Test structure and method for insulation breakdown or partial discharge of variable frequency motor

Abstract

The invention relates to the technical field of insulation testing of high-voltage variable frequency motors, in particular to a testing structure and method for insulation breakdown or partial discharge of a variable frequency motor, and the structure comprises a hollow metal tube body which is wrapped by an insulating layer for insulation breakdown test or partial discharge test. A coaxial cylinder electrode structure for generating a radial uniform electric field is arranged in the middle of the metal tube body; the insulating layer is positioned on the surface of the coaxial cylinder electrode structure; a winding wire layer is arranged on the outer side of the coaxial cylinder electrode structure, the inner side of the winding wire layer makes contact with the coaxial cylinder electrode structure, and one end of the winding wire layer is led out to serve as an electrode to be connected with an external testing circuit. The two ends of the metal tube body serve as electrodes to be connected with an external test circuit. According to the invention, the electrical stress borne by insulation under the actual operation condition can be effectively simulated, and the comprehensive measurement of the insulation breakdown strength and the partial discharge characteristic can be realized. The structure is reasonable in design and convenient to manufacture, and has good repeatability and adaptability.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage variable-frequency motor insulation testing, in particular to a testing structure and method for insulation breakdown or partial discharge of a variable-frequency motor. Background Art

[0002] Variable frequency drive motors (such as traction motors for new energy electric vehicles and aerospace motors) are subject to high, steep-edge pulse voltages generated by power electronic devices during operation. The fast-rising square wave pulses and high-switching-frequency voltages applied to the motor windings create a harsher electrical stress environment for the insulation system. While existing motor insulation materials often utilize corona-resistant structures and possess high impulse voltage and partial discharge resistance, they can still degrade and even experience partial discharge (PD) under long-term, repeated high-frequency, high-voltage stress. The occurrence of partial discharge is a significant sign of aging and deterioration in motor insulation, and timely detection and evaluation of insulation performance under such high-frequency stress is crucial to ensuring safe and reliable motor operation.

[0003] Traditional motor insulation breakdown voltage tests are typically conducted at power frequency (50 / 60 Hz), often using actual large wire rods (the straight rod portion of the motor coil) or specially manufactured large specimens. This approach presents issues with large specimen size and high production costs, and it is difficult to simulate the high-frequency voltage stress environment encountered during variable-frequency motor operation. Furthermore, for partial discharge detection, high-frequency sensors (such as ultra-high frequency antennas, coupling capacitors, or high-frequency current sensors) are typically installed on the running motor to detect partial discharge signals. Existing methods either rely on the motor's structure for signal coupling (such as utilizing the principle of slot antennas in the motor casing) or require the motor to be modified and equipped with sensors, which is complex to implement. Furthermore, there is a lack of standardized, easily reproducible specimen structures for comparative laboratory studies of the breakdown and partial discharge characteristics of different insulation materials or structures under high-frequency voltage. Summary of the Invention

[0004] In view of this, an object of the present invention is to provide a test structure and method for insulation breakdown or partial discharge of a variable frequency motor, so as to solve the technical problems in the background technology.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a test structure for insulation breakdown or partial discharge of a variable frequency motor, comprising a hollow metal tube, the outer side of which is wrapped with an insulating layer for performing an insulation breakdown test or a partial discharge test, a coaxial cylindrical electrode structure for generating a radially uniform electric field being provided in the middle of the metal tube, and the insulating layer being located on the surface of the coaxial cylindrical electrode structure;

[0007] A winding wire layer is provided on the outer side of the coaxial tube electrode structure, the inner side of the winding wire layer is in contact with the coaxial tube electrode structure, one end of the winding wire layer is led out as an electrode to be connected to an external test circuit; the two ends of the metal tube body are connected to the external test circuit as electrodes.

[0008] In one embodiment of the present application, a metal foil wrapped around the insulating layer is provided in the middle of the metal tube body, and the metal foil, the middle of the insulating layer and the metal tube body form the coaxial cylindrical electrode structure.

