Method for testing and analyzing shaft voltage in bearing electrocorrosion

Abstract

The invention provides a device for testing the shaft voltage in bearing electrocorrosion, which comprises a rotating shaft, a pair of bearings is mounted on the rotating shaft, one end of the rotating shaft is connected with a servo motor through a magnetic coupling, the servo motor is connected with a frequency converter, the rotating shaft is connected with a function signal generator, and the function signal generator is connected with a signal generator. The voltage measuring point of the bearing is connected with an oscilloscope, an adjustable resistor is connected in series between the voltage measuring point of the outer diameter of the bearing and the oscilloscope, and the oscilloscope is in communication connection with an upper computer through a data switch; based on the device, on the second aspect, the invention provides a method for testing and analyzing the shaft voltage in bearing electro-corrosion, a corresponding recognition algorithm is designed according to the data collected by the oscilloscope and a bearing capacitor discharge event, and then the bearing electro-corrosion is identified through the applied common-mode voltage and the measured shaft voltage. And bearing capacitance, breakdown voltage, discharge energy and discharge times are calculated, so that data support is provided for subsequent motor bearing fault prediction and life evaluation.

Description

Technical Field

[0001] The present invention belongs to the technical field of motor bearing testing, and particularly relates to a method for testing and analyzing shaft voltage in bearing electro-corrosion. Background Art

[0002] Bearings are widely used in modern mechanical industry and are essential mechanical parts in motors. The electrical performance of bearings directly affects the severity of the motor shaft voltage problem. Bearings mainly play the roles of support and transmission, maintaining a certain air gap between the stator and rotor cores of the motor while effectively transmitting loads. A bearing consists of an inner raceway, an outer raceway, balls, a cage, and lubricating grease. In recent years, due to the widespread popularity of electric vehicles, the problem of bearing electro-corrosion in motors has become increasingly acute. The shaft voltage in bearing electro-corrosion is a key parameter. Different shaft voltages affect the oil film thickness and the number of oil film breakdowns between the inner and outer raceways of the bearing. The oil film thickness and the number of oil film breakdowns are respectively related to the equivalent capacitance and equivalent resistance of the bearing. At present, the measurement method and data processing of the shaft voltage in the bearing electrical parameters are not precise enough, and there is a lack of effective means to obtain the number of discharges and discharge power during the electro-erosion process of the motor bearing. Summary of the Invention

[0003] Object of the Invention: The object of the present invention is to provide a method for testing and analyzing shaft voltage in bearing electro-corrosion, aiming to realize the detection and acquisition of discharge voltage, discharge times, and discharge power during the electro-erosion process of the motor bearing, and further provide data support for the subsequent prediction of motor bearing faults and the assessment of service life.

[0004] Technical Solution: To achieve the above object, in the first aspect of the present invention, a test device for shaft voltage in bearing electro-corrosion is proposed, including a rotating shaft, on which a pair of bearings are installed. The pair of bearings are fixed on a test bench through bearing seats. One end of the rotating shaft is connected to a servo motor through a magnetic coupling, the servo motor is connected to a frequency converter, the other end of the rotating shaft is connected to a function signal generator through a brush. Voltage measurement points are provided on the inner diameter and outer diameter of the bearing, and an oscilloscope is connected to the voltage measurement points. An adjustable resistor is connected in series between the voltage measurement point on the outer diameter of the bearing and the oscilloscope. The oscilloscope is communicatively connected to a host computer through a data switch.

[0005] Preferably, the test bench is a rubber-insulated tabletop, and a pair of bearing seats are fixedly installed on the rubber-insulated tabletop.

[0006] Preferably, the adjustable resistor is a precision adjustable resistor, and the precision adjustable resistor is immersed in an insulating coolant.

