A method for on-line measurement of oil film impedance of motor bearing

Abstract

The application relates to an online measurement method for motor bearing oil film impedance. The method introduces an excitation voltage into a rotating shaft of a motor, and obtains the voltage U m between the rotating shaft and the ground and the current I m in a test loop through online measurement, calculates the bearing impedance Zb, and further determines the bearing oil film capacitance C b and the resistance R b . The method can realize online testing of the motor bearing oil film impedance for a single bearing structure without special tooling modification of the motor and construction of a special bearing test bed, better monitors the performance state of the bearing during motor operation, judges the health condition of the bearing, and can be applied to online oil film impedance testing of a high-power motor during operation.

Description

Technical Field

[0001] This invention relates to the field of motor bearing oil film impedance testing, specifically to an online method for measuring the oil film impedance of motor bearings. Background Technology

[0002] Currently, many new energy motors, such as those for electric vehicles and wind power generation, commonly adopt an integrated generator-gearbox design. These motors use a single-bearing structure, making bearing reliability crucial for stable and efficient motor operation. Bearing oil film impedance refers to the equivalent impedance of the dynamic lubricating oil film formed between the rolling elements and raceways of the bearing. By measuring and analyzing changes in bearing impedance, bearing wear, faults, and other abnormalities can be accurately assessed, and it is also a key parameter for shaft current modeling and analysis. Therefore, real-time monitoring of bearing oil film impedance changes is significant for improving the reliability of high-power motors and reducing maintenance costs. However, because this type of motor generally uses an embedded bearing structure, existing methods struggle to achieve online measurement.

[0003] Existing methods for measuring bearing oil film parameters mainly include: optical interferometry, capacitance method, resistance method, and RC oscillation method. [1] Optical interferometry can accurately measure oil film thickness, but it requires one of the contact conditions to be made of a light-transmitting material, making it unsuitable for online measurement of rolling bearing oil film thickness. Capacitance method. [2] Resistance method [3] and RC oscillation method [4] All these methods are based on measuring bearing oil film parameters using electrical quantities. The capacitance method derives the bearing capacitance by utilizing the time constant of the bearing's charge and discharge. It is simple to test and can quantitatively measure the oil film thickness on the contact surface under full-film lubrication conditions. However, this method fails once metal-to-metal micro-peak contact occurs. The resistance method has a simple test circuit and is an effective method for measuring the film formation rate of rolling bearings and qualitatively analyzing the bearing lubrication state. However, this method cannot quantitatively measure the bearing oil film thickness. The RC oscillation method combines the advantages of the resistance and capacitance methods and can be used for both full-film and partial-film elastohydrodynamic testing.

[0004] The aforementioned measurement methods share a common problem: they cannot achieve online monitoring of the oil film in large wind turbine bearings. This requires a specially constructed bearing test bench, which necessitates complex loading and insulation designs to simulate actual operating conditions of the motor bearing while ensuring good insulation between the tested bearing and other components. Furthermore, specialized capacitance meters, impedance meters, or optical measurement equipment are also required. [5，6] .

[0005] Existing online monitoring methods [7 , 8]A signal generator is used as an excitation applied to the motor, and the volt-ampere characteristics of the bearing capacitance are experimentally determined during frequency conversion power supply. However, this method requires modification of the motor end cover structure, adding an insulation layer, and simultaneously measuring the shaft voltage and the current flowing through the bearing. In applications such as wind power generation and electric vehicles, the aforementioned tooling modification scheme is difficult to implement and is not suitable for motors already in mass production. Furthermore, this method uses the current flowing through the test leads as the bearing current during data processing, ignoring the error caused by the current flowing through the insulation layer, resulting in an overestimation of the bearing impedance measurement. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an online method for measuring the oil film impedance of motor bearings. The method provided by this invention can monitor the bearing performance status in real time, determine the bearing's health condition, and take necessary maintenance and upkeep measures to extend the bearing's service life and improve equipment reliability.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for online measurement of oil film impedance of motor bearings, characterized by comprising the following steps:

