An on-line motor insulation detection device and method

Abstract

This invention relates to the field of motor testing technology, and discloses an online motor insulation testing device and method. The device includes a detection circuit, a sampling circuit, and a microcontroller. The detection circuit is electrically connected to both the motor housing and windings, and is used to apply a high-voltage detection signal between the housing and windings. The sampling circuit collects the initial voltage signal at the sampling resistor in the detection circuit, and then converts the initial voltage signal via an optocoupler for transmission to the microcontroller. The microcontroller compares the received voltage signal sampling value with a preset voltage reference value to determine whether the motor insulation is good. This invention improves the isolation between circuits through optocouplers, thereby ensuring testing safety and improving the accuracy of the testing results.

Description

Technical Field

[0001] This invention relates to the field of motor testing technology, specifically to an online motor insulation testing device and method. Background Technology

[0002] During motor operation, especially in high-humidity, dusty, or corrosive environments such as water pumps, the insulation between the windings and the casing is prone to gradual deterioration due to aging, contamination, or moisture absorption, which can lead to safety accidents such as leakage and short circuits. Therefore, testing the insulation of motors is of significant engineering importance.

[0003] Traditional insulation testing usually relies on manual periodic shutdowns to measure insulation resistance using equipment such as megohmmeters. However, such methods are not real-time and are inefficient, making it difficult to meet the maintenance needs of continuously operating systems.

[0004] To address this, some existing technologies have proposed online detection solutions. For example, patent application CN115598528A discloses an automatic motor insulation detection scheme. This scheme applies a high-voltage signal between the motor coil and the casing through a detection circuit, and uses a sampling resistor in the detection circuit to obtain the voltage signal. The insulation resistance of the motor is then calculated based on known circuit parameters, enabling quantitative analysis of insulation performance. However, in its sampling circuit structure, the isolation of the electrical signal transmission path is low, and the risk of interference coupling between circuits is significant. This can lead to measurement errors and even safety hazards when facing high-voltage detection signals, especially in high-noise or complex grounding environments. Furthermore, in practical applications, due to process variations and individual differences in some components of the detection circuit, their electrical transmission characteristics often deviate from theoretical or nominal values, which can significantly affect the calculation results. Summary of the Invention

[0005] To address the technical problems of safety hazards and inaccurate test results in motor insulation testing due to low circuit isolation in existing technologies, this invention provides an online motor insulation testing device and method.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention discloses an online motor insulation testing device, comprising: a detection circuit, a sampling circuit, and a microcontroller; the detection circuit is electrically connected to the motor housing and windings respectively, and is used to apply a high-voltage detection signal between the housing and windings; the sampling circuit is used to acquire the initial voltage signal at the sampling resistor in the detection circuit, and then converts the initial voltage signal through an optocoupler to transmit it to the microcontroller; the microcontroller is used to determine whether the motor insulation is good by comparing the received voltage signal sampling value with a preset voltage reference value.

[0008] As a further improvement to the above solution, the microcontroller adopts a single-chip microcomputer, which is equipped with four I / O interfaces IO1 to IO4, of which IO3 is used as the ADC sampling interface. The single-chip microcomputer is powered by VCC. The detection circuit includes: transistor N1, diode D1, resistor R1, resistor R4, transformer T1 and relay RELAY1.

[0009] One end of resistor R4 is connected to the VDD power supply, and the other end of resistor R4 is connected to the negative terminal of diode D1 and one end of the primary coil of transformer T1 respectively; the positive terminal of diode D1 is connected to the collector terminal of transistor N1 and the other end of the primary coil of transformer T1 respectively; the emitter terminal of transistor N1 is grounded, and the base terminal of transistor N1 is connected to the IO2 interface.

[0010] One end of the secondary coil of transformer T1 is connected to the machine casing through a knife switch of relay RELAY1, and the other end of the secondary coil of transformer T1 is connected to one end of resistor R1 through another knife switch of relay RELAY1; resistor R1 serves as a sampling resistor, and its other end is connected to any one phase winding of the motor.

