Motor stator enameled wire damage detection method

Abstract

The invention discloses a motor stator enameled wire damage detection method, which comprises the following steps of: assembling a rotor core on a shaft of a supporting structure, enabling the rotor core to penetrate through an inner hole of a to-be-detected motor stator which is not dipped in paint and embedded with a plurality of temperature sensors, and forming an air gap between the to-be-detected motor stator and the rotor core; the method comprises the following steps of: introducing sine alternating current into a winding of a to-be-detected motor stator, and detecting the temperature rise condition of the winding through a temperature sensor during the electrifying period; and according to the position of the temperature sensor with abnormal temperature rise, an enameled wire area with broken enameled leather is positioned. The method is simple to operate and high in detection efficiency, can detect the insulation performance of the internal coil of each phase winding, ensures that the insulation performance of the stator has no problem before paint dipping, avoids the situation that the stator can only be scrapped or repaired when problems are found during subsequent motor assembly and test, can reduce the waste of manpower and material cost, and improves the product percent of pass.

Description

Technical Field

[0001] This invention relates to a method for detecting damage to enameled wire in motor stator, belonging to the field of enameled wire testing technology. Background Technology

[0002] High-speed rotating electric motors generally consist of a stator and a rotor. The stator mainly comprises a rotor core, stator windings, and insulation components. Most high-speed motors have three-phase windings, namely U, V, and W, with each phase winding made of enameled wire of the same diameter, typically made of copper. Enameled wire has a temperature resistance rating; excessively high temperatures can lead to insulation failure, causing anything from motor malfunction to personal injury. Therefore, it is crucial to monitor the stator winding temperature rise in real time and to reduce stator winding losses. For high-speed motors, the frequency of current flowing through the stator windings is generally above 200Hz, and some motors may reach 1000Hz. Therefore, high-frequency AC losses constitute a major portion of stator winding losses. To reduce high-frequency AC losses, stator windings are typically made by winding multiple strands of enameled wire in parallel.

[0003] Current stator testing methods typically involve testing the insulation resistance between the phase windings and the core, as well as the inter-turn insulation of the phase windings, using instruments or devices similar to a stator comprehensive tester after the stator is manufactured to determine whether the insulation requirements are met. This testing method can only detect whether there is insulation between phase windings and between phase windings and the core. However, it cannot detect whether there is any damage to the enamel coating of the multiple strands of enameled wire within the same phase winding. This is because the ends of the multiple strands of parallel-wound enameled copper wire are made into a whole through methods such as tinning and cold-pressing terminals. The stator comprehensive tester tests by connecting the ends of each phase, so it cannot test the internal coils of a single phase.

[0004] When the enamel coating of multiple enameled wires within the same phase winding is damaged, the wires are no longer insulated, causing a rapid increase in high-frequency AC losses and consequently, an increase in stator temperature rise. If the insulation performance of the stator coils cannot be tested in the early stages, the coils, after subsequent processes such as enamel impregnation, can only be assembled into a motor. During actual operation, pre-embedded temperature sensors are used to identify localized high-temperature points. If the enamel coating is damaged and the temperature rise fails to meet requirements, the stator becomes unusable and needs to be scrapped. The motor may also need to be scrapped directly or replaced with a new stator, severely impacting production time and costs, and causing material waste. Summary of the Invention

[0005] The purpose of this invention is to provide a method for detecting damage to the enameled wire of a motor stator. This method can detect the insulation performance of the coils inside each phase winding, ensuring that the stator insulation performance is not problematic before impregnation, thereby improving the product qualification rate.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for detecting damage to enameled wire in a motor stator involves assembling a rotor core onto a shaft of a support structure, then inserting the rotor core through the inner hole of the un-enamel-impregnated stator containing several temperature sensors. An air gap exists between the stator and the rotor core. A sinusoidal alternating current is passed through the windings of the stator, and the temperature rise of the windings is detected by the temperature sensors during energization. Based on the location of the temperature sensors where the temperature rise is abnormal, the area of ​​the enameled wire with broken enamel is located.

[0007] Preferably, when AC current is applied to the winding of the stator of the motor under test, the AC power supply is connected between the two output terminals of the winding, or between any phase output terminal and the center point of the winding of the same phase.

