EP2665838B1 - Process for heating and drying a good - Google Patents

Description

The invention relates to a method for heating and drying a good, which has an insulation, according to the preamble of claim 1.

Various methods and devices for drying a product, in particular the insulation of transformers, are known from the prior art. Thus, drying methods are known in which the material to be dried is in an autoclave and heated by means of a circulation process with hot air and then moisture is removed from the material by means of vacuum. During heating, the walls of the autoclave are heated to a temperature of approx. 120 ° C. The passing air absorbs the heat from the walls and heats up to approx. 110 ° C. After heating the insulation, the autoclave is evacuated and the residual moisture removed from the insulation.

The material to be dried may be, for example, transformers, capacitors, current transformers, current feedthroughs, etc., which have hygroscopic isolations on a pulp and / or plastic base. The material has a portion of insulation containing the water to be extracted and a core in which substantially no or no insulation is provided. Particularly in the case of transformers, there is a need to extract water from the paper insulation of the transformer, so that the insulating properties of the oil-paper dielectric are not adversely affected.

Out EP 0 801 405 A2 a device is known in which the heating of a winding containing a solid insulation, by means of a heater and a circulated in the autoclave hot air flow takes place. The winding is through the Heating device energized and leads to a warming of the insulation from the inside. At the same time carried by convection, a heat transfer of hot air to the insulation, which causes a warming of the insulation from the outside. The air temperature is below the temperature of the winding, and the air circulation within the autoclave is below the atmospheric pressure. The drying of the winding takes place in a subsequent heating process drying process in which the autoclave is evacuated.

Due to the fact that the substantial heating of the material takes place via the electric heating device, local overheating in the insulation results. These local overheating is reinforced by the fact that the insulation is a poor conductor of heat and thus the heat is distributed very slowly evenly within the insulation, which leads to impairments and quality losses of the insulation. The high temperature differences within the insulation can not be sufficiently compensated for by the hot air inside the autoclave because the heat given off by the air is too small due to the low heat capacity of air and low pressure to compensate for temperature differences within the insulation. The air temperature is limited to a value of about 110 ° C, since above this value, a significant reaction of the oxygen takes place with the material of the insulation, which can damage the insulation.

In DE 196 37 313 A1 discloses a device for heating and drying a good, which operates according to the so-called vapor-phase method. In this case, after an evacuation of the autoclave kerosene vapor is fed to the autoclave. By condensing the kerosene vapor, its latent heat is released to the surface of the material and this heated it. After heating the insulation to a temperature of about 125 ° C, the admission is set with Kerosindampf and the good finally dried by evacuation of the autoclave in a drying process.

The disadvantage of this method is that during the heating process, the condensed kerosene penetrates into the insulating material and in the pores the outlet opposes the water vapor. In addition, during the heating process, a considerable proportion of the kerosene vapor is conducted with the steam from the autoclave and condensed in a condenser. Thus, in this process, a significant loss of energy associated with the drying process.

US 4,812,608 A discloses an oven for thermo-magnetic treatment of a toroidal coil. The furnace has heating disks for heating the toroidal coils, and an inert gas can be supplied to the furnace for promoting the heating operation. As an alternative to supplying the inert gas into the furnace interior, it can be evacuated.

US 2002/0178604 A1 discloses an apparatus for drying and heating a transformer, the apparatus having an autoclave. In the heating process, a condensation of the solvent vapor takes place at the solid insulation.

In EP 1 248 061 A1 and the article "Modern vapor drying processes and plants" by Micafil Vacuumtechnik; 1992; In each case, PK Gmeiner discloses a device in which a solvent / water / vapor mixture is used for heating or drying an article in an autoclave.

US 4,411,075 describes a method for heating and drying a solvent-laden material by means of a drying chamber which is open to the environment, uses a stream of inert gas as heating gas and prevents the entry of air into the drying space by an inert gas-flushed lock chamber.

EP 1 406 056 A1 discloses the drying of a good in an autoclave, wherein the heating of the material to be dried on the heat of condensation of a vapor takes place, which is reflected in this good.

The object of the invention is to provide a method for heating and drying a good, which does not have at least the above disadvantages.

The object is achieved by a method according to claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

According to the invention, a method is provided for heating and drying a product, which has an electrical insulation. The device has an evacuable autoclave into which a gaseous heating medium can be introduced. The device is designed such that during the heating process, the heating medium remains in the gaseous state throughout the process. The gaseous heating medium is in particular an inert gas.