[0007] Based on the above test device, in the second aspect of the present invention, a method for testing and analyzing shaft voltage in bearing electro-corrosion is proposed, including the following steps:

[0008] Step 1: ， Spray uniform lubricating grease between the inner balls of the bearing and the inner and outer raceways of the bearing, apply a common-mode voltage to the rotating shaft through a function signal generator, and at the same time drive the rotating shaft to rotate through a servo motor;

[0009] Step 2: Obtain the shaft voltage signal on the bearing through an oscilloscope and upload it to the host computer through a data switch;

[0010] Step 3: The host computer obtains the bearing electrical erosion parameters according to the applied common-mode voltage and the measured shaft voltage. The electrical erosion parameters include the bearing equivalent capacitance, discharge energy, discharge times, and average discharge power; and form a data set with the analysis results;

[0011] Step 4: Change the speed of the servo motor through a frequency converter, and change the amplitude and frequency of the common-mode voltage through a function signal generator, and repeat Steps 1-3.

[0012] Step 5: Analyze the influence of the common-mode voltage and speed on the bearing electrical erosion according to the electrical erosion parameter data in the database.

[0013] Preferably, in Step 1, the amplitude of the common-mode voltage is 50V-100V, and the frequency is a square wave of 2kHz, 4kHz, 6kHz, 8kHz, 10kHz.

[0014] Preferably, in Step 3, sample the bearing electrical erosion parameters once per hour, and use the sampling result of this time as the average value within the hour.

[0015] Preferably, in Step 3, the process of obtaining the bearing equivalent capacitance includes equivalent the bearing and the adjustable resistor as an RC circuit, and the voltage across the bearing equivalent capacitance satisfies the following equation:

[0016]

[0017] where u m (t) is the capacitance voltage, U s is the power supply voltage, τ is the RC circuit time constant, τ = RC;

[0018] According to the bearing voltage waveform data sequence [u m (T-3Δt), u m (T-2Δt), u m (T-Δt), u m (T)], u m (T) = V bd , substitute into calculate the time constant τ, and then determine the bearing capacitance C at the time of this discharge, V bdIt represents the magnitude of the bearing voltage and reflects the voltage change generated inside the bearing due to the electro-corrosion phenomenon.

[0019] Preferably, in step 3, the process of obtaining the number of discharges includes: when the bearing is in a capacitive state, the function signal generator charges the capacitor through a variable resistor. When the upper computer detects that the peak voltage of the bearing is higher than the set threshold voltage, it is considered that a discharge event has occurred in the bearing.

[0020] Preferably, in step 3, the process of obtaining the discharge energy includes: evaluating the discharge energy with the discharge power, and the calculation formula is as follows:

[0021]

[0022] In the formula, C is the bearing capacitance, and U is the voltage at the time of oil film breakdown.

[0023] Preferably, in step 3, the expression of the average discharge power is:

[0024]

[0025] In the formula, R c is the charging resistance, T is the time for the capacitor to charge and discharge once, τ is the discharge time constant of the circuit, and U m,i is the capacitor voltage.

[0026] Beneficial effects:

[0027] Compared with the prior art, the present invention can achieve the following technical effects:

[0028] The present invention applies different excitation signals to the bearing through a function generator to simulate a more accurate actual common-mode voltage. At the same time, there is only one capacitor in the entire loop of the shaft voltage in the present invention, that is, the capacitor with the raceway and rolling elements as the metal plates and the oil film as the insulating medium, avoiding the influence of other stray capacitors, and can better study the discharge situation of the capacitor at both ends of the bearing and provide more effective data support for studying the electro-corrosion of the bearing. Brief description of the drawings

[0029] Figure 1 It is a schematic diagram for measuring the electrical parameters of the bearing.

[0030] Figure 2 It is the circuit diagram for shaft voltage loading.

[0031] Figure 3 It is the comparison diagram of the number of discharges of the left bearing at 35°C under different voltages.

[0032] Figure 4 It is the comparison diagram of the number of discharges of the right bearing at 35°C under different voltages.

[0033] Figure 5Average discharge power comparison chart of the left bearing at 35°C under different voltages

[0034] Figure 6 It is the average discharge power comparison chart of the right bearing at 35°C under different voltages.