[0008] Preferably, the frequency F of the sinusoidal alternating current is greater than or equal to 200 Hz, and the current amplitude I is less than or equal to 100 A.

[0009] Preferably, the air gap g between the stator and rotor core of the motor under test satisfies: 0 < g ≤ 10 mm.

[0010] Preferably, the support structure is a transverse support structure, comprising: The stator support platform has an inverted trapezoidal groove on the top for placing and fixing the stator of the motor under test. The rotor shaft has a rotor core fitted onto the shaft body, and the rotor core is inserted into the inner hole of the stator of the motor under test. Two support frames are symmetrically arranged on both sides of the rotor shaft to support the rotor shaft and make the supporting rotor, rotor core and stator of the motor under test coaxial.

[0011] Preferably, a limiting ring is formed on the shaft of the rotor shaft to axially limit the rotor core.

[0012] Preferably, the support structure is a vertical support structure, including a base for supporting the stator of the motor under test, a boss for supporting the rotor core formed on the base, and a shaft passing through the rotor core formed on the boss. The base, the boss and the shaft are coaxially arranged.

[0013] The beneficial effects of this invention are as follows: This method is simple to operate and has high testing efficiency. It can test the insulation performance of the coils inside each phase winding, ensuring that the stator insulation performance is not problematic before impregnation. This avoids problems being discovered during subsequent motor assembly and testing, which would force scrapping or rework. It can reduce the waste of manpower and material costs and improve the product qualification rate. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the cross-section of the transverse support structure; Figure 2 This is a schematic diagram of the stator of the motor under test; Figure 3 This is a schematic diagram of the rotor core; Figure 4 This is a schematic diagram of the rotor shaft structure; Figure 5 This is a schematic diagram of the stator support platform structure; Figure 6 This is a schematic diagram of the support frame structure; Figure 7 This is a schematic diagram of the vertical support structure; Figure 8 This is a schematic diagram of the vertical support structure after assembly.

[0015] The meanings of the main reference numerals in the figure are as follows: 1. Stator support platform, 2. Rotor shaft, 3. Support frame, 4. Stator of the motor under test, 5. Rotor core, 6. Limiting ring, 7. Base, 8. Boss, 9. Shaft. Detailed Implementation

[0016] When high-frequency current flows into the stator winding, AC losses occur because the winding coil exhibits skin effect and proximity effect in an alternating magnetic field. To reduce AC losses, motor windings are typically constructed using multiple strands of thin enameled wire. However, if there is localized damage to the enamel coating of these multiple strands, the damaged wire effectively becomes a single, thicker wire. In this case, the AC losses caused by the skin effect increase rapidly, leading to a rapid increase in temperature.

[0017] Based on this, this application provides a method for detecting damage to the enameled wire of a motor stator. Using a high-frequency current injection method, before the motor stator is initially assembled and before impregnation, a sinusoidal alternating current with an amplitude of I and a frequency of F is applied to the winding ends. For a three-phase winding, the ends are denoted as U, V, and W, and the center point is denoted as N. With the center point leading out, U and N, V ​​and N, and W and N can be connected respectively. A high-frequency current is applied, and the temperature rise is detected by a pre-embedded temperature sensor. If an abnormal temperature rise is detected, the location of the temperature sensor determines the location of the enamel damage, and the damaged area is replaced. Besides connecting the ends and the center point, the ends can also be directly connected, such as U and W, U and V, and V and W. For multi-phase windings, the connection method is similar and will not be elaborated further.

[0018] Regarding current amplitude and frequency, theoretically, the larger the amplitude and the higher the frequency, the faster the temperature rises, thus shortening the detection time and improving detection efficiency. However, in reality, due to limitations of the power supply equipment, the current amplitude and frequency can only be within a limited range. Since an alternating magnetic field is used, the current frequency F needs to be ≥200Hz. But when the current amplitude I ≤100A, the readings of each temperature sensor on the temperature sensor acquisition unit rise very slowly, and there is no significant difference between the temperature measurement points. Even if the enameled wire is damaged, it is impossible to locate the temperature, so the current must be increased. To reduce the test current, this application introduces a rotor core during detection and provides a support structure suitable for the above method. Depending on the placement direction, the support structure provided in this application is divided into two types: a horizontal support structure and a vertical support structure.

