A method for testing the corona resistance of an enameled wire
By introducing bipolar high-frequency high-voltage pulses and a variable frequency operating condition life model into the corona resistance test of enameled wire, the problem of insufficient accuracy of existing test methods is solved, and high-precision and stable corona resistance performance evaluation is achieved.
Patent Information
- Application Number
- CN202610577385.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-28
- Publication Date
- 2026-06-02
AI Technical Summary
Existing corona resistance testing methods for enameled wires are not adapted to frequency conversion conditions, resulting in low test accuracy and large errors, and failing to accurately reflect the true corona resistance of enameled wires under frequency conversion environments.
A bipolar high-frequency high-voltage pulse test was adopted, and a variable frequency operating condition life model was constructed by combining the pulse edge steepness attenuation factor η and the high-temperature thermal aging correction term τ. The test parameters were dynamically adjusted through pre-breakdown screening and real-time fault monitoring to ensure the accuracy and stability of the test results.
It achieves accurate corona resistance performance evaluation under variable frequency operating conditions. The test results are highly consistent with the actual operating conditions, with an error of less than ±3% and a repeatability of up to 98%.
Smart Images
Figure CN122131100A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of enameled wire manufacturing technology, and in particular to a method for testing the corona resistance of enameled wire. Background Technology
[0002] In fields such as variable frequency motors and electrical equipment, enameled wire is a core conductive and insulating component. Its corona resistance directly determines the operational stability, service life, and safety and reliability of the equipment. Therefore, accurate testing of the corona resistance of enameled wire is of utmost importance.
[0003] Currently, most corona resistance testing methods for enameled wires use fixed parameter testing modes, simply applying high-voltage pulses and recording the breakdown time. These methods are not optimized for actual use scenarios under variable frequency conditions. They do not consider the interference of pulse rise edge differences, temperature effects, and the material's own characteristics on the test results, resulting in low test accuracy and large errors.
[0004] Specifically, existing testing methods rely solely on fixed formulas to calculate theoretical withstand voltage, without adjusting or correcting parameters based on actual operating conditions such as pulse rise edge range, ambient temperature and humidity, and circuit impedance changes. This makes them unsuitable for testing requirements with different pulse rise edges. Furthermore, they fail to dynamically adjust for environmental changes and equipment operating status during the testing process, resulting in test results that are out of sync with the actual operating conditions of the enameled wire. Consequently, they cannot accurately reflect the true corona resistance of the enameled wire under frequency conversion environments, making it difficult to meet the demand for precise performance evaluation of enameled wires in industrial production.
[0005] Therefore, it is urgent for technical personnel to solve the above problems. Summary of the Invention
[0006] The purpose of this invention is to provide a method for testing the corona resistance of enameled wires, aiming to solve the problem that existing designs only use fixed formulas for calculation and lack dynamic correction mechanisms, resulting in low test accuracy and data that is out of sync with actual working conditions.
[0007] This invention relates to a method for testing the corona resistance of enameled wire, comprising the following steps: S1. Place the enameled wire sample to be tested in a constant temperature oven and apply a bipolar high-frequency high-voltage pulse to it; S2. Set test parameters: pulse frequency is 20kHz, duty cycle is 50%, pulse peak-to-peak voltage is 3kV, pulse rise time is adjustable between 100ns, 200ns, and 400ns, and the test environment temperature is controlled at 90±2℃. S3. Real-time detection of insulation breakdown signal of enameled wire sample, and when insulation breakdown is detected, immediately cut off high voltage output and record the cumulative corona resistance time T of the sample. S4. Introduce the pulse edge steepness attenuation factor η and the high-temperature thermal aging correction term τ to construct the variable frequency operating condition life model: ); Where A and n are characteristic constants of the enameled wire insulation material, with A taking values ranging from 1.2 × 10⁻⁶. 3 ~1.8×10 3 The value of n ranges from 1.5 to 2.0; η is the peak voltage of the pulse; η is the pulse steepness attenuation factor, with a value ranging from 0.8 to 1.2; τ is the thermal aging coefficient corresponding to the test temperature, with a value ranging from 0.9 to 1.1. S5. The theoretical maximum withstand pulse voltage of the enameled wire is calculated based on the life model. The theoretical calculation results are compared with the measured corona resistance time to complete the evaluation of the corona resistance performance level of the enameled wire.