[0035] Wherein: 1. Rotating shaft; 2. Bearing seat; 3. Bearing; 4. Servo motor; 5. Frequency converter; 6. Oscilloscope; 7. Data switch; 8. Host computer; 9. Adjustable resistor; 10. Cooling liquid; 11. Function generator; 12. Magnetic coupling; 13. Test bench. Specific implementation mode

[0036] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0037] The present invention first proposes a test device for shaft voltage in bearing electro-corrosion, as Figure 1 shown, including a rotating shaft 1, on which a pair of bearings 3 are installed. The pair of bearings 3 are fixed on a test bench 13 through a bearing seat 2. One end of the rotating shaft 1 is connected to a servo motor 4 through a magnetic coupling 12. The servo motor 4 is connected to a frequency converter 5. The other end of the rotating shaft 1 is connected to a function signal generator 11 through a brush. Voltage measurement points are provided on the inner and outer diameters of the bearing 3, and an oscilloscope 6 is connected to the voltage measurement points. An adjustable resistor 9 is connected in series between the voltage measurement point on the outer diameter of the bearing 3 and the oscilloscope 6. The oscilloscope 6 is communicatively connected to a host computer 8 through a data switch 7.

[0038] The measurement circuit is connected to the inner ring of the bearing 3 through a brush installed at the end of the rotating shaft 1, that is, connected to the rotating shaft. The two bearings 3 are connected in series through the rotating shaft 1, and at the same time, power is supplied to the two bearings 3 (simulating common-mode voltage) and shaft voltage measurement points are provided.

[0039] A servo motor 14 and a rotating shaft 1 are connected through a magnetic coupling 12 to drive the rotation of the bearing 3. At the same time, a frequency converter 5 is used to control the speed, acceleration and running time of the rotating shaft, facilitating the extraction and analysis of bearing capacitance parameters under different test conditions.

[0040] The rotating shaft 1 and the bearing 3 are fixed through corresponding bearing seats 2. At the same time, the entire test table uses a rubber tabletop, which is convenient for insulating the voltage and current on the bearing seat 2, making the measured data more accurate.

[0041] Based on the above test device, the present invention proposes a method for testing and analyzing shaft voltage in bearing electro-corrosion, including the following steps:

[0042] Step 1: Spray uniform lubricating grease between the inner balls of the bearing 3 and the inner and outer raceways of the bearing. Apply a common-mode voltage to the rotating shaft 1 through the function signal generator 11, and at the same time drive the rotating shaft 1 to rotate through the servo motor 4;

[0043] The shaft voltage measurement refers to the voltage between the inner raceway of the bearing and the base. The measurement method is as follows: Use a brush at the end of the rotating shaft, and lead out two wires from both ends of the brush. The two wires at one end of the brush are fixed to the inner raceway of the bearing at the same time, and the two wires at the other end of the brush are respectively connected to the function signal generator and the oscilloscope. The wire connected to the signal generator applies a square wave with an amplitude V g of 50 - 100V and frequencies of 2kHz, 4kHz, 6kHz, 8kHz, 10kHz to simulate the shaft voltage; while the wire connected to the oscilloscope is a measurement wire for the shaft voltage. At the same time, a suitable precision adjustable resistor R 1 (R 2 ) needs to be connected in series between the function generator and the bearing. The function of this resistor is to limit the current when the bearing is in a resistive state; and to charge the bearing capacitor C tot when the bearing is in a capacitive state. The series-connected precision adjustable resistor needs to be completely immersed in the coolant to play a role in cooling and heat dissipation.

[0044] The bases are completely isolated from each other. Uniform lubricating grease needs to be completely sprayed between the inner balls of the bearing and the inner and outer raceways of the bearing, which plays an insulating and lubricating role before the lubricating oil film is discharged and broken down.

[0045] Step 2: Obtain the shaft voltage signal on the bearing 3 through the oscilloscope 6, and upload it to the upper computer 8 through the data switch 7;

[0046] Step 3: The upper computer 8 obtains the bearing electrical erosion parameters according to the applied common-mode voltage and the measured shaft voltage. The electrical erosion parameters include the bearing equivalent capacitance, discharge energy, discharge times, and average discharge power; and form a data set with the analysis results;

[0047] Based on the data collected by the oscilloscope, design a corresponding recognition algorithm according to the bearing capacitance discharge event, and then calculate the bearing capacitance, breakdown voltage, discharge energy, and discharge times through the applied common-mode voltage and the measured shaft voltage. The method is as follows:

