EP0076208A1 - Transformer, especially of the explosion-proof type - Google Patents

Abstract

1. Transformer, especially of the explosion proof type, i.e. where the coils (14) of high and low voltage are provided in a metallic tray which is resistant to the pressure arising in case of an internal explosion of an explosive gaseous mixture and which prevents the transmission of the explosion to the surrounding atmosphere, said tray being formed of a lateral wall (5) and two covers (8, 9) which support the connecting boxes (20-22) of high and low voltage, and which tray is equipped with heat exchangers (23, 24, 25, 26), mounted head to tail at least approximately parallel to the axis of the lateral wall (5) and arranged with their receiving side, in the free space separating the coils from said wall, whereas their dissipating side is positioned beyond said covers at the outside of the tray, receiving (33) and dissipating (46) wings being provided, respectively, on the receiving and dissipating sides of the heat exchangers, characterized in that the heat exchangers (23, 24, 25, 26) are mounted between a central bearing (27) receiving the ends of two opposed heat exchangers and output clamps (41) traversed with light play by the heat exchangers and fixed on the covers (8, 9) of the tray (4).

Description

The subject of the invention is a transformer, in particular of the explosion-proof type, that is to say the high and low voltage windings of which are housed in a pressure-resistant metal tank developed during an internal explosion of a gas mixture. explosive, and which prevents the transmission of the explosion to the surrounding atmosphere, tank consisting of a side wall and two covers supporting the high and low voltage connection boxes.

We know that all transformers have their power output conditioned by their ability to dissipate the calories generated by electrical and electromagnetic phenomena. This is, of course, a completely general problem which presents itself whatever the type of transformer, a problem which will be studied in what follows with particular reference to explosion-proof transformers. But it goes without saying that the invention is in no way limited to this type of transformers, and that, on the contrary, it applies to all other types, whether they are in a gaseous or liquid atmosphere, in natural or forced circulation , or subject to any security imperative.

With regard to the explosion-proof transformers, it is recalled that without being watertight, they are in principle with a gaseous atmosphere and with natural circulation. The gas which they contain and which is often air, circulates naturally around the windings and thus creates a hot zone at the upper part of the tank on either side of the heads of the windings. The calories concentrated in this zone as well as to a lesser extent the calories carried by the gas in circulation in all the other zones of the transformer, can be evacuated only by convection, and this is why besides the side wall is constituted the more often by a sheet with large undulations.

On another level, such transformers have their power capacity limited by their very size. For example, they are often used in the mining industry and even if they are totally or partially mounted on site, they are subject to volume requirements resulting obviously from the sites where they are housed and the dimensions of the tracks. routing to these sites.

In practice, and taking into account all these constraints, it has hardly been possible to date to provide users with explosion-proof transformers with a gaseous atmosphere of a power greater than 1000 KVA.

The object of the invention is to remedy this state. of thing thanks to transformers which are of higher power for the same gauge. To do this, it relates to a transformer which is characterized in that heat pipes mounted head to tail, at least approximately parallel to the axis of the side wall, are arranged, for their receiving side, in the free space separating the windings of this wall, between a central bearing receiving the ends of two heat pipes and outlet flanges fixed on the covers, while their dissipative side is located beyond said flanges outside the tank, the receiving fins and heat sinks being provided respectively on the receiver and heat sink sides of the heat pipes.

First of all, it is recalled that heat pipes are called heat transporting devices which are in the form of a tube closed at both ends, the inner wall of which is lined with a capillary network and which contain a fluid partially the liquid state and partially in the saturated vapor state.

If the two ends of such a tube are brought into contact with a cold source on the one hand and a hot source on the other hand, it can be understood that the hot source instantly causes partial vaporization of the fluid at l liquid state, vaporization which creates an increase in fluid pressure in the saturated vapor state, which in turn causes a displacement of the fluid in the saturated vapor state towards the end in contact with the cold source. At this level, the cold source, by an inverse phenomenon, causes a partial liquefaction of the vapor and the liquid returns to the hot part by capillary action along the capillary network.