[0009] In one embodiment of the present application, an outermost fixing adhesive layer is further included, and the fixing adhesive layer fixes the insulating layer, the wound wire layer and the metal foil on the metal tube body.

[0010] In one embodiment of the present application, fixed lengths of unwrapped sections are retained at both ends of the metal tube, and the unwrapped sections serve as electrodes connected to an external test circuit;

[0011] One end of the winding wire layer is led out to the outside of the fixing adhesive layer as an electrode connected to an external test circuit.

[0012] In one embodiment of the present application, the winding wire layer is formed by winding bare copper wire with a set cross-sectional diameter, and the coverage of the winding wire layer is consistent with the coverage of the metal foil, or the coverage of the winding wire layer is smaller than the coverage of the metal foil.

[0013] The present application also provides a test method for insulation breakdown or partial discharge of a variable frequency motor, comprising the steps of:

[0014] Connecting the end of the metal tube to an external potential terminal, and connecting the lead-out electrode of the wound wire layer to a measurement and observation device;

[0015] Applying excitation to the potential terminal to generate an electric field in the coaxial cylindrical electrode structure;

[0016] A breakdown test, a partial discharge test or a transient response test is performed on the insulating layer based on the electric field, and data waveforms generated during the breakdown test, partial discharge test or transient response test on the insulating layer are collected and recorded.

[0017] In one embodiment of the present application, when performing a breakdown test, one end of the metal tube is connected to a high voltage, the lead portion is grounded, and the lead electrode of the wound wire layer is grounded and connected to a measurement and observation device;

[0018] Control the high-voltage AC power supply to increase the voltage according to the target boost rate until insulation breakdown occurs; and record the corresponding breakdown voltage value and discharge characteristic signal when a target phenomenon caused by insulation breakdown occurs through the measurement and observation equipment, wherein the target phenomenon is a sudden current pulse or a voltage drop of the measurement and observation equipment.

[0019] In one embodiment of the present application, when performing a partial discharge test, both ends of the metal tube are connected to the output end of a high-voltage variable-frequency power supply, and the lead-out electrodes of the wound wire layer are grounded and connected to a measurement and observation device;

[0020] The high-voltage variable-frequency power supply is controlled to output a high-frequency signal, and when partial discharge occurs in the insulating layer, the amplitude and phase of the partial discharge are recorded by the measurement and observation equipment.

[0021] In one embodiment of the present application, when performing a transient response test, both ends of the metal tube are connected to the output end of a high-voltage variable-frequency power supply, and the lead-out electrodes of the wound wire layer are grounded and connected to a measurement and observation device;

[0022] The high-voltage variable-frequency power supply is controlled to output a high-voltage shock pulse with a rising edge of n microseconds, and the response signal of the insulating layer to the high-voltage shock pulse is monitored by the measurement and observation equipment.

[0023] In one embodiment of the present application, the measurement and observation device is an ultra-high frequency partial discharge detection module with filtering and pre-amplification.

[0024] The beneficial effects of the present invention are as follows: the test structure and method for insulation breakdown or partial discharge of a variable frequency motor of the present invention include a hollow metal tube body, the outer side of the metal tube body is wrapped with an insulating layer for performing an insulation breakdown test or a partial discharge test, a coaxial tube electrode structure for generating a radially uniform electric field is provided in the middle of the metal tube body, and the insulating layer is located on the surface of the coaxial tube electrode structure; a winding wire layer is provided on the outer side of the coaxial tube electrode structure, the inner side of the winding wire layer is in contact with the coaxial tube electrode structure, and one end of the winding wire layer is led out as an electrode to be connected to an external test circuit; the two ends of the metal tube body are connected as electrodes to the external test circuit. The present application can effectively simulate the electrical stress on the insulation under actual operating conditions and realize a comprehensive measurement of the insulation breakdown strength and partial discharge characteristics. The structure is rationally designed, easy to manufacture, has good repeatability and adaptability, and can be widely used in the research of motor insulation materials, the development of new insulation structures, and the experimental verification of motor insulation online monitoring sensing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0026] Figure 1Schematic diagram of a test structure for insulation breakdown or partial discharge of a variable frequency motor according to an embodiment of the present invention;

