EP0454805A1

EP0454805A1 - Controlled drying-impregnation-polymerization processes

Info

Publication number: EP0454805A1
Application number: EP90916023A
Authority: EP
Inventors: René PIOCH
Original assignee: Cahueau Colette (heritiere De L'inventeur Decede); Pioch Evelyne (heritiere De L'inventeur Decede); Pioch Olivier (heritiere De L'inventeur Decede); Pioch Sylvie (heritiere De L'inventeur Decede); Pioch Isabelle (heritiere De L'inventeur Decede)
Current assignee: Cahueau Colette (heritiere De L'inventeur Decede); Pioch Evelyne (heritiere De L'inventeur Decede); Pioch Olivier (heritiere De L'inventeur Decede); Pioch Sylvie (heritiere De L'inventeur Decede); Pioch Isabelle (heritiere De L'inventeur Decede)
Priority date: 1989-11-09
Filing date: 1990-10-12
Publication date: 1991-11-06
Also published as: WO1991007764A1; JPH05505279A; FR2654249B1; FR2654249A1; US5258594A

Abstract

Le procédé de séchage-imprégnation-polymérisation contrôlés nécessite durant toutes les opérations que les appareils à traiter soient placés dans une enceinte dans laquelle est maintenu le vide. Les bobinages sont directement chauffés par un générateur de fréquence. L'ensemble des opérations est piloté et contrôlé par un automate qui prend en compte les principaux paramètres et en particulier la résistance d'isolement des bobinages. Le procédé est applicable à l'encapsulage des bobinages par des résines polymérisables. Le vide et le chauffage sont maintenus après séchage et la polymérisation horizontale est réglable. Les bobinages sont directement suspendus dans le moule sans aucun point de contact avec le moule (exception faite des connexions électriques) par des sangles tissées isolantes qui seront coupées ou lâchées lorsque la hauteur des bobinages encapsulés dans la résine polymérisée sera suffisante pour assurer leur maintien. Le temps et la consommation peuvent être divisés par quatre par rapport aux procédés traditionnels. Le pilotage et le contrôle permettent d'atteindre pratiquement le ''zéro défaut''.The controlled drying-impregnation-polymerization process requires, during all operations, that the devices to be treated are placed in an enclosure in which the vacuum is maintained. The windings are directly heated by a frequency generator. All operations are controlled and controlled by an automaton which takes into account the main parameters and in particular the insulation resistance of the windings. The method is applicable to the encapsulation of the windings with polymerizable resins. The vacuum and the heating are maintained after drying and the horizontal polymerization is adjustable. The windings are directly suspended in the mold without any point of contact with the mold (except for electrical connections) by insulating woven straps which will be cut or released when the height of the windings encapsulated in the polymerized resin is sufficient to ensure their maintenance. Time and consumption can be divided by four compared to traditional methods. The piloting and the control allow to reach practically the `` zero defect ''.

Description

CONTROLLED DRYING-IMPREGNATION-POLYMERIZATION PROCESSES

The life of a transformer depends greatly on drying, the di¬ electric in which its windings are immersed and that of its solid insulators which moreover must not have suffered from the heating to which they were subjected to be dried. Similarly, no trace of air should remain or be trapped during filling-impregnation-po¬ polymerization.

For submerged transformers, these operations are carried out in two stages: first drying in an oven heated with air or kerosene for a period depending on the size of the transformer but which is always more than several hours to reach several days.

With the increase in production worldwide, vacuum drying systems have been abandoned because they are too expensive compared to those of hot air drying. Only the filling is done under vacuum in small autoclaves containing only a few devices. But the quality and speed of vacuum drying are recognized and regretted. Low frequency vacuum heating methods exist but, as for the previous system, their cost did not allow them to generalize. For power transformers which have tanks capable of supporting vacuum, these two operations are carried out directly in the closed or welded tank. The drying is done by a succession of heatings followed by vacuum meats, this for several days. Vacuum filling follows drying. Many small repairers or manufacturers do not have a vacuum filling system because of their very high price for their capacity. None of the methods or installations used is really controllable and controllable, and the manufacturers continue to take into account an important safety factor, determined by experience, resulting in manufacturing costs higher than those that could be expected. wish, especially in the Third World, where the needs are greatest.

The process which is the subject of the invention provides a reliable and economical solution whatever the type or the importance of the manufacturing.

DESCRIPTION The process which is the subject of the present invention consists in causing the heating necessary for the drying of the active parts (2) by circulating, generally in the primary windings, a high frequency current. produced by a generator (9), to obtain losses by Joule effect. The frequency and intensity are determined for each type of transformer either by an abacus or by an automaton.

