JPH01303038A - Method and device for drying motor coil - Google Patents

Abstract

PURPOSE:To prevent leak and to enable microwave drying, by setting the microwave irradiation output to a level corresponding to the inner volume of a drying furnace. CONSTITUTION:An object to be dried, i.e. a stator coil M, is placed in a drying furnace 1 and dried through a microwave drier 3. In the first process, a vacuum pump 6 is operated to reduce the pressure in the drying furnace 1 then microwave is produced and irradiated onto the object to be dried, i.e. the stator. The microwave output is set lower than 0.45a+1.20, assuming the volume of the drying furnace is (a). In the second process, atmospheric pressure is brought into the drying furnace in order to discharge evaporated vapor, then vacuum lower than 10Torr is provided and drying operation is continued.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to insulation recovery repair work for recovering the insulation resistance value of motor coils, that is, stator and rotor.
This relates to heating and drying, which evaporates and removes moisture that has penetrated and absorbed into the inside of the coil during the steam cleaning process.

[Conventional technology] Insulation recovery and repair work for electric motors involves removing dust that has adhered and solidified over time in the motor coils, stator coils and rotor coils, restoring the insulation resistance value and extending the life of the motor. The aim is to extend this period.

The work process for this insulation recovery repair usually involves disassembling the motor.
The process consists of cleaning, drying, varnishing, and assembly, and dust and the like are removed by blowing away with steam during this cleaning process. The drying process involved in the present invention is to completely evaporate and remove the moisture that has penetrated and absorbed into the inside of the coil by blowing off the steam described above.
Conventionally, methods for removing moisture have been steam thermal drying, hot air drying, or a combination of the two in terms of efficiency.

In addition, as a prior art related to this belief invention, Japanese Unexamined Patent Publication No. 5
It is disclosed in publications such as No. 3-/14643, Japanese Utility Model Application Publication No. 58-1.091.94, and Japanese Patent Application Publication No. 61-1.40779.

[Problems to be Solved by the Invention] If the moisture inside the coil is not completely removed during the drying process, voids will occur during the subsequent varnish treatment, causing insulation deterioration, which will greatly affect the life of the motor. For this reason, it is essential to completely remove moisture, but since the conventional silk drying using "steam insulation and hot air" uses an external heating method that transfers heat from the surface to the inside, the drying time takes about 20 hours. There were problems such as a large amount of energy wasted, poor workability, and furthermore, there was concern about complete removal of moisture absorbed inside the coil.

In addition, according to the publicly known technology according to the above-mentioned publication related to the present invention, 1. microwave heating drying is performed under reduced pressure for non-metallic materials such as food processing products and textile materials. Irradiating microwaves to large metal objects such as motor coils can cause electrical leakage (hereinafter referred to as leakage).
Due to the risk of generation, it has not yet been put into practical use, and it has not been disclosed in patent documents.

[Means for Solving the Problems] The present invention has been made in order to solve the problem of drying of moisture that has penetrated and absorbed into the motor coil, and has not been put to practical use so far. Microwave irradiation heating of the motor coils, stator, and rotor has been realized by the solution described below, and as a result, the conventional external heating method of "steam insulation + hot air", which required a long time, has been replaced by microwave irradiation. By changing to an internal heating method using irradiation and adding drying in a reduced pressure atmosphere, the drying time was shortened and highly efficient drying was made possible.

That is, the motor coil is dried from the inside by heating by the dielectric effect of microwaves, and the pressure of the drying oven is reduced to lower the boiling point of water, making it easier to dry even at low temperatures.

The reason why it has become possible to irradiate the motor coil, which is the object to be dried, with microwaves, which was conventionally difficult due to the risk of leakage, has been achieved by solving the following problem.

First, we irradiated the motor coil (stator, rotor) with microwaves and investigated the location where the leak occurred by varying the amount of microwave output. As shown in Fig. At the hearth bottom 2 of the furnace (made of steel), and at the rotor, there are a bearing 24 and a mounting table 25 that support the rotor 23.
This occurs between the tiny gaps between the iron pieces on which the items to be dried are placed, and in the coil winding, disconnection of the coil,
It has become clear that leaks occur at short-circuited locations.

Naturally, it is possible to prevent leaks from occurring in this mounting area by laying an insulating material, but considering the heat resistance and safety of the insulating material, for example, laminated mica or glass varnish cloth must be used. Since the drying method is expensive and the material to be dried is heavy, the installation work is complicated and it is difficult to use it. Therefore, in the present invention, we have investigated the relationship between this leakage problem and the amount of microwave oscillation output, and have determined the microwave oscillation output limit at which leakage occurs.