[0011] As a further improvement to the above scheme, the sampling circuit includes: resistor R2, resistor R3, optocoupler O1, capacitor C1 and diode D2;

[0012] Specifically, one end of resistor R3 is connected to the end of resistor R1 connected to the RELAY1 knife switch, and the other end of resistor R3 is connected to the positive terminal of the emitter of optocoupler O1 and the negative terminal of diode D2. The positive terminal of diode D2 is connected to the negative terminal of the emitter of optocoupler O1 and the end of resistor R1 connected to the motor winding. The emitter terminal of the receiver of optocoupler O1 is connected to one end of capacitor C1 and grounded. The collector terminal of the receiver of optocoupler O1 is connected to one end of resistor R2, the other end of capacitor C1, and the ADC sampling interface. The other end of resistor R2 is connected to the VCC power supply.

[0013] As a further improvement to the above scheme, diode D2 is a reverse Zener diode.

[0014] As a further improvement to the above solution, the detection device also includes a motor control circuit; the motor control circuit is used to supply power to the three-phase windings of the motor according to the motor control signal sent by the microcontroller in a timing sequence to drive the motor to rotate; wherein, the UVW three-phase interfaces of the motor control circuit are respectively connected to the three-phase windings of the motor through the three-phase knife switch of the relay RELAY2.

[0015] As a further improvement to the above solution, the detection device also includes a relay control circuit; the relay control circuit includes transistor N2, diode D3, transistor N3 and diode D4;

[0016] The base of transistor N2 is connected to the IO1 interface, and the emitter of transistor N2 is grounded. The collector of transistor N2 is connected to the positive terminal of diode D3 and one end of the coil of relay RELAY1. The negative terminal of diode D3 is connected to the VDD power supply and the other end of the coil of relay RELAY1.

[0017] The base of transistor N3 is connected to the IO4 interface, and the emitter of transistor N4 is grounded. The collector of transistor N4 is connected to the positive terminal of diode D4 and one end of the coil of relay RELAY2. The negative terminal of diode D4 is connected to the VDD power supply and the other end of the coil of relay RELAY2.

[0018] This invention also discloses an online motor insulation testing method, using the online motor insulation testing device described above; the method includes the following steps:

[0019] S1. Control relay RELAY2 is disconnected to separate the motor from the motor control circuit. After a delay, control relay RELAY1 is turned on to connect the motor to the detection circuit.

[0020] S2. Output a pulse signal with a set frequency and duty cycle to the detection circuit through the IO2 interface, so that the secondary coil of transformer T1 generates a high voltage detection signal.

[0021] S3. Obtain the voltage signal sampling value through the ADC sampling interface, then stop the output of the IO2 interface and disconnect the relay RELAY1;

[0022] S4. Based on the received voltage signal sample value and a preset voltage reference value, determine whether the motor insulation is qualified by comparison.

[0023] As a further improvement to the above scheme, in step S3, the voltage signal is sampled and converted multiple times to obtain multiple voltage signal sample values; by averaging the multiple voltage signal sample values, a voltage signal sample average value is obtained.

[0024] In step S4, when the average value of the voltage signal sampling is lower than the voltage reference value, the motor insulation is determined to be unqualified and step S5 is executed; otherwise, it is qualified and step S6 is executed. The quality of motor insulation is positively correlated with the level of the average value of the voltage signal sampling.

[0025] S5. Generate an alarm signal;

[0026] S6. Control relay RELAY2 to turn on to restore motor drive.

[0027] As a further improvement to the above solution, before step S1, the method further includes the following steps:

[0028] Upon receiving a detection command, the microcontroller initializes, then reads the saved learning flag, and determines whether parameter learning is required based on whether the set number of learning cycles has been reached. If parameter learning is required, the learning flag FLG is set to 1, and then step S1 is executed. If parameter learning is not required, step S1 is executed directly.

[0029] After step S3, the method further includes the following steps:

[0030] Determine whether the learning flag FLG=1 is set; if the learning flag FLG=1 is not set, proceed to the actual detection stage, i.e., execute step S4; if the learning flag FLG=1 is set, save the current average voltage signal sampling value as the learning result, and save the learning flag to complete one parameter learning, and then determine whether the parameter learning is completed based on whether the set number of learning rounds has been reached.

[0031] If parameter learning is completed, the learning results of all rounds are processed by removing extreme values ​​and taking the average to obtain an effective voltage reference value, and step S6 is executed. Subsequently, the voltage reference value is periodically calibrated according to the set motor service cycle. If parameter learning is not completed, step S6 is executed.