[0009] Step 1: Measure the capacitance C1 between the stator winding short-circuit point and the motor housing; the capacitance C2 between the stator winding short-circuit point and the rotor; and the capacitance C3 between the rotor and the stator housing. Obtain the stray capacitance parameters of the motor using the following formula:

[0010]

[0011]

[0012]

[0013] In the above formula: C wf For the stator winding capacitance to the chassis, C wr C is the stator winding capacitance to the rotor. rf For rotor-to-casing capacitance, C iso For capacitors with insulated end caps;

[0014] Step 2: Apply a high-frequency sinusoidal voltage between the motor rotor and the casing; measure the static voltage U of the motor shaft to ground when the motor is stationary. m-s and the static current I in the circuit m-s And obtain the corresponding phasors and ;Measure the dynamic voltage U between the motor shaft and ground while the motor is running. m-d and the dynamic current I in the circuit m-d And obtain the corresponding phasors and

[0015] Step 3, based on the motor's stationary state obtained in Step 2 and Calculate the line loss resistance R ac and parasitic inductance L ac As shown in the following formula:

[0016]

[0017]

[0018]

[0019] In the above formula, These are the voltage and current phasors measured and acquired under static conditions. For static conditions The calculated measured impedance, Z m-s for The model; and They are respectively and phase angle; f c The frequency of the applied voltage;

[0020] Step 4: Calculate the bearing impedance based on the measurement results obtained in Step 2 under the motor's operating condition. As shown in the following formula:

[0021]

[0022]

[0023]

[0024] In the above formula, The dynamic measurement impedance is calculated based on the measurement results under motor operating conditions. The impedance is a stray parameter inside the motor. Parasitic impedance of the voltage-loaded circuit;

[0025] Step 5, based on the bearing impedance obtained in Step 4 Determine the bearing oil film capacitance C b and resistance R b As shown in the following formula:

[0026]

[0027]

[0028] In the above formula, bearing impedance The magnitude is the impedance value; θ is... The phase angle is the impedance angle.

[0029] Based on the above scheme, step 2 specifically includes:

[0030] Step 2-1: Connect the signal generator and the power amplifier, adjust the frequency of the target sinusoidal voltage output by the signal generator, and adjust the amplitude of the target sinusoidal voltage output by the power discharger; connect the positive terminal of the power amplifier to the motor's current-conducting carbon brush, and the negative terminal to the grounding point of the electrode housing, so as to introduce high-frequency voltage excitation into the rotating shaft.

[0031] Step 2-2: With the motor stationary, use the differential voltage probe CH2 to measure the voltage between the current-carrying carbon brush and the motor housing, i.e., the static voltage U of the shaft to ground. m-s Simultaneously, a high-frequency current probe CH1 is used to measure the current on the power amplifier return line, i.e., the quiescent current I in the test circuit. m-s ;

[0032] Steps 2-3: With the motor running, use the differential voltage probe CH2 to measure the voltage between the current-carrying carbon brush and the motor housing, i.e., the dynamic voltage U of the shaft to ground. m-d Simultaneously, a high-frequency current probe CH1 is used to measure the current on the power amplifier return line, i.e., the dynamic current I in the test circuit. m-d ;

[0033] Based on the above plan,

[0034] In step 2-2, the power amplifier output frequency range is 1kHz-10kHz;

[0035] In steps 2-3, the power amplifier output frequency is greater than 1MHz.

[0036] The online measurement method for oil film impedance of motor bearings described in this invention has the following advantages:

[0037] (1) The present invention can realize online testing of bearing oil film impedance for motors with single bearing structure, which can better monitor the performance status of bearings during motor operation and judge the health status of bearings.

[0038] (2) The present invention adopts the technical route of online testing, which can be tested during the operation of high-power motors without the need to build a special bearing test bench.

[0039] This invention tests the bearing oil film impedance based on the volt-ampere method. The test equipment used includes a signal generator, a power amplifier (optional), an oscilloscope, and voltage and current probes. These are commonly used equipment in electrical engineering, and high-precision testing of bearing oil film impedance can be achieved without the need for a dedicated capacitance tester.

