Online diagnosis method for potential grounding of main insulation of traction motors for rail transit

Abstract

The present invention relates to the technical field of insulation diagnosis of traction motors for pipeline transportation, and specifically to an online diagnosis method for potential grounding of the main insulation of traction motors for rail transportation. In order to solve the above-mentioned defects of the motor insulation diagnosis method in the prior art, a new online diagnosis method for potential grounding of the main insulation of traction motors for rail transportation is provided, including ground voltage data acquisition, normalization, DC component removal data processing, calculation of the fundamental amplitude of the motor current and the fundamental frequency of the motor current, design of a bandpass filter, ground voltage bandpass filtering, removal of grid voltage and power frequency interference, and calculation of the fault characteristic frequency band energy in the remaining frequency band. E_Ugd、 Calculate fault feature extraction value, dynamic threshold learning and analysis judgment. The patent of this invention only needs to perform simple signal processing method and feature calculation on the existing key signals in the grounding detection loop of the traction converter, with low implementation cost, simple diagnostic algorithm and obvious effect.

Description

Technical Field

[0001] The present invention relates to the technical field of insulation diagnosis of traction motors for pipeline transportation, and in particular to an online diagnosis method for potential grounding of main insulation of traction motors for rail transportation. Background Art

[0002] As the rail transit field has higher and higher requirements for the speed of traction motors, the operating frequency of the inverter switching device IGBT is getting higher and higher, and the IGBT voltage level is also getting higher and higher. The operating environment and working conditions of the traction motor are becoming more and more complex and changeable. The stator insulation system has to bear higher and higher requirements in all aspects. These requirements have further accelerated the aging process of the traction motor stator insulation and seriously affected the healthy state of the insulation. Once the healthy state of the traction motor insulation develops to the point where the main insulation is broken down and grounded to the ground, a large current will appear in the motor, which will cause the motor insulation to burn and the stator core to burn, indirectly causing damage to the inverter traction electric drive system. More seriously, it will cause the inverter drive power module IGBT tube to explode and other very serious adverse effects and losses, and even threaten driving safety and personal safety.

[0003] In order to avoid serious adverse effects and losses caused by traction motor stator insulation failure, it is necessary to detect potential insulation failures in time and remind the driver to make decisions in time. The traditional approach is to conduct regular preventive offline tests to check whether the stator insulation has defects, so as to arrange maintenance in time and avoid failures. However, offline detection cannot guarantee the real-time normal state of the motor's online operation. If the potential fault of the motor insulation can be diagnosed online in time, and the motor control system is prompted to shut down or reduce power, or the driver is prompted to observe, the impact of the insulation problem can be minimized, and the maintenance component will be greatly increased. Therefore, online diagnosis of potential grounding faults in the main insulation of the traction motor is very important.

[0004] Prior art 1: An online insulation assessment method and device based on partial discharge of a traction motor with application number 202010664760.8. The partial discharge signal of the variable frequency motor described in this technical solution is easily interfered by the high-frequency noise signal generated by the traction inverter, and has problems of low efficiency and inaccurate monitoring. It also involves complex algorithms such as neural networks and machine learning, and is not suitable for implementation in general embedded processing chips.

[0005] Prior art 2: A non-contact online monitoring method for variable frequency motor insulation with application number 202310721484.8. The non-contact high-frequency sensor described in the technical solution is set on the variable frequency motor side in the form of three-phase sleeve penetration, phase line sleeve penetration or ground line sleeve penetration. The deployment method is complex, the measurement accuracy is high, and the cost is expensive. In addition, the inherent frequency characteristics and current amplitude of the trailing modal component of the switching oscillation current involved in the extraction are not easy to extract for the converter system whose switching frequency of the switching device itself is very high. Summary of the invention

[0006] In order to solve the above-mentioned defects of the motor insulation diagnosis method in the prior art, the present invention provides a new online diagnosis method for potential grounding of the main insulation of a traction motor for rail transit.