Heating therefore begins from inside the coils (8) and is diffused by contact to the outside (secondary) (8a) and to the interior (magnetic core) (10). This heating being done in a vacuum, practically all the losses by radiation are eliminated, from where a significant gain of energy; and the three windings being connected to control devices such as a thermostat (11) and a mehometer (12), it is possible to control the temperature so that at no time does it exceed the temperature limit of solid insulators (class ^' B 105 ° C for example).

The state of the drying is in turn controlled by the megometer which indicates the insulation resistance, which makes it possible to follow this drying - but above all to stop it as soon as it is sufficient, that is to say to say that the resistance to isolation has reached a stable value.

It is then that either the automaton or a controller, warned by a signal, stops the heating and starts the filling by putting the oil reservoir (5) in communication with the tank (1) by operation of the valve (13) of the transformer. The active parts are at around 100 ° C,

The impregnation is very good since the insulators are expanded and the fluidity of the oil is increased by heating by conductivity or because it has itself been heated as explained below. A calibrated level (14) with which the rod (15) is fitted makes it possible to put under a pressure determined by the winding-oil temperatures and calculated by the tomato oil inside the tank.

Of course, the insulation resistance continues to be measured during the filling operation to be certain, in particular, that no bubble has remained trapped. Against one or more walls of the autoclave is arranged an oil dryer. Which consists of a chute (16) through which the oil arrives and which trickled on each side of a panel constituted by a fabric or a thin mesh (17), thus providing an exchange surface practically double that of the panel under a small thickness (slot of the chute). At the lower part of the panel is arranged a gutter (19) collecting the oil which is directed towards the lower part of a tank (5) to be pumped there (20), either to be re-treated, or to fill the tanks. Oil insulation resistance is continuously measured in the gutter so that the treatment is stopped when the desired value is reached. Since this operation is done in hidden time, it is possible to continue it until the time of filling. It is also possible to heat the panel since no heat will be supplied by radiation, the whole being under vacuum, to facilitate drying.

When using a false tank (fig.l), it is the cover (2d) of the transformer to which the active part (2) is suspended which serves as a cover. The bottom (21) of this false tank is connected by means of a three-way valve (13) to the vacuum pump (7) and to the oil tank (5). The procedure is identical, but after filling the false tank and impregnating the windings (control, insulation resistance), the tank is emptied and the active parts are introduced into their tank placed nearby, a chute preventing drops of oil to fall to the ground. After fixing the cover, the filling is completed through a small reservoir (22) which is fixed on the filling orifi¬ and which allows to visually check that the level remains stable and that no bubbles come out of the tank. The transformer terminals remained connected to the measuring devices to check the insulation resistance. The vacuum is only interrupted when this resistance is correct. The oil volumes being low, it is possible to equip one or two walls of the false tank of the oil dryer (6) described above. With this process, heating and drying are extremely fast and the time required is divided by five to seven compared to traditional methods. On the other hand, the vacuum volume is very low since the false tank is designed for a single device. It is advantageous to make the false tanks as and when required and to have them of various sizes, their construction being very simple and suitable for the installation of vacuum, heating and control.

In the case of large manufacturing with drying ovens and vacuum autoclaves for filling, it is possible to equip these autoclaves (A) to do all of the drying and filling operations there. However, these operations are longer than just filling, so a second autoclave must be provided. But the saving of time is such that a second autoclave is generally sufficient, which considerably reduces the cost of the investment since a large part is recoverable. This is also the case for power transformers (fig. 3) because only the frequency generator and the command and control cabinet are to be supplied, all the other necessary elements (vacuum pump, re¬ oil, etc ...) already existing. In the case of coated transformers, the process can be used to polymerize epoxy resins under vacuum. In this case, it is possible to act on the manner of polymerization, therefore on the tensions which develop during the polymerization phase.

When the polymerization must be carried out under vacuum, it is the molds which are heated. Regardless of the fact that their manufacture is more complicated, the polymerization, therefore the solidification, is done from the outside inwards and it is the windings which support all the stresses, unlike the patented process. More generally, the mold filled under vacuum is placed in an oven where the entire resin is mass polymerized with weak parts formed by the support and centering bridges which, although made of the same material, are present interfaces to facilitate pathways and microcracks. With the present method, the windings to be encapsulated (fig. 4) are introduced into their molds (27) suspended by insulating straps (23), the connections for the switch (24) helping to immobilize and center the winding, although that the judiciously arranged straps are sufficient. The winding is connected to the generator (9) and when the autoclave is closed, the vacuum pump is started. After the drying controlled by the insulation resistance and the maintenance of the vacuum, the resin (25) is left poured along the walls with a flow rate such that its setting is made with a small thickness and horizontally. In this way, no large volume will ever be in the polymerization phase, another advantage of the process is that when a large part of the winding is already encapsulated (26), it is possible, by a simple remote controlled mechanical operation , cut or drop in the mold the straps which will in turn be encapsulated. It is thus possible to obtain an encapsulated bobi¬ swimming without any mechanical bridge with the outside which would create risks of pathways and which would oblige to considerably increase the thicknesses of resin along the vertical walls and especially in the lower part.