[0040] (3) The present invention does not require special tooling modifications to the motor to meet the test conditions of shaft current. Voltage loading and online testing can be completed using only the inherent carbon brush grounding device of the motor. Attached Figure Description

[0041] The present invention includes the following figures:

[0042] Figure 1 Flowchart of the method described in this invention;

[0043] Figure 2 Equivalent circuit diagram of motor stray capacitance described in this invention;

[0044] Figure 3 A schematic diagram of port capacitance measurement according to the present invention;

[0045] Figure 4 Schematic diagram of the external high-frequency sinusoidal voltage test described in this invention;

[0046] Figure 5 Equivalent circuit diagram for bearing impedance testing as described in this invention;

[0047] Figure 6 Simplified schematic diagram of the equivalent circuit for bearing impedance testing according to the present invention;

[0048] Figure 7 The equivalent circuit diagram of the bearing oil film described in this invention;

[0049] Figure 8 The measurement waveform of the motor in a stationary state as described in the embodiments of the present invention;

[0050] Figure 9 The measurement waveform of the motor under operating conditions as described in the embodiments of the present invention; Detailed Implementation

[0051] The present invention will be further described in detail below with reference to the accompanying drawings.

[0052] 1. Motor stray capacitance parameter test

[0053] This application employs an online measurement technique and does not require additional tooling modifications to the tested motor and bearings, making it impossible to directly measure the current flowing through the bearings within the motor. Therefore, the online measurement data only provides the overall impedance of the motor and bearings, necessitating a solution to the separation of motor impedance from bearing impedance. Before conducting online testing, stray capacitance parameters of the motor in a stationary state are first measured.

[0054] Equivalent circuit of stray capacitance inside the motor, such as Figure 2 As shown: the capacitance of the stator winding to the casing is C. wf The stator winding capacitance to the rotor is C. wr The rotor capacitance to the housing is C. rf The insulation capacitance of the bearing end cap is C. iso The stray capacitance of the motor is tested under static conditions, and there is no bearing capacitance, so only the capacitance of the insulating end cap is considered.

[0055] To separate the stray capacitance of the motor from the bearing impedance parameters, it is first necessary to test and calculate the stray capacitance parameters inside the motor. Using an LCR meter or impedance analyzer at a low frequency (1kHz), the motor port capacitance is tested, such as... Figure 3 As shown:

[0056] Measure the capacitance between each pair of terminals of the motor (this must be done with the motor fitted with insulating end covers or insulating flanges to ensure the casing and rotor are not conductive): Short-circuit the three-phase stator windings and measure the capacitance C1 between the stator winding short-circuit point and the casing; measure the capacitance C2 between the stator winding short-circuit point and the rotor; measure the capacitance C3 between the rotor and the stator casing; measure the capacitance C of the insulating end cover. iso The relationship between the port capacitance and the motor stray capacitance is shown in the following formula:

[0057]

[0058]

[0059]

[0060] Among them, C′ rf =C rf +C iso .

[0061] Combining equations (1)-(3) above, the stray capacitance parameters of the motor can be obtained, as shown in the following equation:

[0062]

[0063]

[0064]

[0065] 2. External high-frequency sinusoidal voltage test

[0066] Bearing impedance testing involves applying a high-frequency sinusoidal voltage between the motor rotor and housing using a signal generator and power amplifier, driven by a frequency converter and based on the voltmeter-ammeter method. A differential voltage probe and a high-precision current probe are used to collect the shaft-to-ground voltage and the current in the circuit. The bearing impedance is calculated based on the amplitude and phase relationship of the collected voltage and current waveforms. The high-frequency voltage excitation method and the measurement points for voltage and current are crucial factors. Figure 4 As shown:

[0067] In the voltage loading section, adjust the frequency of the target sinusoidal voltage output by the signal generator and adjust the amplitude of the target sinusoidal voltage output by the power discharger. Remove the two grounding carbon brush leads fixed to the motor frame and use them as rotor leads. Grounding carbon brush 1 serves as a current-conducting carbon brush, and grounding carbon brush 2 serves as a test carbon brush. Connect the positive clamp of the power amplifier to the extension line of the current-conducting carbon brush, and connect the negative clamp to the grounding point of the motor housing. The current-conducting carbon brush slides in contact with the rotor, introducing high-frequency voltage excitation into the shaft, flowing through the bearings and motor housing to form a closed loop.

