INSULATION INSPECTION METHOD AND INSULATION INSPECTION APPARATUS

In an insulation inspection method for detecting creeping discharge that occurs in a coil in an armature, a predetermined impulse voltage is applied to the coil, and an electrical current value of a current that flows to a current detector that is connected to the coil is detected. The detected electrical current value is analyzed to acquire a relationship between a frequency and an electrical current value spectrum in the detected electrical current value. Based on the acquired relationship, a total sum of electrical current value spectrum areas in a high-frequency band is calculated as a high-frequency spectrum area. The high-frequency band differs from a predetermined low-frequency band in which partial discharge that occurs in a portion of a thin coating of the wire configuring the coil can be detected. Based on a magnitude of the calculated high-frequency spectrum area, creeping discharge that occurs in the coil is detected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2022-106304, filed on Jun. 30, 2022. The entire disclosure of the above application is incorporated herein by reference.

BACKGROUND

The present disclosure relates to an insulation inspection method and an insulation inspection apparatus. An insulation inspection method and an insulation inspection apparatus that inspect an insulation state of a coil that is provided in an armature that configures a rotating electric machine are known.

SUMMARY

One aspect of the present disclosure provides an insulation inspection method for detecting creeping discharge that occurs through a space inside a resin portion between metal portions of wires of phases that configure a coil that is provided in an armature that is a subject to be inspected and includes at least a portion of the coil molded by resin. The insulation inspection method includes: applying a predetermined impulse voltage to the coil and detecting an electrical current value of a current that flows to a current detector that is connected to the coil; analyzing the detected electrical current value to acquire a relationship between a frequency and an electrical current value spectrum; and calculating, based on the acquired relationship between the frequency and the electrical current value spectrum, a total sum of electrical current value spectrum areas in a high-frequency band as a high-frequency spectrum area, the high-frequency band differing from a predetermined low-frequency band in which partial discharge that occurs in a portion of a thin coating of the wire that configures the coil can be detected; and detecting creeping discharge that occurs in the coil based on a magnitude of the calculated high-frequency spectrum area.

DESCRIPTION OF THE EMBODIMENTS

The present disclosure relates to an insulation inspection method and an insulation inspection apparatus for inspecting an insulation state of a coil that is provided in an armature (that is, a stator or a rotor) that configures a rotating electric machine.

Conventionally, an insulation inspection method and an insulation inspection apparatus for inspecting an insulation state of a coil that is provided in an armature that configures a rotating electric machine are known.

An insulation inspection apparatus described in JP 2005-274440 A applies an impulse voltage to a motor and detects partial discharge that occurs in a portion of a wire in which a coating is thin, the wire being a wire that configures a three-phase coil. Specifically, in an insulation inspection, the following three inspections are performed. First is an insulation inspection between a wire of a predetermined phase and a wire of another phase that configure the three-phase coil. Second is an insulation inspection between wires of a predetermined phase that configure the three-phase coil. Third is an insulation inspection between a wire of a predetermined phase and a core that configure the three-phase coil.

Here, the armature that configures the rotating electric machine may be an armature in which, in the coil that is provided in the armature, a portion that protrudes from a slot (that is, a coil end) is resin-molded. In this case, a void may be formed inside a resin portion in which the coil is molded. Furthermore, a pinhole may be formed in the coating of the wire that configures the coil. When metal portions of the wires of the phases that configure the coil are connected by spaces (that is, voids and pinholes), creeping discharge may occur through an inner wall surface of the space. In the insulation inspection for the armature, creeping discharge and partial discharge are required to be detected separately (that is, so as to be distinguished therebetween).

However, in the above-described insulation inspection method described in JP 2005-274440 A, partial discharge and creeping discharge are detected in a mixed state, and the creeping discharge alone cannot be detected. In this way, an insulation inspection method and an insulation inspection apparatus that detects creeping discharge and partial discharge separately (that is, so as to be distinguished therebetween), with the resin-molded coil that is

It is thus desired to provide an insulation inspection method and an insulation inspection apparatus that are capable of detecting creeping discharge.