[0007] The present invention is achieved by adopting the following technical solutions:

[0008] The train traction system includes a pre-charging module, a four-quadrant rectifier module, an intermediate DC circuit, a traction inverter module, a traction motor, and an auxiliary converter. The intermediate DC circuit grounding detection method is used to detect it. When the motor phase A is grounded, without considering the zero working state mode of the traction inverter module, the upper bridge arm of the phase A is turned on, which is similar to the positive grounding of the intermediate DC bus; the lower bridge arm of the phase A is turned on, which is similar to the negative grounding of the intermediate DC bus. Therefore, the amplitude of the grounding voltage Ugd varies between 0 and Udc, and the duty cycle is about 50%. The frequency of change is related to the switching frequency of the A bridge arm IGBT of the inverter and the fundamental frequency of the motor current. This method of using the ratio of the effective value of the grounding voltage to the effective value of the intermediate DC bus voltage is mainly suitable for diagnosing whether the motor has been completely grounded, whether the motor insulation resistance has been reduced to below the grounding monitoring resistance R2 (about 100kΩ), and whether the motor has been unable to work normally. The aging process of traction motor insulation is a process in which the equivalent resistance of the insulation gradually decreases, and the corresponding grounding voltage will also change accordingly within a specific frequency band. Therefore, online diagnosis of potential insulation grounding can be performed by online monitoring of changes in Ugd.

[0009] Through the research and analysis of the failure mechanism of traction motor insulation aging, the fault characteristics of motor insulation aging and insulation potential grounding driven by inverter are summarized as follows:

[0010] a. The amplitude of the spectrum of the ground voltage Ugd at the fundamental frequency of the traction motor power supply and the amplitude at the switching frequency of the inverter IGBT gradually increase with the degree of insulation aging;

[0011] b. In the spectrum of the ground voltage Ugd, the amplitude at the 6k±1 harmonic frequency of the motor power supply in the frequency band between the fundamental frequency of the traction motor power supply and the switching frequency of the inverter IGBT also increases to a certain extent with the degree of insulation aging, but it is not as obvious as the amplitude at the fundamental frequency of the traction motor power supply and the switching frequency of the inverter IGBT;

[0012] c. Since the spectrum of the ground voltage Ugd has an obvious amplitude at the grid voltage frequency of 50Hz and its harmonic frequencies when the traction motor is in a normal state, the amplitude remains unchanged when the traction motor insulation is aged;

[0013] d. In the normal state of the traction motor, the spectrum of the ground voltage Ugd has a weak amplitude at the fundamental frequency of the traction motor power supply and a weak amplitude at the switching frequency of the inverter IGBT, and the magnitude of the two amplitudes is proportional to the fundamental amplitude in the spectrum of the traction motor current signal. In the state of aging of the traction motor insulation, the spectrum of the ground voltage Ugd has a weak amplitude at the fundamental frequency of the traction motor power supply and a significant increase in the amplitude at the switching frequency of the inverter IGBT;

[0014] e. Under normal conditions of the traction motor, the spectrum of the ground voltage Ugd has an obvious amplitude at the 6k±1 harmonic frequency of the traction motor power supply, and the amplitude is proportional to the fundamental amplitude in the spectrum of the traction motor current signal. Under aging conditions of the traction motor insulation, the spectrum of the ground voltage Ugd has a slight increase in amplitude at the 6k±1 harmonic frequency of the traction motor power supply;

[0015] f. Except for the frequency components and DC components mentioned above, there are no other frequency components in the ground voltage spectrum.

[0016] Based on the above fault characteristics, a new online diagnosis method for potential grounding of the main insulation of traction motors for rail transit is designed, which includes the following steps:

[0017] 1) Collecting ground voltage data through a ground voltage sensor;

[0018] 2) Performing normalized data processing on the ground voltage data;

[0019] 3) The data processed in step 2) is processed to remove the DC component. The DC component removal data processing formula is as follows: gd =U gd -mean(U gd ), where U gd 、u gd They are the instantaneous value of the ground voltage and the instantaneous value after removing the DC component;

[0020] 4) Calculate the fundamental amplitude and fundamental frequency of the motor current:

[0021] a. Collect the motor current through the motor current sensor and perform normalized data processing on the collected data;

[0022] b. Perform FFT on any normalized current of the motor to obtain the spectrum function F(f);

[0023] c. It is known that the maximum current frequency of the motor is f max , find (0,f max +5) The maximum value F_i of the spectrum function amplitude within the frequency range and the corresponding frequency f_i, that is, the fundamental amplitude of the motor current and the fundamental frequency of the motor current respectively;