[0068] In the testing section, a differential voltage probe CH2 was used to measure the voltage between the carbon brush extension cable and the motor housing, and a high-frequency current probe CH1 was used to measure the current on the power amplifier return line. Then, the following steps were performed for testing:

[0069] (1) Static Testing

[0070] With the motor stationary, adjust the output frequency of the power amplifier to a sinusoidal voltage of 1kHz to 10kHz, adjust the frequency and amplitude of the applied excitation until a voltage and current waveform with good sinusoidal characteristics is observed, and collect and record the data.

[0071] (2) Online testing

[0072] When the inverter drives the motor, the common-mode voltage output by the inverter will induce a shaft voltage with a frequency equal to the switching frequency on the shaft. Therefore, by setting the output voltage frequency of the signal generator to be much higher than the switching frequency of the inverter, the voltage and current signals generated at that frequency can be separated. The frequency of the output voltage is adjusted using the signal generator, and the signal generator output is connected to a power amplifier. The amplitude of the output voltage is adjusted using the power amplifier, and a sinusoidal voltage with a frequency of 1MHz or higher is applied between the motor shaft and the casing. Under different operating conditions, the frequency and amplitude of the applied excitation are adjusted until a voltage and current waveform with good sinusoidal characteristics is observed and recorded.

[0073] 3. Sensor data processing and error elimination

[0074] The sensor measurement data undergoes signal denoising processing. Since voltage loading and voltage testing are performed on the current-carrying carbon brush and the test carbon brush, respectively, the errors caused by carbon brush impedance, carbon brush extension wire impedance, and power amplifier internal resistance can be ignored. It is only necessary to eliminate the errors caused by the parasitic inductance and parasitic resistance inside the motor in the test circuit.

[0075] Calculate the loop impedance Z based on the test results under static conditions. l The circuit impedance originates from the parasitic resistance and inductance between the rotor core, bearings, shaft barrel, casing, and grounding point. Since the stray capacitance inside the motor is on the order of nF, and the equivalent impedance is MΩ, which is much larger than the circuit impedance, the motor impedance at this frequency can be considered negligible. The circuit impedance exhibits resistive-inductive characteristics, with the voltage slightly leading the current by a certain angle. According to the following formulas (7)-(9), the parasitic resistance and inductance in the test circuit can be calculated.

[0076]

[0077]

[0078]

[0079] In the above formula, These are the voltage and current phasors measured and acquired under static conditions. and To obtain the measurement and The phase angle; The measured impedance is calculated from the voltage and current phasors under static conditions; Z m-s for The model; R ac L is the parasitic resistance in the circuit. ac f is the parasitic inductance in the circuit; c The frequency of the applied voltage.

[0080] Based on the parasitic resistance and parasitic inductance in the circuit, the parasitic impedance of the circuit under different applied voltage frequencies can be calculated. As shown in the following formula:

[0081]

[0082] 4. Separate motor impedance and bearing impedance

[0083] By further processing and analyzing the data measured online by the sensors, the components of motor impedance and bearing impedance are separated.

[0084] The equivalent circuit of the test loop, such as Figure 5 As shown in the figure. V comC is the common-mode voltage at the motor input terminal. wf For the stator winding capacitance to the chassis, C wr C is the stator winding capacitance to the rotor. rf For rotor-to-casing capacitance, L ac R ac Z represents the parasitic resistance and parasitic inductance in the circuit; b L is the equivalent impedance of the bearing; g R g For carbon brush resistors and inductors; V sine For the power amplifier power supply, R in This is the internal resistance of the power amplifier.