[0032] As a further improvement to the above scheme, in step S4, the motor insulation resistance value is also calculated using the following formula:

[0033]

[0034] In the formula, R 绝缘 , where is the insulation resistance of the motor winding to the motor housing; ADC is the average value of the voltage signal sampling; VCC is the power supply voltage of the microcontroller; V1 is the output voltage of transformer T1; R1, R2 and R3 are the resistance values ​​of resistors R1, R2 and R3 respectively; k is a constant; N is the conversion bit of the ADC module in the microcontroller.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] 1. The online motor insulation testing device disclosed in this invention realizes automatic online qualitative analysis of motor insulation by integrating a microcontroller, a detection circuit and a sampling circuit. Compared with the traditional manual measurement method, it avoids the risks of machine shutdown and electric shock, and improves the safety and real-time performance of the test.

[0037] Furthermore, since a high-voltage detection signal needs to be applied between the motor windings and the housing during the testing process, if there is no effective electrical isolation between the sampling circuit and the microcontroller, the coupling between different potentials may lead to error accumulation or even safety hazards. This invention introduces an optocoupler with isolation capabilities to reliably isolate the high-voltage detection section from the low-voltage control section, thereby effectively preventing short circuits, voltage interference, and other problems, improving the system's measurement stability and electrical safety, and making it suitable for more complex or harsh industrial environments.

[0038] 2. The online motor insulation testing method disclosed in this invention, by applying the above-mentioned circuit structure and designing the control logic of a microcontroller, can automatically detect the insulation status periodically or as needed, effectively improving the reliability of motor operation and the level of intelligent maintenance.

[0039] This invention also incorporates a parameter learning mechanism into the detection method, enabling qualitative identification of the insulation state and avoiding reliance on device parameters such as the transmission ratio of optocouplers. This improves the versatility and stability of the detection scheme. Because the transmission characteristics (e.g., transmission ratio) of isolation components such as optocouplers vary across different batches, temperatures, and aging conditions, directly using their nominal parameters for insulation resistance calculation and analysis can easily lead to detection errors. This invention introduces a parameter learning mechanism, collecting multiple sample values ​​during the initial service of the motor and extracting their stable value as a reference voltage value. In subsequent periodic tests, only this reference value needs to be compared to determine the trend of insulation performance changes, achieving qualitative analysis. This approach effectively avoids dependence on the accuracy of components such as optocouplers, improving the adaptability and engineering practicality of the detection method.

[0040] 3. Based on the qualitative analysis described above, the detection method of the present invention also provides a calculation formula based on the known parameters in the detection circuit, which can be used to deduce the insulation resistance between the motor winding and the casing. It has a certain quantitative analysis capability, which helps to make a more intuitive numerical assessment of the insulation status and is also beneficial for maintenance personnel to make trend judgments and fault analysis. Attached Figure Description

[0041] Figure 1 This is a circuit diagram of the online motor insulation testing device in Embodiment 1 of the present invention.

[0042] Figure 2 This is a flowchart of the online motor insulation testing method in Embodiment 1 of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Example 1

[0045] Please see Figure 1 This embodiment provides an online motor insulation testing device, including: a detection circuit, a sampling circuit, and a microcontroller, and may also include a motor control circuit and a relay control circuit.

[0046] The detection circuit is electrically connected to the motor housing and windings respectively, and is used to apply a high voltage detection signal between the housing and windings; the sampling circuit is used to collect the initial voltage signal at the sampling resistor in the detection circuit, and then convert the initial voltage signal through an optocoupler to transmit it to the microcontroller; the microcontroller is used to determine whether the motor insulation is good by comparing the received voltage signal sampling value with a preset voltage reference value.

[0047] In this embodiment, the microcontroller can be a single-chip microcomputer, which is the core of the detection device. Most single-chip microcomputers currently available can meet the requirements, such as ES7P169C and ES8P5066. The single-chip microcomputer has four I / O interfaces, IO1 to IO4, of which IO3 is used as the ADC sampling interface. The single-chip microcomputer is powered by VCC.

[0048] The detection circuit includes: transistor N1, diode D1, resistor R1, resistor R4, transformer T1, and relay RELAY1.

[0049] One end of resistor R4 is connected to the VDD power supply, and the other end of resistor R4 is connected to the negative terminal of diode D1 and one end of the primary coil of transformer T1, respectively; the positive terminal of diode D1 is connected to the collector terminal of transistor N1 and the other end of the primary coil of transformer T1, respectively; the emitter terminal of transistor N1 is grounded, and the base terminal of transistor N1 is connected to the IO2 interface.