A first exemplary embodiment of the present disclosure provides an insulation inspection method for detecting creeping discharge that occurs through a space inside a resin portion between metal portions of wires of phases that configure a coil that is provided in an armature that is a subject to be inspected and includes at least a portion of the coil molded by resin. The insulation inspection method includes: applying a predetermined impulse voltage to the coil and detecting an electrical current value of a current that flows to a current detector that is connected to the coil; analyzing the detected electrical current value to acquire a relationship between a frequency and an electrical current value spectrum; and calculating, based on the acquired relationship between the frequency and the electrical current value spectrum, a total sum of electrical current value spectrum areas in a high-frequency band as a high-frequency spectrum area, the high-frequency band differing from a predetermined low-frequency band in which partial discharge that occurs in a portion of a thin coating of the wire that configures the coil can be detected; and detecting creeping discharge that occurs in the coil based on a magnitude of the calculated high-frequency spectrum area.

As a result, in an insulation inspection for the coil that is provided in the armature, creeping discharge and partial discharge can be detected separately (that is, so as to distinguish therebetween) through use of the high-frequency band that differs from the predetermined low-frequency band that is used to detect partial discharge. Consequently, as a result of this insulation inspection method, an armature that has faulty insulation and in which creeping discharge occurs, and a good armature in which creeping discharge does not occur can be accurately distinguished.

A second exemplary embodiment of the present disclosure provides an insulation inspection apparatus for detecting creeping discharge that occurs through a space inside a resin portion between metal portions of wires of phases that configure a coil that is provided in an armature that is a subject to be inspected and includes at least a portion of the coil molded by resin. The insulation inspection apparatus includes: an impulse power supply that applies a predetermined impulse voltage to the coil; a current detector that detects an electrical current value of a current that flows when the predetermined impulse voltage is applied to the coil; and a determination apparatus. The determination apparatus analyzes the detected electrical current value to acquire a relationship between a frequency and an electrical current value spectrum, calculates, based on the acquired relationship between the frequency and the electrical current value spectrum, a total sum of electrical current value spectrum areas in a high-frequency band as a high-frequency spectrum area, the high-frequency band differing from a predetermined low-frequency band in which partial discharge that occurs in a portion of a thin coating of the wire that configures the coil can be detected, and detects creeping discharge that occurs in the coil based on a magnitude of the calculated high-frequency spectrum area.

As a result, in an insulation inspection for the coil that is provided in the armature, creeping discharge and partial discharge can be detected separately (that is, so as to distinguish therebetween) through use of the high-frequency band that differs from the predetermined low-frequency band that is used to detect partial discharge. Consequently, as a result of this insulation inspection apparatus, an armature that has faulty insulation and in which creeping discharge occurs, and a good armature in which creeping discharge does not occur can be accurately distinguished.

Here, reference numbers within parentheses that are attached to constituent elements and the like indicate an example of corresponding relationships between the constituent elements and the like, and specific constituent elements and the like according to embodiments described hereafter.

Embodiments

An embodiment of the present disclosure will hereinafter be described with reference to the drawings. As shown inFIGS.1to3, an insulation inspection apparatus according to the present embodiment is an apparatus that, with a stator1as a subject to be inspected, detects an insulation state of a coil2that is provided in the stator1. The stator1is an example of an armature that configures a rotating electric machine (not shown). Here, for example, a motor generator that is mounted to an electric vehicle is used as the rotating electric machine.

The stator1includes an annular core3(that is, a stator core), a coil2that is inserted into slots (not shown) that are provided in the core3, and the like. The coil2is a three-phase coil that configures a portion of a three-phase alternating-current circuit. In addition, as shown inFIG.1, the stator1includes a resin portion5in which a portion (that is, a coil end) of the coil2that protrudes from the slots in the core3is molded. Here, the resin portion5is formed by the coil end being immersed in molten resin during a manufacturing process or the like. Power lines6a,7a, and8aprotrude from a portion of the resin portion5in which the coil end is molded. The power lines6a,7a, and8aare electrically connected to respective wires of a U-phase coil6, a V-phase coil7, and a W-phase coil8that configure the three-phase coil2.

As shown inFIG.2, the insulation inspection apparatus includes an impulse power supply10, a current detector12, a determination apparatus13, and the like. The coil2that is provided in the stator1to be inspected is described using a Y-connection coil as an example.