[0085] Because the test carbon brush is used for loading and measurement, the carbon brush impedance and power amplifier internal resistance will not affect the measurement results. Since the online test voltage loading frequency is above MHz, the common-mode interference source of the inverter can be ignored. Based on the motor stray capacitance test and static applied voltage test, the internal stray capacitance and parasitic resistance R of the motor in the circuit are... ac and parasitic inductance L ac Given quantities. Figure 5 After simplification, we get Figure 6 The equivalent circuit is shown. Based on the voltage across the housing at the end of the CH2 shaft barrel and the current in the CH1 loop, the bearing impedance Z can be calculated. b .

[0086] bearing impedance The calculation is shown in the following formula:

[0087]

[0088]

[0089]

[0090] In equations (11)-(13) above, if the motor bearing does not have an insulating end cap or insulating flange:

[0091]

[0092] If the motor bearings are equipped with insulating end caps or insulating flanges:

[0093]

[0094] In equations (11)-(13) above, For bearing impedance; The measured impedance is calculated based on the voltage and current measured during motor operation. The impedance is the stray parameter inside the motor.

[0095] 5. Determine parameters such as bearing oil film capacitance and resistance.

[0096] Based on the separated bearing impedance data, parameters such as bearing oil film capacitance and resistance can be determined through calculation or model matching. These parameters reflect the characteristics of the bearing lubrication condition and provide key indicators for evaluating the bearing's lubrication status.

[0097] Lubrication conditions are classified into three main types: boundary lubrication, mixed lubrication, and fluid lubrication. When bearing characteristics are low, the bearing is in boundary lubrication, with an oil film thickness approximately the size of molecules. At this stage, lubrication is almost entirely direct metal-to-metal contact, and the bearing exhibits resistivity with very low resistance. In mixed lubrication, the moving surfaces are separated, but some metal-to-metal contact remains. Fluid lubrication means that the two friction surfaces are completely separated by grease, and the bearing rolling elements and inner and outer rings form an electrically insulating state, resulting in capacitive bearing impedance. This capacitance can be considered as the total capacitance of multiple parallel rolling elements and the individual capacitors formed by the bearing's inner and outer rings. The extracted bearing capacitance and resistance are macroscopically equivalent results for all rolling elements, such as... Figure 7 As shown.

[0098] Based on the obtained bearing impedance The magnitude is the impedance value. The phase angle is the impedance angle θ. The equivalent capacitance C of the bearing oil film can be determined based on the bearing oil film impedance. b and equivalent resistance R b The value is calculated using the following formula:

[0099]

[0100]

[0101] 6. Assess the bearing oil film lubrication condition.

[0102] Based on the determined bearing oil film capacitance and resistance parameters, combined with preset thresholds or standards, the bearing lubrication status is evaluated in real time. Based on the evaluation results, the bearing's operating condition is determined, and fault diagnosis and maintenance recommendations are provided.

[0103] 7. Output test results

[0104] The bearing lubrication status information is output to the user interface, control system, or other devices for further processing, recording, and analysis.

[0105] Through the above method, the present invention can realize online measurement of bearing oil film impedance of single bearing structure motor and accurately evaluate the lubrication status and operating condition of the bearing, providing an important technical means for fault early warning, maintenance optimization and reliability improvement of single bearing structure motor.

[0106] Example:

[0107] This embodiment uses a megawatt-class permanent magnet synchronous wind turbine as an example to illustrate the process of extracting bearing oil film parameters:

[0108] (1) Motor stray capacitance parameter test

[0109] First, use an LCR impedance meter to measure the port capacitances between the motor windings and the housing, the windings and the shaft, and the shaft and housing. The results are shown in Table 1. (Note: The motor must use an insulated end cap or insulated flange structure to ensure that the motor rotor and housing are not short-circuited.)