The heat pipe thus ensures the transfer of calories from the hot source to the cold source with a yield which can be multiple and for example more than 10 times greater than what would be the yield of a metal rod of the same diameter.

The tests carried out have demonstrated that, quite surprisingly, in a transformer equipped in accordance with the invention, the heat pipes manage to double the quantity of calories capable of being dissipated and consequently make it possible to increase the useful power transformer in considerable proportions, which can reach 25% inexpensively and without changing the size of the device or at least its size at the time of transport, since the heat pipes can easily be mounted on the site of use .

It should also be observed that the invention applies both to new transformers, that is to say delivered from the outset equipped with their heat pipes, as to * existing transformers and already in service as the 'can be fitted in accordance with the invention, by modifications relating to simple mechanics, either on site or in the factory.

In an embodiment of the invention to which it seems that there is reason to give preference, the transformer comprises at least two pairs of heat pipes mounted head to tail in the upper part of the tank on either side of the magnetic winding circuit.

We know indeed, and this is particularly the case in explosion-proof transformers with a gaseous atmosphere, that the hottest zone of the device is located in the upper part of the tank and it turns out that we have at this level two longitudinal free spaces on either side of the magnetic circuit of the windings. The heat pipes mounted in these free spaces therefore capture a maximum of calories. By the resulting cooling, they also greatly improve the natural circulation of gas along the windings and the side wall.

It is ultimately not only the upper parts of the windings but the windings as a whole which work in better conditions, which further increases the capacity of the devices and certainly avoids any operational incident.

Advantageously, the heat pipes have a slight inclination such that their dissipating side is higher than their receiving side, even if the transformer is not perfectly horizontal. This provision greatly improves the efficiency of heat pipes, by facilitating whatever the position of the transformer on the site the flow of liquid along the capillary wall from the cold end to the hot end.

According to an improvement coming within the scope of the invention, the bearings each consist of a socket with flared openings, provided with a central stop and mounted on an upper spar of the transformer. This arrangement ensures, on the one hand, easy assembly of the heat pipes, the end of which is easily introduced into the socket; on the other hand, it leaves a certain clearance necessary to take account of the coefficients of expansion which can be different for the heat pipe and for the whole of the device.

According to another improvement, the ends of the heat pipes supported by the bearings have a tapered advantageously frustoconical shape. This further facilitates the installation of the heat pipes which must be done from the outside of the transformer already mounted through a small opening. Indeed, the ends of the heat pipes are guided to the final position by their tapered or frustoconical end which cooperates with the flared opening of the bearing.

According to a new improvement within the framework of the invention, the outlet flanges through which the heat pipes pass with very slight play, are fixed on demand on stronger plates mounted on the covers to ensure the closing of a window allowing the passage of the internal fins, while the passage of the heat pipes through the plates is made by a relatively large orifice.

The installation of heat pipes faces contradictory requirements, in particular with regard to explosion-proof transformers. On the one hand their positioning must be precise with interstices fixed by imperative standards, while on the other hand, they form with the internal fins a body of relatively large dimension, both in section and in length. In addition, once mounted and equipped, the transformer must meet, without being leakproof, equally imperative standards of resistance, in particular to internal pressure.

Thanks to the provisions which have just been described, these contradictory imperatives are satisfied. Strong plates obstruct perfectly safe windows that allow the passage of heat pipes with their internal fins. The relatively wide orifice of each of the plates then allows precise positioning on demand of the heat pipes and flanges, which ensure the passage of the heat pipes, the minimal but imperative clearance necessary for safety.

As regards the internal fins now, it has proved advantageous to constitute them in the form of circular disks threaded on the heat pipes and welded on the latter by the curved edge of their central opening over the entire internal part of the heat pipes. except for a portion located at the end on the outlet side, on which a retaining ring is threaded.

The internal fins thus occupy practically all the free space available and optimally transfer calories.