Thus, this process can be adapted very flexibly to all manufacturers of transformers regardless of their production capacity under economical conditions to improve quality. Figure 1 shows an individual installation with a false tank supporting the vacuum (IA) into which are introduced the parts acti¬ ves (2) to dry-impregnate with the materials ensuring operations and their control: generator (9), cabinet control (4) and control, oil tank (5), vacuum pump (7).

Figure 2 shows the process applied to a large production with a complete autoclave (A) replacing the false tank and being able to contain the desired number of devices, the active parts (2) already in their tank (1) and connected to the generator ( 9) and to the command and control cabinet (4), the tank to the oil tank (5). An oil drying device (6) can be added thereto as well as means for recording the results (3).

FIG. 3 shows the process applied to a large power transformer with its tank (the), the generator (9), the control and command cabinet (4), the oil tank (5), the vacuum pump (7) and the recording means (3), etc.

FIG. 4 shows a particular application to the encapsulation-polymerization of windings (8) by the same high frequency heating process of the windings to provide the heat necessary for the vacuum polymerization of the resin.

Figure 5 shows the oil drying device in the auto¬ clave (A) with the chute (16), the panel consisting of the fabric (17) and the gutter (19) which collects the oil (5h ), the oil tank (5) and the circulation pump (20) with the sealed pipes (18) for recycling.

Claims

1) Controlled drying-impregnation-polymerization process characterized by the fact that the significant parameters are measured, recorded and processed to ensure the control, control and progress of the process, the apparatus being enclosed in an enclosure where maintained a high vacuum, while being connected to a frequency generator and an oil and resin tank.

2) Controlled drying-impregnation-polymerization process caractéri¬ se according to claim 1 by the fact that the drying is obtained by heating the windings by connecting them to the terminals of the generator whose frequency, intensity and voltage are defined by compared to the device to be treated in order to have the best heating, this generator being able to be connected to several identical or different devices.

3) controlled drying-impregnation-polymerization process caractéri¬ sé according to claim 1 by the fact that the control and the piloting of the drying are obtained by measuring and treating the insulation resistance of the windings, permanently or alternatively with the heating in the case where a single connection is possible and where the superposition of two currents is impossible, as well as by measuring and processing the internal temperature of the windings so that drying can be stopped as soon as the conditions are met and 1 The next operation is triggered by putting the oil tank in communication with the device to be impregnated automatically or manually by a controller warned by a signal.

4) Process of drying-impregnation-polymerization controlled character according to claim 1 by the fact that the control and control of the impregnation of the parts still hot and expanded is obtained by measuring and treating the insulation resistance of the impregnated windings as well as the information transmitted by a calibrated level of precision in such a way that this impregnation is stopped as soon as the complete filling is carried out, that the gassing has stopped and that the initial pressure having to exist in the tank and determined by taking into account the winding-oil temperatures is reached.

5) controlled drying-impregnation-polymerization process caractéri¬ se according to claim 1 by the fact that when the impregnation is replaced by an encapsulation in a polymerizable resin, this polymerization is obtained by maintaining the heating after drying and letting the resin flow into the mold at a controlled rate We want the polymerization to take place only in a small thickness and horizontally in order to reduce internal tensions, the coils being suspended in the mold by insulating woven straps which will be cut or released when the height of the coils encapsulated in the polymerized resin will be sufficient to maintain them in the mold, thus eliminating any holding part which would cause weakening of the encapsulation and risks of tracking.

6) controlled drying-impregnation-polymerization process caractéri¬ se according to claim 1 by the fact that the drying of the oil for the impregnation is obtained by running the oil on each side of a panel vertical disposed inside the enclosure where the vacuum is maintained and constituted by a fabric or a fine mesh, of¬ frant thus a double exchange surface in a very thin; a pump and a reservoir allowing the oil to be reprocessed as necessary until the measurement of its insulation resistance measured at the bottom of the panel has reached the required value.

7) controlled drying-impregnation-polymerization process caractéri¬ se according to claim 1 by the fact that when the tank of the transformer to be treated can withstand the vacuum as is the case for power transformers, this tank is used as enclosure where the vacuum is maintained, the process being used by directly connecting the transformer terminals to the frequency generator and to the control-command cabinet.

8) A process of drying-impregnation-polymerization controlled character according to claim 1 by the fact that the enclosure in which the vacuum is made can be a false tank when it is necessary to treat only one device at a time, this which is the case for many repairers or winders, the cover of the apparatus being able to serve as a cover for this false tank, several being able to be used simultaneously, and the device for drying the oil being able to be placed inside close of a vertical wall.