For the purposes of the invention, an autoclave is understood as meaning a substantially vacuum-tight chamber or a vacuum-tight housing. The autoclave is additionally designed in such a way that an overpressure can prevail in the chamber or the housing.

For the purposes of the invention, inert gas means all gases which do not react with the isolation of the material or whose tendency to react with the insulation is less than the propensity to react of the air, in particular of the oxygen. For example, nitrogen can be used as the inert gas. The advantage of using nitrogen is that it can be procured inexpensively and thus the operating costs of the device are low. Of course, other inert gases, such as helium, argon, neon or the like can be used. The insulation may be a hygroscopic insulation based on pulp and / or plastic.

The use of inert gas as a gaseous heating medium has the advantage that the damaging effect of oxygen on the insulation is excluded because the gaseous heating medium does not react with the insulating material and thus can not damage it. In contrast to the use of air, the inert gas can be heated to temperatures of over 120 ° C, without having to fear damage to the insulation. Due to the high temperature of the gaseous heating medium, the convective heat input into the insulation increases, which reduces the heating time of the insulation.

Furthermore, there is an advantage with the use of a gaseous heating medium, in particular inert gas, in that it can be removed very quickly and completely from the autoclave during an intermediate process during a heating process or during drying during a drying process. This is possible because the gaseous heating medium does not condense and does not oppose the exit of the water vapor as the condensed Kerosindampf.

In an advantageous embodiment of the invention, the autoclave may have a discharge line and a feed line connected to the discharge line. The autoclave, the The discharge line and the supply line can form a circle, in particular a closed heating circuit. By providing a closed heating circuit can be ensured that the inert gas is not released during the heating process in the environment, whereby the energy loss of the device is reduced again. The gaseous heating medium or the mixture of gaseous heating medium and the evaporated water from the insulation flows during the heating process within the circle in which it can be dried and / or heated.

During a drying process, the autoclave is evacuated. The evacuation of the autoclave has the advantage that an additional diffusion gradient for the water vapor is generated. The mixture in the autoclave can be removed from the autoclave via a vacuum pump set. The vacuum pump set may be formed as an open circuit. In this case, the discharged mixture is discharged into the environment. Of course, the vacuum pump set may be formed as a closed circuit, so that after the drying process, the gaseous heating medium can be supplied to the autoclave again. In the vacuum surge set, a dryer may be provided for separating the condensed water from the mixture so as to ensure that only the gaseous dry heating medium is returned to the autoclave.

According to a preferred embodiment, the heating process can take place at several intervals in which the material is heated and subsequently the pressure in the autoclave is lowered. Of course, the pressure is not lowered as much as in the final drying process, in which the autoclave is evacuated.

Within the autoclave, a circulation device may be provided. By means of the circulation device is ensured in a simple manner that the inert gas flows around the estate completely. As a result, a uniform heating of the goods is achieved. The circulation of the gaseous heating medium in the autoclave can be carried out in particular at atmospheric pressure or overpressure. The circulation of the gaseous heating medium at overpressure offers the advantage that the energy content of the Heating medium and thus the heat transfer to the goods is high. Further, baffles may be provided within the autoclave, which can deflect the gaseous heating medium, so that heating of the goods can be done, for example, from bottom to top.

In the heating circuit, a dryer, in particular a condenser and / or an absorption dryer may be provided between the discharge line and the supply line. By means of the dryer, the mixture taken from the autoclave is dried from, for example, inert gas and steam. Between the dryer and the discharge line, a heat exchanger can be arranged. In the heat exchanger, the mixture taken from the autoclave is cooled before entering the dryer. The released during the cooling heat can be used to heat the gaseous heating medium before it is fed via the supply line to the autoclave. Of course, there is also the possibility to use the released heat for other applications. The provision of the heat exchanger has the advantage that the energy loss of the device is reduced. Additionally or alternatively, a further heat exchanger may be provided, which is arranged between the dryer and the feed line. In the heat exchanger, the gaseous heating medium can be heated prior to feeding into the autoclave.

The supply of heated, dry gaseous heating medium in the autoclave has the advantage that in addition to the heating of the insulation for the steam generated in the insulation, a partial pressure gradient is generated and thus there is a diffusion from the isolation to the gaseous dry heating medium. Thus, by the supply of gaseous heating medium already during the heating process, a predrying of the insulation can be achieved.