It was feared that in the event of an internal deflagration, the overpressure created could cause the heat pipe to be ejected through the orifices of the plates by deformation of the internal fins, and it was to avoid this risk that we put on the 'inner end outlet side of the heat pipe, a retaining ring. The latter prohibits any ejection since for there to be ejection, there would have to be -tearing by the ring of all the welds of all the fins on the heat pipe considered.

The technological _imperatives q _hat are subject external dissipating fins are different, since the volume is available to them is hardly restricted, while on the contrary, there is great interest to limit the length of the outer part heat pipes which increases the overall size of the equipped transformer.

This is why, in accordance with the invention, the dissipating fins form, for each heat pipe, a parallelepiped block consisting of two corrugated sheets welded on two parallel plates mounted on two jaws which enclose the heat pipe, the parallelepiped blocks being advantageously arranged obliquely on the heat pipes so as to respect the size of the transformer.

Advantageously, the external dissipating fins are protected by a cover which can be constituted by curved sheets matching the size of the transformer, fixed on the covers and joined two by two on their outer periphery by crosspieces.

The purpose of this arrangement is to protect the external fins from shocks which could damage them, but also and this is much more serious, deteriorate the heat pipes themselves or have repercussions on the fixing of the outlet flanges at the expense of safety. It should be noted, however, that such covers do not in any way harm the exchange of calories at the level of the external fins and therefore do not reduce the efficiency of the transformer.

An embodiment of the invention will now be described by way of nonlimiting example with reference to the indexed drawings in which.

• Figure 1 is a diagram illustrating the operation of a heat pipe.
• Figure 2 is a schematic longitudinal sectional view of a transformer according to the invention.
• Figure 3 is a schematic cross-sectional view of the same transformer.
• Figure 4 is a side view of the same transformer.
• FIG. 5 is a view similar to that according to FIG. 4, the external fins being omitted, and
• Figure 6 is an enlarged sectional view along line-VI-VI of Figure 4.

Referring first to Figure 1, we see that a heat pipe consists essentially of a cylindrical tube (1) closed at its two ends in (2) and whose inner walls are coated with a capillary network (3). This tube contains a fluid (which in some cases may be water) in such a quantity that it is partially in the liquid state and partially in the state of saturated vapor.

If we suppose that we bring calories to the part of the tube located on the left according to the figure, by placing this left side in a space at high temperature, we understand that the calories entering the tube according to the arrows F1 will vaporize a certain quantity of the fluid which is in liquid phase in the capillary network. The resulting increase in pressure will instantly move the vapor formed according to arrow F2 to the cooler part of the tube on the right. Precisely because of this colder temperature, the vapor will liquefy in this right part, releasing calories which spread according to the arrows F3. The liquid thus formed will in turn go again towards the left part, according to the arrows F4, inside the capillary network.

Such a heat pipe therefore makes it possible to transfer calories at an almost instantaneous speed. In practice, yields are obtained which are incommensurate with the usual yields of conventional heat transfer systems and this over much greater distances.

This reminder being made, we will now refer to Figures 2 to 6 which show a transformer according to the invention.

In the example chosen, it is an explosion-proof transformer with a gaseous atmosphere (generally air), the tank (4) of which is conventionally composed of a corrugated side wall (5) forming two rectilinear vertical sections connected by semi-cylindrical upper and lower arches, wall welded at its ends on two rigid rings (6), on which are bolted at (7) the front (8) and rear (9) covers of the tank. The assembly is supported by a base (10) and stiffened by external crosspieces such as (11) at the camber, and by internal and external flat bars (12) and (13) on the flat parts.

We know that a tank of this kind is intended to contain the transformer windings which are three in number in the example shown and which each consist of a body (14), extended at the top by a head (15 ) and at the bottom by a foot (16) constituting the projecting parts of the magnetic circuits. The windings are carried by four longitudinal beams (17) which support the heads and feet of the coils and which are in turn fixed on feet (18) integral with the tank.

