JP5310412B2 - Coil nondestructive inspection method - Google Patents

Description

  The present invention relates to a method for inspecting an electrical insulation state of a coil mounted on a motor core in a non-destructive state.

A coil mounted on a stator core or a rotor core (referred to as a motor core) of a motor is configured by winding a number of coated conductors whose outer peripheral surfaces are covered with an insulating resin. The electrical insulation of these numerous coated conductors is a very important characteristic in motor performance.
Conventionally, as a method for inspecting the insulation state of a coil formed by winding a coated conductor, there is a pinhole inspection using a saline solution.

  In this method, as shown in FIG. 7, a conductive test solution 91 composed of saline (0.2%) and phenolphthalein is stored in a test container 92, and the motor core 8 is mounted in the test solution 92. This is performed by immersing the coil 7 and the electrode 93. The electrode 93 and the terminal portion 71 of the coil 7 are connected by an electric wire 15 and a DC voltage is applied between them by a DC power source 11 disposed therebetween. When the insulating film of the coated conductor constituting the coil is damaged, the hydrogen bubbles 99 generated by electrolysis react with phenolphthalein and the solution turns red. The position P of the scratch can be specified by the red change.

  However, in the method using the conductive test solution composed of the above-described saline solution and phenolphthalein, even if the position of the wound on the coil can be confirmed, the extent of the wound is practically used. It is unclear whether it will be a problem. In addition, since the above test solution containing saline has the property of corroding the motor core, the inspected motor core and coil cannot be made into a product even if the wound of the coil is not found and must be discarded. I don't get it.

  In order to solve such problems, there has been proposed an inspection method using an inspection solution in which isopropyl alcohol, which is a conductive alcohol, is mixed with a corrosion-resistant fluorine-based inert solution that does not corrode the motor core (patent) Reference 1). According to this method, it is supposed that the magnitude | size of the damage | wound of an insulating film can be determined quantitatively by measurement of an electric current value.

Japanese Patent No. 3646645

  However, it has been found that when a test solution in which isopropyl alcohol is mixed with the fluorine-based inert solution is used, isopropyl alcohol, which is a conductive alcohol, damages the insulating film of the coil. This is thought to be because isopropyl alcohol penetrates into the film and causes crazing, swelling, and the like. Since damage to such an insulating film lowers its insulating properties, the motor core and coil after the inspection of Patent Document 1 cannot be made into a product.

  The present invention has been made in view of such conventional problems. A nondestructive inspection method for a coil that can be commercialized without damaging the insulating film after inspecting the state of the scratch on the insulating film of the coil. It is something to be offered.

The present invention provides a test solution comprising a conductive liquid composed of an organic compound having a solubility parameter (SP value) of 10.3 cal / cm ² or less and a molecular weight of 78 or more, and a fluorine-based inert solution. In a test container,
Immerse the coil mounted on the motor core and the electrode in the test solution of the test container,
The present invention provides a nondestructive inspection method for a coil, wherein a voltage state is applied between the coil and the electrode and a value of a current flowing between the coil and the electrode is measured to determine a state of damage to the coil. (Claim 1).

The present invention uses, as the above-mentioned inspection liquid, a base which is based on a corrosion-resistant fluorine-based inert solution that does not corrode the motor core, and is mixed with a conductive liquid made of an organic compound having the above specific physical properties. ing. Thereby, the damage | inspection can be implemented, without giving damage to an insulating film. Therefore, the motor core and the coil after the test can be applied to the product as they are by thoroughly removing the test liquid by drying. The fact that there is almost no damage to the insulating film by using the inspection method of the present invention has been confirmed by experiments to be described later.
Further, by measuring the current value, the size (area) of the scratch can be easily obtained from the value, and the scratch can be quantitatively determined.

  Thus, according to the present invention, it is possible to provide a nondestructive inspection method of a coil that can be commercialized without damaging the insulating film after inspecting the state of the wound of the insulating film of the coil.

Explanatory drawing which shows the structure of the inspection apparatus which performs the nondestructive inspection method of a coil in Example 1. FIG. FIG. 3 is an explanatory diagram showing the results of a preliminary test in Example 1. Explanatory drawing which shows the result of the test | inspection test which used 3-methoxy-3-methyl- 1-butanol in Example 1 as an electroconductive liquid. Explanatory drawing which shows the result of the inspection test which used the butyl acetate as an electroconductive liquid in Example 1. FIG. Explanatory drawing which shows the result of the test which used benzene as an electroconductive liquid in Example 1. FIG. Explanatory drawing which shows the result of the test | inspection test which used heptane as an electroconductive liquid in Example 1. FIG. Explanatory drawing which shows the structure of the inspection apparatus which performs the nondestructive inspection method of a coil in a prior art example.