In a preferred embodiment, a heating device for supplying energy to the goods can be provided in the device. The heater may be formed for example as a resistance heater, which allows a conversion of electrical energy into thermal energy. The energy supply to the good can be provided to a provided in the good electrical line, in particular a coil-shaped line, done. The line, in particular the transformer coil, is arranged in the material such that both the insulation and the core of the material, which has substantially no insulation, are warmed up. By providing the heating device can be ensured that the insulation of the material in addition to the heat input through the gaseous heating medium additional heat energy is supplied from the inside. Consequently, the provision of the heater allows a uniform heating of the poor thermal conductivity insulation. In this case, the gaseous heating medium may have a higher temperature than the located in the estate heated, electrical line, in particular a coil-shaped line.

The energy supply from the heater to the estate can be done during the heating process as well as during the drying process, which is followed by the heating process of the goods. An energy supply during the drying process has the advantage that heat losses can be compensated, which can arise during the drying process. In particular, a loss of heat may occur in the evaporation of the water contained in the insulation, which leads to a reduction in the temperature of the insulation. Furthermore, heat loss may be due to heat being transferred from the insulation of the material to a portion of the good adjacent to the insulation, such as e.g. the core of the material flows, whose temperature is lower than the temperature of the insulation. The power supply by the heater can be done during all or part of the drying process. In particular, the energy supply can be switched off towards the end of the drying process.

By the heater, for example, the core of the material can be heated to a temperature where the heat flow in the insulation to this section is low. In particular, the core of the material can be heated in such a way that its temperature is above a condensation temperature of the water evaporating from the insulation of the material. This can prevent the water evaporated from the insulation from condensing on the core.

In a preferred embodiment, the material is designed as a transformer. In this case, the core corresponds to the transformer core, which may consist of individual, mutually electrically insulated core sheets. The heating device energizes a low voltage coil and / or a high voltage coil of the transformer. In particular, a sole energization of the undervoltage coil has the advantage that the transformer core can be heated in a simple manner. This is possible because the undervoltage coil is located close to the core of the transformer. In particular, it is possible that the high-voltage coil and / or low-voltage coil are energized differently during the heating process or the drying process. Thus, both coils can be energized during the heating process and during the drying process, only the lower voltage coil. Of course, further energizing possibilities of the two coils during the heating process or during the drying process are conceivable. In particular, the two coils can be energized to different degrees.

The heater may be designed as a DC or low frequency or high frequency device. In particular, the provision of the heater as a high-frequency device has the advantage that the skin effect can be exploited. As a result of the skin effect, the current density at high-frequency alternating currents is greater on the outside of the conductor than in the middle of the conductor, which increases the resistance in the line and thus the heat transfer into the material, in particular into the core.

In an advantageous embodiment of the invention, a measuring unit may be provided in the vacuum pump set, by means of which a measurement of the dew point can take place in a vacuum line. Depending on the result of the measurement, the drying process can be ended.

The invention is not limited to the drying of a product whose insulation contains water. Of course, with the device according to the invention or the process according to the invention also dried a good that has a different substance to be evaporated than water.

Other objects, advantages, features and applications of the present invention will become apparent from the following description of an embodiment with reference to the drawings, wherein identical or equivalent elements are usually provided with the same reference numerals. All described and / or illustrated features alone or in any meaningful combination form the subject matter of the present invention, also independent of their summary in the claims and their dependency.

Show:

Fig. 1:

a basic structure of a device for heating and drying a good,

Fig. 2:

a section of a schematic representation of a transformer.

In the FIG. 1 1 for heating and drying a product 4 has an autoclave 10, a heating device 14, a heating circuit 2 and a vacuum pump set 3.

The autoclave 10 is formed as a chamber which is designed so that it can be both evacuated and pressurized. Within the autoclave 10, the material is arranged, wherein it may be, for example, a transformer active part 4, at the estate. Furthermore, a circulation device 13 is provided within the autoclave 10, by means of which the gaseous heating medium in the autoclave 10 can be circulated. The circulating device 13 is driven by a motor, not shown in the figures.

The heating circuit 2 is formed as a closed circuit and has a discharge line 23 and a supply line 24, which are connected to each other. Via the discharge line 23, the mixture contained in the autoclave 10 is removed and fed via the feed line 24 to the autoclave 10. The heating circuit 2 has, viewed in the flow direction of the removed mixture, a first heat exchanger 22, a dryer 20 and a second heat exchanger 21.

