Shaft voltage monitoring method and device

Abstract

The invention discloses a shaft voltage monitoring method and device. A shaft voltage and shaft current monitoring device of an existing generator is difficult to effectively identify a current component formed by oil film breakdown. The monitoring method comprises the following steps: adding a metal leading-out point on a bearing bush on the excitation side of the generator, and monitoring the voltage difference between the leading-out point and the ground potential, namely the voltage to ground of the bearing bush; monitoring the shaft voltage, wherein the ground potential of the shaft voltage is consistent with the ground potential of the voltage to ground of the bearing bush; calculating a difference value between the shaft voltage and the voltage to earth of the bearing bush; judging the overall waveform characteristics of the shaft voltage; and identifying the oil film breakdown fault by combining one or more methods of harmonic analysis, peak comparison, phase analysis and judgment and correlation analysis according to the result of the overall waveform characteristic judgment. Whether the oil film breaks down or not can be directly judged without depending on shaft current monitoring, the function of the monitoring device is improved, meanwhile, the shaft current monitoring link is omitted, and the cost of the monitoring device is saved.

Description

Technical Field

[0001] The invention belongs to the technical field of motor monitoring, and in particular to a shaft voltage monitoring method and device. Background Art

[0002] Existing large motors, especially generators, have shaft voltage and shaft current monitoring devices that monitor shaft voltage on the excitation side and shaft current on the prime mover side. Figure 1 As shown, both domestic and foreign products use this method. In many years of field production practice, the above method has the limitation of low sensitivity of oil film breakdown monitoring. The main reason is that large motors, especially generators and other equipment will set insulation on the excitation side bearing. After the oil film breaks down, due to the existence of bearing insulation, the insulation structure of the shaft to the ground is only partially broken down without forming grounding, which will not cause a significant drop in shaft voltage. The shaft current monitored on the prime mover side is difficult to effectively identify the current component formed by oil film breakdown due to the large rotor shaft length and other reasons.

[0003] Oil film breakdown may cause electro-corrosion and damage the bearing, resulting in increased rotor vibration, further affecting the load-carrying capacity of the unit, and may cause operational risks if it develops seriously. At the same time, various reasons can cause abnormal shaft voltage. The typical characteristics of shaft voltage of motors with different structures, such as hidden pole synchronous motors and variable frequency drive motors, also have obvious differences. The contact between the carbon brush used for shaft voltage monitoring and the main shaft will also affect the accuracy of shaft voltage monitoring. It is of great practical significance to develop methods and devices that can effectively monitor and identify oil film breakdown faults for various shaft voltage characteristics and cover a wide range of motors. Summary of the invention

[0004] In view of this, the present invention provides a shaft voltage monitoring method, which adds a metal lead-out point at the bearing and monitors the voltage of the bearing to the ground. The difference between the shaft voltage and the voltage of the bearing to the ground is used to analyze the relationship between the difference and the shaft voltage in terms of amplitude, phase, peak value and correlation. It can directly determine whether the oil film has broken down without relying on shaft current monitoring, so as to improve the function of the monitoring device while omitting the shaft current monitoring link and saving the cost of the monitoring device.

[0005] To achieve the above purpose, the present invention adopts the following technical solution.

[0006] In a first aspect, the present invention provides a shaft voltage monitoring method, comprising:

[0007] Step 1), add a metal lead point on the bearing on the excitation side of the generator, and monitor the voltage difference between the lead point and the ground potential, that is, the bearing-to-ground voltage U1;

[0008] Step 2), monitoring the voltage of the rotor shaft to the ground, that is, the shaft voltage U, the ground potential of the shaft voltage U is consistent with the ground potential of the bearing shell to the ground voltage U1;

[0009] Step 3), calculate the difference between the shaft voltage U and the bearing-to-ground voltage U1, that is, the equivalent oil film voltage U2 = (U-U1);

[0010] Step 4), judging the overall waveform characteristics of the shaft voltage U;

[0011] Step 5), based on the result of the overall waveform feature judgment, one or more methods including harmonic analysis, peak value comparison, phase analysis and judgment, and correlation analysis are combined to identify the oil film breakdown fault.

[0012] Furthermore, in step 4), the overall waveform characteristics of the shaft voltage U are divided into the following three cases: case 1, the overall waveform of the shaft voltage U is a sine wave and there is an obvious pulse-type peak value; case 2, the overall waveform of the shaft voltage U is a sine wave and there is no obvious pulse-type peak value; case 3, the overall waveform of the shaft voltage U is a non-sinusoidal wave.