[0008] As a further improvement to the technical solution disclosed in this invention, the bipolar high-frequency high voltage pulse is output by a two-stage series H-bridge circuit composed of eight insulated-gate bipolar transistors. The H-bridge circuit is divided into a symmetrical first output circuit and a second output circuit. Both the first output circuit and the second output circuit contain four insulated-gate bipolar transistors connected in series, and the diagonal insulated-gate bipolar transistors are alternately turned on to output ±1500V bipolar high voltage, forming a pulse square wave with a peak value of 3kV.
[0009] As a further improvement to the technical solution disclosed in this invention, a 100pF / 3kV equalizing capacitor is connected in parallel between the collector and emitter of the insulated gate bipolar transistor, and a transient voltage suppression diode is connected in parallel across its terminals.
[0010] As a further improvement to the technical solution disclosed in this invention, the insulated gate bipolar transistor uses an insulated gate bipolar transistor driver to convert the 0-24V input signal into a -5V to +15V gate drive voltage. The +15V is used for fast turn-on, and the -5V is used for forced fast turn-off. The drive circuit has two parallel and then series current-limiting protection resistors, along with a 20V-level transient voltage suppression diode and an absorption capacitor.
[0011] As a further improvement to the technical solution disclosed in this invention, the testing process is controlled in real time by the lower-level hardware and communicates with the upper-level computer through a serial port; the testing system monitors four fault signals in real time: high-voltage fault, oven door opening status, insulated gate bipolar transistor overheating, and sample breakdown. When any fault is triggered, the pulse output is immediately stopped and the high voltage is locked.
[0012] As a further improvement to the technical solution disclosed in this invention, when the enameled wire sample breaks down, the test circuit detects a sudden current change and a voltage drop signal. The lower-level computer turns off all insulated gate bipolar transistors within microseconds and quickly cuts off the high-voltage output.
[0013] As a further improvement to the technical solution disclosed in this invention, in step S1, a pre-breakdown screening treatment is performed on the enameled wire sample before the formal corona resistance test is performed. The specific steps for pre-breakdown screening are as follows: Place the enameled wire sample in a constant temperature environment of 90±2℃, apply a bipolar pulse with a peak-to-peak value of 1.5kV, a frequency of 20kHz, and a rise time of 200ns, and continue applying it for 30s; if a current surge greater than 5mA is detected during this period, the sample is judged to be an insulation defect and is directly rejected; if no breakdown occurs and the current is stable at 0.1~0.3mA, the sample is judged to be a qualified sample and enters the subsequent formal testing stage.
[0014] As a further improvement to the technical solution disclosed in this invention, in step S4, the pulse edge steepness attenuation factor η in the lifetime model is dynamically corrected; when the pulse rise edge is 100ns, η is set to 1.2 times the initial value; when the pulse rise edge is 200ns, η is kept at the initial value; when the pulse rise edge is 400ns, η is set to 0.8 times the initial value.