The impulse power supply10applies a predetermined impulse voltage that is based on a designated voltage to the coil2.FIG.2shows an example of a method of connection between wires14and15that extend from the impulse power supply10, and the coil2. In the method of connection shown inFIG.2, one wire14that extends from the impulse power supply10is connected to an end portion of the power line6athat extends from a predetermined phase (such as the U-phase coil6) of the coil2. The other wire15that extends from the impulse power supply10branches off part-way and is connected to end portions of the two power lines7aand8athat respectively extend from the other two phases (such as the V-phase coil7and the W-phase coil8) of the coil2.

Here, the method of connection between the wires14and15that extend from the impulse power supply10, and the coil2is not limited to that shown inFIG.2. For example, as shown inFIG.3, the other wire15that extends from the impulse power supply10may be connected to the end portion of one power line8athat extends from another phase (such as the W-phase coil8) of the coil2.

When the predetermined impulse voltage is applied from the impulse power supply to the coil2, partial discharge and creeping discharge may occur between the wire of a predetermined phase that is connected to the power line that is connected to the one wire14that extends from the impulse power supply10, and the wire of another phase that is connected to the power line that is connected to the other wire15that extends from the impulse power supply10. The insulation inspection apparatus detects the partial discharge and the creeping discharge separately (that is, so as to distinguish therebetween).

FIGS.4to7show cross-sections of the wire (hereafter, referred to as a “positive-side wire” for convenience) of the predetermined phase that is connected to the power line that is connected to the one wire14that extends from the impulse power supply10and the wire (hereafter, referred to as a “negative-side wire” for convenience) of another phase that is connected to the power line that is connected to the other wire15that extends from the impulse power supply10.

Specifically,FIG.4shows wires that each have a coating20(that is, a normal coating) that is formed to have a thickness that is within a design range. In this case, discharge does not occur even when the predetermined impulse voltage is applied from the impulse power supply10to the coil2.

FIG.5shows wires that each have a coating (that is, a thin coating26) that is formed to be thinner than the thickness that is within the design range. In this case, when the predetermined impulse voltage is applied from the impulse power supply10to the coil2, partial discharge occurs between a metal portion21that configures the positive-side wire and a metal portion21that configures the negative-side wire, through the thin coatings26.FIGS.6and7show an aspect in which, as a result of a pinhole22that is formed in the coating20of each wire and a void23that is formed inside the resin portion5in which the wires are molded, the metal portion21that configures the positive-side wire and the metal portion21that configures the negative-side wire are connected by a space (that is, the void23and the pinholes22). In this case, when the predetermined impulse voltage is applied from the impulse power supply10to the coil2, as indicated by a broken-line arrow, creeping discharge occurs through an inner wall surface of the space (that is, the void23and the pinholes22) between the metal portion21that configures the positive-side wire and the metal portion21that configures the negative-side wire.

As shown inFIGS.2and3, the current detector12detects an electrical current value of a current that flows when the predetermined impulse voltage is applied from the impulse power supply10to the coil2. The electrical current value that is detected by the current detector12is transmitted to the determination apparatus13.

The determination apparatus13is configured by a computer, an oscilloscope, and the like. The computer includes a processor, a memory, and the like. The determination apparatus13is configured such that the processor runs a program that is stored in the memory and determines whether creeping discharge has occurred in the coil2.

A determination process that is performed by the determination apparatus13will be described with reference to a flowchart inFIG.8.

At step S10, the determination apparatus13acquires the electrical current value that is detected by the current detector12when the predetermined impulse voltage is applied from the impulse power supply10to the coil2.

Next, at step S20, the determination apparatus13analyzes the electrical current value that is detected by the current detector12by fast Fourier transform (FFT) or the like and acquires a relationship between a frequency and an electrical current value spectrum such as that shown by a graph inFIG.11. Here, the electrical current value spectrum is also referred to as a current amplitude or a current strength.

