WO2013034382A1 - Device for heating and drying a good - Google Patents

Abstract

The invention relates to a device (1) for heating and drying a good (11) having an electrical isolation and to a method for heating and drying a good (11). The device (1) has an autoclave (10) into which a gaseous heating medium can be introduced. The gaseous heating medium remains in a gaseous state during the heating process, wherein the gaseous heating medium is an inert gas.

Description

 Description: The invention relates to a device for heating and drying a product, which has an electrical insulation, according to the preamble of claim 1. Furthermore, the invention relates to a method for heating and drying of a material having an insulation, according to the preamble of claim 9. From the prior art, various methods and apparatus for drying a good, in particular the insulation of transformers are known. 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. In the

Heating the walls of the autoclave are heated to a temperature of about 120 ° C. The passing air absorbs the heat from the walls and heats up to approx. 1 10 ° 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 pulp and / or plastic base. The estate has one

Section with insulations, in which the water to be extracted is contained, 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. From EP 0 801 405 A2 a device is known in which the heating of a

Winding, which contains a solid insulation, by means of a heater and a recirculated in the autoclave hot air flow. 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 the hot air to the

Isolation, 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 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 over the electrical

Heating device occurs, there are local overheating in the insulation. These local overheating is exacerbated by the fact that the insulation is a poor conductor of heat and thus the heat within the insulation is very slow

evenly distributed, which leads to impairments and quality losses of the insulation. The high temperature differences within the insulation can not be sufficiently compensated 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 the temperature differences within the autoclave

Balance insulation. The air temperature is limited to a value of about 1 10 ° C, since above this value, a significant reaction of the oxygen takes place with the material of the insulation, which can damage the insulation.

DE 196 37 313 A1 discloses a device for heating and drying a product, 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 a furnace 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 a device for drying and heating a transformer, the device having an autoclave. In the heating process, a condensation of the solvent vapor takes place at the solid insulation.

The object of the invention is to provide an apparatus and a method for heating and drying a good, at least the above

Do not have disadvantages. The object is achieved by a device according to claim 1 and a method according to claim 9. Advantageous embodiments of the invention are the subject of the dependent claims.

According to the invention, an apparatus and a method for heating and drying a good is provided, 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 throughout the process remains in the gaseous state. 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 isolation on pulp and / or cellulose

Act plastic base. 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 operation 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

Aufheizkreises can be ensured that the inert gas during the

Heating process is not discharged into the environment, causing the

Energy loss of the device again reduced. 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 as a

be formed closed circuit, so that after the drying process, the gaseous heating medium can be supplied to the autoclave again. By doing

Vacuum pump 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 may be between the discharge line and the supply line

Be provided dryer, in particular a condenser and / or an absorption dryer. 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 pre-drying 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 heater can be ensured that the insulation of the goods in addition to the heat input by the gaseous heating medium additional

Heat energy is supplied from the inside. Consequently, by providing the

Heating device allows uniform heating of 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 during the

Heating process as well as during the drying process, which is followed by the heating process of the goods carried out. An energy intake during the

Drying process has the advantage of compensating for heat losses that may occur during the drying process. In particular, a

Heat loss during evaporation of the water contained in the insulation

arise, 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

Energy 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 insulation of the material

is evaporating water. This can prevent that from the

Isolation evaporated water condenses 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

Undervoltage coil can be energized differently during the heating process or the drying process. So both coils can during the

 Heating process and during the drying process, only the undervoltage coil are energized. 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 can be DC or low frequency or

Radio frequency device be designed. In particular, the provision of

Heating device as a high-frequency device has the advantage that the skin effect can be exploited. As a result of the skin effect is high-frequency

 Alternating current density on the outside of the conductor greater than in the middle of the conductor, which increases the resistance in the line and thus the heat transfer into the good, in particular in the core. In an advantageous embodiment of the invention, a measuring unit in the

Vacuum pump set be provided by means of which a measurement of the dew point can be done 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 a

 Embodiment with reference to the drawings, wherein the same 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.

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

2 shows a detail of a schematic representation of a transformer. The device 1 shown in Figure 1 for heating and drying a good 4 has an autoclave 10, a heater 14, a heating circuit 2 and a

Vacuum pump set 3 on.