Finally, the transformer windings are connected by connections not shown so as to facilitate understanding of the drawing, on the terminals (19) of a connection box (20) for high voltage on the one hand, and on the terminals (21 ) a connection box (22) for the low voltage on the other hand.

According to the invention, there are arranged in the upper part of the tank on either side of the row of heads (15) four heat pipes (23) and (24) on the right part according to FIG. 3 and (25 ) and (26) on the left side according to the same figure. We will focus in the following more particularly on the heat pipes (23) and (24), it being understood that the heat pipes (25) and (26) are perfectly identical and perfectly symmetrical.

The heat pipes (23) and (24) are mounted one after the other on either side of a central bearing (27). The first (23) passes through the cover 8, on the high voltage side, and extends outside the transformer, the second (24) passes through the cover (9), on the low voltage side, and extends symmetrically beyond the transformer.

In the case of two devices mounted head to tail in a perfectly symmetrical manner, more particularly will be described in the following the assembly and operation of the heat pipe (23), high voltage side.

At its inner end, cut into a cone shape (28), the heat pipe (23) is introduced into the bearing (27) which is a cylindrical tubular body, provided with two flared inlets (29) and through which one has placed a locking pin (30). This bearing, in line with two shoulders (31) is welded to two brackets (32) which, in turn, are bolted to the vertical part of the side members (17).

There is then on the heat pipe (23) a series of receiving fins constituted by flat discs (33) whose central opening has been bent by stamping at (34) to be welded on the heat pipe (23), with a clearance suitable which can be of the order of a centimeter. These fins completely cover the heat pipe from the bearing (27) to the relatively thick retaining ring (35), simply threaded onto the heat pipe.

Beyond the ring (35), the heat pipe passes through a strong plate (36) intended to obstruct the window pierced in the cover for the introduction of the heat pipe. This plate is generally hexagonal to allow the passage of four large mounting bolts (37).

Each of these bolts cooperates with a screwing sleeve (38) welded to the right of a shoulder on the cover (8). It crosses an overflowing range (39) of the plate (36), and its head is protected by a socket (40) located on this range (39).

On the heat pipe (23) is then threaded a flange (41) with circular interlocking with a clearance limited to the explosion-proof gap, flange which comprises an annular shoulder of low height (42). This flange is mounted on the plate (36) using four screws (43), arranged in four shouldered holes (44) of the flange and screwed onto the plate in tapped holes (45), executed on demand as it will be explained later.

Beyond the part (42) of the flange, the heat pipe (23) receives the external heat-dissipating fins (46). These fins are formed as seen in Figures 4 and 6, by two jaws (47) on which are welded two parallel plates (48), the assembly being tightened on the heat pipe (23) by bolts such as (49 ). On each of the plates (48) is welded a metal sheet (50) folded so as to present in section the appearance of successive triangles. These two sheets constitute two parallel layers which are the actual heat sink elements.

The assembly constituting the outer fins (46) is arranged obliquely so as not to go beyond the size of the transformer.

Each outer fin (46) is protected by a protective cover (51) formed by a curved sheet metal to match the size of the tank. This sheet is fixed on the corresponding cover (8) by two brackets (52). To ensure the rigidity of the assembly, the two covers (51) on the same face, are connected to their outer part by two horizontal crosspieces (53) and (54), welded respectively at their lower ends and at their upper ends. .

