JPH11135348A - Method for drying transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further shorten time for drying a transformed by arranging an electric mat having a resistance wire built inside an insulator in direct contact with the transformer, then carrying out drying processing while causing a current to flow through the resistance wire of the electric mat, and then remov ing the electric mat. SOLUTION: A three-phase transformer, on which an electric mat 2 having a resistance wire built inside an insulator is wound, is housed in a drying tank. At a heating step in drying of the transformer, a hot wind heating method, a vapor heating method, a radiation heating method, and a method combining these methods are used, and in addition, a current is caused to flow through the electric mat 2. After drying of the transformer, the electric mat 2 can be easily removed. In this case, upper and lower frames 1 of the three-phase transformer having a winding 3 wound on an iron core 4 narrowly hold the iron core 4 and tightens the winding 3 through an insulating support 5. Around the upper and the lower frames 1, the electric mat 2 is wound in direct contact with the frames 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drying an oil-filled transformer and a gas-insulated transformer, and more particularly to a method for drying a transformer which requires a short drying time.

[0002]

2. Description of the Related Art If moisture is contained in an insulator of a transformer, the dielectric strength and mechanical strength of the insulator are reduced, so that the contents of the transformer (a state in which a winding is wound around an iron core) are reduced. After being assembled, the transformer is dried in the assembled state.
In the method of drying the transformer, the transformer is heated to about 100 ° C. while the contents of the transformer are housed in a drying tank, and the drying tank is evacuated to remove water vapor generated from the insulator. Among them, as a method for heating the transformer, there have conventionally been a hot air heating method, a gas phase heating method, a radiant heating method, and a method combining these methods.

[0003] The hot air heating method is a method in which air preheated by a heater outside a drying tank is guided into a drying tank and blown to a transformer. In the gas phase heating method, one kerosene (white kerosene, which is also used as fuel for household stoves and fuel for jet aircraft propulsion) is used outside the drying tank in advance.
In this method, kerosene vapor is heated to about 30 degrees to produce kerosene vapor, the kerosene vapor is led to a drying tank, and then falls down to a transformer. Kerosene vapor provides latent heat of vaporization to the cooler transformer, so that kerosene liquefies and flows down to the bottom of the drying tank, where the transformer receives the latent heat of vaporization from the kerosene vapor and is heated.

The radiant heating method is a method in which a heater is provided along the wall of a drying tank, and the transformer is heated by radiant heat radiated from the heater. This method is an auxiliary means of the hot air heating method or the gas phase heating method. If the transformer is heated and evacuated to drain the water, the water will take away the latent heat of evaporation from the insulator of the transformer when the water evaporates, so that the temperature of the transformer itself will drop. Therefore, it is necessary to continuously heat the transformer by the radiant heating method at the stage of extracting moisture by evacuation.

[0005] In the above-described method, the vapor phase heating method can heat the transformer very quickly. At present, there is a method in which the transformer is vapor-phase heated and then switched to radiation heating only to perform evacuation. Most often used. The air and the residual kerosene vapor in the drying tank are extracted to the outside together with water vapor by evacuation. As another heating method of the transformer, there is an energization heating method in which a DC current is supplied to the winding conductor to warm the transformer, but this method is not often used. The reason for this is that the temperature of the insulating coating inside the winding that is in contact with the conductor cannot be directly monitored because the winding conductor is insulated. The average temperature of the winding conductor can be determined by measuring the resistance of the conductor from both ends of the winding, but even if the insulation coating is scorched due to local overheating in the winding conductor due to the current flowing while the transformer is drying. This is because there is a disadvantage that it cannot be found.

[0006]

However, the conventional apparatus as described above has a problem that the drying time of the transformer is very long. That is, the drying time of the transformer is
Depending on the size of the transformer, a large capacity transformer takes about a week. The reason why the drying time becomes longer as the transformer becomes larger is that the water content increases with it.However, since the iron core, which is a lump of metal, also becomes larger, the heat capacity also increases, and the overall temperature does not rise. It is also due to. Reducing the drying time of the transformer as much as possible can lead to a shortened production delivery time and more efficient drying equipment.

An object of the present invention is to further reduce the drying time of a transformer.