Then, at step S30inFIG.8, the determination apparatus13calculates a total sum (that is, an integrated value) of the electrical current value spectrum areas in a high-frequency band in which creeping discharge can be detected. According to the present embodiment, the frequency band in which creeping discharge can be detected is a higher frequency band than a frequency band in which partial discharge can be detected. The determination apparatus13calculates the total sum of the electrical current value spectrum areas in the high-frequency band in which creeping discharge can be detected.

Here, in the present specification, the total sum of the electrical current value spectrum areas in the high-frequency band that is set for detecting creeping discharge is referred to as a “high-frequency spectrum area.” In addition, the total sum of the electrical current value spectrum areas in the low-frequency band that is set for detecting partial discharge is referred to as a “low-frequency spectrum area.”

Next, at step S40, the determination apparatus13determines whether the high-frequency spectrum area is greater than a predetermined first threshold. The first threshold is set by an experiment or the like in advance and stored in the memory of the determination apparatus13.

When the high-frequency spectrum area is greater than the predetermined first threshold at step S40, the process proceeds to step S50. At step S50, the determination apparatus13determines that creeping discharge has occurred in the coil2.

Meanwhile, when the high-frequency spectrum area is less than the predetermined first threshold at step S40, the process proceeds to step S60. At step S60, the determination apparatus13determines that creeping discharge has not occurred in the coil2.

In this manner, the determination apparatus13is capable of determining whether creeping discharge has occurred in the coil2.

In addition, the determination apparatus13according to the present embodiment is also capable of performing a determination process other than the determination process described above.

The other determination process that is performed by the determination apparatus13will be described with reference to a flowchart inFIG.9. In this determination process, the determination apparatus13is capable of detecting partial discharge that occurs in the coil2, in addition to detecting creeping discharge that occurs in the coil2, by a single inspection.

In the flowchart inFIG.9, steps S10to S60are identical to the steps described with reference to the flowchart inFIG.8.

At step S70following step S20, the determination apparatus13calculates the total sum (that is, the integrated value) of the electrical current value spectrum areas in a predetermined low-frequency band in which partial discharge can be detected. According to the present embodiment, the frequency band in which partial discharge can be detected is a lower frequency band than the frequency band in which creeping discharge can be detected. Therefore, the determination apparatus13calculates the total sum of the electrical current value spectrum areas in the low-frequency band in which partial discharge can be detected (that is, the low-frequency spectrum area).

Next, at step S80, the determination apparatus13determines whether the low-frequency spectrum area is greater than a predetermined second threshold. The second threshold is set by an experiment or the like in advance and stored in the memory of the determination apparatus13.

When the low-frequency spectrum area is greater than the predetermined second threshold at step S80, the process proceeds to step S90. At step S90, the determination apparatus13determines that partial discharge has occurred in the coil2.

Meanwhile, when the low-frequency spectrum area is less than the second threshold at step S80, the process proceeds to step S100. At step S100, the determination apparatus13determines that partial discharge has not occurred in the coil2.

In this manner, the determination apparatus13is capable of detecting partial discharge that occurs in the coil2, in addition to detecting creeping discharge that occurs in the coil2, by a single inspection.

Next, a verification test that was performed to verify effectiveness of the insulation inspection by the insulation inspection apparatus, described above, will be described. In the verification test, the coil2to which a test piece25is connected was used as the coil2that is provided in the stator1. As shown inFIGS.6and7, the test piece25is a test piece in which, as a result of the pinhole22that is formed in the coating20of each wire and the void23that is formed inside the resin portion5in which the wires are molded, the metal portions21of the two wires are connected by a space (that is, the void23and the pinholes22).

As shown inFIG.10, in verification test1, the power line6athat extends from a predetermined phase (such as the U-phase coil6) of the coil2that is provided in the stator1and one wire of the test piece25are connected. The power line7athat extends from another phase (such as the V-phase coil7) of the coil2and the other wire of the test piece25are connected. In this state, a predetermined impulse voltage was applied from the impulse power supply10to the coil2, and a relationship between the frequency and the electrical current value spectrum was analyzed by fast Fourier transform (FFT) being performed on the electrical current value detected by the current detector12. Results of the analysis are indicated by a broken line A in a graph inFIG.11.