[0024] 5) Design of bandpass filter:

[0025] Get the switching frequency f_igbt of the IGBT in the traction inverter module of the motor from the traction control unit, define f_igbt+f_i / 3 as the upper cutoff frequency of the bandpass filter, define f_i-f_i / 3 as the lower cutoff frequency of the bandpass filter, the transition band is f_i / 3, the center frequency of the bandpass filter is (f_igbt+f_i) / 2, the passband frequency range is [f_i-f_i / 3,f_igbt+f_i / 3], the maximum attenuation of the passband is 3dB, the minimum attenuation of the stopband is 9dB, and the bandpass filter is designed using the Hamming window function;

[0026] 6) Ground voltage bandpass filtering:

[0027] performing band-pass filtering on the ground voltage from which the DC component has been removed in step 3);

[0028] 7) Eliminate grid voltage and power frequency interference:

[0029] Perform FFT on the signal after bandpass filtering to obtain the spectrum function F ugd (f), let f be the spectrum function F in the frequency bands of (49.9, 50.1), (99.9, 100.1), (149.9, 150.1), (199.9, 200.1), (249.9, 250.1) ugd =0;

[0030] 8) Calculate the fault characteristic frequency band energy E_Ugd in the remaining frequency band after removing the grid voltage power frequency interference:

[0031]

[0032] 9) Calculating fault feature extraction:

[0033] Let the fault characteristic energy distortion rate E_Ugd / F_i in the ratio grounding voltage be used as the fault characteristic extraction value of the potential grounding of the main insulation of the traction motor;

[0034] 10) Dynamic threshold learning and analysis and judgment:

[0035] When driving the traction inverter module and the traction motor for joint debugging test, the basic data of the normal state under various working conditions is learned, and the initial threshold of the fault characteristic amplitude is determined. After the motor is put into operation, dynamic threshold learning is carried out, the initial threshold is optimized and adjusted, and finally the warning threshold of the fault characteristic amplitude is determined. When the fault feature extraction value exceeds the warning threshold of the fault feature amplitude for 10 consecutive times and there is an increasing trend, it is determined that the traction motor has a potential main insulation grounding fault.

[0036] Furthermore, when the fault feature extraction value exceeds the warning threshold of the fault feature amplitude for 10 consecutive times and has an increasing trend, the relevant fault data needs to be stored, otherwise the daily data is stored.

[0037] Furthermore, when it is determined that the traction motor has a potential main insulation grounding fault, an alarm prompt for a potential main insulation grounding fault is issued.

[0038] The beneficial effects of the present invention are as follows: the diagnostic method described in the present invention can realize the dynamic changes of the insulation aging characteristic index of the grounding voltage of the converter grounding detection circuit in real time when the main insulation of the traction motor driven by the inverter is aging, and can realize that when the traction motor insulation shows a slight aging phenomenon and the insulation has a potential grounding risk, a fault judgment can be made to remind the operating personnel to pay attention to the motor operation status in real time, and perform power reduction operation or shutdown inspection when necessary to avoid the motor running with a fault, minimize the impact of the motor insulation aging problem, avoid more serious damage to the motor and its drive system, and reduce the maintenance cost as much as possible; at the same time, the patent of the present invention only needs to perform a simple signal processing method and feature calculation on the existing key signals in the grounding detection circuit of the traction converter, and extract the insulation aging and potential grounding characteristics of the motor from the perspective of the aging failure mechanism of the insulation. Not only does it not need to add additional detection equipment, the implementation cost is low, and the diagnostic algorithm is simple and the effect is obvious. It can be implemented in a general embedded system, with strong real-time performance and high execution efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0041] Figure 1 It is the main circuit topology diagram of the train traction system;

[0042] Figure 2 It is a flow chart of the online diagnosis method of potential grounding of main insulation according to the present invention;

[0043] Figure 3 The time and frequency domain waveforms of the motor in normal and fault states after preprocessing to remove the DC component;

[0044] Figure 4 The time and frequency domain waveforms of the ground voltage signal in the normal state and the fault state of the motor after bandpass filtering;