In the present invention, the conductive liquid is made of an organic compound having a solubility parameter (SP value) of less than 11.0 cal / cm ² and a molecular weight of 70 or more.
The SP value is a solubility parameter that is a measure of the dissolving power useful for selecting various appropriate solvents including petroleum-based solvents. The larger the SP value, the stronger the solubility and the higher the polarity. In the present invention, the penetration of the coil into the insulating coating is suppressed by limiting the SP value to less than 11.0 cal / cm ² . On the other hand, when the SP value exceeds 11.0 cal / cm ² , the penetration of the conductive liquid into the insulating film cannot be suppressed, and it is difficult to avoid damage to the insulating film. The lower limit of the SP value is not particularly limited, but if the SP value is equivalent to that of the fluorine inert solution, the SP value in the solution becomes uniform and becomes a stable solution. It is preferably 6 cal / cm ² .

Moreover, although the said molecular weight is a number average molecular weight, the damage to an insulating film is avoided by limiting this to 70 or more. The reason for this is considered that the smaller the molecular weight of the conductive liquid, the more likely it is that the insulating liquid of the coil enters and swells at the microscopic level of the insulating coating of the coil, and the effect of lowering the insulating property is likely to occur. The upper limit value of the molecular weight value is not particularly limited, but if the molecular weight value is the same as that of the fluorine-based inert solution, the molecular weight distribution becomes more uniform and the liquid state is stable. Therefore, the upper limit value of the molecular weight value is 238. Preferably it is.
And the said conductive liquid in this invention has suppressed the damage to an insulating film by employ | adopting the organic compound in which both the said SP value and molecular weight fall in the said specific range.

  The conductive liquid is preferably an ether, glycol ether, or hydrocarbon. In these systems, it is possible to relatively easily select a compound having both the SP value and the specific range of the molecular weight.

  In particular, the conductive liquid is preferably butyl acetate, 3-methoxy-3-methyl-1-butanol, benzene, or heptane (Claim 3). These can produce a highly accurate inspection result while avoiding damage to the insulating film. Among these, in particular, 3-methoxy-3-methyl-1-butanol is most preferable because it can realize excellent accuracy and sensitivity in the implementation of the above-described inspection method, as shown in the examples described later. One reason for this is thought to be that 3-methoxy-3-methyl-1-butanol has higher conductivity than the other three.

  The mixing ratio of the conductive liquid and the fluorine-based inert solution is preferably 3 to 5% in volume ratio of the conductive liquid with respect to the total amount of both (claim 4). When the content of the conductive liquid is less than 3%, sufficient conductivity cannot be obtained, and it is necessary to increase the voltage to be applied in the inspection as compared with the conventional case, and the associated equipment measures are required. In addition, when the content of the conductive liquid exceeds 5%, the solution itself becomes a target of a flammable substance according to the organic law, which causes a problem that the handling and storage of the solution is complicated. .

Example 1
A nondestructive inspection method for a coil according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, an inspection apparatus 1 that performs a nondestructive inspection method for a coil according to this example includes an inspection container 10 that contains an inspection liquid 4 containing a conductive liquid and a fluorine-based inert solution. Yes. A DC power source 11 and an ammeter 12 connected to the DC power source 11 are provided outside the cuvette 10. The DC power supply 11 and the ammeter 12 are electrically connected to the electrode 2 immersed in the cuvette 10 and the coil 7 mounted on the motor core 8 that is also dipped in the cuvette 10 via the electric wires 15. Connected. It is possible to connect a switch (not shown), a control circuit for analyzing the current value, and the like to the electric circuit including the DC power supply 11 and the ammeter 12.

The coil 7 and the electric wire 15 are connected by connecting the terminal portion 71 and the electric wire 15 with the terminal portion 71 of the coil 7 exposed above the liquid surface of the test liquid 4.
And the inspection method using the said inspection apparatus 1 gives the voltage from the DC power supply 11 between the coil 7 and the electrode 2, and measures the value of the electric current which flows between both by the ammeter 12. This is a method for determining the state of scratches on the coil.