[0027] Figure 2 Schematic diagram of the internal structure of a test structure for insulation breakdown or partial discharge of a variable frequency motor in one embodiment of the present invention;

[0028] Figure 3 FIG. 4 is a cross-sectional schematic diagram of a test structure in one embodiment of the present invention. DETAILED DESCRIPTION

[0029] Figure 1 Schematic diagram of a test structure for insulation breakdown or partial discharge of a variable frequency motor in one embodiment of the present application. Figure 2 FIG. 1 is a schematic diagram of the internal structure of a test structure for insulation breakdown or partial discharge of a variable frequency motor according to an embodiment of the present invention. Figure 1-Figure 2 As shown, the test structure for insulation breakdown or partial discharge of a variable frequency motor in the present application includes a hollow metal tube 1, the outer side of the metal tube 1 is wrapped with an insulating layer 2 for performing insulation breakdown test or partial discharge test, and a coaxial cylindrical electrode structure for generating a radially uniform electric field is provided in the middle of the metal tube 1, and the insulating layer 2 is located on the surface of the coaxial cylindrical electrode structure;

[0030] A wound conductor layer 3 is provided on the outside of the coaxial cylindrical electrode structure. The inside of the wound conductor layer 3 contacts the coaxial cylindrical electrode structure. One end of the wound conductor layer 3 is extended to serve as an electrode connected to an external test circuit. Both ends of the metal tube 1 also serve as electrodes connected to the external test circuit. A metal foil 4 wrapped around the insulating layer 2 is provided in the middle of the metal tube 1. The metal foil 4, the middle of the insulating layer 2, and the metal tube 2 form the coaxial cylindrical electrode structure.

[0031] The specimen used for variable-frequency motor insulation testing is a rod-shaped structure, consisting of a metal tube 1, an insulating layer 2 wrapped around it, and a coaxial cylindrical electrode structure. The metal tube 1 is preferably made of a metal material with good electrical conductivity and sufficient mechanical strength. Its length and diameter can be selected based on actual needs, for example, within a range of tens of centimeters in length and a few centimeters in diameter. For example, the metal tube 1 can be a hollow aluminum tube, replacing traditional large wire rods. This significantly reduces the difficulty and cost of sample production. The hollow structure also facilitates the insertion of other sensors or fillers (for example, to further study the electric field distribution within the insulating space).

[0032] Unwrapped sections of fixed length are retained at both ends of the metal tube body 1 to form electrical connection terminals for easy connection with a high-voltage power supply or a grounding fixture.

[0033] Figure 3 FIG. 1 is a cross-sectional diagram of a test structure in an embodiment of the present invention. Figure 3As shown, the present invention comprises, from the inside to the outside, a metal tube body 1, an insulating layer 2, a metal foil 4, a winding wire layer 3, and a fixing adhesive layer 5. The manufacturing process and principle of the test structure for insulation breakdown or partial discharge of a variable frequency motor in the present invention are as follows:

[0034] The central area of the aluminum tube is wrapped according to the specified insulation structure: first, an insulating layer 2 is tightly wrapped around the aluminum tube surface. This insulating material can be a combination of one or more materials. For example, in one embodiment, two layers of mica tape are evenly wrapped around the aluminum tube, followed by a layer of fiberglass cloth, and then several layers of polyimide film are wrapped around it to ensure that the total insulation thickness meets the desired dielectric strength requirements. The length of the insulating layer 2 is wrapped longer than the subsequent tin foil electrode to create an insulating buffer zone at both ends of the electrode, thereby preventing premature partial discharge caused by electric field edge effects.

[0035] After the insulation layer is laid, a layer of metal foil 4 is applied to the outer surface of a selected area in the middle of the aluminum tube. The metal foil 4 is about 2 cm wide and fits tightly to the surface of the insulation layer 2, so that the metal foil 4 axially surrounds the aluminum tube to form an electrode.