The vacuum pump set 3 is designed to be open and has a vacuum line 30 which communicates with the interior of the autoclave 10. Furthermore, the vacuum pump set 3 has a measuring unit 31, by means of which the dew point in a bypass line 33 of the vacuum line 30 is measured and a third heat exchanger 32.

The heater 14 is connected to the transformer 4, in particular the coil of the transformer 4. The in FIG. 2 shown transformer 4 has a transformer core 40 and a coil. The coil has a low voltage coil 41 and a high voltage coil 42, both of which extend around the transformer core 40. In this case, the undervoltage coil 41 is arranged closer to the transformer core 40 than the high-voltage coil 42 FIG. 2 The transformer shown, the insulation is not shown.

The gaseous heating medium used is inert gas, in particular nitrogen.

In the following, the operation of the device 1 will be described by means of heating and drying of a transformer. Of course, the operation of the device 1 is not limited to heating and drying a transformer.

During the heating process, the transformer 4 is heated. In this regard, the walls of the autoclave 10 are heated, whereby the gaseous heating medium in the autoclave 10 also heats up. By the circulation device 13, the gaseous heating medium is circulated within the autoclave 10. In the circulation of the gaseous heating medium is a Heat emission from this to the not shown in the figures insulation of the transformer 4. The dry gaseous heating medium leads to the heating in addition to a partial pressure gradient is generated, so that there is a diffusion of water vapor from the insulation to the gaseous heating medium.

The mixture of gaseous heating medium and water vapor is removed via the discharge line 23 from the autoclave 10 and flows through the first heat exchanger 22, in which it is cooled. Following this, the mixture flows through a dryer 20, in which the water vapor is deposited. The condensed water flows into a collecting tank, not shown in the figures. The dried gaseous heating medium flows through the dryer 20 after a second heat exchanger 21, in which the gaseous heating medium is heated.

During the heating process, the coil of the transformer 4 is energized by the heater 14. This ensures that the transformer core 40 and the insulation, not shown, are heated, so that a uniform temperature distribution within the transformer 4 is achieved.

As soon as the insulation 4 of the transformer has reached a specific temperature, in particular 120 ° C., the heating process is ended and the drying process is started. During the drying process, the mixture in the autoclave is sucked off via the vacuum line 30 or the autoclave is evacuated. By lowering the pressure in the autoclave, an additional diffusion gradient for the water vapor is generated, whereby the drying of the insulation accelerates and / or improves. The extracted mixture is discharged into the environment, wherein previously a heat exchange takes place in the third heat exchanger 32 between the mixture and, for example, cooling water of the device 1. By means of the measuring unit 31, the dew point of the extracted mixture is measured in the bypass line 32 and, depending on this value, it is decided whether the drying process has ended or not.

reference numeral

1

Device for heating and drying a good

2

Aufheizkreis

3

Vacuum pump set

4

transformer

10

autoclave

13

circulation

14

heater

20

dryer

21

first heat exchanger

22

second heat exchanger

23

discharge

24

feed

30

vacuum line

31

measuring unit

32

third heat exchanger

33

bypass line

40

transformer core

41

Under voltage coil

42

High voltage coil

Claims (6)

1. Method for heating up and drying a good (4) that has an electrical insulation, wherein a gaseous heating medium flows within an autoclave (10) and remains in the gaseous state during the heating process, wherein subsequent to heating the good (4) a drying process is carried out, in which the autoclave is evacuated, characterized in that the gaseous heating medium is an inert gas.
2. Method according to claim 1, characterized in that a circulation of the gaseous heating medium is carried out in the autoclave (10), in particular at atmospheric pressure or overpressure.
3. Method according to one of the claims 1 or 2, characterized in that at least one interval is carried out for heating the good (4) and subsequent lowering of the pressure in the autoclave (10).
4. Method according to one of the claims 1 to 3, characterized in that, in particular during the drying process energy is supplied to the good (4) by a heating appliance (14), in particular in such a manner that an inside temperature of a core of the good is achieved that is above a condensation temperature of the substance that is to be vaporized in the good (4), in particular water.
5. Method according to one of the preceding claims 1 to 4, characterized in that a mixture that is extracted from the autoclave (10), in particular a mixture of the gaseous heating medium and the water vapor, is dried and/or in that the mixture is cooled down before being dried.
6. Method according to one of the preceding claims 1 to 5, characterized in that the gaseous heating medium is heated up before being supplied into the autoclave, in particular by means of the heat that is being released as the mixture is cooling down.

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