In addition, in the verification test1, the predetermined impulse voltage was applied from the impulse power supply10to the coil2, and the relationship between the frequency and the electrical current value spectrum was analyzed by fast Fourier transform (FFT) being performed on the electrical current value detected by the current detector12, for the stator1in which the test piece25is not connected to the coil2provided therein (that is, a good stator1) as well. Results of the analysis are indicated by a solid line B in the graph inFIG.11.

Furthermore, for each of the stator1in which the test piece25is connected, indicated by the broken line A inFIG.11, and the good stator1indicated by the solid line B, the total sum of the electrical current value spectrum areas in a predetermined low-frequency band (such as 20 to 200 MHz) in which partial discharge can be detected (that is, the low-frequency spectrum area) was calculated. In addition, for each of the stator1in which the test piece25is connected, indicated by the broken line A inFIG.11, and the good stator1indicated by the solid line B, the total sum of the electrical current value spectrum areas in a predetermined high-frequency band (such as 300 to 500 MHz) in which creeping discharge can be detected (that is, the high-frequency spectrum area) was calculated.

Here, in the verification test1, the impulse voltage that is applied from the impulse power supply10to the coil2was applied ten times each for voltages from a predetermined designated voltage (such as 1 kV) to a designated voltage (such as 4.5 kV) that is greater than the predetermined designated voltage, in 100 V increments, for example. The analysis results indicated in the graph inFIG.11are those when the designated voltage is V_1in the graphs inFIGS.12and13described hereafter.

The graph inFIG.12shows the designated voltage (referred to, hereafter, as simply the “designated voltage”) of the impulse voltage that is applied from the impulse power supply10to the coil2on a horizontal axis and the low-frequency spectrum area on a vertical axis.

In the test results of the test performed using the stator1in which the test piece25is connected to the coil2provided therein, a solid line C inFIG.12indicates a relationship between the designated voltage and the low-frequency spectrum area.

In the test results of the test performed using the stator1in which the test piece25is not connected to the coil2provided therein (that is, the good stator1), a shaded area between a solid line D and a solid line E inFIG.12shows an area within ±4 standard deviations (a) from an average of 10 tests (referred to, hereafter, as a “±46 area”). That is, the solid line D is +46 and the solid line E is −46.

As shown inFIG.12, in terms of the low-frequency spectrum area, the solid line C that indicates the test results of the test that was performed with the test piece25connected to the coil2is near the ±46 area of the test results of the test that was performed using the good stator1, between the designated voltages V_2to V_4. Here, at the designated voltage V_3, the solid line C and the solid line D are in contact. Therefore, the stator1that has the coil2in which creeping discharge occurs and the good stator1are difficult to distinguish even when the low-frequency spectrum area is calculated. Consequently, in an inspection method in which the low-frequency spectrum area is calculated (that is, in a conventional inspection method for partial discharge), the stator1that has the coil2in which creeping discharge occurs may not be distinguished from the good stator1.

In contrast, the graph inFIG.13shows the designated voltage on the horizontal axis and the high-frequency spectrum area on the vertical axis.

In the test results of the test performed using the stator1in which the test piece25is connected to the coil2provided therein, a solid line F inFIG.13indicates the relationship between the designated voltage and the high-frequency spectrum area.

In the test results of the test performed using the stator1in which the test piece25is not connected to the coil2provided therein (that is, the good stator1), a shaded area between a solid line G and a solid line H inFIG.13shows an area within ±56 standard deviations (σ) from an average of 10 tests (referred to, hereafter, as a “±56 σ area”). That is, the solid line G is +56 σ and the solid line E is −56σ.

As shown inFIG.13, in terms of the high-frequency spectrum area, the solid line F that indicates the test results of the test that was performed using the coil2to which the test piece25is connected significantly deviates from the ±56 σ area of the test results of the test that was performed using the good stator1, between the designated voltages V_1to V_4. Therefore, it is verified that the stator1that has the coil2in which creeping discharge occurs and the good stator1can be reliably distinguished by the impulse voltages between the designated voltages V_1to V_4being applied to the coil2and the high-frequency spectrum area being calculated. Consequently, in the inspection method in which the high-frequency spectrum area is calculated, the stator1that has the coil2in which creeping discharge occurs can be prevented from mixing with the good stator1.