As the inspection liquid 4, a liquid which is based on a corrosion-resistant fluorine-based inert solution that does not corrode the motor core and is mixed with a conductive liquid made of an organic compound is used. In this example, a mixture of conductive liquids (samples 1 to 8) made of a plurality of types of organic compounds was prepared. As shown in Table 1, as the conductive liquid, three types of alcohols, one type of glycols, one type of ethers, one type of glycol ethers, and two types of hydrocarbons were prepared.
About each electroconductive liquid, it showed in Table 1 about the characteristic of SP value, molecular weight (number average molecular weight), a boiling point, electrical conductivity, and a density.

  In order to confirm whether or not the above eight kinds of conductive liquids are suitable for the inspection method of the present invention, a preliminary test was performed. In this preliminary test, the coated conductor constituting the coil 7 is immersed in 100% of the conductive liquid for 1 hour, and then the coated conductor is taken out and left in a normal temperature and humidity state for 24 hours. The dielectric breakdown voltage value is obtained by the glycerin method. In the glycerin method, the middle part of the wire sample is immersed in a glycerin solution that is electrically connected to the positive electrode, and one end of the wire sample is electrically connected to the negative electrode, and the pressure increase rate is 500 V / sec between the pair of electrodes. This is a test method in which a voltage is applied until the insulation film in the wire sample is broken, and the higher the breakdown voltage, the higher the insulation.

  Among the above eight kinds of conductive liquids, as a representative, isopropyl alcohol (symbol B) of sample 1, 3-methoxy-3-methyl-1-butanol (symbol C) of sample 6, butyl acetate (symbol D) of sample 5 ), Benzene of sample 7 (symbol E), and heptane of sample 8 (symbol F) were subjected to the above preliminary test. For comparison, the preliminary test was also performed on a coated conductor (reference A) (hereinafter referred to as a reference material as appropriate) that was not immersed in a conductive liquid.

  The preliminary test was carried out 28 times (n = 28) for the reference material (reference A), isopropyl alcohol (reference B), and 3-methoxy-3-methyl-1-butanol (reference C), and butyl acetate ( About the benzene (code | symbol E) of the code | symbol D), the sample 7, and the heptane (code | symbol F) of the sample 8, it implemented 10 times (n = 10), the average value (ave), an upper limit (max), and a lower limit (Min) was determined. The result is shown in FIG. In the figure, the horizontal axis represents the test material with the above-mentioned symbol, and the vertical axis represents the dielectric breakdown voltage value (kV) in the glycerin solution.

As shown in the figure, the isopropyl alcohol (symbol B) of the sample 1 has a greatly reduced dielectric breakdown voltage value lower than 10 kV compared to the reference material (symbol A). In contrast, 3-methoxy-3-methyl-1-butanol of sample 6 (symbol C), butyl acetate of sample 5 (symbol D), benzene of sample 7 (symbol E), and heptane of sample 8 (symbol F) ), The dielectric breakdown voltage value hardly decreases compared to the reference material (symbol A), indicating excellent insulation characteristics.
For samples 2 to 4 not shown in the figure, it was confirmed by a similar preliminary test that the dielectric breakdown voltage value was greatly reduced as in sample 1 (symbol B).

  From the results of the above preliminary tests, at least 3-methoxy-3-methyl-1-butanol (symbol C) of sample 6, butyl acetate (symbol D) of sample 5, benzene (symbol E) of sample 7, and sample It was found that the heptane of 8 (reference F) hardly damaged the insulating film of the coated conductor.

Here, the characteristics of each of the conductive liquids are shown below.
<Alcohol>
Alcohol is a general term for substances in which a hydrogen atom of a hydrocarbon is replaced with a hydroxy group. Those substituted with hydrogen atoms on the aromatic ring are called phenols and are distinguished from alcohols. The alcohol is characterized by having a hydroxy group. Hydroxyl groups form hydrogen bonds with other molecules, and alcohol molecules have the properties of polar substances.

<Glycol>
Glycol is a kind of alcohol (polyol), which is a compound having a structure in which one hydroxy group is substituted for two carbon atoms of a chain aliphatic hydrocarbon or a cyclic aliphatic hydrocarbon. Also called a compound. Glycols are colorless liquids at room temperature, but have properties that their melting points and viscosities are higher for their molecular weight than ordinary alcohols. This is because there are many hydrogen bonds through the hydroxy group.