[0015] In practical applications, the corona resistance testing method for enameled wires disclosed in this invention can achieve at least the following beneficial technical effects, specifically: 1) By introducing a pulse edge steepness attenuation factor η and a high-temperature thermal aging correction term τ, a life model adapted to variable frequency operating conditions is constructed. By quantifying the impact of pulse edge variation on the corona resistance of insulation materials and the effect of temperature on insulation aging, pulse waveform parameters, ambient temperature, material properties, and test results are deeply integrated. Among them, the pulse edge steepness attenuation factor η can accurately capture the differences in electric field distribution at different pulse rising edges. By quantifying the degree of electric field distortion corresponding to different rising edge levels, deviations in the testing process are corrected to ensure that the test results can truly reflect the insulation withstand capability of the enameled wire. The high-temperature thermal aging correction term τ is combined with the test ambient temperature to accurately match the aging rate of insulation materials at different temperatures, which is consistent with the temperature fluctuation scenarios in actual industrial operation. 2) By monitoring the changes in the insulation state of the enameled wire in real time, the insulation breakdown time can be accurately captured and the corona resistance time can be reliably recorded. Combined with the lifetime model, multi-parameter coupled quantitative analysis can be carried out to achieve accurate evaluation of the corona resistance performance of the enameled wire, and ensure the repeatability of the test process and the stability of the results. Attached Figure Description
[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0017] Figure 1 This is a schematic diagram of the overall circuit structure of the corona resistance testing system for enameled wire disclosed in this invention.
[0018] Figure 2 This is a schematic diagram of the two-stage series H-bridge pulse output circuit disclosed in this invention. Detailed Implementation
[0019] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.
[0020] The corona resistance test method for enameled wire uses bipolar high-frequency high-voltage pulses as the test excitation signal and a variable frequency operating condition life model as the calculation basis. The entire test system consists of a two-stage series H-bridge pulse output circuit, an insulated gate bipolar transistor drive circuit, a lower-level real-time control unit, an upper-level communication unit, and a constant temperature oven.
[0021] Figure 1 The overall circuit structure diagram of the corona resistance testing system for enameled wire disclosed in this invention is shown. It can be seen that the bipolar high-frequency high-voltage pulse is output by a two-stage series H-bridge circuit composed of eight insulated-gate bipolar transistors; as shown... Figure 2 As shown, the two-stage series H-bridge circuit is divided into a symmetrical first output circuit and a second output circuit. Both the first and second output circuits include four insulated gate bipolar transistors connected in series. By alternately turning on the diagonal insulated gate bipolar transistors, a bipolar high voltage of ±1500V is output, forming a pulse square wave with a peak value of 3kV.
[0022] A 100pF / 3kV equalizing capacitor is connected in parallel between the collector and emitter of the insulated-gate bipolar transistor (IGBT), and a transient voltage suppressor diode is connected in parallel across the collector and emitter of the IGBT. The IGBT uses an IGBT driver to convert a 0-24V input signal into a -5V to +15V gate drive voltage. The +15V is used for fast turn-on of the IGBT, and the -5V is used for forced fast turn-off. Two current-limiting protection resistors connected in parallel and then in series are set in the drive circuit, and are used in conjunction with a 20V-level transient voltage suppressor diode and an absorption capacitor.
[0023] The testing process is controlled in real time by the lower-level hardware and communicates with the upper-level computer via serial port. The testing system monitors four fault signals in real time: high-voltage fault, oven door opening status, insulated-gate bipolar transistor overheating, and sample breakdown. When any fault is triggered, the pulse output is stopped immediately and the high voltage is locked. When the enameled wire sample breaks down, the test circuit detects the current change and voltage drop signals. The lower-level computer turns off all insulated-gate bipolar transistors within microseconds and quickly cuts off the high-voltage output.
[0024] This invention introduces a pulse edge steepness attenuation factor η and a high-temperature thermal aging correction term τ to construct a variable frequency operating condition life model. The mathematical model expression is as follows: ); In the formula: T represents the cumulative corona resistance time of the enameled wire sample; A and n are characteristic constants of the enameled wire insulation material, with A ranging from 1.2 × 10⁻⁶. 3 ~1.8×10 3 The value of n ranges from 1.5 to 2.0; U_p is the peak voltage of the pulse; η is the pulse steepness attenuation factor, and the value of η ranges from 0.8 to 1.2; τ is the thermal aging coefficient corresponding to the test temperature, with a value range of 0.9 to 1.1.