[0013] Furthermore, when the overall waveform of the shaft voltage U meets the condition 1, the oil film breakdown fault is diagnosed by harmonic analysis, peak comparison and phase analysis: Harmonic analysis is performed on the shaft voltage U, and the sum of the voltage components in the shaft voltage U that are lower than the preset frequency N is U , using (U- U ) to obtain the pulse peak value waveform in U; ​​the same method as above is used to carry out harmonic analysis of U1 and U2, and the following are obtained respectively: U 1 and U 2;

[0014] When at the same time point (U- U ) and (U1- U 1) When both voltage peaks exist and the ratio of the difference between the two voltage peaks to the maximum value is within the preset value N1, C1 = 1, otherwise C1 = 0;

[0015] when U The amplitude change rate is less than the preset value N1, U 2 decreases in magnitude, U 1 increases, through U , U 1 and U 2 phase analysis to determine whether the oil film has broken down: U and U 1 is less than the preset value N1, U When the phase of 2 lags behind the phase of the amplitude change time point by 85 to 90 degrees, C2 = 1, otherwise C2 = 0;

[0016] When (C1+C2)≥1, it is determined that the oil film has been broken down.

[0017] Furthermore, when the overall waveform of the shaft voltage U meets the second situation, when the amplitude change rate of the shaft voltage U is less than the preset value N1, the amplitude of the equivalent oil film voltage U2 decreases, and the amplitude of the bearing-to-ground voltage U1 increases, the phase analysis of the shaft voltage U, the bearing-to-ground voltage U1 and the equivalent oil film voltage U2 is used to determine whether the oil film has broken down: when the phase change rate of the shaft voltage U and the bearing-to-ground voltage U1 is less than the preset value N1, and the phase of the equivalent oil film voltage U2 lags by 85 to 90 degrees compared to the phase at the time point when the amplitude change occurs, it is determined that the oil film has broken down.

[0018] Furthermore, when the overall waveform of the shaft voltage U meets the third condition, correlation analysis is used to determine whether the oil film has a breakdown fault:

[0019] Select the starting time points of the rising and falling edges of the bearing-to-ground voltage U1 waveform to form a set T u1 , select the starting time points of the rising and falling edges of the equivalent oil film voltage U2 waveform to form a set T u2 , select the starting time points of the rising and falling edges of the shaft voltage U waveform to form a set T u3 , T = T u1 ∪(T u2 ∩T u3 ), the interval between adjacent time points in T is a time interval;

[0020] For each time interval obtained, the correlation X1 between the shaft voltage U and the bearing-to-ground voltage U1, and the correlation X2 between the shaft voltage U and the equivalent oil film voltage U2 are calculated in each time interval; X1 and X2 are compared, and when X1>X2, it is determined that the oil film has broken down.

[0021] In a second aspect, the present invention provides a shaft voltage monitoring device, which includes a bearing voltage monitoring unit, a shaft voltage monitoring unit, an oil film voltage calculation unit, a waveform feature judgment unit and an oil film breakdown judgment unit;

[0022] The bearing voltage monitoring unit is as follows: a metal lead-out point is added to the bearing on the excitation side of the generator, and the voltage difference between the lead-out point and the ground potential is monitored, that is, the bearing voltage to ground U1;

[0023] The shaft voltage monitoring unit: monitors the voltage of the rotor shaft to the ground, that is, the shaft voltage U, and the ground potential of the shaft voltage U is consistent with the ground potential of the bearing shell to the ground voltage U1;

[0024] The oil film voltage calculation unit calculates the difference between the shaft voltage U and the bearing-to-ground voltage U1, that is, the equivalent oil film voltage U2=(U-U1);

[0025] The waveform characteristic judgment unit judges the overall waveform characteristic of the shaft voltage U;

[0026] The oil film breakdown judgment unit is composed of one or more subunits of a harmonic analysis subunit, a peak comparison subunit, a phase judgment subunit, a time interval selection subunit, and a correlation calculation subunit, and identifies the oil film breakdown fault according to the judgment result of the waveform feature judgment unit.

[0027] Furthermore, in the waveform characteristic judgment unit, the overall waveform characteristics of the shaft voltage U are divided into the following three situations: situation one, the overall waveform of the shaft voltage U is a sine wave and there is an obvious pulse-type peak value; situation two, the overall waveform of the shaft voltage U is a sine wave and there is no obvious pulse-type peak value; situation three, the overall waveform of the shaft voltage U is a non-sinusoidal wave.

[0028] Furthermore, when the overall waveform of the shaft voltage U meets the condition 1, the oil film breakdown fault is diagnosed by the harmonic analysis, peak comparison and phase analysis subunits: the shaft voltage U is subjected to harmonic analysis, and the sum of the voltage components in the shaft voltage U that are lower than the preset frequency N is U , using (U- U ) to obtain the pulse peak value waveform in U; ​​the same method as above is used to carry out harmonic analysis of U1 and U2, and the following are obtained respectively: U 1 and U 2;

[0029] When at the same time point (U- U ) and (U1- U 1) When both voltage peaks exist and the ratio of the difference between the two voltage peaks to the maximum value is within the preset value N1, C1 = 1, otherwise C1 = 0;

[0030] when U The amplitude change rate is less than the preset value N1, U 2 decreases in magnitude, U 1 increases, through U , U 1 and U 2 phase analysis to determine whether the oil film has broken down: U and U 1 is less than the preset value N1, U When the phase of 2 lags behind the phase of the amplitude change time point by 85 to 90 degrees, C2 = 1, otherwise C2 = 0;

[0031] When (C1+C2)≥1, it is determined that the oil film has been broken down.

