EP1253389B1 - Process for drying an active part, and apparatus for carrying out this process - Google Patents

Description

TECHNICAL AREA

The invention is based on a method and a device for drying at least one winding and solid insulation containing active part according to the preambles of claims 1 and 8. Bei the implementation of the method is the active part in a vacuum-tight housing The device is arranged and sprayed by spraying oil in the housing and by a guided in the at least one winding current to a through the Temperature of the winding heated specific temperature. At a compared to atmosphere reduced pressure is the heated active part of water withdrawn.

With suitable process control are with the generic method and the generic device reaches a properly dried active part.

STATE OF THE ART

A method and a device of the type mentioned in DE 195 01 323 A1. In the described method are in a Vacuum-resistant housing the windings of a transformer with electricity and parallel to this by spraying heated oil to a set temperature heated and dried. The oil is first at atmospheric pressure and then - in a variant of the method - at gradually reducing pressure sprayed. By lowering the pressure to typically 200 mbar is the Degassing and drainage of the windings improved.

Another method for drying solid insulation has W. Müntener / Company Micafil AG, Zurich / Switzerland at a 1999 in Stuttgart / Germany held symposium on "LFH - drying: experience and trends" presented. In this method, an active part of an arranged in the field and oil-filled transformer dried. For this purpose will be a mobile LFH - system (LFH = Low Frequency Heating) to those contained in the active part High-voltage windings of the transformer connected. The Undervoltage windings are short-circuited. The transformer housing is connected to an oil treatment plant and to a vacuum system.

For drying, the active part is first through one of the LFH - plant heated low-frequency electricity and heated by transformer oil, wherein the oil is heated and circulated through the oil treatment plant.

If the active part heated to a predetermined target temperature, so will hot transformer oil removed from the transformer housing and the pressure in the transformer housing taking into account the Paschen law reduced to atmospheric pressure. During the pressure reduction takes place intensive evaporation of existing in the solid insulation of the active part Water. This will depend on the pressure inside the Transformer housing and the height of the temperature of the upper and / or the Undervoltage winding changes the size of the current, so a gentle Reheating and thus a permanent evaporation of the water from the To achieve isolation.

An effective withdrawal of water occur in this process and the Method according to DE 195 01 323 A1 only when the active part on the heated predetermined set temperature and the housing pressure after removing the Oil is lowered far below atmospheric pressure.

BRIEF SUMMARY OF THE INVENTION

The invention, as indicated in the claims and 8, the object is to provide a method of the type mentioned, which is a rapid and particularly gentle drying, as well as an easy to to provide implementing device for performing this method.

In the process according to the invention, prior to the spraying of the heated oil the pressure in the housing is reduced to a working value which is greater than one by the Paschengesetz certain pressure setpoint and less than one opposite Atmospheric pressure a high evaporation rate of water from the active part ensuring upper pressure limit. In addition, the oil contributes to the labor value powered stream in the housing, and is sprayed during the spraying of the oil, collecting the sprayed oil on the caseback as well Reheating and re-spraying the collected oil Temperature of the winding kept greater than the temperature of the oil. The Active part is thus already dried intensively at the beginning of the heating process. It is at this time in a virtually oil-free, evacuated housing, by spraying the previously heated oil and by LFH heating is heated effectively. The process is therefore particularly fast.

Since that in the hygroscopic solid insulation of the active part to be dried initially existing water even at relatively low temperatures from the Insulation is removed, and because the active part on the current-carrying winding of inside and over the sprayed oil is heated from the outside at the same time, the Drying process not only fast but also gentle. A reduction of the dielectric properties of the solid insulation by Polymerization is thereby largely excluded. As the temperature of the Oil below the temperature of the arranged in the interior of the active part winding held, the internal parts of the insulation of the active part heat up stronger than the oil exposed exterior parts. That from the active part to be removed water is therefore due to diffusion processes from the Interior of the active part out particularly quickly to the outside.

Due to the rapid drying process and the small amount of oil is the Energy consumption comparatively low and can the inventive method be carried out in a very economical manner. This especially because of that because of the small amount of oil one the treatment and heating of the oil exporting facility can be kept small.