FIG. 3 shows the limit of the amount of microwave oscillation output without leakage. As can be seen from the figure, leakage changes depending on the internal volume of the drying oven, and the relationship is that the larger the internal volume is, the higher the microwave oscillation output will be.This is because, of course, as the internal volume becomes larger, the microwaves are attenuated. Therefore, the microwave heating oscillation output amount is 0.45a+, which is within the leak-free range.
], If the microwave irradiation is performed by determining the output amount appropriately without considering the drying furnace volume and heating efficiency at a value of 20 or less, heating drying can be performed without the risk of leakage.

On the other hand, in order to prevent leaks due to wire breaks and short circuits in the coil windings, we use an inspection method that measures the winding resistance balance before microwave heating to check for wire breaks and short circuits. By determining whether or not to implement the process, it is possible to prevent leaks from occurring.

The drying method of the present invention makes it possible to irradiate the motor coil with microwaves by taking measures to prevent leaks as described in (2) below, and then safely removes the moisture present in the motor coil in a drying oven equipped with reduced pressure. It is also characterized by being able to be efficiently removed by drying.

Next, a description will be given of a motor coil drying apparatus in which the internal volume of the drying oven is variable in accordance with the size of the object to be dried in carrying out the method of the invention.

That is, in a vacuum drying device comprising a microwave generator, a drying oven connected to the microwave generator via a waveguide, and a vacuum pump for reducing the pressure in the drying oven, a microwave seal is installed in the drying oven. This drying apparatus is provided with partition panels for 1 to 1 and has a structure in which the internal volume of the microwave heating of the drying oven is variable.

Furthermore, the drying device will be explained in detail based on the drawings.

FIG. 1 shows an example of a microwave heating drying apparatus according to the present invention in which the internal volume of microwave heating is variable with a partition panel.

In Figure 1, (A) is a side sectional view, and (B) is a plan sectional view. 1 in the figure is a structure that houses and dries the motor coil, which is the object to be dried, and maintains airtightness under reduced pressure. This drying oven is made of steel, and one end of this drying oven 1 is provided with 2 doors for taking in and out the materials to be dried, and of course there are 17 doors on the inner edge of the door 2 to prevent air leakage. Used by Patsukin.

3 is a microwave generator for supplying microwaves to microwave the material to be dried, 5 is a rectangular waveguide for conducting the microwaves to the drying furnace 1, and 4 is a waveguide. 5
This is a vacuum seal part that blocks the flow of air between the drying oven 1 and the depressurized drying oven 1. A sealing member is interposed in the vacuum sealing portion 4, and this sealing material is made of a material with good microwave permeability, for example, quartz glass. 11 is a microwave irradiation port. 6 is a vacuum pump for reducing the pressure in the drying oven 1; 7 is a vacuum pipe for communicating the vacuum pump 6 and the drying oven 1; 8 is air sucked in by the vacuum pump 6 and exhausted from the vacuum pump to the outside of the apparatus. This is the exhaust pipe.

9 is a vacuum adjustment valve for adjusting the degree of vacuum in the drying oven 1 to a predetermined pressure, and 10 is a vacuum gauge for checking the degree of vacuum.

The structure of the partition panel according to the present invention, which allows the internal volume of the microwave heating inside the drying oven 1 to be varied according to the size of the object to be dried, will be further described.

FIG. 1 shows an example of a structure in which the partition panel 12 is incorporated into the drying oven 1.
It is an assembly-type box-shaped structure in which 13 mesh panels are fixed to the pillars with 15 tightening bolts on 4 sides (left and right sides, ceiling surface, and one end surface), and it is a partition that surrounds the entire motor coil M (stator in this figure). be.

The partition panel 12 is placed and fixed on the front surface of the microwave irradiation port 11 with the side on which the mesh panel is not attached.

The members of the mesh panel] 3 and the pillars 14 may be made of iron, aluminum, or copper, and holes 16 of a size that satisfies the microwave shielding effect are provided on almost the entire surface of the mesh panel 13, for example, holes 5 mm in diameter at approximately 5 mm intervals. is open.

If you prepare several types of partition panel boxes of different sizes, you can select the appropriate one according to the motor coil size of the item to be dried, and one wide-capacity drying oven can handle many sizes of motor coils. Efficient microwave heating is possible over a long period of time.

[Example] An embodiment of the present invention will be described with reference to FIG.

The size of the drying oven 1 is 1. ．． 2m x length 1.2m x depth 1
．． The internal volume of 2 m is 1.7 m, and the microwave oscillator 3 is fully oscillated.

Crab 1.5 oscillation frequency: 2450 Mt+z, vacuum pump 6 pumping speed: 1200 Q/mjn
This drying device consists of these main components and has the ability to: The motor coil for the material to be dried is an AC cylindrical motor with a capacity of 30K.
11 stator coils, and the work involved evaporating and drying the moisture that permeated inside the coils that occurred during steam cleaning. Note that we have confirmed in advance that there are no problems with disconnections or short circuits in the stator coil windings through resistance value testing.