[0036] Metal foil 4 forms the other electrode surface of the sample, positioned roughly midway along the length of the aluminum tube. To ensure a tight fit, the electrode is secured with tape before proceeding to the next winding step. Specifically, tin foil is used as the coaxial electrode between the aluminum tube and the foil, ensuring uniform electric field distribution and obtaining stable and reliable breakdown voltage and partial discharge inception voltage data.

[0037] In addition, a winding wire layer 3 is provided on the outer side of the metal foil 4 along its circumferential surface. It is preferred to use a bare copper wire with a certain cross-section diameter, and wind it several times so that it evenly covers the tin foil electrode area. The coverage of the winding wire layer 3 is consistent with the coverage of the metal foil 4, or the coverage of the winding wire layer 3 is smaller than the coverage of the metal foil 4. In practice, the winding density of the winding wire layer 3 can be adjusted according to the needs of signal extraction: if a larger electromagnetic coupling signal is desired, the number of winding turns can be increased or a braided winding method can be adopted; if it is desired to be mainly used for signal injection, the number of turns can be appropriately reduced to control the distributed capacitance and inductance values. In this embodiment, the winding wire layer 3 is wound until the turns are arranged in parallel and close together. After the winding is completed, one end of the copper wire is reserved as a lead-out end.

[0038] The copper wire wound around the outside of the metal foil 4 has both the injection and coupling functions of high-frequency signals, thereby realizing direct extraction of partial discharge signals and improving the sensitivity of weak signal detection.

[0039] In addition, the present application also includes an outermost fixing adhesive layer 5, which fixes the insulating layer 2, the wound wire layer 3, and the metal foil 4 to the metal tube body 1. The fixing adhesive layer 5 is transparent adhesive. In the final stage of production, the present application uses several turns of transparent tape to wrap the tin foil electrode and the copper wire on it together in the axial direction to tightly cover it. The transparent tape not only fixes the electrode but also provides a certain degree of insulation protection for the electrode surface. The lead end of the copper wire is led to the outside of the transparent tape and ensures that it is long enough to connect to the measuring device or signal source.

[0040] Multiple specimens prepared using the above method can be used in a series of comparative tests. In a typical experimental process, several different insulation material combinations are selected according to the test plan, and several specimens are prepared for each combination. To facilitate identification, each specimen is assigned a unique number and stored in a centralized location. Each specimen number corresponds to its insulation structure and formulation, among other information. This numbering system ensures that the identity and characteristics of each specimen can be accurately tracked during testing.

[0041] The structure of this application supports the application of high-voltage AC or pulse voltage in the frequency range of 5kHz to 8kHz, simulating the actual operating voltage environment of variable-frequency motors, which is impossible with traditional power-frequency testing. By numbering and managing multiple specimens and testing them separately, the withstand voltage and partial discharge characteristics of different insulation schemes under high-frequency voltage can be systematically compared, providing data support for the selection and improvement of motor insulation materials.

[0042] The test structure for insulation breakdown or partial discharge of a variable frequency motor can be used to test insulation breakdown, partial discharge, and transient response of partial discharge of the variable frequency motor.

[0043] (1) Insulation breakdown test

[0044] (1-2) Connect one end of the metal tube 1 to the output end of a high-voltage AC power supply, and ground the other end of the metal tube 1, and ground the lead-out electrode of the wound wire layer 3 and connect it to a measurement and observation device;

[0045] (1-3) Controlling the high-voltage AC power supply to increase the voltage at a target boost rate until insulation breakdown occurs; and recording the corresponding breakdown voltage value and discharge characteristic signal when a target phenomenon caused by insulation breakdown occurs through a measuring and observing device, wherein the target phenomenon is a sudden current pulse or a voltage drop of the measuring and observing device.