[0019] See Figure 1-6 As shown, the transverse support structure includes a stator support platform 1, a rotor shaft 2, and two support frames 3. The top of the stator support platform 1 has an inverted trapezoidal groove extending axially along the stator 4 of the motor under test. The stator 4 of the motor under test is placed in the groove, and the outer wall of its lower half abuts against the side wall of the groove, so it cannot rotate (i.e., it is fixed). The rotor shaft 2 is fitted with a rotor core 5, and a limiting ring 6 is formed on one side of the rotor shaft 2 to axially limit the rotor core 5. The rotor core 5 is inserted into the inner hole of the stator 4 of the motor under test. The two support frames 3 are symmetrically arranged on both sides of the rotor shaft 2, and the top of each frame has a slot for supporting the rotor shaft 2 and making the rotor shaft 2, rotor core 5, and stator 4 of the motor under test coaxial.

[0020] The power supply used for the test is an AC power supply, used to generate sinusoidal AC current with a current frequency F ≥ 200Hz and a current amplitude I ≤ 100A. The stator 4 of the motor under test is a pre-assembled, unvarnished stator. The rotor core 5 is placed inside the inner hole of the stator 4, with a gap g between it and the inner hole: 0 < g ≤ 10mm. The rotor core 5 is made of stacked silicon steel sheets, with a circular outer edge. The overall shape can be annular, circular with a square inner edge, or other shapes. Its main function is to enhance the magnetic field inside the stator and reduce eddy current losses generated in the rotor core 5 due to the alternating magnetic field. In actual testing, the rotor core 5 does not rotate.

[0021] The stator support platform 1 is mainly used to place and fix the stator 4 of the motor under test. It can be made of hard non-metallic materials, such as wood or plastic. The rotor shaft 2 is placed in the inner hole of the rotor core 5 and is clearance-fitted with the rotor core 5 for easy disassembly and reuse. Both ends extend out of the rotor core 5, and the extended parts are placed on the support frame 3 to ensure that the rotor core 5 and the stator 4 of the motor under test are coaxial. One end has a limit ring 6 for limiting the rotor core 5. The rotor shaft 2 can be made of metal or hard non-metallic materials. The support frame 3 is mainly used to support the rotor shaft 2 and can also be made of metal or hard non-metallic materials.

[0022] The temperature sensor in stator 4 of the motor under test can be a thermocouple or a thermistor. Some of them are embedded during the stator assembly process according to the design requirements, and the other part can be randomly embedded before the test to increase the temperature measurement area. The temperature of the enameled wire at the location of the temperature sensor can be read by the temperature sensor acquisition device.

[0023] For vertical support structures, see [link to relevant documentation]. Figure 7-8 As shown, the main components include a base 7 for supporting the stator 4 of the motor under test, a boss 8 for supporting the rotor core 5 formed on the base 7, and a shaft 9 that passes through the rotor core 5 formed on the boss 8. The base 7, boss 8, and shaft 9 are coaxially arranged. This structure is simpler and suitable for smaller and lighter stators 4 of the motor under test.

[0024] These two support structures can be selected based on the actual test conditions and stator size.

[0025] As an example, such as Figure 1 As shown, the stator 4 of the motor under test is placed on the stator support platform 1. Temperature sensors (not shown in the figure) have been pre-embedded in different locations inside the windings of the stator 4. Here, platinum resistance thermometers (PT100) are used. The inner diameter of the stator 4 is D. The rotor core 5 is annular with an outer diameter of d, where d = D - 1 mm. The rotor core 5 is fitted onto the rotor shaft 2, with one end coinciding with the limiting ring 6. The outer diameter of the limiting ring 6 is between the inner diameter of the rotor core 5 and its outer diameter, ensuring that the rotor core 5 does not move axially to one side. The rotor core 5 and the rotor shaft 2 are placed inside the inner hole of the stator 4, supported at both ends by two support brackets 3. This ensures that the entire rotor core 5 covers the core portion of the stator 4 axially, while maintaining a 0.5 mm gap between the outer diameter of the rotor core 5 and the inner diameter of the stator 4 radially.