Next, as shown inFIG.14, in the verification test2, a portion that is close to a neutral point9in a predetermined phase (such as the U-phase coil6) of the coil2that is provided in the stator1and one wire of the test piece25are connected, and a portion that is close to the neutral point9in another phase (such as the V-phase coil7) of the coil2and another wire of the test piece25are connected. In this state, the predetermined impulse voltage was applied from the impulse power supply10to the coil2, and the relationship between the frequency and the electrical current value spectrum was analyzed by fast Fourier transform (FFT) being performed on the electrical current value detected by the current detector12. The results of the analysis are indicated by a broken line I in a graph inFIG.15.

In addition, in this verification test2as well, the predetermined impulse voltage was applied from the impulse power supply10to the coil2, and the relationship between the frequency and the electrical current value spectrum was analyzed by fast Fourier transform (FFT) being performed on the electrical current value detected by the current detector12, for the stator1in which the test piece25is not connected to the coil2provided therein (that is, the good stator1). Results of the analysis are indicated by a solid line J in the graph inFIG.15.

Furthermore, for each of the stator1in which the test piece25is connected, indicated by the broken line I inFIG.15, and the good stator1indicated by the solid line J, the total sum of the electrical current value spectrum areas in a predetermined low-frequency band (such as 20 to 200 MHz) in which partial discharge can be detected (that is, the low-frequency spectrum area) was calculated. In addition, for each of the stator1in which the test piece25is connected, indicated by the broken line I inFIG.15, and the good stator1indicated by the solid line J, the total sum of the electrical current value spectrum areas in a predetermined high-frequency band (such as 300 to 500 MHz) in which creeping discharge can be detected (that is, the high-frequency spectrum area) was calculated. Here, as the test piece25is connected to a position that is closer to the neutral point9in the coil2of each phase, the impulse voltage decreases as a result of resistance in the wire. Therefore, difficulty in detection increases.

In the verification test2as well, the impulse voltage that is applied from the impulse power supply10to the coil2was applied ten times each for voltages from a predetermined designated voltage (such as 1 kV) to a designated voltage (such as 4.5 kV) that is greater than the predetermined designated voltage, in 100 V increments, for example. The graph inFIG.15described above is that when the designated voltage is V_21in the graphs inFIGS.16and17described hereafter.

The graph inFIG.16shows the designated voltage on the horizontal axis and the low-frequency spectrum area on the vertical axis.

In the test results of the test performed using the stator1in which the test piece25is connected to the coil2provided therein, a solid line K inFIG.16indicates a relationship between the designated voltage and the low-frequency spectrum area.

In the test results of the test performed using the stator1in which the test piece25is not connected to the coil2provided therein (that is, the good stator1), a shaded area between a solid line L and a solid line M inFIG.16shows an area within ±4 standard deviations (a) from an average of 10 tests (referred to, hereafter, as a “±4 σ area”). That is, the solid line L is +4 σ and the solid line M is −4σ.

As shown inFIG.16, in terms of the low-frequency spectrum area, the solid line K that indicates the test results of the test that was performed with the test piece25connected to the coil2overlaps or is near the ±46 area of the test results of the test that was performed using the good stator1, between the designated voltages V_20to V_25. Therefore, when a section in which creeping discharge occurs is present in a portion near the neutral point9of the coil2, the stator1that has the coil2in which creeping discharge occurs and the good stator1are difficult to distinguish, even when the low-frequency spectrum area is calculated. Consequently, in the inspection method in which the low-frequency spectrum area is calculated (that is, in the conventional inspection method for partial discharge), the stator1that has the coil2in which the creeping discharge occurs may not be distinguished from the good stator1.

In contrast, the graph inFIG.17shows the designated voltage on the horizontal axis and the high-frequency spectrum area on the vertical axis.

In the test results of the test performed using the stator1in which the test piece25is connected to the coil2provided therein, a solid line N inFIG.17shows the relationship between the designated voltage and the high-frequency spectrum area.