[0046] When carrying out breakdown voltage test, one end aluminum tube of sample can be connected to the output terminal of high voltage AC power supply by wire, the other end aluminum tube is grounded, and tinfoil / copper wire electrode is grounded (for monitoring leakage current and discharge signal) by measuring resistance or coupling capacitor.Then control high voltage power supply to promote the voltage applied on the aluminum tube with predetermined rate, until insulation breakdown occurs.Breakdown is usually manifested as sudden current pulse or voltage drop occurring on the monitoring device connected in the tinfoil electrode loop, now record breakdown voltage value and discharge characteristic signal.Because sample size of the present invention is smaller and electric capacity is lower, can withstand rapid voltage rise and be difficult for large electric heat accumulation, thereby is suitable for carrying out repeated breakdown test to obtain statistical data.

[0047] (2) Partial discharge test

[0048] (2-1) Connect both ends of the metal tube 1 to the output end of the high-voltage variable-frequency power supply, and ground the lead-out electrodes of the wound wire layer 3 and connect them to the measurement and observation equipment;

[0049] (2-2) The high-voltage variable-frequency power supply is controlled to output a high-frequency signal. When partial discharge occurs in the insulating layer 2, the amplitude and phase of the partial discharge are recorded by measuring and observing equipment.

[0050] When conducting partial discharge testing, one end of the aluminum tube can be connected to a high-voltage variable-frequency power supply (the frequency can be adjusted to the desired experimental frequency). The other electrode end (the tin foil and copper wire) is grounded and connected to an oscilloscope or other PD detection device via a high-frequency current sensor or coupling capacitor. When partial discharge occurs in the insulation layer, a high-frequency current pulse flows between the tin foil and the aluminum tube, inducing a voltage signal through the coupled copper wire. Using an oscilloscope or PD detector connected to the copper wire lead-out end, information such as the amplitude and phase (relative to the excitation power cycle) of the partial discharge can be observed in real time.

[0051] (3) Transient response test

[0052] (3-1) Connect both ends of the metal tube 1 to the output terminals of the high-voltage variable-frequency power supply, and ground the lead-out electrodes of the wound wire layer 3 and connect them to the measurement and observation equipment;

[0053] (3-2) Control the high-voltage variable-frequency power supply to output a high-voltage shock pulse with a rising edge of n microseconds, and monitor the response signal of the insulation layer 2 to the high-voltage shock pulse through a measurement and observation device.

[0054] A rapid, high-voltage shock pulse (with a rising edge of a few microseconds and frequency components covering tens of kilohertz) is applied between the aluminum tube and the tin foil electrode. The insulation's response to this pulse is monitored through the copper wire. This pulse response test simulates the propagation of partial discharge in the insulation and captures the high-frequency characteristics of the specimen's equivalent circuit parameters (such as dielectric constant, loss, and partial discharge equivalent circuit parameters). By comparing the response waveforms of different specimens under the same pulse excitation, we can deepen our understanding of the behavioral differences between different insulation material structures under high-frequency transient conditions.

[0055] Furthermore, if the signal-to-noise ratio needs to be improved during the aforementioned testing process, the copper wire leads can be connected to a UHF PD detection module with filtering and preamplification to extract clearer discharge signal characteristics. By comparing the PD inception voltage and discharge pulse characteristics of differently numbered specimens, the PD resistance of different insulation structures under high-frequency stress can be evaluated.

Claims

1. A test structure for insulation breakdown or partial discharge of variable frequency motors, characterized in that: The invention comprises a hollow metal tube (1), the outer side of the metal tube (1) is wrapped with an insulating layer (2) for performing an insulation breakdown test or a partial discharge test, a coaxial tube electrode structure for generating a radially uniform electric field is provided in the middle of the metal tube (1), and the insulating layer (2) is located on the surface of the coaxial tube electrode structure; A winding wire layer (3) is provided on the outer side of the coaxial tube electrode structure, the inner side of the winding wire layer (3) is in contact with the coaxial tube electrode structure, and one end of the winding wire layer (3) is led out as an electrode to be connected to an external test circuit; and both ends of the metal tube body (1) are connected to the external test circuit as electrodes.