[0026] Set the three-phase AC power supply output current frequency to 200Hz and the current amplitude to 50A. Connect the AC power supply to the U, V, and W terminals of the three-phase windings of the stator of the motor under test. Keep the power on for 5 minutes and observe the readings of each temperature sensor on the temperature sensor acquisition unit. If the reading rises rapidly and the upward trend is significantly greater than that of other temperature sensors, the insulation of the winding at the corresponding position is substandard and the stator winding needs to be removed and replaced. If the readings of each temperature sensor are similar or the upward trend is basically the same, the insulation performance of the stator is qualified and subsequent assembly can proceed.

[0027] As another embodiment, such as Figure 8 As shown, to simplify the device, the stator 4 of the motor under test is placed vertically with the lead-out end on top and the non-lead-out end on the bottom, and the non-lead-out end is placed on the vertical support structure of the rotor. This eliminates the need for the support frame 3 and the stator support platform 1. The vertical support structure is shown in the attached figure. Figure 7 As shown, it is divided into three parts from top to bottom: shaft, boss 8, and base 7. The shaft fits into the inner hole of the rotor core 5. The boss 8 supports the rotor core 5 and also limits its position, ensuring that the rotor core 5 and the rotor core coincide vertically. The base 7 supports the stator 4 of the motor under test. The subsequent testing is the same as described above and will not be repeated here.

[0028] Without a rotor core, when directly performing damage detection on the stator of the motor under test, using the same current frequency, current amplitude, and wiring method, and with the same energizing time, it is observed that the temperature sensor readings on the temperature sensor acquisition unit rise very slowly, and there is no significant difference between the temperature measurement points. Even if there is a break in the enameled wire, it is impossible to locate the problem; only increasing the current will solve the problem. However, with the rotor core introduced, under the same current, the temperature sensor readings on the temperature sensor acquisition unit rise rapidly, and the temperature rises even faster at the location of the broken enameled wire, thus making it easier to locate the damage.

Claims

1. A method for detecting damage to the enameled wire of a motor stator, characterized in that, The process involves assembling the rotor core onto the shaft of the support structure, then inserting the rotor core into the inner hole of the stator of the motor under test, which is un-varnished and contains several temperature sensors. There is an air gap between the stator and the rotor core. Alternating current is applied to the windings of the stator of the motor under test. During the energization, the temperature rise of the windings is detected by the temperature sensors. Based on the location of the temperature sensor where the temperature rise is abnormal, the area of ​​the enameled wire with broken enamel is located.

2. The method for detecting damage to the enameled wire of a motor stator according to claim 1, characterized in that, When sinusoidal alternating current is applied to the winding of the stator of the motor under test, the AC power supply is connected between the two output terminals of the winding, or between any phase output terminal and the center point of the winding of the same phase.

3. The method for detecting damage to the enameled wire of a motor stator according to claim 1, characterized in that, The frequency F of the sinusoidal alternating current is greater than or equal to 200 Hz, and the current amplitude I is less than or equal to 100 A.

4. The method for detecting damage to the enameled wire of a motor stator according to claim 1, characterized in that, The air gap g between the stator and rotor core of the motor under test satisfies: 0 < g ≤ 10 mm.

5. The method for detecting damage to the enameled wire of a motor stator according to claim 1, characterized in that, The supporting structure is a lateral supporting structure, including: The stator support platform has an inverted trapezoidal groove on the top for placing and fixing the stator of the motor under test; The rotor shaft has a rotor core fitted on its shaft body, and the rotor core is inserted into the inner hole of the stator of the motor under test. Two support frames are symmetrically arranged on both sides of the rotor shaft to support the rotor shaft and make the supporting rotor, rotor core and stator of the motor under test coaxial.

6. The method for detecting damage to the enameled wire of a motor stator according to claim 5, characterized in that, A limit ring is formed on the rotor shaft to axially limit the rotor core.

7. The method for detecting damage to the enameled wire of a motor stator according to claim 1, characterized in that, The support structure is a vertical support structure, including a base for supporting the stator of the motor under test, a boss for supporting the rotor core formed on the base, and a shaft passing through the rotor core formed on the boss. The base, boss and shaft are coaxially arranged.

Images