[0025] Furthermore, the pulse edge steepness attenuation factor η in the variable frequency operating condition life model is dynamically corrected: when the pulse rise time is 100ns, the pulse edge steepness attenuation factor η is set to 1.2 times the initial value; when the pulse rise time is 200ns, the pulse edge steepness attenuation factor η is kept at the initial value; when the pulse rise time is 400ns, the pulse edge steepness attenuation factor η is set to 0.8 times the initial value.
[0026] Before applying a bipolar high-frequency high-voltage pulse and performing the formal corona resistance test, the enameled wire samples undergo a pre-breakdown screening process. The specific steps of the pre-breakdown screening are as follows: the enameled wire samples are placed in a constant temperature environment of 90±2℃, and a bipolar pulse with a peak-to-peak value of 1.5kV, a frequency of 20kHz, and a rise time of 200ns is applied for 30s. If a current surge greater than 5mA is detected during this period, the sample is judged to be an insulation defect and is directly rejected. If no breakdown occurs and the current is stable at 0.1~0.3mA, the sample is judged to be a qualified sample and proceeds to the subsequent formal testing stage.
[0027] Test method for corona resistance of enameled wire Example 1 S1. Place the enameled wire sample to be tested in a constant temperature oven and perform pre-breakdown screening treatment at a constant temperature of 90±2℃. Apply a bipolar pulse with a peak-to-peak value of 1.5kV, a frequency of 20kHz, and a rise time of 200ns for 30s to obtain qualified samples. S2. Place the qualified sample in a constant temperature oven and apply a bipolar high-frequency high-voltage pulse to it. Set the test parameters as follows: pulse frequency is 20kHz, duty cycle is 50%, peak-to-peak voltage is 3kV, pulse rise time is 100ns, and the test environment temperature is controlled at 90±2℃. S3. Dynamically correct the pulse steepness attenuation factor η, setting η to 1.2 times the initial value, the high-temperature thermal aging coefficient τ to 1.0, and the characteristic constant A of the enameled wire insulation material to 1.5 × 10⁻⁶. 3 n is set to 1.8, and the above parameters are substituted into the variable frequency operating condition life model; S4. Real-time detection of insulation breakdown signal of enameled wire sample. When the test circuit detects current change and voltage drop signal, the lower computer turns off all insulated gate bipolar transistors within microseconds, quickly cuts off high voltage output, and records the cumulative corona resistance time T of the sample. S5. The theoretical maximum withstand pulse voltage of the enameled wire is calculated based on the life model of variable frequency operating conditions. The theoretical calculation results are compared with the measured corona resistance time to complete the corona resistance performance level evaluation of the enameled wire. S6. The lower-level computer monitors fault signals in real time throughout the test. If a fault is triggered, the output is stopped immediately and the high voltage is locked to ensure test safety.
[0028] Example 2 S1. Place the enameled wire sample to be tested in a constant temperature oven and perform pre-breakdown screening treatment at a constant temperature of 90±2℃. Apply a bipolar pulse with a peak-to-peak value of 1.5kV, a frequency of 20kHz, and a rise time of 200ns for 30s to obtain qualified samples. S2. Place the qualified sample in a constant temperature oven and apply a bipolar high-frequency high-voltage pulse to it. Set the test parameters as follows: pulse frequency is 20kHz, duty cycle is 50%, peak-to-peak voltage is 3kV, pulse rise time is 200ns, and the test environment temperature is controlled at 90±2℃. S3. Keep the pulse edge steepness attenuation factor η at its initial value, set the high-temperature thermal aging coefficient τ to 1.0, and set the characteristic constant A of the enameled wire insulation material to 1.2 × 10⁻⁶. 3 n is set to 1.5, and the above parameters are substituted into the variable frequency operating condition life model; S4. Real-time detection of insulation breakdown signal of enameled wire sample. When the test circuit detects current change and voltage drop signal, the lower computer turns off all insulated gate bipolar transistors within microseconds, quickly cuts off high voltage output, and records the cumulative corona resistance time T of the sample. S5. The theoretical maximum withstand pulse voltage of the enameled wire is calculated based on the life model of variable frequency operating conditions. The theoretical calculation results are compared with the measured corona resistance time to complete the corona resistance performance level evaluation of the enameled wire. S6. The lower-level computer monitors fault signals in real time throughout the test. If a fault is triggered, the output is stopped immediately and the high voltage is locked to ensure test safety.