[0048] Bearing capacitance calculation: When the bearing oil film is established, a capacitor is formed with the raceway and rolling elements as metal plates and the oil film as the insulating medium. The measuring device charges the bearing capacitance through the resistor R c When the voltage across the capacitor exceeds the oil film voltage breakdown threshold, the energy stored in the bearing capacitance discharges to the raceway and rolling elements to form an electro-discharge machining current (EDM Current), asFigure 2 as shown

[0049] The magnitude of the released energy depends on the breakdown voltage and the bearing capacitance of this discharge. It can be considered that the energy stored in the bearing capacitance is completely released to form electrical damage on the raceway and rolling elements. The magnitude of the bearing capacitance can be calculated from the data during the charging phase in the bearing voltage waveform. During the charging phase, the voltage source U s charges the RC series circuit, and the voltage across the capacitor satisfies the following equation.

[0050]

[0051] where u m (t) is the capacitor voltage, U s is the power supply voltage, τ is the RC circuit time constant, τ = RC. According to the bearing voltage waveform data sequence [u m (T - 3Δt), u m (T - 2Δt), u m (T - Δt), u m (T)], u m (T) = V bd , substituting into the above equation can calculate the time constant τ and then determine the bearing capacitance C during this discharge. V bd represents the magnitude of the bearing voltage and reflects the voltage change inside the bearing due to the electro-corrosion phenomenon.

[0052] Calculation of the number of discharges: Since the bearing discharge event is a random event, the number of discharges in a period of time is calculated. An oscilloscope recorder with a large capacity and high sampling rate is used to collect the bearing voltage. The shaft voltage time series is transmitted to the host computer through Ethernet and analyzed by the host computer software. According to different working conditions, a voltage threshold is set. When the shaft voltage is higher than the voltage threshold, it is determined as a discharge event. The short-term occurrence frequency of the discharge event is averaged. When the bearing is in the capacitive state, the power supply charges the capacitor through the load resistor R L and the algorithm detects the magnitude of the bearing peak voltage. When the peak voltage is higher than the threshold voltage, it is considered that a discharge event has occurred in the bearing.

[0053] Discharge energy: The bearing capacitance of each discharge event can be identified from the bearing voltage sequence, and the energy released by the discharge is evaluated by the discharge power. The calculation formula is as follows:

[0054]

[0055] where C is the bearing capacitance and U is the voltage at the oil film breakdown.

[0056] The calculation expression of the average discharge power is as follows:

[0057]

[0058] In the formula, R c is the charging resistance, T is the time for one charge and discharge cycle of the capacitor, τ is the discharge time constant of the circuit, and U m,i is the capacitor voltage.

[0059] During the test, the bearing continuously bears electric erosion. The recording frequency is once per hour sampling, and the statistical result of this time is used as the average value within the hour.

[0060] Statistically calculate relevant parameters such as the effective discharge times, total discharge energy, and average discharge power in the dataset.

[0061] Step 4: Change the speed of the servo motor 4 through the frequency converter 5, and change the amplitude and frequency of the common-mode voltage through the function signal generator 11, and repeat steps 1 - 3.

[0062] Step 5: Analyze the influence of the common-mode voltage and speed on the bearing electric erosion according to the electric erosion parameter data in the database.

[0063] As Figures 3 - 6 shown, the analysis of the test results at 35°C shows that as the voltage increases, the discharge times and discharge power increase significantly. This is because when the voltage increases, the electric field strength also increases. The stronger the electric field strength, the stronger the interaction force between charges, and the easier it is to destroy the molecular structure of the dielectric, resulting in the occurrence of discharges.

[0064] Although the specific implementation manners of the present invention have been described above, those skilled in the art should understand that these are only examples, and various changes or modifications can be made to these implementation manners without departing from the principle and essence of the present invention. The scope of the present invention is only defined by the appended claims.

Claims

1. A test device for shaft voltage in bearing electrical corrosion, characterized in that: The invention comprises a rotating shaft (1), a pair of bearings (3) are mounted on the rotating shaft (1), the pair of bearings (3) are fixed on a test bench (13) through a bearing seat (2), one end of the rotating shaft (1) is connected to a servo motor (4) through a magnetic coupling (12), the servo motor (4) is connected to a frequency converter (5), the other end of the rotating shaft (1) is connected to a function signal generator (11) through a brush, voltage measurement points are provided on the inner diameter and outer diameter of the bearing (3), an oscilloscope (6) is connected to the voltage measurement points, an adjustable resistor (9) is connected in series between the voltage measurement point on the outer diameter of the bearing (3) and the oscilloscope (6), and the oscilloscope (6) is connected to a host computer (8) through a data switch (7).