[0050] One end of the secondary coil of transformer T1 is connected to the machine casing through a knife switch of relay RELAY1, and the other end of the secondary coil of transformer T1 is connected to one end of resistor R1 through another knife switch of relay RELAY1; resistor R1 serves as a sampling resistor, and its other end is connected to any one phase winding of the motor.

[0051] The sampling circuit includes: resistor R2, resistor R3, optocoupler O1, capacitor C1, and diode D2.

[0052] Among them, optocoupler O1 is a linear optocoupler; one end of resistor R3 is connected to the end of resistor R1 connected to the relay RELAY1 knife switch, and the other end of resistor R3 is connected to the positive terminal of the emitter of optocoupler O1 and the negative terminal of diode D2 respectively; the positive terminal of diode D2 is connected to the negative terminal of the emitter of optocoupler O1 and the end of resistor R1 connected to the motor winding respectively; the emitter terminal of the receiver of optocoupler O1 is connected to one end of capacitor C1 and grounded, and the collector terminal of the receiver of optocoupler O1 is connected to one end of resistor R2, the other end of capacitor C1 and the ADC sampling interface respectively; the other end of resistor R2 is connected to the VCC power supply.

[0053] The transformer T1 of this invention is used to generate a high-voltage detection signal. The microcontroller applies a pulse signal to the primary coil of transformer T1 through transistor N1, and the secondary coil of transformer T1 generates a high-voltage detection signal for detecting the insulation of the motor. The function of resistor R4 is to limit the primary current of transformer T1. The function of resistor R1 is to be connected in series with the motor winding to divide the detection signal. The divided signal is detected by optocoupler O1 and then sent to the microcontroller. D2 is a reverse Zener diode at the input of the optocoupler to ensure that the signal does not exceed the allowable value at the input of the optocoupler.

[0054] When testing is required, relay RELAY2 disconnects, separating the motor from the motor control circuit. After the motor has completely stopped working, relay RELAY1 connects, reconnecting the motor to the testing circuit. At this time, since T1 is a high-ratio transformer, the microcontroller's IO2 interface outputs pulses of a certain frequency and duty cycle, which act on transistor N1. When transistor N1 is on, the primary coil of transformer T1 is charged; when transistor N1 is off, the energy stored in the primary coil of transformer T1 is released through diode D1. During the charging and discharging process, the secondary coil simultaneously generates a high-voltage signal.

[0055] In practical applications, different transformer ratios (T1) are selected for different applications. For example, a ratio of 20 is used for single-phase 220V motors, while a ratio of 40 is used for three-phase 380V power supply applications.

[0056] When a high-voltage signal is applied between the motor windings and the casing, if the motor insulation is normal, no voltage will be generated across R1, or only a very small voltage, insufficient to make the light-emitting end of optocoupler O1 emit light. When the motor insulation deteriorates, the current in the detection circuit increases, resulting in a higher voltage across resistor R1. When this voltage reaches a certain value, the light-emitting end of optocoupler O1 begins to emit a weak light; the worse the insulation, the higher the voltage across resistor R1, and the stronger the light emission. When the light-emitting end begins to emit light, the light-receiving end of optocoupler O1 begins to generate a signal, and the light-receiving transistor begins to conduct weakly. The worse the insulation, the higher the conduction degree of the light-receiving transistor. The signal generated by the light-receiving end of optocoupler O1 is then sent to the microcontroller's ADC sampling interface via resistors R2 and C1. By detecting the change in the ADC, the microcontroller can obtain the current insulation status.

[0057] According to circuit principles, when the insulation of the motor is worse, the insulation resistance is smaller, and the current in the detection circuit (the circuit corresponding to the secondary winding of the transformer) is larger. The larger this current is, the higher the voltage generated across resistor R1. The higher the voltage across R1, the stronger the light intensity emitted by the optocoupler's light-emitting end. Therefore, the more the light-receiving end conducts, the lower the voltage drop between the C and E terminals of the optocoupler. The ADC samples the voltage corresponding to the light-receiving end of the optocoupler, so the ADC sample value is smaller.

[0058] The motor control circuit is used to supply power to the three-phase windings of the motor according to the motor control signals sent by the microcontroller, thereby driving the motor to rotate. The UVW three-phase interfaces of the motor control circuit are connected to the three-phase windings of the motor via three-phase knife switches of relay RELAY2. The specific structure of the motor control circuit varies depending on the motor type and is not the focus of this invention; therefore, it will not be described in detail here.