The entire outer size of this stator coil is 500mm.
The length of φ was 600 mm and the volume was about 0.12 m3, which was smaller than the internal volume of the drying oven, so it was decided to surround it with partition panels in consideration of microwave heating efficiency. The size of the partition panel is 600mm x 600mm x 70
The internal volume of 0mm is 0.25m3.

Next, regarding the drying operation method, a combination of the first step, which is heating drying using a combination of preliminary vacuum and microwave irradiation, and the second step, which is final drying under high vacuum, was performed. First, in the first step, the vacuum pump 6 is operated to reduce the pressure inside the drying oven 1, and when a predetermined degree of vacuum is reached by adjusting the vacuum adjustment valve 9, microwaves are oscillated and irradiated onto the stator of the object to be dried. The lower the degree of vacuum at this time, the lower the boiling point temperature of water and the shorter the evaporation time. Since it causes discoloration and affects the insulation effect, it is necessary to suppress it to a certain extent.

Here, it is 200 Torr (the boiling point temperature of water is below 70℃)
However, in particular, the smaller the motor capacity, the more susceptible to the above effects, so in such cases, it is best to select the appropriate one according to the situation, such as applying microwave heating first without reducing the pressure and reducing the pressure later. .

The amount of microwave oscillation output is determined when the internal volume of the partition panel is 0.
25 m", the power was set to 1.25 KW (IJ) according to Figure 3, and microwave irradiation was performed until the target insulation resistance value of 60 MΩ for stator coil insulation recovery determined in advance in step [1] was reached. Stator coil temperature at the end of the process is 85°
C, and the required time was 2.5 hours. Of course, there were no leaks. In this way, after heating and drying in the first step, the microwave oscillation is stopped and the second step is performed under high vacuum.
During the second drying period, the moisture evaporated in the first step fills the drying oven and reaches a saturated state, causing dew condensation on the inner wall of the drying oven. The second step aims to discharge the steam in this state and further promote the evaporation of water from the coil.

That is, by opening the vacuum adjustment valve 9 and once returning the pressure inside the drying oven to atmospheric pressure, which has been reduced at the beginning of the second step, a flow of steam inside the oven is created and the steam is discharged, and then the pressure is reduced to 1.0 Torr.
The vacuum is set to a high level below r (the boiling point temperature of water is below 45°C), and evaporation from the coil is promoted, and operation is continued until the coil insulation resistance value reaches 2000 MΩ or more, which is the drying target for stator coil insulation recovery.

However, if there is a tendency for the increase in insulation resistance to slow down during the process, the inside of the furnace may be returned to atmospheric pressure and the steam discharge may be repeated. In this example, the target drying was achieved with only the initial steam discharge. The time required for this second step was 0.5 hours, and the temperature of the stator coil at the final stage was 72°C. Note that the target insulation resistance value, which is an index of insulation recovery of the coil in each of the above steps, was set based on past results.

As mentioned above, the total drying time required for the stator coil of this example was 3
The conventional method required more than 27 hours, but this time could be reduced to less than 179 hours.

[Effects of the Invention] Conventionally, microwave irradiation to metal objects such as motor coils has not been put to practical use due to the risk of leakage. The present invention has discovered that in order to prevent the occurrence of this leak, the oscillation output of microwave irradiation is controlled to an output amount that corresponds to the internal volume of the drying oven. can be safely heated and dried using microwave irradiation, and drying time can be shortened by adding drying in a reduced pressure atmosphere.

Furthermore, in carrying out the present invention, in order to make the interior volume of the drying oven suitable for the size of the motor coil, a variable structure is used with a partition panel, thereby making it possible to increase the efficiency of microwave heating.

[Brief explanation of the drawing]

Fig. 1 is a diagram of an embodiment of the microwave heating drying apparatus according to the present invention, in which the internal volume of microwave heating is made variable with a partition panel. A) is a diagram of the stator coil, (B) is a diagram of the rotor coil, and FIG. 3 is a diagram showing the relationship between the internal volume of the drying oven and the microwave oscillation output on the occurrence of leakage. Patent applicant Nippon Steel Corporation

Claims (2)

[Claims] (1) In the step of drying moisture contained in an object to be dried by combining heating by microwave irradiation and drying in an atmosphere reduced from atmospheric pressure, the object to be dried is a stator or rotor of a motor coil; , and the oscillation output amount of the microwave irradiation is the volume inside the drying oven to which the microwave irradiation is applied.
A method for drying a motor coil characterized by heating and drying the coil to a value smaller than the value of 0.45a + 1.20. (2) In a vacuum drying device consisting of a microwave generator, a drying oven connected to the microwave generator via a waveguide, and a vacuum pump that reduces the pressure of the drying oven, A drying device for a motor coil, characterized in that a partition panel for microwave shielding is provided, and the internal volume of the microwave heating of the drying oven is variable.