[0008]

According to the method of the present invention, a transformer having a winding wound around an iron core is housed in a drying tank, and the transformer is heated. In a method of drying a transformer for removing moisture, an electric mat having a resistance wire embedded in an insulator is disposed so as to directly contact the transformer, and the transformer is dried while energizing the resistance wire of the electric mat. After the drying, the electric mat is preferably removed. This allows heat from the electric mat to be transferred directly to the transformer. Therefore, conventionally, only the radiant heating method can be used for evacuation, but by adding this method, the transformer can be heated also by heat conduction.
When the drying of the transformer is completed, the electric mat becomes unnecessary and is removed. Therefore, the electric mat is placed in the transformer so that it can be easily removed after drying.

In the method, the electric mat may be arranged so as to directly contact a metal part of the transformer. Accordingly, if the electric mat is brought into direct contact with the metal part, for example, the iron core, the heat conduction is improved because the thermal conductivity of the metal part is very large. Further, in such a method, the electric mat may be provided with air permeability. Accordingly, the electric mat itself is formed in a mesh shape, or gaps and many holes are scattered in the electric mat, so that moisture can be easily removed from between the electric mats.

[0010] In this method, the electric mat may be arranged on a lower surface of an upper yoke of the iron core. As a result, even when the water vapor generated from the insulator around the winding reaches the upper frame and the lower surface of the upper yoke, no dew condensation occurs.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments. FIG. 1 is a cross-sectional view showing a method for drying a transformer according to an embodiment of the present invention, and FIG. 2 is a view taken in the direction of arrow A in FIG. Upper and lower frames 1 of a three-phase transformer in which a winding 3 is wound around an iron core 4 sandwich the iron core 4 and fasten the winding 3 via an insulating support 5. Around the upper and lower frames 1, a ribbon-shaped electric mat 2 is wound so as to directly contact the frame 1. The electric mat 2 has a built-in resistance wire in an insulator, and can heat the frame 1 by supplying a current to the resistance wire.

In FIGS. 1 and 2, the three-phase transformer with the electric mat 2 wound is housed in a drying tank (not shown). In the heating step in drying the transformer,
As in the conventional method, a hot air heating method, a gas phase heating method, a radiant heating method, a method combining these, and the like are used. In addition, the electric mat 2 is also energized. In the evacuation step, the electric mat 2 is also energized simultaneously with the radiant heating method. Since only the ribbon-shaped electric mat 2 is wound around the frame 1, the electric mat 2 is dried after the transformer is dried.
It can be easily removed. The frame 1 where the heat from the electric mat 2 is a metal part having a very high thermal conductivity
Therefore, heat is easily conducted to the iron core 4 having a large heat capacity in contact with the frame 1. Therefore, the heating of the transformer has been efficiently performed, and as a result, the drying time of the transformer has been shortened by about 10% compared to the conventional method. If a temperature sensor (not shown) is interposed, the transformer itself can be prevented from overheating during drying by controlling the power supply to the electric mat 2.

In FIG. 2, an electric mat 2 is wound around a ribbon with a gap 2A. in this way,
By providing the electric mat 2 with air permeability, it is easy for moisture to escape from between the gaps 2A in the vacuuming step. Therefore, generally, the electric mat 2
The electric mat 2 may be arranged anywhere in the transformer if air permeability is provided in the transformer. By arranging the electric mat 2 on a metal part having a very high thermal conductivity, the transformer can be dried quickly.

FIG. 3 is a cross-sectional view showing a method for drying a transformer according to another embodiment of the present invention, and FIG. 4 is a view taken in the direction of arrow B in FIG. The upper and lower frames 1 are wrapped in an electric mat 6. Other configurations in FIGS. 3 and 4 are the same as those in FIGS. 1 and 2, respectively. If only the frame 1 is provided, the electric mat 6 does not necessarily need to have air permeability. Compared to the case of FIG. 1, the upper surfaces of the upper and lower frames 1,
Electric mats 6 are also arranged on the lower surface, respectively, so that the transformer can be dried more quickly.

FIG. 5 is a sectional view showing a method of drying a transformer according to still another embodiment of the present invention, and FIG.
FIG. 6 is a view on arrow C in FIG. 5. An electric mat 7 is added to the lower surface of the upper yoke of the upper frame 1 and the iron core 4. The electric mat 7 is interposed between the legs of the iron core 4. Other configurations in FIGS. 5 and 6 are the same as those in FIGS. 3 and 4, respectively. With the radiant heating method alone, the iron core 4 as a large structure is difficult to warm up, and water vapor generated from the insulator around the winding 3 may reach the upper frame 1 and the lower surface of the upper yoke and form dew. Due to the dew condensation, the transformer takes extra time to dry. However, by disposing the electric mat 7 in this portion, water vapor does not condense, and the transformer can be dried more quickly.