In the test results of the test performed using the stator1in which the test piece25is not connected to the coil2provided therein (that is, the good stator1), a shaded area between a solid line O and a solid line PinFIG.17shows an area within ±15 standard deviation (σ) from an average of 10 tests (referred to, hereafter, as a “±15 σ area”). That is, the solid line O is +15 σ and the solid line P is −15σ.

As shown inFIG.17, in terms of the high-frequency spectrum area, the solid line N that indicates the test results of the test that was performed using the coil2to which the test piece25is connected significantly deviates from the ±15 σ area of the test results of the test that was performed using the good stator1, between the designated voltages V_21to V_24. Therefore, it is verified that the stator1that has the coil2in which creeping discharge occurs and the good stator1can be reliably distinguished by the impulse voltages between the designated voltages V_21to V_24being applied to the coil2and the high-frequency spectrum area being calculated, when a section in which creeping discharge occurs is present in a portion near the neutral point9of the coil2. Consequently, in the inspection method in which the high-frequency spectrum area is calculated, the stator1having the coil2in which creeping discharge occurs can be prevented from mixing with the good stator1.

(Summary of the Verification Tests)

As shown inFIGS.18to21, tests similar to the verification tests1and2described above were performed with the test piece25connected to various positions in each phase of the coil2that is provided in the stator1. Here, as described above, the impulse voltage decreases as a result of resistance in the wire as the test piece25is connected in positions closer to the neutral point9of the coil2of each phase. Therefore, difficulty in detection increases. In the description below, regarding the coil2to be inspected, the coil2shown inFIG.18is referred to as “good.” The coil2shown inFIG.19is referred to as “low detection difficulty.” The coil2shown inFIG.20is referred to as “medium detection difficulty.” The coil2shown inFIG.21is referred to as “high detection difficulty.”

FIG.22shows the designated voltage on the horizontal axis and the low-frequency spectrum area on the vertical axis. A solid line Q indicates “good.” A broken line R indicates “low detection difficulty.” A single-dot chain line S indicates “medium detection difficulty.” A two-dot chain line T indicates “high detection difficulty.”

As shown inFIG.22, the stator1that has the coil2in which creeping discharge occurs and the good stator1are difficult to distinguish even when the low-frequency spectrum area is calculated. Consequently, in the inspection method in which the low-frequency spectrum area is calculated (that is, in the conventional inspection method for partial discharge), the stator1that has the coil2in which the creeping discharge occurs may not be distinguished from the good stator1.

In contrast,FIG.23shows the designated voltage on the horizontal axis and the high-frequency spectrum area on the vertical axis. A solid line U indicates “good.” A broken line V indicates “low detection difficulty.” A single-dot chain line W indicates “medium detection difficulty.” A two-dot chain line X indicates “high detection difficulty.”

As shown inFIG.23, as a result of an impulse voltage of a designated voltage V_31 or greater being applied to the coil2and the high-frequency spectrum area being calculated, the stator1that has the coil2in which creeping discharge occurs and the good stator1can be reliably distinguished. Consequently, in the inspection method in which the high-frequency spectrum area is calculated, the stator1that has the coil2in which creeping discharge occurs can be prevented from mixing with the good stator1.

The insulation inspection method and the insulation inspection apparatus according to the present embodiment described above achieve the following configuration and resultant working effects.

(1) The insulation inspection method according to the present embodiment is a method for detecting creeping discharge that occurs in the coil2, with the stator1in which at least a portion of the coil2provided therein is molded in the resin portion5as the subject to be inspected. The insulation inspection method includes the following. That is, a predetermined impulse voltage is applied to the coil2, and the electrical current value of the current that flows to the current detector12that is connected to the coil2is detected. In the relationship between the frequency and the electrical current value spectrum that is acquired through analysis of the detected electrical current value, the total sum of the electrical current value spectrum areas in a high-frequency band that differs from a predetermined low-frequency band in which partial discharge that occurs in the portion of the thin coating26of the wire that configures the coil2can be detected is calculated as the high-frequency spectrum area. Creeping discharge that occurs in the coil2is detected based on a magnitude of the high-frequency spectrum area.