To exclude damage to the active part with sufficient security, the reduced pressure in the housing during oil spraying and heating of the Winding with current above one determined by the Paschen law Pressure setpoint.

An effective control of the drying process according to the invention is possible if during the heating of the active part per unit time from the Active part passing amount of water, for example by measuring the Water vapor partial pressure in the housing, is detected, and if below a Maximums of the amount of water exiting per unit time Winding temperature, especially by oil spray, is kept constant. at switched off current can then be the reduced pressure below the pressure setpoint lowered and then dried very effectively and energy-saving become. In order to improve the degree of drying, it is advisable to increase the pressure to raise a value above the pressure setpoint and the Winding temperature gradually to increase to a final temperature value, as soon as the amount of water per unit of time has fallen below a threshold.

The quality of the drying can be further increased, if after the Oil spray the oil removed from the housing at reduced pressure and the Winding temperature is kept constant by heating with electricity. By Periodic lowering of the reduced pressure with the power off under the Pressure setpoint can then even small amounts of water from the active part be removed.

A suitable device for drying the active part according to claim 8 contains in addition to a Active part receiving vacuum-tight housing, one in the bottom of the housing provided drain, an oil inlet and a via an oil pump with the drain and connected via a pipe with the oil inlet Oil treatment plant also at least one in the ceiling of the housing arranged sprayer and one in the oil treatment plant envisaged oil heater with an output that goes through the pipe and the Oil inlet is connected to the spray device. The oil is so from the top of the Active part sprayed on and can then on a relatively long flow path a lot of heat submit. As a result of the spray device being distributed over the ceiling several Having on the active part aligned spray nozzles, which advantageously are formed adjustable, the oil can be selectively sprayed and so the Efficiency of the device can be additionally increased.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig.1

ein Blockschaltbild einer Vorrichtung zur Durchführung des erfindungsgemässen Verfahrens mit einem ein Aktivteil eines elektrischen Gerätes aufnehmenden Gehäuse, einer LFH-Anlage, einer Ölaufbereitungsanlage und einer Ölsprühvorrichtung, und

Fig.2

ein Diagramm, in dem wichtige Parameter des erfindungsgemässen Verfahrens, wie die Temperaturen T_oil, des zu versprühenden Öls und T_w einer Wicklung des Aktivteils, der Gesamtdruck p im Gehäuse, der Wasserdampfpartialdruck p_H2O im Gehäuse und der von der LFH-Anlage abgegebene Strom I in Funktion der Zeit dargestellt sind.

An embodiment of the invention is shown in simplified form in the drawings, in which:

Fig.1

a block diagram of an apparatus for performing the inventive method with an active part of an electrical device receiving housing, a LFH system, an oil treatment plant and an oil spray device, and

Fig.2

a diagram in which important parameters of the inventive method, such as the temperatures T _oil , the sprayed oil and T _w a winding of the active part, the total pressure p in the housing, the water vapor _partial pressure p _H2O in the housing and the output from the LFH system power I are shown in function of time.

WAYS FOR CARRYING OUT THE INVENTION

In all figures, like reference numerals refer to like-acting parts. In the device shown in Figure 1 for carrying out the inventive Method 1 denotes a vacuum-tight housing which does not have a designated valve assembly with a vacuum system 2 is connectable. The Housing takes an active part 3 of an electrical device, such as a Transformers, on. Is the transformer oil filled, then that can Transformer housing serve as housing 1. The case can also be any other vacuum tight, temperature resistant container with vacuum-sealed electrical feedthroughs and can instead of a large active part also record several small active parts.

The active part 3 contains at least one winding and the winding insulating hygroscopic solid insulation. The apparent from Fig.1 active part contains In addition, an iron core 4 and three each one phase of a three-phase Current associated coil blocks 5, which each have a top and a Have undervoltage winding. The low voltage windings 6 are shorted outside the housing, whereas the High-voltage windings 7 with the current output one outside the Housing 1 arranged low-frequency AC or DC generating LFH - system 8 are connected.