[0059] The relay control circuit is used to control the on / off state of relays RELAY1 and RELAY2. The relay control circuit includes transistor N2, diode D3, and diode D4.

[0060] The base of transistor N2 is connected to the IO1 interface, and the emitter of transistor N2 is grounded. The collector of transistor N2 is connected to the positive terminal of diode D3 and one end of the coil of relay RELAY1. The negative terminal of diode D3 is connected to the VDD power supply and the other end of the coil of relay RELAY1.

[0061] The base of transistor N3 is connected to the IO4 interface, and the emitter of transistor N4 is grounded. The collector of transistor N4 is connected to the positive terminal of diode D4 and one end of the coil of relay RELAY2. The negative terminal of diode D4 is connected to the VDD power supply and the other end of the coil of relay RELAY2.

[0062] In this embodiment, a transistor is used to drive the relay to achieve on / off switching. The driving principle of the two relays is the same, the difference being that RELAY1 is a two-pole relay and RELAY2 is a three-pole relay. Taking RELAY1 as an example, when the base of transistor N2 is at a high level, the transistor conducts, the drive coil of RELAY1 is powered, and the contacts of RELAY1 close and conduct.

[0063] This invention takes into account that different optocouplers have different electrical characteristics. Therefore, in the initial stage (i.e., first application), this detection device needs to learn parameters to obtain baseline parameters. Data from multiple tests over a period of time with good consistency is used as the benchmark. If valid data cannot be obtained consistently, an alarm is triggered, requiring user intervention. Of course, in subsequent tests, data over a period of time also needs to be saved for comparison. If the data change is not significant, it indicates that the insulation has not changed; otherwise, it is considered that there has been a change, and an alarm is triggered to remind the user to take action. Specific details are described later in the method description.

[0064] Please see Figure 2 This embodiment also provides an online motor insulation testing method using the above-mentioned testing device, comprising the following steps:

[0065] Upon receiving a detection command, the microcontroller initializes, then reads the saved learning flag, and determines whether parameter learning is required based on whether the set number of learning cycles has been reached. If parameter learning is required, the learning flag FLG is set to 1, and then step S1 is executed. If parameter learning is not required, step S1 is executed directly.

[0066] It should be noted that the detection commands can be periodically issued through a pre-programmed program in the microcontroller. This allows for on-time online insulation testing as needed after the detection device and motor are assembled and put into service for the first time.

[0067] S1. Control relay RELAY2 is disconnected to separate the motor from the motor control circuit. After a delay, control relay RELAY1 is turned on to connect the motor to the detection circuit.

[0068] S2. Output a pulse signal with a set frequency and duty cycle to the detection circuit through the IO2 interface, so that the secondary coil of transformer T1 generates a high voltage detection signal.

[0069] S3. Obtain the voltage signal sampling value through the ADC sampling interface, then stop the output of the IO2 interface and disconnect the relay RELAY1.

[0070] In step S3, the voltage signal is sampled and converted multiple times to obtain multiple voltage signal sample values; by averaging the multiple voltage signal sample values, a voltage signal sample mean value is obtained.

[0071] Determine whether the learning flag FLG=1 is set; if the learning flag FLG=1 is not set, proceed to the actual detection stage, i.e., execute step S4; if the learning flag FLG=1 is set, save the current average voltage signal sampling value as the learning result, and save the learning flag to complete one parameter learning, and then determine whether the parameter learning is completed based on whether the set number of learning rounds has been reached.

[0072] If parameter learning is completed, the learning results of all rounds are processed by removing extreme values ​​and taking the average to obtain a valid (consistent) voltage reference value, and step S6 is executed. Subsequently, the voltage reference value is periodically calibrated according to the set motor service cycle. If parameter learning is not completed, step S6 is executed.

[0073] S4. Based on the received voltage signal sample value and a preset voltage reference value, determine whether the motor insulation is qualified by comparison.

[0074] In step S4, when the average value of the voltage signal sampling is lower than the voltage reference value, the motor insulation is determined to be unqualified and step S5 is executed; otherwise, it is qualified and step S6 is executed. The quality of motor insulation is positively correlated with the level of the average value of the voltage signal sampling.

[0075] S5. Generate an alarm signal to remind relevant personnel to pay attention to motor safety.