2. The test structure for insulation breakdown or partial discharge of a variable frequency motor according to claim 1, characterized in that: The middle portion of the metal tube (1) is provided with a metal foil (4) wrapped around the insulating layer (2); the metal foil (4), the middle portion of the insulating layer (2) and the metal tube (1) form the coaxial cylindrical electrode structure.

3. The test structure for insulation breakdown or partial discharge of a variable frequency motor according to claim 2, characterized in that: It also includes an outermost fixing adhesive layer (5), wherein the fixing adhesive layer (5) fixes the insulating layer (2), the winding wire layer (3) and the metal foil (4) on the metal tube body (1).

4. The test structure for insulation breakdown or partial discharge of a variable frequency motor according to claim 3, characterized in that: Unwrapped sections of fixed length are retained at both ends of the metal tube (1), and the unwrapped sections serve as electrodes connected to an external test circuit; One end of the winding wire layer (3) is led out to the outside of the fixing adhesive layer (5) to serve as an electrode connected to an external test circuit.

5. The test structure for insulation breakdown or partial discharge of a variable frequency motor according to claim 2, characterized in that: The wound wire layer (3) is formed by winding a bare copper wire having a cross-sectional diameter of a set value, and the coverage of the wound wire layer (3) is consistent with the coverage of the metal foil (4), or the coverage of the wound wire layer (3) is smaller than the coverage of the metal foil (4).

6. A method for testing insulation breakdown or partial discharge of a variable frequency motor, applied to the test structure for insulation breakdown or partial discharge of a variable frequency motor as claimed in claim 1, characterized in that: Including steps: Connecting the end of the metal tube (1) to an external potential terminal, and connecting the lead-out electrode of the wound wire layer (3) to a measurement and observation device; Applying excitation to the potential terminal to generate an electric field in the coaxial cylindrical electrode structure; A breakdown test, a partial discharge test, or a transient response test is performed on the insulating layer (2) based on the electric field, and data waveforms generated during the breakdown test, partial discharge test, or transient response test on the insulating layer (2) are collected and recorded.

7. The method for testing insulation breakdown or partial discharge of a variable frequency motor according to claim 6, characterized in that: When performing a breakdown test, one end of the metal tube body (1) is connected to a high voltage, the lead portion is grounded, and the lead electrode of the wound wire layer (3) is grounded and connected to a measurement and observation device; Control the high-voltage AC power supply to increase the voltage according to the target boost rate until insulation breakdown occurs; and record the corresponding breakdown voltage value and discharge characteristic signal when a target phenomenon caused by insulation breakdown occurs through the measurement and observation equipment, wherein the target phenomenon is a sudden current pulse or a voltage drop of the measurement and observation equipment.

8. The method for testing insulation breakdown or partial discharge of a variable frequency motor according to claim 6, characterized in that: When conducting a partial discharge test, the two ends of the metal tube (1) are connected to the output end of a high-voltage variable-frequency power supply, and the lead-out electrode of the wound wire layer (3) is grounded and connected to a measurement and observation device; The high-voltage variable-frequency power supply is controlled to output a high-frequency signal, and when partial discharge occurs in the insulating layer (2), the amplitude and phase of the partial discharge are recorded by the measuring and observing equipment.

9. The method for testing insulation breakdown or partial discharge of a variable frequency motor according to claim 6, characterized in that: When performing a transient response test, the two ends of the metal tube (1) are connected to the output end of a high-voltage variable-frequency power supply, and the lead-out electrodes of the wound wire layer (3) are grounded and connected to a measurement and observation device; The high-voltage variable-frequency power supply is controlled to output a high-voltage shock pulse with a rising edge of n microseconds, and the response signal of the insulating layer (2) to the high-voltage shock pulse is monitored by the measurement and observation equipment.

10. The method for testing insulation breakdown or partial discharge of a variable frequency motor according to claim 7, 8 or 9, characterized in that: The measurement and observation equipment is an ultra-high frequency partial discharge detection module with filtering and pre-amplification.

Images