[0110] Table 1 Test results of motor port capacitance

[0111] symbol Physical meaning Value / nF <![CDATA[C1]]> Capacitance between stator winding short-circuit point and chassis 198.23 <![CDATA[C2]]> Capacitance between stator winding short-circuit point and rotor 7.02 <![CDATA[C3]]> Capacitance between rotor and stator housing 7.40

[0112] According to equations (5), (6), and (7), the calculation results of the stray capacitance inside the motor are shown in Table 2.

[0113] Table 2 Calculation results of stray capacitance inside the motor

[0114] symbol Physical meaning Value / nF <![CDATA[C wf ]]> Stator winding to housing capacitor 196.94 <![CDATA[C wr ]]> Stator winding to rotor capacitance 0.35 <![CDATA[C′ rf ]]> Rotor to housing capacitance 6.86

[0115] (2) Test of applied high-frequency sinusoidal voltage

[0116] First, with the motor stationary, adjust the signal generator to output a sinusoidal voltage at a frequency of 10kHz, and collect and record the voltage and current waveforms, such as... Figure 8 As shown.

[0117] In the static state, the voltage amplitude is 0.65V, the current amplitude is 0.385A, and the phase difference is 39.5°.

[0118] Secondly, while the motor is running, adjust the output frequency of the signal generator to a 1MHz sinusoidal voltage, and collect and record the voltage and current waveforms, such as... Figure 9 As shown.

[0119] In the rotating state, the voltage amplitude is 1.5V, the current amplitude is 38A, and the phase difference is -84.6°.

[0120] (3) Sensor data processing and error elimination

[0121] Based on the measurement data under static conditions, the parasitic resistance and parasitic inductance in the test circuit can be obtained using formulas (8)-(11), as shown in Table 3.

[0122] Table 3 Calculation results of loop impedance parameters

[0123] variable <![CDATA[R ac ]]> <![CDATA[L ac ]]> numerical values 1.3 / Ω 17.1 / μH

[0124] (4) Separate motor impedance and bearing impedance

[0125] Based on the measurement data under variable frequency drive conditions, the following can be calculated: and

[0126]

[0127]

[0128]

[0129] The bearing impedance was calculated.

[0130]

[0131] (5) Determine the bearing oil film capacitance and resistance parameters

[0132] Calculate the equivalent capacitance and resistance parameters of the bearing oil film based on the bearing oil film impedance parameters.

[0133]

[0134]

[0135] The calculation results of the bearing oil film capacitance and resistance parameters are shown in Table 4.

[0136] Table 4. Test results of bearing oil film parameters

[0137] variable <![CDATA[C b ]]> <![CDATA[R b ]]> numerical values 1.09 / nF 235.29 / Ω

[0138] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0139] References:

[0140] [1] Liu Zhiquan, Ge Peiqi, Zhang Pengshun. Test of oil film thickness and motion parameters of rolling bearings [J]. Bearings, 1996(08): 41-45.

[0141] [2] Zhong He, Zhou Yuxin, Liu Jinjie, et al. Oil film measurement method based on the combination of capacitance method and optical interferometry [J]. Lubrication and Sealing, 2023, 48(02): 135-141.

[0142] [3]Tischmacher H, Gattermann S.Bearing currents in converter operation[C] / / Proceedings of the XIX Intemational Conference on Electrical Machines(ICEM).Rome, Italy: IEEE, 2010: 1-8.

[0143] [4]Wittek E, Kriese M, Tischmacher H, et al.Capacitances and lubricantfilm thicknesses of motor bearings under different operating conditions[C] / / Proceedings of the XIX International Conference on Electrical Machines(ICEM).Rome, Italy: IEEE, 2010: 1-6.

[0144] [5] Guo Lanlan, Zhang Lei, Xue Xiuhui, Xie Aizheng, Wang Jin, Jiang Chen, Wu Wu. A method for detecting bearing oil film capacitance [P]. Shanxi Province: CN115980456A, 2023-04-18.

[0145] [6] Li Wei, Wang Yongqiang, Ma Hao, Li Jiwei, Shi Yongjin. Apparatus and method for testing electrical performance parameters of lubricating oil film in rolling bearings [P]. Shanxi Province: CN115980138A, 2023-04-18.