[0045] Figure 5 The frequency domain waveforms of the ground voltage signals of the motor in normal state and motor fault state after removing the grid voltage and power frequency interference. DETAILED DESCRIPTION

[0046] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0047] In the description, it should be noted that the terms "first" and "second" are only used for descriptive purposes and should not be understood as indicating or implying relative importance. It should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internal communication between two elements. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0048] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0049] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0050] like Figure 1 As shown, the train traction system includes a pre-charging module, a four-quadrant rectifier module, an intermediate DC circuit, a traction inverter module, a traction motor, and an auxiliary converter. The intermediate DC circuit grounding detection method is used to detect it. When the motor phase A is grounded, without considering the zero working state mode of the traction inverter module, the upper bridge arm of the phase A is turned on, which is similar to the positive grounding of the intermediate DC bus; the lower bridge arm of the phase A is turned on, which is similar to the negative grounding of the intermediate DC bus. Therefore, the amplitude of the grounding voltage Ugd varies between 0 and Udc, and the duty cycle is about 50%. The frequency of change is related to the switching frequency of the A bridge arm IGBT of the inverter and the fundamental frequency of the motor current. This method of using the ratio of the effective value of the grounding voltage to the effective value of the intermediate DC bus voltage is mainly suitable for diagnosing whether the motor has been completely grounded, whether the insulation resistance of the motor has been reduced to below the grounding monitoring resistance R2 (about 100kΩ), and whether the motor has been unable to work normally. The aging process of traction motor insulation is a process in which the equivalent resistance of the insulation gradually decreases, and the corresponding grounding voltage will also change accordingly within a specific frequency band. Therefore, online diagnosis of potential insulation grounding can be performed by online monitoring of changes in Ugd.

[0051] Through the above research and analysis of the failure mechanism of traction motor insulation aging, the fault characteristics of motor insulation aging and insulation potential grounding under inverter drive are summarized as follows:

[0052] a. The amplitude of the spectrum of the ground voltage Ugd at the fundamental frequency of the traction motor power supply and the amplitude at the switching frequency of the inverter IGBT gradually increase with the degree of insulation aging;

[0053] b. In the spectrum of the ground voltage Ugd, the amplitude at the 6k±1 harmonic frequency of the motor power supply in the frequency band between the fundamental frequency of the traction motor power supply and the switching frequency of the inverter IGBT also increases to a certain extent with the degree of insulation aging, but it is not as obvious as the amplitude at the fundamental frequency of the traction motor power supply and the switching frequency of the inverter IGBT;

[0054] c. Since the spectrum of the ground voltage Ugd has an obvious amplitude at the grid voltage frequency of 50Hz and its harmonic frequencies when the traction motor is in a normal state, the amplitude remains unchanged when the traction motor insulation is aged;

[0055] d. In the normal state of the traction motor, the spectrum of the ground voltage Ugd has a weak amplitude at the fundamental frequency of the traction motor power supply and a weak amplitude at the switching frequency of the inverter IGBT, and the magnitude of the two amplitudes is proportional to the fundamental amplitude in the spectrum of the traction motor current signal. In the state of aging of the traction motor insulation, the spectrum of the ground voltage Ugd has a weak amplitude at the fundamental frequency of the traction motor power supply and a significant increase in the amplitude at the switching frequency of the inverter IGBT;

[0056] e. Under normal conditions of the traction motor, the spectrum of the ground voltage Ugd has an obvious amplitude at the 6k±1 harmonic frequency of the traction motor power supply, and the amplitude is proportional to the fundamental amplitude in the spectrum of the traction motor current signal. Under aging conditions of the traction motor insulation, the spectrum of the ground voltage Ugd has a slight increase in amplitude at the 6k±1 harmonic frequency of the traction motor power supply;

[0057] f. Except for the frequency components and DC components mentioned above, there are no other frequency components in the ground voltage spectrum.