• On monte d'abord à l'intérieur du transformateur les paliers supports (27) en fixant les potences (32) sur les longerons (17). S'il s'agit d'un transformateur neuf, chacun des couvercles a été pourvu à l'avance des fenêtres entourées des quatre douilles de vissage (38) permettant la mise en place des plaques (36). S'il s'agit d'un transformateur existant dont on veut améliorer le rendement, il suffit de découper ces quatre fenêtres sur les deux couvercles et de monter les douilles (38), toutes opérations particulièrement aisées et peu coûteuses pouvant si nécessaire être réalisées sur le site comme la mise en place des paliers.Le caloduc (23) qui se présente sous la forme d'un tube à extrémité conique en cuivre ou en acier,reçoit par soudage les ailettes intérieures (33) et l'ensemble est ensuite introduit à travers la fenêtre de la face (8). La mise en place est une opération qui est grandement facilitée par la forme conique en (28) de l'extrémité du caloduc et par l'ouverture conique en (29) du palier central (27). La goupille d'arrêt (30) détermine approximativement la position finale du calo- due et l'on peut alors, après avoir enfilé la bague (35), pratiquer le montage de la plaque (36) par vissage et blocage des quatre boulons (37). Grâce au jeu important qui existe au niveau de la traversée de la plaque (36) par le caloduc, on procède ensuite au positionnement définitif du caloduc de façon à ce qu'il soit non pas parfaitement parallèle à l'axe général du transformateur, mais légèrement plus haut à l'extérieur qu'à l'intérieur. On notera à ce propos qu'à l'échelle des dessins, cette légère obliquité des caloducs n'est pas nettement visible, mais qu'en réalité elle existe bien, l'axe d'un caloduc pouvant faire avec l'axe général du transformateur un angle par exemple de 1 ou 2 degrés.

The heat pipes such as (23) are put in place as follows:

• The support bearings (27) are first mounted inside the transformer by fixing the brackets (32) on the side members (17). If it is a new transformer, each of the covers has been provided in advance with the windows surrounded by the four screwing sockets (38) allowing the positioning of the plates (36). If it is an existing transformer whose performance is to be improved, it suffices to cut these four windows on the two covers and to mount the sockets (38), all particularly easy and inexpensive operations which can be carried out if necessary. on site as the installation of bearings. The heat pipe (23) which is in the form of a tube with conical end in copper or steel, receives by welding the internal fins (33) and the assembly is then introduced through the window of the face (8). The establishment is an operation which is greatly facilitated by the conical shape at (28) of the end of the heat pipe and by the conical opening at (29) of the central bearing (27). The locking pin (30) roughly determines the final position of the shell and it is then possible, after having fitted the ring (35), to mount the plate (36) by screwing and locking the four bolts ( 37). Thanks to the large clearance which exists at the level of the crossing of the plate (36) by the heat pipe, one then proceeds to the final positioning of the heat pipe so that it is not perfectly parallel to the general axis of the transformer, but slightly higher outside than inside. It will be noted in this connection that on the scale of the drawings, this slight obliquity of the heat pipes is not clearly visible, but that in reality it does exist, the axis of a heat pipe being able to do with the general axis of the transformer an angle for example of 1 or 2 degrees.

The assembly being held in position and the flange (41) threaded on the heat pipe, we trace thanks to the shouldered holes (44) the exact position that must occupy the four screws (43). Having moved the flange away (41), the blind holes (45) are drilled and tapped, and the flange can then be assembled and blocked, then particularly easy to assemble thanks to the bolts (49) of the assembly (46) constituting the outer fins. When the four heat pipes have been placed as described above, the four hoods (51) are assembled by bolting on the brackets (52) joined together two by two by the welded crosspieces (53) and (54).

Finally, there is a transformer, the size of which for transport has not increased. In fact, the assembly operation which has just been described can, on request, be partially or completely carried out either in the factory or on site.

In the case of an explosion-proof transformer, the explosion-proof properties are fully maintained. It was feared that the heat pipe (23) could be violently ejected in the event of an internal deflagration and thus be the cause of accidents, but this risk was completely eliminated. Indeed, on the one hand, the dimensioning of the parts is such that in the event of tearing caused by an internal overpressure, it is the flange (41) which will ultimately separate from the plate (36) and never the cover plate (36) (8). In addition, all of the inner fins (33) welded to the tube could either tear off or twist and thus pass through the plate (36). This risk is completely eliminated thanks to the ring (.35) which cannot pass through the plate and which in turn cannot be crossed by the fins, because it would then be necessary to have all of the circular welds torn off. the fins.