FIG. 7 is a sectional view showing a method for drying a transformer according to still another embodiment of the present invention, and FIG.
FIG. 8 is a view on arrow D in FIG. 7. This is an example of drying when the iron core 8 of the transformer has five legs. In order to reduce the height of the transformer, return legs 8A may be provided on both sides of the iron core 8. The upper and lower frames 1 are wrapped by an electric mat 6 and the return leg 8A is also wound by a ribbon-shaped electric mat 9. Other configurations in FIGS. 7 and 8 are the same as those in FIGS. 1 and 2, respectively. The iron core 8, which is a large structure, is also heated from the return leg 8A side, and the transformer can be dried more quickly.

FIG. 9 is a sectional view showing a method of drying a transformer according to still another embodiment of the present invention.
FIG. 10 is a view taken in the direction of arrow E in FIG. 9. The entire transformer is wrapped in a reticulated electric mat 10. Other configurations in FIGS. 9 and 10 are the same as those in FIGS. 1 and 2, respectively. Since the electric mat 10 has air permeability, moisture can easily escape from between the electric mats 10. Electric mat 1 for the entire transformer
Since it is wrapped with zero, the transformer can be dried faster. Instead of the electric mat 10, a ribbon-shaped electric mat may be used to form a gap and be wound around the entire transformer, or the entire transformer may be wrapped around an electric mat with many holes scattered.

[0018]

As described above, according to the present invention, an electric mat in which a resistance wire is incorporated in an insulator is arranged so as to be in direct contact with a transformer, and the transformer is dried while energizing the resistance wire of the electric mat. After the drying process, the electric mat is preferably removed. Thus, conventionally, only the radiant heating method could be used for evacuation, but by adding this method, the transformer can be heated also by heat conduction, and the drying time of the transformer can be reduced. , The production delivery time can be shortened, and the efficiency of the drying equipment can be improved.

In this method, the electric mat may be in direct contact with a metal part of the transformer. The very high thermal conductivity of the metal results in better heat transfer and shorter drying time of the transformer. Further, in such a method, the electric mat may be provided with air permeability. As a result, moisture easily escapes from between the electric mats, and the drying time of the transformer is further reduced.

In this method, the electric mat may be arranged on a lower surface of an upper yoke of the iron core. As a result, water vapor generated from the insulator around the winding does not reach the upper frame or the lower surface of the upper yoke and does not condense, so that the drying time of the transformer is further reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a method for drying a transformer according to an embodiment of the present invention.

FIG. 2 is a view taken in the direction of arrow A in FIG. 1;

FIG. 3 is a sectional view showing a method of drying a transformer according to another embodiment of the present invention.

FIG. 4 is a view taken in the direction of arrow B in FIG. 3;

FIG. 5 is a sectional view showing a method for drying a transformer according to still another embodiment of the present invention.

FIG. 6 is a view taken in the direction of arrow C in FIG. 5;

FIG. 7 is a sectional view showing a method for drying a transformer according to still another embodiment of the present invention.

FIG. 8 is a view taken in the direction of arrow D in FIG. 7;

FIG. 9 is a sectional view showing a method for drying a transformer according to still another embodiment of the present invention.

FIG. 10 is a view taken in the direction of arrow E in FIG. 9;

[Explanation of symbols]

1: Frame, 2, 6, 7, 9: Electric mat, 3: Winding, 4: Iron core

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takashi Takahagi 1-1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fuji Electric Co., Ltd.

Claims (4)

[Claims] In a method of drying a transformer, wherein a transformer having windings wound around an iron core is housed in a drying tank, and the transformer is heated to remove moisture, a resistance wire is incorporated in an insulator. Electric mat is placed in direct contact with the transformer,
A method for drying a transformer, characterized in that the transformer is dried while energizing the resistance wire of the electric mat, and the electric mat is removed after the drying process. 2. The method for drying a transformer according to claim 1, wherein the electric mat is disposed so as to directly contact a metal part of the transformer. 3. The method for drying a transformer according to claim 1, wherein said electric mat has air permeability. 4. The method for drying a transformer according to claim 1, wherein said electric mat is disposed on a lower surface of an upper yoke of an iron core.