[0029] Example 3 S1. Place the enameled wire sample to be tested in a constant temperature oven and perform pre-breakdown screening treatment at a constant temperature of 90±2℃. Apply a bipolar pulse with a peak-to-peak value of 1.5kV, a frequency of 20kHz, and a rise time of 200ns for 30s to obtain qualified samples. S2. Place the qualified sample in a constant temperature oven and apply a bipolar high-frequency high-voltage pulse to it. Set the test parameters as follows: pulse frequency is 20kHz, duty cycle is 50%, peak-to-peak voltage is 3kV, pulse rise time is 400ns, and the test environment temperature is controlled at 90±2℃. S3. Dynamically correct the pulse edge steepness attenuation factor η, setting η to 0.8 times the initial value, the high-temperature thermal aging coefficient τ to 1.0, and the characteristic constant A of the enameled wire insulation material to 1.8 × 10⁻⁶. 3 n is set to 2.0, and the above parameters are substituted into the variable frequency operating condition life model; S4. Real-time detection of insulation breakdown signal of enameled wire sample. When the test circuit detects current change and voltage drop signal, the lower computer turns off all insulated gate bipolar transistors within microseconds, quickly cuts off high voltage output, and records the cumulative corona resistance time T of the sample. S5. The theoretical maximum withstand pulse voltage of the enameled wire is calculated based on the life model of variable frequency operating conditions. The theoretical calculation results are compared with the measured corona resistance time to complete the corona resistance performance level evaluation of the enameled wire. S6. The lower-level computer monitors fault signals in real time throughout the test. If a fault is triggered, the output is stopped immediately and the high voltage is locked to ensure test safety.
[0030] Comparative Example S1. Place the enameled wire sample to be tested directly in a room temperature environment; S2. The test is conducted using a conventional unipolar high-voltage pulse with fixed pulse parameters: pulse frequency 20kHz, duty cycle 50%, peak-to-peak voltage 3kV, and pulse rise time fixed at 400ns. S3. The theoretical withstand voltage is calculated using traditional empirical formulas. S4. Rely on manual observation to determine the breakdown state of the sample; S5. Manually record the cumulative time from the application of the pulse to the breakdown of the enameled wire sample, and use this time as the evaluation basis to complete the evaluation of the corona resistance performance of the enameled wire.
[0031] The corona resistance test results of the enameled wires obtained in Examples 1-3 and the comparative examples were tested, and the test results are shown in the table below: Test results show that the corona resistance test method for enameled wire adopted in Examples 1-3 of this invention can significantly improve the accuracy of corona resistance test by pre-breakdown screening, dynamic correction of pulse edge steepness, calculation of life model for frequency conversion conditions, and synergistic effect of multi-fault monitoring and protection. The relative error between theoretical and measured data can be controlled within ±3%, the repeatability of test data is higher than 98%, the fault response is fast and stable, and the test results truly reflect the actual insulation resistance of enameled wire under frequency conversion conditions.