<Ether>
Ether is one of the classes of organic compounds, and the structural formula is R—O—R ′ (R and R ′ are organic groups such as alkyl groups and aryl groups, and O is an oxygen atom). Point to. The R—O—R ′ moiety contained in the ether is referred to as an ether bond. Since oxygen has an unshared electron pair, it exhibits Lewis basicity and hydrogen bond acceptability. Diethyl ether, tetrahydrofuran (THF), etc. have many uses as aprotic solvents because they dissolve many organic compounds well and are chemically relatively stable.

<Glycol ether>
Glycol ethers are versatile molecules that combine the best solubility of alcohol and ether. Glycol ethers are miscible and soluble in a wide range of organic chemicals as well as water. For this reason, glycol ethers are used routinely as an active solvent for resins, as a surface coating industry, as a brake fluid industry as a solvent, as an anti-icer in various petroleum-based fuels, as a petroleum industry, as an antifreeze, in the automobile industry as well as daily It is considered that it is excellent in special products.

  Considering the results of the preliminary test based on the above contents, it is considered as follows. Ether has a relatively stable solution because oxygen has an unshared electron pair, but alcohol is unstable because the hydroxyl group forms a hydrogen bond with the molecule, and the alcohol molecule has the properties of a polar substance. Solution. Glycol ether has both characteristics, and since it contains an ether bond, it becomes a stable solution compared to alcohol, so it does not cause much damage to the insulation film, and it is thought that there is no decrease in insulation. .

  Next, with respect to 3-methoxy-3-methyl-1-butanol (sample 6), butyl acetate (sample 5), benzene (sample 7), and heptane (sample 8), respectively, corrosion-resistant fluorine-based inertness A test solution 4 was prepared by mixing the solution into a base, and a test test was conducted by the nondestructive test method for the coil. Specifically, Novec HFE-7100 (manufactured by Sumitomo 3M) was used as the corrosion-resistant fluorine-based inert solution. The mixing ratio was 95.2% for the corrosion-resistant fluorine-based inert solution and 4.8% for each conductive liquid.

The inspection test is to prepare a test coil whose wound area of the coil 7 is known in advance, and to examine the correlation between the damaged area and the leakage current measured by the ammeter 12. The results are shown in FIGS. In each figure, the horizontal axis represents the scratch area (mm ² ), and the vertical axis represents the leakage current (nA).

FIG. 3 shows the results when 3-methoxy-3-methyl-1-butanol (sample 6) is used as the conductive liquid. As is known from the figure, in this case, R ² indicating the correlation between the scratch area and the leakage current is close to 1, and the slope is steep, and the sensitivity and accuracy are higher than in other examples described later. It turns out that it can be set as an inspection method.

  4 to 6 show the results when butyl acetate (sample 5), benzene (sample 7), and heptane (sample 8) are used as the conductive liquid, respectively. As can be seen from these figures, they exhibit almost the same linearity and are slightly inferior in sensitivity and accuracy to 3-methoxy-3-methyl-1-butanol (sample 6), but are sufficiently conductive. It can be seen that it functions as an ionic liquid.

DESCRIPTION OF SYMBOLS 1 Inspection apparatus which performs the nondestructive inspection method of a coil 10 Test container 11 DC power supply 12 Ammeter 2 Electrode 4 Inspection liquid 7 Coil 8 Motor core

Claims (4)

A test solution containing a conductive liquid made of an organic compound having a solubility parameter (SP value) of 10.3 cal / cm ² or less and a molecular weight of 78 or more and a fluorine-based inert solution is placed in the test container. Housed in
Immerse the coil mounted on the motor core and the electrode in the test solution of the test container,
A nondestructive inspection method for a coil, characterized in that a state of a flaw in the coil is determined by applying a voltage between the coil and the electrode and measuring a value of a current flowing between the coil and the electrode.   2. The nondestructive inspection method for a coil according to claim 1, wherein the conductive liquid is ether, glycol ether, or hydrocarbon.   3. The nondestructive inspection method for a coil according to claim 1, wherein the conductive liquid is butyl acetate, 3-methoxy-3-methyl-1-butanol, benzene, or heptane.   In any 1 item | term of Claims 1-3, the mixing ratio of the said electroconductive liquid and the said fluorine-type inert solution is 3-5% in content ratio of the said electroconductive liquid with respect to the total amount of both in volume ratio. A non-destructive inspection method for a coil, characterized in that:

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