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, seen 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, a measuring unit 31, by means of the dew point in a

Bypass line 33 of the vacuum line 30 is measured and a third

Heat exchanger 32 on.

The heater 14 is connected to the transformer 4, in particular the coil of the transformer 4. The transformer 4 shown in FIG. 2 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. In the case of that shown in FIG

Transformer, 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 based on a heating and

Drying a transformer described. Of course, the operation of the device 1 is not limited to heating and drying a transformer.

During the heating process, the heating of the transformer 4.

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 passed over the

Outlet line 23 is removed 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 through the

 Heating device 14 energized. 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 in the third heat exchanger 32 between the

Mixture and, for example, cooling water of the device 1 takes place. By means of

Measuring unit 31 is measured in the bypass line 32, the dew point of the extracted mixture and decided depending on this value, whether the drying process is finished or not. reference numeral

1 device for heating and drying a good

2 heating circuit

 3 vacuum pump set

 4 transformer

 10 autoclave

 13 circulation device

 14 heating device

 20 dryers

 21 first heat exchanger

 22 second heat exchanger

 23 discharge line

 24 supply line

 30 vacuum line

 31 measuring unit

 32 third heat exchanger

 33 bypass line

 40 transformer core

 41 undervoltage coil

 42 high-voltage coil

Claims

claims 1 . Device (1) for heating and drying one, an electrical insulation  having, Good (4) with an evacuable autoclave (10), in which the good (4) is provided and in which a gaseous heating medium can be introduced, wherein during a heating process, the gaseous heating medium in  remains gaseous state, and a vacuum pump set for evacuating the autoclave after the heating process, characterized in that the gaseous heating medium is an inert gas, in particular nitrogen. 2. Device (1) according to claim 1, characterized in that the autoclave (10) has a discharge line (23) and a supply line connected thereto (24), wherein the autoclave (10), the discharge line (23) and the supply line (24) form a closed circuit (2), in particular a circuit for drying and / or heating the gaseous heating medium and / or a mixture. 3. Device (1) according to one of the preceding claims, characterized  in that a circulation device (13) is provided inside the evacuable autoclave (10). 4. Device (1) according to one of the preceding claims, characterized  in that a dryer (20), in particular an adsorption dryer or a condenser, is arranged between the discharge line (23) and the feed line (24). 5. Device (1) according to one of the preceding claims 2 to 4, characterized  in that a heat exchanger (21, 22) is arranged in the circuit (2). 6. Device (1) according to one of the preceding claims, characterized in that a heating device (14) is provided for supplying energy to the product (4), in particular a pipe provided in the product. 7. Device (1) according to claim 6, characterized in that the material (4) is designed as a transformer and the heating device (14) a  Low voltage coil (41) and / or a high voltage coil (42) of the  Energized transformer. 8. Device (1) according to one of claims 6 or 7, characterized in that the heating device (14) as a DC, low-frequency or  High-frequency device is designed. 9. Method for heating and drying a good (4), which is an insulation  wherein a gaseous heating medium flows within an autoclave (10) and remains in the gaseous state during the heating process, wherein after a heating of the material (4) a drying operation in which the autoclave is evacuated is carried out, characterized in that the gaseous Heating medium is an inert gas. 10. The method according to claim 9, characterized in that a circulation of the gaseous heating medium in the autoclave (10), in particular at  Atmospheric pressure or overpressure, is performed. 1 1. Method according to one of claims 9 or 10, characterized in that at least in an interval for heating the goods (4) and finally lowering the pressure in the autoclave (10) is performed. 12. The method according to any one of claims 9 to 1 1, characterized in that, in particular during the drying process, the good (4) by a  Heating device (14) energy is supplied, in particular such that an internal temperature of a core of the material above a condensation temperature of the material (4) to be evaporated in the material, in particular water, is achieved. Method according to one of the preceding claims 9 to 1 2, characterized in that a mixture taken from the autoclave (10), in particular a mixture of the gaseous heating medium and the water vapor, is dried and / or the mixture is cooled before drying. Method according to one of the preceding claims 9 to 13, characterized in that the gaseous heating medium is heated before being fed into the autoclave, in particular by the released during the cooling of the mixture heat.