In the bottom of the housing 1, a drain 9 is provided by the on Caseback collected oil 10 by means of an oil pump 11 in a Oil heater 12 an oil treatment plant 13 can be deducted. Of the Output of Öhleritzer 12 is via an oil inlet 14 with a in the ceiling of the Housing 1 arranged spraying device 15 is connected. These Spray device has a plurality of spray nozzles 16 distributed over the ceiling, which are aligned to the active part. At least some of the spray nozzles 16 can also be arranged on the side walls of the housing 1. Thereby and by adjustably aligned spray nozzles, the active part 3 targeted and not be sprayed only from above, but also from the side.

The operation of this device will be explained in more detail with reference to FIG. 2: In the loaded with the active part 3 housing 1, the pressure p is first reduced with the vacuum system 2. The working value of the reduced pressure used in carrying out the method should be greater than a pressure setpoint p _pasch specified by the Paschen _law . Below this pressure setpoint, it could happen due to the Paschen law when in an electric field to rollovers. When applying a heating voltage to the active part then electrical discharges could occur, which could lead to an impairment of the insulating capacity of the active part. The working value of the reduced pressure should also be as small as possible in order to have a high evaporation rate for the water to be removed from the active part. The working value is below 100 mbar, typically at 10 to 30 mbar.

At a time point t _1, the pressure is sufficiently reduced. The active part is then heated with a low-frequency alternating current I passed through the high-voltage windings 7 and with an induced current induced in the low-voltage windings 6. At the same time, heated oil is conducted to the spraying device 15 in the oil preparation plant 13 and sprayed onto the surface of the active part 3 from there. The combined heating with electricity and with oil ensures that the heat required to dry the active part is supplied simultaneously from the inside and the outside.

As a result, a particularly rapid and gentle drying is achieved. Water bound in the solid-state insulation is conducted away from the heated windings to the outside of the surfaces of the solid-state insulation and evaporated. Since the active part 3 is exposed to a reduced pressure during heating, the water can evaporate already at the beginning of the heating of the active part 3. The amount of water evaporating per unit of time is determined indirectly by means of a partial pressure of water vapor pressure and is shown in FIG. 2 as a curve p _H2O . At the same time, the temperatures T _{oil of} the sprayed oil and T _{w of} the windings of the active part 3 are detected. While the oil temperature T _{oil is determined} directly with a temperature sensor, the winding temperature Tw is based on a mean value calculated in a known manner from the temperatures of the upper and lower voltage windings (cf., for example, the cited state of the art according to W. Müntener). The corresponding temperature curves are also entered in FIG. As can be seen, T _{w is} always kept slightly larger than T _oil during the drying process. It is thus ensured that the water present in the active part 3 is guided from the inside to the outside. The evaporated water is sucked off via the vacuum system 2.

At time t ₂ , the winding _temperature T _{w1 is} already relatively large and is no longer very far (for example, 10 or 20 ° C) below an allowable temperature _{end value} T _end, for example, 110 ° C. Since at this temperature P _H2O a maximum of the amount of water delivered per unit time is exceeded, the winding temperature T _{w is kept} constant at T _w1 at this time. The oil temperature is kept constant. The constant can be effected mainly by oil spray. However, it is advisable to heat intermittently with electricity, because then it is ensured on the one hand that T _{w is} always above T _oil and diffuses the water in the active part from the inside to the outside, and then there on the other during a pause of power p under pressure lowered the pressure setpoint T _Pasch and the outwardly guided water can be better evaporated from the active part.

At time t ₃ does not fall much more water on. Therefore, from this point on, the oil and the winding _{temperature are} successively increased at a pressure p above the pressure setpoint p. At each increase in temperature initially falls to a comparatively large amount of water. After exceeding a maximum, in each case the oil and the winding temperatures are kept constant again, and with intermittent heating current I in current pauses, the pressure p is lowered below the desired pressure value p _Pasch .

At time t ₄ , the final temperature T _{end is} reached and the heating is set by oil spray. Power heating keeps the active part at the final temperature. At an above the pressure setpoint p _pasch pressure, the oil 10 is now completely withdrawn from the housing 1. With the removal of the oil at the same time also by the oil from the active part rinsed impurities are removed from the housing.

