EP1253389A1 - Process for drying an active part, and apparatus for carrying out this process - Google Patents

Abstract

The method involves heating the active part to a final temperature value (Tend) by spraying with warm oil in a housing and passing current through the coil(s) and extracting water from the active part by a pressure reduced relative to atmospheric. Before spraying heated oil, the pressure (p) in the housing is reduced to a value greater than a desired value (ppasch) and lower than an upper limit ensuring a high water evaporation rate. AN Independent claim is also included for the following: an arrangement for implementing the method.

Description

TECHNICAL AREA

The invention is based on a method for drying a active part containing at least one winding and solid insulation the preamble of claim 1. Here, the active part in one vacuum-proof housing and is arranged by spraying oil in the housing and through a current carried in the at least one winding onto one the temperature of the winding heated certain final temperature. at the heated active part becomes at a reduced pressure compared to the atmosphere Deprived of water.

With appropriate process control, the generic method is used perfectly dried active part reached.

STATE OF THE ART

A method of the type mentioned is described in DE 195 01 323 A1. In this process, the windings are placed in a vacuum-proof housing of a transformer with current and in parallel by spraying heated oil heated to a set temperature and dried. The oil will first at atmospheric pressure and then - in a variant of the process - at gradually reducing pressure sprays out. By lowering the pressure The degassing and dewatering of the is typically to 200 mbar Windings improved.

Another method for drying solid insulation has W.Müntener / company Micafil AG, Zurich / Switzerland at a 1999 in Stuttgart / FRG held symposium on "LFH - Drying: Experience and Trends" presented. With this method, an active part is arranged in the field and dried with oil-filled transformer. For this purpose, 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 closed briefly. The transformer housing is connected to an oil treatment plant and a vacuum plant.

The active part is first dried by one from the LFH system supplied low-frequency electricity and heated by transformer oil, whereby the oil is heated and circulated through the oil treatment plant.

If the active part is heated to a predetermined target temperature, it will hot transformer oil removed from the transformer housing and the pressure in the transformer housing taking into account the Paschen law reduced compared to atmospheric pressure. A occurs during the pressure reduction intensive evaporation of the solid insulation of the active part Water. Here, depending on the pressure inside the Transformer housing and the level of the temperature of the top and / or Undervoltage winding changes the size of the current, so a gentle one Reheat and thus permanent evaporation of the water from the To achieve isolation.

Effective water withdrawal occur with this method and the Process according to DE 195 01 323 A1 only when the active part on the predetermined target temperature is heated and the housing pressure after removing the Oil is lowered far below atmospheric pressure.

SUMMARY OF THE INVENTION

The object of the invention is as set out in the claims to create a method of the type mentioned, which a allows quick and particularly gentle drying, as well as easy to specify implementing device for performing this method.

In the method according to the invention, before the heated oil is sprayed the pressure in the housing is reduced to a work value which is greater than one pressure setpoint determined by the Paschen law and less than one opposite Atmospheric pressure a high evaporation rate of the water from the active part ensuring upper pressure limit. In addition, the oil will contribute to the labor value switched on current is sprayed in the housing, and is during the spraying the oil, collecting the sprayed oil on the housing base and Reheating and spraying the collected oil again Temperature of the winding kept higher than the temperature of the oil. The In this way, the active part is intensively dried at the start of the heating process. It is currently in a practically oil-free, evacuated housing, by spraying the previously heated oil and by LFH heating is effectively heated. The process is therefore particularly quick.

Because that in the hygroscopic solid insulation of the active part to be dried initially available water from the Isolations is removed, and since the active part on the current winding of both inside and over the sprayed oil is heated from outside Drying process not only quick, but also gentle. A reduction in the dielectric properties of the solid insulation by This largely excludes polymerization. Because the temperature of the Oil below the temperature of the winding arranged inside the active part is held, the inner parts of the insulation of the active part heat up stronger than the external parts exposed to the oil. That from the active part Water to be removed is therefore due to diffusion processes from the Inside the active part led out very quickly.

Due to the rapid drying process and the small amount of oil, the Energy consumption is comparatively low and the method according to the invention can be carried out in a very economical manner. Most of all because Because of the small amount of oil, the preparation and heating of the oil executing plant can be kept small.

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

Effective control of the drying process according to the invention is possible if during the heating up of the active part the per time unit from the Active part emerging amount of water, for example by measuring the Water vapor partial pressure in the housing, is detected, and if below one Maximum of the amount of water escaping per unit of time Winding temperature, especially by spraying oil, is kept constant. at switched off current can then the reduced pressure below the pressure setpoint lowered and then dried in a particularly effective and energy-saving manner become. To improve the degree of dryness, it is recommended to put the pressure on raise a value above the pressure setpoint and the Gradually increase the winding temperature to a final temperature value as soon as the amount of water generated per unit of time has fallen below a limit.