Now with regard to the efficiency of the apparatus, tests have been carried out on an explosion-proof transformer with gaseous atmosphere of conventional design with a power of 1000 KVA which has been equipped with four heat pipes providing a heat-receiving surface. approximately 3 m ² , thanks to the four series of interior fins. The external exchange surface of the dissipating fins (46) was of the same order.

The transformer in question, by natural cooling by convection and by internal circulation of air, could not dissipate more than 10 KW.

Thanks to the installed heat pipes, it has been found that about 25% of the calories are evacuated, that is to say 3 kw. It was therefore possible to increase the power of the device and tests have shown that it is possible without risk and without overheating, to bring this power to at least 1250 KVA.

The invention makes it possible to gain around 25% in transformer power, without increasing the volume and for a particularly reasonable cost price, whether it be new appliances or appliances transformed in the factory or on site.

Claims (13)

1. Transformer in particular of the explosion-proof type, that is to say the high and low voltage windings (14) are housed in a pressure-resistant metal tank (4) developed during an internal explosion of a mixture explosive gas, and which prevents the transmission of the explosion to the surrounding atmosphere, tank consisting of a side wall (5) and two covers (8-9) supporting the boxes (20-22) of high and low connection tension, characterized in that heat pipes (23,24,25,26) mounted head to tail, at least approximately parallel to the axis of the side wall (5), are arranged, for their receiving side, in space free separating the windings of this wall, between a central bearing (27) receiving the ends of two heat pipes and outlet flanges (41) fixed on the covers (8,9), while their dissipative side is located beyond said flanges outside the tank, receiving fins (33) and dissipating fins (46) being provided respe on the receiving and dissipating sides of the heat pipes. 2. Transformer according to claim 1, characterized in that it comprises at least two pairs of heat pipes (23,24), (25,26) mounted head to tail in the upper part of the tank on either side of the magnetic circuit (15) of the windings. 3. Transformer according to claim 1 or claim 2, characterized in that the heat pipes have a slight inclination such that their dissipating side is higher than their receiving side. 4. Transformer according to one of claims 1 to 3, characterized in that the bearings each consist of a sleeve (27) with flared openings (29) provided with a central stop (30) and mounted on an upper spar ( 17) of the transformer. 5. Transformer according to one of the preceding claims, characterized in that the ends (28) of the heat pipes supported by the bearings have a tapered advantageously frustoconical shape. 6. Transformer according to one of the preceding claims, characterized in that the outlet flanges (41) traversed by the heat pipes with a very slight play, are fixed on demand on stronger plates (36), mounted on the covers (8,9) to ensure the closing of a window allowing the passage of the internal fins. 7. A transformer according to claim 6, characterized in that the passage of the heat pipes through the plates is made by an orifice of relatively large dimension. 8. Transformer according to one of the preceding claims, characterized in that the internal receiving fins (33) are circular discs threaded on the heat pipes and welded onto the latter by the curved edge (34) of their central opening. 9. Transformer according to claim 8, characterized in that the receiving fins occupy the entire inner part of the heat pipes, with the exception of a portion located at the end on the outlet side, on which is threaded a retaining ring (35) . 10. Transformer according to one of the preceding claims, characterized in that the dissipating fins form, for each heat pipe, a parallelepiped block consisting of two corrugated sheets (50) welded on two parallel plates (48), mounted on two jaws (47 ) which enclose the heat pipe. 11. Transformer according to claim 10, characterized in that the parallelepipedic blocks are arranged obliquely on the heat pipes so as to respect the size of the transformer. 12. Transformer according to one of the preceding claims, characterized in that the external dissipating fins are protected by a cover (51). 13. Transformer according to claim 12, characterized in that the covers (51) consist of curved sheets matching the size of the transformer, fixed on the covers and joined two by two on their outer periphery by crosspieces (53, 54) .

Images