At time t ₅ , the oil is removed. It can now be removed in a subsequent fine vacuum phase by intermittent heating and pressure lowering remaining water from the active part. Finally, with the electrical heating switched off, the housing can then be ventilated and the dried active part removed or fresh oil filled into the housing.

LIST OF REFERENCE NUMBERS

1

casing

2

vacuum system

3

active part

4

iron core

5

coil block

6

Low-voltage winding

7

High-voltage winding

8th

LFH - plant

9

outflow

10

oil

11

Oil pump

12

oil heater

13

Oil treatment plant

14

oil inlet

15

sprayer

16

spray nozzles

I

Power of an LFH system

p

total pressure

p _H2O

water vapor

p _pash

Index pressure value

T

temperature

T _end

temperature value

T _w

winding temperature

T _w1

constant winding temperature

T _oil

oil temperature

t

Time

t ₁ , t ₂ , t ₃ , t ₄ , t ₅

timings

Claims (10)

1. Method for drying an active part (3) containing at least one winding (6, 7) and solid insulations, in a vacuum-tight housing (1), in which the active part is heated to a final temperature value (T_fin) by warmed oil (10) being sprayed in the housing (1) and by means of a current (I) carried in the at least one winding, and, at a pressure (p) reduced in relation to atmospheric pressure, water is extracted from the active part (3), characterized in that, before the spraying of the warmed oil, the pressure (p) in the housing is reduced to a working value which is higher than a desired pressure value (p_pasch) determined Paschen's Law and lower than an upper pressure limit value which, in relation to atmospheric pressure, ensures a high evaporation rate of the water from the active part, in that at the working value, the oil is sprayed in the housing (10), with the current (I) switched on, and in that, during the spraying of the oil (10), the collection of the sprayed oil on the housing bottom and also the rewarming and renewed spraying of the collected oil (10) at the working pressure, and with the current (I) switched on, the temperature (T_w) of the winding is kept higher than the temperature (T_oil) of the oil.
2. Method according to Claim 1, characterized in that, during the spraying of the oil and heating of the winding by means of current, the reduced pressure in the housing is maintained above a desired pressure value (p_pasch) determined by means of Paschen's Law.
3. Method according to one of Claims 1 and 2, characterized in that, during the heating of the active part, the quantity of water (p_H2O) emerging from the active part (3) per unit time is detected, and in that, below a maximum water quantity emerging per unit time, the temperature (T_w) of the current-heated winding is kept constant.
4. Method according to Claim 3, characterized in that, at a constant winding temperature (T_w1) and with the current (I) switched off, the reduced pressure (p) is lowered below the desired pressure value (p_pasch).
5. Method according to Claim 4, characterized in that, below a limit value of the water quantity occurring per unit time, the pressure is raised to a value above the desired pressure value and the winding temperature (T_w) is then increased successively to the final temperature value (T_fin).
6. Method according to one of Claims 1 to 5, characterized in that, after the spraying of oil (t₄), the oil is removed from the housing at reduced pressure and the winding temperature is at the same time kept constant by heating with current.
7. Method according to Claim 6, characterized in that, after the removal of the oil (t₅), the reduced pressure is lowered periodically below the desired pressure value (p_pasch), with the current switched off.
8. Device for carrying out the method according to one of Claims 1 to 7, containing a vacuum-tight housing (1) accommodating the active part (3), an outflow (9) provided in the bottom of the housing (1), an oil 1 inlet (14) and an oil 1 preparation plant (13) which is connected to the outflow (9) via an oil feed pump (11) and to the oil inlet (14) via a line, characterized in that at least one spray device (15) is arranged in the ceiling of the housing (1), and in that the oil preparation plant (13) contains an oil heater (12) having an outlet which is connected to the spray device (15) via the line and the oil inlet (14).
9. Device according to Claim 8, characterized in that the spray device (15) has a plurality of spray nozzles (16) distributed over the ceiling and oriented towards the active part (3).
10. Device according to Claim 9, characterized in that the spray nozzles are designed adjustably.

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