2. A testing device for shaft voltage in bearing electrical corrosion according to claim 1, characterized in that: The test bench (13) is a rubber insulating tabletop, and a pair of bearing seats (2) are fixedly mounted on the rubber insulating tabletop.

3. A testing device for shaft voltage in bearing electrical corrosion according to claim 1, characterized in that: The adjustable resistor (9) is a precision adjustable resistor, and the precision adjustable resistor is immersed in the insulating coolant (10).

4. A method for testing and analyzing the shaft voltage in the electrical corrosion of a bearing using the device as claimed in claim 1, characterized in that: The following steps are involved: Step 1: Spray lubricating grease evenly between the inner ball of the bearing (3) and the inner raceway and the outer raceway of the bearing, apply a common mode voltage to the rotating shaft (1) through a function signal generator (11), and drive the rotating shaft (1) to rotate through a servo motor (4); Step 2: Obtain the shaft voltage signal on the bearing (3) through an oscilloscope (6), and upload it to a host computer (8) through a data switch (7); Step 3: The host computer (8) obtains the bearing electrocorrosion parameters according to the applied common mode voltage and the measured shaft voltage, wherein the electrocorrosion parameters include the bearing equivalent capacitance, discharge energy, discharge times, and average discharge power; and forms the analysis results into a data set; Step 4: Change the speed of the servo motor (4) through the frequency converter (5), change the amplitude and frequency of the common mode voltage through the function signal generator (11), and repeat steps 1-3; Step 5: Analyze the influence of common mode voltage and rotation speed on bearing electrocorrosion based on the electrocorrosion parameter data in the database.

5. The method for testing and analyzing shaft voltage in bearing electrical corrosion according to claim 4 is characterized in that: In step 1, the amplitude of the common mode voltage is 50V-100V, and the frequency is a square wave of 2kHz, 4kHz, 6kHz, 8kHz, and 10kHz.

6. The method for testing and analyzing shaft voltage in bearing electrical corrosion according to claim 4, characterized in that: In step 3, the bearing electro-corrosion parameters are sampled once every hour, and the sampling result is taken as the average value within the hour.

7. The method for testing and analyzing shaft voltage in bearing electrical corrosion according to claim 4, characterized in that: In step 3, the process of obtaining the bearing equivalent capacitance includes equating the bearing and the adjustable resistor (9) to an RC circuit, and the voltage across the bearing equivalent capacitance satisfies the following equation: Where u m (t) is the capacitor voltage, U s is the power supply voltage, τ is the RC circuit time constant, τ = RC; According to the bearing voltage waveform data sequence [u m (T-3Δt),u m (T-2Δt),u m (T-Δt),u m (T)],u m (T) = V bd , bring in Calculate the time constant τ and then determine the bearing capacitance C during the discharge, where V bd Indicates the size of the bearing voltage and reflects the voltage changes caused by electrical corrosion inside the bearing.

8. The method for testing and analyzing shaft voltage in bearing electrical corrosion according to claim 4 is characterized in that: In step 3, the process of obtaining the number of discharges includes: when the bearing is in a capacitive state, the function signal generator (11) charges the capacitor through the adjustable resistor (9), and when the host computer (8) detects that the peak voltage of the bearing is higher than the set threshold voltage, it is considered that a discharge event has occurred in the bearing.

9. The method for testing and analyzing shaft voltage in bearing electrical corrosion according to claim 4, characterized in that: In step 3, the process of obtaining the discharge energy includes: evaluating the discharge energy using the discharge power, and the calculation formula is as follows: In the formula, C is the bearing capacitance and U is the voltage when the oil film breaks down.

10. The method for testing and analyzing shaft voltage in bearing electrical corrosion according to claim 4, characterized in that: In step 3, the expression of the average discharge power is: In the formula, R c is the charging resistor, T is the time it takes for the capacitor to charge and discharge once, τ is the discharge time constant of the circuit, and U m,i is the capacitor voltage.

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