[0076] S6. Control relay RELAY2 to turn on to restore motor drive and wait for the next detection command to be issued.

[0077] Because this invention uses optocouplers, the actual current transfer ratio of the optocoupler may differ from its nominal current transfer ratio at the factory in practical applications. Therefore, even optocouplers of the same model may exhibit individual differences in current transfer ratio. While it's possible to conduct experiments on each optocoupler individually to obtain parameters such as the actual transfer ratio, this is time-consuming and labor-intensive, unsuitable for large-scale applications. Therefore, this invention introduces a parameter learning step. For a brand-new motor and optocoupler, parameter learning is performed a set number of times. A baseline value is determined based on the average of previously consistent voltage signal samples. This baseline value is then used to determine whether the motor's insulation has deteriorated, thus achieving qualitative analysis. Of course, in subsequent use, the learning process can be re-run periodically (e.g., annually). If the learning result differs significantly from the initial learning result, a problem is indicated, triggering an alarm for manual intervention. This invention uses "parameter learning" to replace the reliance on precise parameters in traditional quantitative calculation methods, significantly improving the adaptability and engineering practicality of the detection device.

[0078] Example 2

[0079] This embodiment provides an online method for testing the insulation of a motor. Based on the testing method in Embodiment 1, this embodiment further calculates the motor insulation resistance value in step S4 to achieve quantitative analysis. The calculation formula is as follows:

[0080]

[0081] In the formula, R 绝缘 V represents the insulation resistance between the motor windings and the motor housing; ADC represents the average value of the voltage signal samples; ACC represents the power supply voltage of the microcontroller; V S R is the output voltage of transformer T1; R1, R2, and R3 are the resistance values ​​of resistors R1, R2, and R3, respectively; k is a constant; N is the number of bits of the ADC module (i.e., analog-to-digital converter) in the microcontroller (which determines the conversion accuracy). For example, if a 12-bit ADC is used, then N = 12.

[0082] It should be noted that during the safety monitoring of motors, the primary focus is on whether there has been a significant change in their insulation. The significant difference between the calculated motor insulation resistance value and the reference value can be used as the basis for judgment. For example, in practical applications, a difference exceeding 10% is considered a significant change in insulation.

[0083] In practical applications, the ADC results are usually compared directly without calculating the insulation resistance. However, there is a one-to-one correspondence between the insulation resistance and the ADC value. Some controllers with displays can also show the calculated resistance value for user reference.

[0084] Furthermore, in practical applications, it is necessary to obtain the value of the constant k. The constant k is related to the optocoupler O1, resistors R1, R2, and R3, and is determined experimentally. In this embodiment, k is set to 180. This constant affects the accuracy of insulation resistance detection. Experiments showed that changing the optocoupler O1, resistors R1, R2, and R3 resulted in a total practical impact of less than 5%.