[0058] like Figure 2 As shown, based on the above fault characteristics, a new online diagnosis method for potential grounding of the main insulation of traction motors for rail transit is designed. The following is a detailed description of the implementation and verification process of the online diagnosis method for potential grounding of the main insulation of traction motors for rail transit based on the test data of the motor at 1 / 4 rated speed, i.e. 680r / min, 1 / 2 rated torque test conditions, and insulation aging simulation conditions where the first coil of the stator V-phase winding is connected to a 10M ohm grounding resistor, which includes the following steps:

[0059] 1) Collecting ground voltage data through a ground voltage sensor;

[0060] 2) Performing normalized data processing on the ground voltage data;

[0061] 3) The data processed in step 2) is processed to remove the DC component. The DC component removal data processing formula is as follows: gd =U gd -mean(U gd ), where U gd 、u gd They are the instantaneous value of the ground voltage and the instantaneous value after removing the DC component. The time and frequency domain waveforms of the motor in normal state and fault state after removing the DC component preprocessing are shown in Figure 3 As shown;

[0062] 4) Calculate the fundamental amplitude and fundamental frequency of the motor current:

[0063] a. Collect the motor current through the motor current sensor and perform normalized data processing on the collected data;

[0064] b. Perform FFT on any normalized current of the motor to obtain the spectrum function F(f);

[0065] c. It is known that the maximum current frequency of the motor is f max , find (0,f max+5) The maximum value F_i of the spectrum function amplitude within the frequency range and the corresponding frequency f_i, that is, the fundamental amplitude of the motor current and the fundamental frequency of the motor current respectively;

[0066] It can be concluded that the fundamental wave amplitudes of the normal motor and the faulty motor under this working condition are 0.988 and 0.982 respectively, and the fundamental wave frequencies of the normal motor and the faulty motor are both 23.6Hz;

[0067] 5) Design of bandpass filter:

[0068] Get the switching frequency f_igbt of the IGBT in the traction inverter module of the motor from the traction control unit, define f_igbt+f_i / 3 as the upper cutoff frequency of the bandpass filter, define f_i-f_i / 3 as the lower cutoff frequency of the bandpass filter, the transition band is f_i / 3, the center frequency of the bandpass filter is (f_igbt+f_i) / 2, the passband frequency range is [f_i-f_i / 3,f_igbt+f_i / 3], the maximum attenuation of the passband is 3dB, the minimum attenuation of the stopband is 9dB, and the bandpass filter is designed using the Hamming window function;

[0069] Among them, it is concluded that the switching frequency of the IGBT in the traction inverter module is 354Hz;

[0070] 6) Ground voltage bandpass filtering:

[0071] The ground voltage after the DC component is removed in step 3) is band-pass filtered. The ground voltage signals in the normal state and the fault state of the motor after band-pass filtering are shown in the time and frequency domain waveforms as follows: Figure 4 As shown;

[0072] 7) Eliminate grid voltage and power frequency interference:

[0073] Perform FFT on the signal after bandpass filtering to obtain the spectrum function F ugd (f), let f be the spectrum function F in the frequency bands of (49.9, 50.1), (99.9, 100.1), (149.9, 150.1), (199.9, 200.1), (249.9, 250.1) ugd =0, and the spectrum function in the remaining frequency band is obtained;

[0074] At this time, the frequency domain waveforms of the ground voltage signal in the normal state and the fault state of the motor are as follows: Figure 5 As shown;

[0075] 8) Calculate the fault characteristic frequency band energy E_Ugd in the remaining frequency band after removing the grid voltage power frequency interference:

[0076]

[0077] 9) Calculating fault feature extraction:

[0078] Let the fault characteristic energy distortion rate E_Ugd / F_i in the ratio grounding voltage be used as the fault characteristic extraction value of the potential grounding of the main insulation of the traction motor;

[0079] It can be concluded that the energy of the motor in the frequency band range of [16Hz, 362Hz] is 0.00625 and 0.0099 in the normal state and fault state respectively, and the current fundamental amplitude in the normal state and fault state is 0.988 and 0.982 respectively. Therefore, the fault feature ratios in the normal state and fault state of the motor are 0.00632 and 0.0101 respectively. After calculating all the test condition data, it is verified that the fault feature extraction value is obviously higher in the fault state than in the normal state. Therefore, by extracting the fault feature frequency band energy of the ground voltage signal, the weak fault feature of the potential grounding of the insulation of the inverter-driven traction motor can be effectively extracted.