As a result, in the insulation test for the coil2that is provided in the stator1, as a result of the high-frequency band that differs from the predetermined low-frequency band used to detect partial discharge being used, creeping discharge and partial discharge can be detected separately (that is, so as to be distinguished therebetween). Consequently, as a result of this insulation inspection method, the stator1that has faulty insulation and in which creeping discharge occurs, and the good stator1in which creeping discharge does not occur can be accurately distinguished.

(2) The insulation inspection method according to the present embodiment further includes, in addition to detecting creeping discharge that occurs in the coil2based on the magnitude of the high-frequency spectrum area, calculating the total sum of the electrical current value spectrum areas in the predetermined low-frequency band as the low-frequency spectrum area, and detecting partial discharge that occurs in the coil2based on a magnitude of the low-frequency spectrum area.

Consequently, in the insulation inspection for the coil2that is provided in the stator1, partial discharge and creeping discharge can be detected separately (that is, so as to be distinguished therebetween) by a single inspection.

(3) The insulation inspection apparatus according to the present embodiment includes the impulse power supply10, the current detector12, and the determination apparatus13. The impulse power supply10applies the predetermined impulse voltage to the coil2. The current detector12detects the electrical current value of the current that flows to the current detector12when the predetermined impulse voltage is applied to the coil2. The determination apparatus13is configured to analyze the electrical current value detected by the current detector12to acquire the relationship between the frequency and the electrical current value spectrum, calculate, based on the acquired relationship between the frequency and the electrical current value spectrum, the total sum of the electrical current value spectrum areas in a high-frequency band as the high-frequency spectrum area, the high-frequency band differing from a predetermined low-frequency band in which partial discharge that occurs in the portion of the thin coating26of the wire that configures the coil2can be detected, and detect creeping discharge that occurs in the coil2based on the magnitude of the calculated high-frequency spectrum area.

As a result, the insulation inspection apparatus is capable of detecting the creeping discharge and the partial discharge separately (that is, so as to distinguish therebetween) by using the high-frequency band that differs from the predetermined low-frequency band used to detect partial discharge. Consequently, as a result of the insulation inspection apparatus, the stator1that has faulty insulation and in which creeping discharge occurs, and the good stator1in which creeping discharge does not occur can be accurately distinguished.

(4) According to the present embodiment, the determination apparatus13is configured to calculate, based on the acquired relationship between the frequency and the electrical current value spectrum, the total sum of the electrical current value spectrum areas in the predetermined low-frequency band, and detect partial discharge that occurs in the coil2based on the magnitude of the calculated low-frequency spectrum area, in addition to detecting the creeping discharge that occurs in the coil2based on the magnitude of the calculated high-frequency spectrum area.

Consequently, the insulation inspection apparatus can detect the partial discharge and the creeping discharge separately (that is, so as to distinguish therebetween) by a single inspection.

Other Embodiments

(1) According to the above-described embodiments, the armature that serves as the subject to be inspected is described as the stator1. However, this is not limited thereto. The armature to be inspected may be a rotor that includes the coil2.

(2) According to the above-described embodiments, as the coil2that is provided in the stator1to be inspected, the coil2that has a Y connection is described. However, this is not limited thereto. A coil that has a Δ connection, a ΔY connection, a ΔΔ connection, a YY connection, or the like can also be used.

The present disclosure is not limited to the above-described embodiments. Modifications can be made as appropriate within the scope of claims. In addition, the above-described embodiments and portions of the coil can be combined as appropriate unless the embodiments and portions of the coil are unrelated to each other or clearly not able to be combined. Furthermore, according to the above-described embodiments, it goes without saying that an element that configures an embodiment is not necessarily a requisite unless particularly specified as being a requisite, clearly considered a requisite in principle, or the like.

In addition, according to the above-described embodiments, in cases in which a numeric value, such as quantity, numeric value, amount, or range, of a constituent element is stated, the present disclosure is not limited to the specific number unless particularly specified as being a requisite, clearly limited to the specific number in principle, or the like. In a similar manner, according to the above-described embodiments, when a shape, a positional relationship, or the like of a constituent element or the like is mentioned, excluding cases in which the shape, the positional relationship, or the like is clearly described as particularly being a requisite, is clearly limited to a specific shape, positional relationship, or the like in principle, or the like, the present disclosure is not limited to the shape, positional relationship, or the like.