[0032] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A method for testing the corona resistance of enameled wire, characterized in that, Includes the following steps: S1. Place the enameled wire sample to be tested in a constant temperature oven and apply a bipolar high-frequency high-voltage pulse to it; S2. Set test parameters: pulse frequency is 20kHz, duty cycle is 50%, pulse peak-to-peak voltage is 3kV, pulse rise time is adjustable between 100ns, 200ns, and 400ns, and the test environment temperature is controlled at 90±2℃. S3. Real-time detection of insulation breakdown signal of enameled wire sample, and when insulation breakdown is detected, immediately cut off high voltage output and record the cumulative corona resistance time T of the sample. S4. Introduce the pulse edge steepness attenuation factor η and the high-temperature thermal aging correction term τ to construct the variable frequency operating condition life model: ); Where A and n are characteristic constants of the enameled wire insulation material, with A taking values ranging from 1.2 × 10⁻⁶. 3 ~1.8×10 3 The value of n ranges from 1.5 to 2.0; This is the peak voltage of the pulse. η is the pulse steepness attenuation factor, with a value ranging from 0.8 to 1.2; τ is the thermal aging coefficient corresponding to the test temperature, with a value ranging from 0.9 to 1.
1. S5. The theoretical maximum withstand pulse voltage of the enameled wire is calculated based on the life model. The theoretical calculation results are compared with the measured corona resistance time to complete the evaluation of the corona resistance performance level of the enameled wire.
2. The method for testing the corona resistance of enameled wire according to claim 1, characterized in that, The bipolar high-frequency high-voltage pulse is output by a two-stage series H-bridge circuit composed of eight insulated-gate bipolar transistors. The H-bridge circuit is divided into a symmetrical first output circuit and a second output circuit. Both the first output circuit and the second output circuit contain four of the insulated-gate bipolar transistors connected in series. The diagonally opposite insulated-gate bipolar transistors are alternately turned on to output a ±1500V bipolar high voltage, forming a pulse square wave with a peak value of 3kV.
3. The method for testing the corona resistance of enameled wire according to claim 2, characterized in that, The insulated gate bipolar transistor has a 100pF / 3kV equalizing capacitor connected in parallel between its collector and emitter, and a transient voltage suppressor diode connected in parallel across its terminals.
4. The method for testing the corona resistance of enameled wire according to claim 2, characterized in that, The insulated gate bipolar transistor uses an insulated gate bipolar transistor driver to convert a 0-24V input signal into a -5V to +15V gate drive voltage. The +15V is used for fast turn-on, and the -5V is used for forced fast turn-off. The drive circuit has two parallel and then series current-limiting protection resistors, along with a 20V-level transient voltage suppression diode and an absorption capacitor.
5. The method for testing the corona resistance of enameled wire according to claim 2, characterized in that, The testing process is controlled in real time by the lower-level hardware and communicates with the upper-level computer via serial port. The testing system monitors four fault signals in real time: high-voltage fault, oven door opening status, insulated gate bipolar transistor overheating, and sample breakdown. The pulse output is stopped immediately and the high voltage is locked when any fault is triggered.
6. The method for testing the corona resistance of enameled wire according to claim 5, characterized in that, When the enameled wire sample breaks down, the test circuit detects a sudden current change and a voltage drop signal. The lower-level computer shuts down all the insulated gate bipolar transistors within microseconds and quickly cuts off the high-voltage output.
7. The method for testing the corona resistance of enameled wire according to any one of claims 16, characterized in that, In step S1, a pre-breakdown screening treatment is performed on the enameled wire sample before the formal corona resistance test is performed. The specific steps of the pre-breakdown screening are as follows: Place the enameled wire sample in a constant temperature environment of 90±2℃, apply a bipolar pulse with a peak-to-peak value of 1.5kV, a frequency of 20kHz, and a rise time of 200ns, and continue to apply it for 30s; if a current change greater than 5mA is detected during this period, the sample is judged to be an insulation defect sample and is directly rejected. If no breakdown occurs and the current remains stable between 0.1 and 0.3 mA, the sample is deemed qualified and proceeds to the subsequent formal testing phase.
8. The method for testing the corona resistance of enameled wire according to any one of claims 16, characterized in that, In step S4, the pulse edge steepness attenuation factor η in the lifetime model is dynamically corrected; when the pulse rise time is 100ns, η is set to 1.2 times the initial value; when the pulse rise time is 200ns, η is kept at the initial value; when the pulse rise time is 400ns, η is set to 0.8 times the initial value.