[0146] [7]Romanenko A, Ahola J, Muetze A, et al.Study of incipient bearingdamage monitoring in variable-speed drive systems[C] / / Proceedings of the 16thEuropean Conference on Power Electronics and Applications(EPE′14-ECCEEurope).Lappeenranta, Finland: IEEE, 2014: 1-10.

[0147] [8]Niskanen V,Muetze A,Ahola J.Study on bearing impedance propertiesat several hundred kilohertz for different electric machine operatingparameters[J].IEEE Transactions on Industry Applications,2014,50(5):3438-3447.

Claims

1. A method for online measurement of oil film impedance in motor bearings, characterized in that, Includes the following steps: Step 1: Insulate the motor housing and rotor using insulated bearings or insulated end caps. Use an RLC meter or impedance analyzer to measure the capacitance C1 between the stator winding short-circuit point and the housing; the capacitance C2 between the stator winding short-circuit point and the rotor; and the capacitance C3 between the rotor and the stator housing. Obtain the stray capacitance parameters of the motor using the following formula: In the above formula: C wf For the stator winding capacitance to the chassis, C wr C is the stator winding capacitance to the rotor. rf For rotor-to-casing capacitance, C iso For capacitors with insulated end caps; Step 2: Apply a high-frequency sinusoidal voltage between the motor rotor and the casing; measure the static voltage U of the motor shaft to ground when the motor is stationary. m-s and the static current I in the circuit m-s And obtain the corresponding phasors and Measure the dynamic voltage U of the motor shaft to ground while the motor is running. m-d and the dynamic current I in the circuit m-d And obtain the corresponding phasors and Step 3, based on the motor's stationary state obtained in Step 2 and Calculate the parasitic resistance R of the circuit ac and parasitic inductance L ac As shown in the following formula: In the above formula, These are the voltage and current phasors measured and acquired under static conditions. For static conditions The calculated measured impedance, Z m-s for The model; and They are respectively and phase angle; f c The frequency of the applied voltage; Step 4: Calculate the bearing impedance based on the measurement results obtained in Step 2 under the motor's operating condition. As shown in the following formula: In the above formula, The dynamic measurement impedance is calculated based on the measurement results under motor operating conditions. The impedance is a stray parameter inside the motor. The strange impedance of the voltage-loaded circuit; Step 5, based on the bearing impedance obtained in Step 4 Determine the bearing oil film capacitance C b and resistance R b As shown in the following formula: In the above formula, |Z b | for bearing impedance The magnitude is the impedance value; θ is... The phase angle is the impedance angle.

2. The method for online measurement of oil film impedance of motor bearings as described in claim 1, characterized in that: Step 2 specifically involves: Step 2-1: Connect the signal generator and the power amplifier, adjust the frequency of the target sinusoidal voltage output by the signal generator, and adjust the amplitude of the target sinusoidal voltage output by the power discharger; connect the positive terminal of the power amplifier to the motor's current-conducting carbon brush, and the negative terminal to the grounding point of the electrode housing, so as to introduce high-frequency voltage excitation between the shaft and the housing. Step 2-2: With the motor stationary, use the differential voltage probe CH2 to measure the voltage between the current-carrying carbon brush and the motor housing, i.e., the static voltage U of the shaft to ground. m-s Simultaneously, a high-frequency current probe CH1 is used to measure the current on the power amplifier return line, i.e., the quiescent current I in the test circuit. m-s ; Steps 2-3: With the motor running, use the differential voltage probe CH2 to measure the voltage between the current-carrying carbon brush and the motor housing, i.e., the dynamic voltage U of the shaft to ground. m-d Simultaneously, a high-frequency current probe CH1 is used to measure the current on the power amplifier return line, i.e., the dynamic current I in the test circuit. m-d .

3. The method for online measurement of oil film impedance of motor bearings as described in claim 2, characterized in that: In step 2-2, the power amplifier output frequency range is 1kHz-10kHz; In steps 2-3, the power amplifier output frequency is greater than 1MHz.

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