlike the usual manufacturing process, the end wave is not formed like the other waves 3, but is replaced by several folds less deep than the folds of waves 3, but made in the same way. and on the same tool. In the example considered, these folds are organized in two successive series 13 and 14, the first comprising three folds which will form the internal daughter waves 11, the second having the four folds constituting the external daughter waves 10 of the wave mother 9.

Note the indication on the base strip 12 of three points A, B and C, which constitute the folding axes of this strip making it possible to produce this mother wave 9 by passing from the blank of corrugated panel of FIG. 3 to wavy panel completed in figure 4.

• 1. pliage de la bande 12 à angle droit autour du point A dans le sens anti-horaire. On forme ainsi la face interne 15 de l'onde mère porteuse 9;
• 2. pliage de 180° autour du point B dans le sens des aiguilles d'une montre. On forme alors la face externe 8' de l'onde mère 9;
• 3. on termine par un pliage anti-horaire de 90° autour du point C pour ramener à l'horizontale le bout restant de la bande de base 12 avant découpe à longueur.

This passage takes place according to the following three successive folding operations, presented in an unassigned order:

• 1. folding the strip 12 at right angles around point A counterclockwise. The internal face 15 of the carrier mother wave 9 is thus formed;
• 2. 180 ° folding around point B clockwise. The external face 8 ′ of the mother wave 9 is then formed;
• 3. we finish with an anti-clockwise folding of 90 ° around point C to bring the remaining end of the base strip 12 horizontally before cutting to length.

After sealing by free sealing of the free edges of the folds formed in the strip 12, the corrugated panel is then ready to be mounted on the tank frame to form one of the sides of the side wall, the aesthetics of which will then be preserved after its immersion in a galvanizing bath.

The daughter waves on the internal side can have a height of 3 to 5 cm approximately. The device for folding the steel strip constituting the corrugated panel will therefore have, if necessary, a space sized accordingly to perform the bending at right angles to the end wave provided with its daughter waves without being hampered by the 'previous wave.

As will be understood, it is the daughter waves 10 on the external face of the main wave 9 which are essential for obtaining an undeformed end fin, therefore of aesthetic preservation.

However, the presence of daughter waves 11 also on the internal face is useful, otherwise it would be this face which, subjected to maximum deformation stresses, would risk undergoing a strong deformation, although, in this case, the appearance aesthetic would suffer only moderately since this face is not very visible, in any case much less than the opposite face.

The spacing between the daughter waves, of the order of 4 to 6 cm approximately, may be the same on each side.

In this way, the external face 8 'of the end fin 9 will be provided with 4 or 5 daughter waves on a transformer tank of 500 to 1000 KVA of power, for example.

As shown in FIG. 5, in accordance with an alternative embodiment of the invention, the waveguide 9 can be formed, no longer by folding around the line B, but from two half waves 16 and 17 assembled by sealed welding 18 of their periphery. As can be seen, the end of the half-waves can advantageously be bent at 90 ° to facilitate the positioning of the parts before welding.

The internal half-wave 17 carries the internal daughter waves 11 coming from the folds 13, while the external half-wave 16 is provided with the external daughter waves 10 coming from the folds 14.

This way of operating makes it possible, as shown in FIG. 6, to produce on the same strip of base metal 19, therefore in one piece, an assembly 20 formed of two external half-waves 16 and 16 ′ arranged side by side. side at right angles. This part 20 then advantageously constitutes a corner of the side wall of the tank by adjusting to the corresponding internal half-waves 17 and 17 'provided to receive them at the neighboring ends of two adjacent sides. The assembly is completed after forming waterproof weld beads 18 and 18 'along the edges.

The invention applies to any fin heat exchanger intended to form one side of the side wall of a tank for transformer, or to form a radiator attached to this tank and which will be coated with a protective material, such as a zinc film, by immersion in a bath of this molten material at high temperature.

It preserves the aesthetics of the exchanger after immersion which would otherwise be degraded by permanent deformation of the flatness of the faces of the waves visible to an outside observer.

It goes without saying that the invention is not limited to the examples which have just been described, but extends to multiple variants or equivalents insofar as the definition of the invention given by the claims below is reproduced. .

Claims (6)

1) Method for manufacturing a heat exchanger, which can be coated by immersion in a bath of coating material in fusion at high temperature, such as a galvanizing bath, for tank or immersed transformer radiator constituted by a corrugated panel, characterized in that it consists in replacing the last wave situated at each end of the corrugated panel by a constitutive structure itself of a corrugated panel on a reduced scale which has a main plane wave (9) parallel to the other waves (13) and which is provided with daughter waves (10) at least on its external face (16). 2) Method according to claim 1, characterized in that there are also daughter waves (11) on the internal face of the main wave (9). 3) Heat exchanger of submerged electric transformer tank formed from a wavy panel, characterized in that said wavy panel comprises an end wave (9) itself constituting a wavy panel on a reduced scale and all of which the daughter waves (10,11) are hollow, their internal volume being placed in communication with that of said end wave meter (9). 4) Heat exchanger according to claim 3, characterized in that the end wave (9) carries daughter waves (10, 11) on its two faces. 5) Heat exchanger according to claim 3, characterized in that the end wave (9) is formed of two half-waves (16, 17) assembled in a sealed manner (18) by their periphery. 6) Heat exchanger according to claim 5, characterized in that it constitutes the side wall (1) of a transformer tank of which at least one corner is formed by a part (20) constituted by two half-waves (17, 17 ') arranged side by side at right angles.

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