[0080] 10) Dynamic threshold learning and analysis and judgment:

[0081] When driving the traction inverter module and the traction motor for joint commissioning test, the basic data of the normal state under various working conditions is learned, and the initial threshold of the fault characteristic amplitude is determined. After the motor is put into operation, dynamic threshold learning is carried out, the initial threshold is optimized and adjusted, and finally the warning threshold of the fault characteristic amplitude is determined. When the fault characteristic extraction value exceeds the warning threshold of the fault characteristic amplitude for 10 consecutive times and there is an increasing trend, it is determined that the traction motor has a potential main insulation grounding fault and a grounding fault alarm is issued. At the same time, the relevant fault data is stored, otherwise the daily data is stored.

[0082] The above is only a specific implementation of the present invention, which enables those skilled in the art to understand or implement the present invention. Although detailed descriptions are given with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments, and they should all be covered by the protection scope of the claims.

Claims

1. An online diagnostic method for potential grounding of main insulation of traction motor for rail transit, characterized in that: The steps include: 1) Collecting ground voltage data through a ground voltage sensor; 2) Performing normalized data processing on the ground voltage data; 3) The data processed in step 2) is processed to remove the DC component. The DC component removal data processing formula is as follows: gd =U gd -mean(U gd ), where U gd 、u gd They are the instantaneous value of the ground voltage and the instantaneous value after removing the DC component; 4) Calculate the fundamental amplitude and fundamental frequency of the motor current: a. Collect the motor current through the motor current sensor and perform normalized data processing on the collected data; b. Perform FFT on any normalized current of the motor to obtain the spectrum function F(f); c. It is known that the maximum current frequency of the motor is f max , find (0,f max +5) The maximum value F_i of the spectrum function amplitude within the frequency range and the corresponding frequency f_i, that is, the fundamental amplitude of the motor current and the fundamental frequency of the motor current respectively; 5) Design of bandpass filter: Get the switching frequency f_igbt of the IGBT in the traction inverter module of the motor control from the traction control unit, define f_igbt+f_i / 3 as the upper cutoff frequency of the bandpass filter, define f_i-f_i / 3 as the lower cutoff frequency of the bandpass filter, the transition band is f_i / 3, the center frequency of the bandpass filter is (f_igbt+f_i) / 2, the passband frequency range is [f_i-f_i / 3,f_igbt+f_i / 3], the maximum attenuation of the passband is 3dB, the minimum attenuation of the stopband is 9dB, and the bandpass filter is designed using the Hamming window function; 6) Ground voltage bandpass filtering: Performing band-pass filtering on the ground voltage from which the DC component has been removed in step 3); 7) Eliminate grid voltage and power frequency interference: Perform FFT on the signal after bandpass filtering to obtain the spectrum function F ugd (f), let f be the spectrum function F in the frequency bands of (49.9, 50.1), (99.9, 100.1), (149.9, 150.1), (199.9, 200.1), (249.9, 250.1) ugd =0; 8) Calculate the fault characteristic frequency band energy E_Ugd in the remaining frequency band after removing the grid voltage power frequency interference: 9) Calculating fault feature extraction: Let the fault characteristic energy distortion rate E_Ugd / F_i in the ratio grounding voltage be used as the fault characteristic extraction value of the potential grounding of the main insulation of the traction motor; 10) Dynamic threshold learning and analysis and judgment: When driving the traction inverter module and the traction motor for joint debugging test, the basic data of the normal state under various working conditions is learned, and the initial threshold of the fault characteristic amplitude is determined. After the motor is put into operation, dynamic threshold learning is carried out, the initial threshold is optimized and adjusted, and finally the warning threshold of the fault characteristic amplitude is determined. When the fault feature extraction value exceeds the warning threshold of the fault feature amplitude for 10 consecutive times and there is an increasing trend, it is determined that the traction motor has a potential main insulation grounding fault.

2. The online diagnosis method for potential grounding of main insulation of traction motor for rail transit according to claim 1 is characterized in that: When the fault feature extraction value exceeds the warning threshold of the fault feature amplitude for 10 consecutive times and has an increasing trend, the relevant fault data needs to be stored, otherwise daily data is stored.

3. The online diagnosis method for potential grounding of main insulation of traction motor for rail transit according to claim 2 is characterized in that: When it is determined that the traction motor has a potential main insulation grounding fault, a main insulation potential grounding fault alarm is issued.

Images