The quality of the drying can be increased if after Oil spray removes the oil from the housing at reduced pressure and the Winding temperature is kept constant by heating with electricity. By periodically lowering the reduced pressure with the current switched off below the The pressure setpoint can then also contain small amounts of water from the active part be removed.

A suitable device for carrying out the method according to the invention has an oil treatment system for removing the on the housing base collected oil, for heating the extracted oil and for supplying the collected oil and one arranged in the ceiling of the housing Spray device, which with a heated oil from the processing plant supply line is connected. The oil is thus from the top of the active part sprayed on and can then heat a lot on a relatively long flow path submit. The fact that the spray device distributed several over the ceiling and has spray nozzles aligned to the active part, which advantageously are adjustable, the oil can be sprayed in a targeted manner and so the Efficiency of the device can also be 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_H20 im Gehäuse und der von der LFH - Anlage abgegebene Strom I in Funktion der Zeit dargestellt sind.

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

Fig.1

2 shows a block diagram of a device for carrying out the method according to the invention with a housing receiving an active part of an electrical device, an LFH system, an oil treatment system and an oil spray device, and

Fig.2

a diagram in which important parameters of the method according to the invention, such as the temperatures T _{oil of} the _oil to be sprayed and T _{w of} a winding of the active part, the total pressure p in the housing, the water vapor _partial pressure p _H20 in the housing and the current I emitted by the LFH system are represented as a function of time.

WAYS OF CARRYING OUT THE INVENTION

In all figures, the same reference numerals refer to parts having the same effect. In the device shown in Figure 1 for performing the inventive Method 1 denotes a vacuum-tight housing, which does not have a designated valve assembly can be connected to a vacuum system 2. The Housing takes an active part 3 of an electrical device, such as one Transformer, on. If the transformer is filled with oil, it can Serve transformer housing as housing 1. The housing can also any other vacuum tight, temperature resistant container will be with vacuum-tight current feedthroughs and can replace a large active part also accommodate several small active parts.

The active part 3 contains at least one winding and the winding insulating hygroscopic solid insulation. The active part shown in Fig.1 contains in addition, an iron core 4 and three each one phase of a three-phase Current-associated coil blocks 5, each having an upper and a Have undervoltage winding. The undervoltage windings 6 are short-circuited outside the housing, whereas the High-voltage windings 7 with the current output outside the Housing 1 arranged low-frequency alternating current or direct current generating LFH system 8 are connected.

In the bottom of the housing 1, a drain 9 is provided through which Oil 10 collected in the housing bottom with the help of an oil pump 11 in a Oil heater 12 of an oil treatment plant 13 can be removed. The Output of the oil heater 12 is via an oil inlet 14 with a in the ceiling of the Housing 1 arranged spray device 15 connected. This Spray device has a plurality of spray nozzles 16 distributed over the ceiling, which are aimed at 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 means of adjustable spray nozzles, the active part 3 can be targeted and not be sprayed only from above, but also from the side.

The mode of operation of this device is explained in more detail with reference to FIG. 2:
In the housing 1 loaded with the active part 3, 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, due to the Paschen law, flashovers could occur in an electric field. When a heating voltage is applied to the active part, electrical discharges could then occur, which could impair the insulation capacity of the active part. However, 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 10 to 30 mbar.

At a time t ₁ , the pressure is reduced sufficiently. The active part is now heated with a low-frequency alternating current I conducted through the high-voltage windings 7 and with an induction current caused in the undervoltage windings 6. At the same time, heated oil is led in the oil treatment system 13 to the spray device 15 and sprayed from there onto the surface of the active part 3. The combined heating with electricity and oil ensures that the heat required to dry the active part is supplied simultaneously from the inside and outside.

This ensures particularly quick and gentle drying. Water bound in the solid insulation is led away from the heated windings to the surfaces of the solid insulation and evaporated. Since the active part 3 is exposed to a reduced pressure during heating, the water can evaporate from the active part 3 already at the beginning of the heating process. The amount of water evaporating per unit of time is determined indirectly via a water vapor partial pressure measurement and is shown in FIG. 2 as 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 also recorded. While the oil temperature T _{oil is determined} directly with a temperature sensor, the winding temperature Tw is based on a mean value which is calculated in a known manner from the temperatures of the upper and lower voltage winding (see, for example, the prior art cited at the outset according to W. Müntener). The corresponding temperature curves are also entered in FIG. 2. Evidently, during the drying process, T _{w is} always kept slightly larger than T _oil . This ensures that the water present in the active part 3 is led 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 high and is no longer very far (for example 10 or 20 ° C.) below a permissible _{final temperature value} T _end of, for example, 110 ° C. Since at this temperature p _H2O a maximum of the amount of water dispensed per unit of time is exceeded, the winding temperature T _{w is kept} constant at T _w1 at this time. The oil temperature is also kept constant. Maintaining constant can mainly be achieved by spraying oil. However, it is advisable to heat intermittently with electricity, because on the one hand it is ensured that T _{w is} always above T _oil and the water in the active part diffuses from the inside out, and on the other hand the pressure p below during a power break the pressure setpoint T _{pasch is} reduced and the water that is led outside can be better evaporated from the active part.