[0085] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An on-line electrical machine insulation detection method, characterized by, An online motor insulation testing device is disclosed. The device includes a detection circuit, a sampling circuit, a microcontroller, and a motor control circuit. The detection circuit is electrically connected to the motor housing and windings, respectively, and is used to apply a high-voltage detection signal between the housing and windings. The sampling circuit is used to acquire the initial voltage signal at the sampling resistor in the detection circuit, and then converts the initial voltage signal through an optocoupler for transmission to the microcontroller. The microcontroller is used to determine whether the motor insulation is good by comparing the received voltage signal sampling value with a preset voltage reference value. The microcontroller is a single-chip microcomputer with four I / O interfaces IO1~IO4, of which IO3 is used as the ADC sampling interface. The single-chip microcomputer is powered by VCC. The detection circuit includes: transistor N1, diode D1, resistor R1, resistor R4, transformer T1, and relay RELAY1. One end of resistor R4 is connected to the VDD power supply, and the other end of resistor R4 is connected to the negative terminal of diode D1 and one end of the primary coil of transformer T1 respectively; the positive terminal of diode D1 is connected to the collector terminal of transistor N1 and the other end of the primary coil of transformer T1 respectively; the emitter terminal of transistor N1 is grounded, and the base terminal of transistor N1 is connected to the IO2 interface. One end of the secondary coil of transformer T1 is connected to the machine casing through a knife switch of relay RELAY1, and the other end of the secondary coil of transformer T1 is connected to one end of resistor R1 through another knife switch of relay RELAY1; resistor R1 serves as a sampling resistor, and its other end is connected to any one phase winding of the motor. The sampling circuit includes: resistor R2, resistor R3, optocoupler O1, capacitor C1, and diode D2; In this configuration, one end of resistor R3 is connected to the end of resistor R1 connected to the RELAY1 knife switch; the other end of resistor R3 is connected to the positive terminal of the emitter of optocoupler O1 and the negative terminal of diode D2; the positive terminal of diode D2 is connected to the negative terminal of the emitter of optocoupler O1 and the end of resistor R1 connected to the motor winding; the emitter terminals of the receiver of optocoupler O1 are connected to one end of capacitor C1 and grounded; the collector terminals of the receiver of optocoupler O1 are connected to one end of resistor R2, the other end of capacitor C1, and the ADC sampling interface; the other end of resistor R2 is connected to the VCC power supply; and diode D2 is a reverse Zener diode. The motor control circuit is used to supply power to the three-phase windings of the motor according to the motor control signal sent by the microcontroller in a timing sequence to drive the motor to rotate; wherein, the UVW three-phase interfaces of the motor control circuit are respectively connected to the three-phase windings of the motor through the three-phase knife switch of the relay RELAY2. The method includes the following steps: Upon receiving a detection command, the microcontroller initializes, then reads the saved learning flag, and determines whether parameter learning is required based on whether the set number of learning cycles has been reached. If parameter learning is required, the learning flag FLG=1 is set, and then step S1 is executed. If parameter learning is not required, step S1 is executed directly. S1. Control relay RELAY2 is disconnected to separate the motor from the motor control circuit. After a delay, control relay RELAY1 is turned on to connect the motor to the detection circuit. S2. Output a pulse signal with a set frequency and duty cycle to the detection circuit through the IO2 interface, so that the secondary coil of transformer T1 generates a high voltage detection signal. S3. Obtain the voltage signal sample value through the ADC sampling interface, then stop the output of the IO2 interface and disconnect the relay RELAY1; wherein, the voltage signal is sampled and converted multiple times to obtain multiple voltage signal sample values; by averaging the multiple voltage signal sample values, a voltage signal sample average value is obtained; Determine whether the learning flag FLG=1 is set; if the learning flag FLG=1 is not set, proceed to the actual detection stage, i.e., execute step S4; if the learning flag FLG=1 is set, save the current average voltage signal sampling value as the learning result, and save the learning flag to complete one parameter learning cycle. Then, determine whether the parameter learning is complete based on whether the set number of learning cycles has been reached. If parameter learning is completed, the learning results of all rounds are processed by removing extreme values ​​and taking the average to obtain an effective voltage reference value, and step S6 is executed. Subsequently, the voltage reference value is periodically calibrated according to the set motor service cycle. If parameter learning is not completed, step S6 is executed. S4. Based on the received voltage signal sampling value and a preset voltage reference value, determine whether the motor insulation is qualified by comparison; wherein, when the average voltage signal sampling value is lower than the voltage reference value, the motor insulation is determined to be unqualified and step S5 is executed, otherwise it is qualified and step S6 is executed; wherein, the quality of motor insulation is positively correlated with the level of the average voltage signal sampling value, and the motor insulation resistance value is calculated by the following formula: In the formula, is the insulation resistance of the motor winding to the motor shell; is the average value of the voltage signal sampling; is the power supply voltage of the single-chip microcomputer; is the output voltage of the transformer T1; , and are the resistance values of the resistors R1, R2 and R3, respectively; k is a constant; N is the conversion bit number of the ADC module in the single-chip microcomputer; S5. Generate an alarm signal; S6. Control relay RELAY2 to turn on to restore motor drive.

2. The online motor insulation testing method according to claim 1, characterized in that, The detection device further includes a relay control circuit; the relay control circuit includes transistor N2, diode D3, transistor N3 and diode D4; The base of transistor N2 is connected to the IO1 interface, and the emitter of transistor N2 is grounded. The collector of transistor N2 is connected to the positive terminal of diode D3 and one end of the coil of relay RELAY1. The negative terminal of diode D3 is connected to the VDD power supply and the other end of the coil of relay RELAY1. The base of transistor N3 is connected to the IO4 interface, and the emitter of transistor N4 is grounded. The collector of transistor N4 is connected to the positive terminal of diode D4 and one end of the coil of relay RELAY2. The negative terminal of diode D4 is connected to the VDD power supply and the other end of the coil of relay RELAY2.

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