At time t ₃ , there is no longer a lot of water. Therefore, from this point in time at a pressure p above the pressure setpoint p _pasch , the oil and the winding _{temperature are} gradually increased. Every time the temperature rises, there is a comparatively large amount of water. After a maximum has been exceeded, the oil and the winding temperatures are kept constant again and, in the case of intermittent heating current I, the pressure p is reduced below the pressure setpoint p _{pasch during current pauses} .

At time t ₄ , the _end temperature T _{end is} reached and heating is stopped by oil spraying. The active part is kept at the final temperature by current heating. At a pressure above the pressure setpoint p _pasch , the oil 10 is now completely drawn out of the housing 1. When the oil is removed, impurities rinsed off by the oil from the active part are also removed from the housing.

At time t ₅ the oil is removed. In a subsequent fine vacuum phase, residual water can now be removed from the active part by intermittent heating and pressure reduction. Finally, with the electrical heating switched off, the housing can 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 facility

9

outflow

10

oil

11

Oil pump

12

oil heater

13

Oil treatment plant

14

oil inlet

15

sprayer

16

spray nozzles

I

Electricity from an LFH system

p

total pressure

p _H20

water vapor

p _pasch

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)

Method for drying an active part (3) containing at least one winding (6, 7) and solid insulation in a vacuum-tight housing (1), in which the active part by spraying heated oil (10) in the housing (1) and by one in the at least a winding-conducted current (I) is heated to a final temperature value (T _end ) and water is withdrawn from the active part (3) at a pressure (p) which is reduced in relation to the atmosphere, characterized in that, before the heated oil is sprayed, the pressure (p) im Housing is reduced to a work value which is greater than a pressure setpoint (p _pasch ) determined by the Paschen law and less than an upper pressure limit value ensuring a high evaporation rate of the water from the active part in relation to atmospheric pressure,
that the oil is sprayed into the housing (10) at the work value when the current (I) is switched on, and
that during the spraying of the oil (10), collecting the sprayed oil on the housing base and reheating and spraying the collected oil (10) again at working pressure and switched on current (I), the temperature (T _w ) of the winding is kept higher than the temperature ( T _oil ) of the oil. A method according to claim 1, characterized in that during the oil spraying and heating of the winding with current, the reduced pressure in the housing is kept above a pressure setpoint (p _pasch ) determined by the Paschen law. Method according to one of claims 1 or 2, characterized in that during the heating of the active part, the amount of water (p _H2O ) exiting from the active part (3) per time unit is recorded, and that the temperature is below a maximum of the water quantity exiting per time unit (T _w ) the current-heated winding is kept constant. A method according to claim 3, characterized in that at a constant winding _temperature (T _w1 ) and when the current (I) is switched off, the reduced pressure (p) is reduced below the pressure setpoint (p _pasch ). A method according to claim 4, characterized in that the pressure is raised to a value above the pressure setpoint below a limit value of the amount of water accumulating per unit of time and then the winding temperature (T _w ) is successively increased to the final temperature value (T _end ). Method according to one of claims 1 to 5, characterized in that after the oil spraying (t ₄ ) the oil is removed from the housing at reduced pressure and the winding temperature is kept constant by heating with electricity. A method according to claim 6, characterized in that after removal of the oil (t ₅ ), the reduced pressure is periodically lowered below the pressure setpoint (p _pasch ) when the current is switched off. Device for carrying out the method according to one of claims 1 to 7 with an oil treatment system (13) for withdrawing the oil (10) heated on the housing base, for heating the extracted oil and for supplying the heated oil, characterized in that in the ceiling of the housing (1) at least one spray device (15) is provided, which is connected to a line supplying heated oil from the oil treatment plant (13). Apparatus according to claim 8, characterized in that the spray device (15) has a plurality of spray nozzles (16) distributed over the ceiling and aligned with the active part (3). Apparatus according to claim 9, characterized in that the spray nozzles are adjustable.

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