[0032] Furthermore, when the overall waveform of the shaft voltage U meets the second condition, when the amplitude change rate of U is less than the preset value N1, the amplitude of U2 decreases and the amplitude of U1 increases, the phase judgment subunit analyzes U, U1 and U2, determine whether the oil film has broken down: when the phase change rate of U and U1 is less than the preset value N1, and the phase of U2 lags behind the phase at the time point of the amplitude change by 85 to 90 degrees, it is determined that the oil film has broken down.

[0033] Furthermore, when the overall waveform of the shaft voltage U meets the third condition, the time interval selection subunit and the correlation calculation subunit are used to perform correlation analysis to determine whether the oil film has a breakdown fault:

[0034] The time interval selection subunit selects the starting time points of the rising edge and the falling edge of the bearing-to-ground voltage U1 waveform to form a set T u1 , select the starting time points of the rising and falling edges of the equivalent oil film voltage U2 waveform to form a set T u2 , select the starting time points of the rising and falling edges of the shaft voltage U waveform to form a set T u3 , T = T u1 ∪(T u2 ∩T u3 ), the interval between adjacent time points in T is a time interval;

[0035] The correlation calculation subunit: for each obtained time interval, calculates the correlation X1 between the shaft voltage U and the bearing-to-ground voltage U1, and the correlation X2 between the shaft voltage U and the equivalent oil film voltage U2 in each time interval; compares X1 and X2, and when X1>X2, it is determined that the oil film has undergone a breakdown failure.

[0036] The beneficial effects of the present invention are as follows: by adding a metal lead-out point at the bearing shell and monitoring the voltage between the bearing shell and the ground, the difference between the shaft voltage and the voltage between the bearing shell and the ground is used to analyze the relationship between the difference and the shaft voltage in terms of amplitude, phase, peak value, correlation, etc., it is possible to directly determine whether the oil film has broken down without relying on shaft current monitoring. The scope of application covers large hidden-pole synchronous motors such as generators, phase regulators and variable-frequency drive motors. Different typical shaft voltage waveforms can be analyzed and diagnosed, thereby improving the function of the monitoring device while omitting the shaft current monitoring link and saving the device cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The following is a brief introduction to the drawings required for describing the embodiments of the present invention.

[0038] Figure 1 This is a schematic diagram of a typical shaft voltage and shaft current monitoring device in use;

[0039] Figure 2 A flow chart of a shaft voltage monitoring method of the present invention;

[0040] Figure 3 This is a structural diagram of a shaft voltage monitoring device of the present invention;

[0041] Figure 4 This is a schematic diagram of the shaft voltage monitoring device of the present invention when in use. DETAILED DESCRIPTION

[0042] The following will further describe the specific implementation of the present invention in combination with the accompanying drawings of the embodiments of the present invention, so that the technical solution of the present invention is easier to understand and grasp. It should be understood that the specific embodiments described here are only used to explain part of the embodiments of the invention, rather than all the embodiments. Other embodiments obtained by ordinary technicians in this field without making creative work are all within the scope of protection of the present invention.

[0043] Example 1

[0044] This embodiment provides a shaft voltage monitoring method, such as Figure 2 As shown, the steps are as follows:

[0045] Step 1), add a metal lead point on the bearing on the excitation side of the generator, and monitor the voltage difference between the lead point and the ground potential, that is, the bearing-to-ground voltage U1;

[0046] Step 2), monitoring the voltage of the rotor shaft to the ground, that is, the shaft voltage U, the ground potential of the shaft voltage U is consistent with the ground potential of the bearing shell to the ground voltage U1;

[0047] Step 3), calculate the difference between the shaft voltage U and the bearing-to-ground voltage U1, that is, the equivalent oil film voltage U2 = (U-U1);

[0048] Step 4), judging the overall waveform characteristics of the shaft voltage U;

[0049] Step 5), based on the result of the overall waveform feature judgment, one or more methods including harmonic analysis, peak value comparison, phase analysis and judgment, and correlation analysis are combined to identify the oil film breakdown fault.

[0050] In step 4), the overall waveform characteristics of the shaft voltage U are divided into the following three cases: Case 1, the overall waveform of the shaft voltage U is a sine wave and there is an obvious pulse-type peak value; Case 2, the overall waveform of the shaft voltage U is a sine wave and there is no obvious pulse-type peak value; Case 3, the overall waveform of the shaft voltage U is a non-sinusoidal wave.

[0051] When the overall waveform of the shaft voltage U meets the condition 1, the oil film breakdown fault is diagnosed by harmonic analysis, peak comparison and phase analysis: Harmonic analysis is performed on the shaft voltage U, and the sum of the voltage components in the shaft voltage U that are lower than the preset frequency N is U , using (U- U ) to obtain the pulse peak value waveform in U; ​​the same method as above is used to carry out harmonic analysis of U1 and U2, and the following are obtained respectively:U 1 and U 2, N can be selected as 350Hz. The pulse peak value in the shaft voltage monitoring waveform may be formed by a variety of reasons. The use of harmonic analysis method to extract the pulse peak value is helpful for the accuracy of the analysis result.

[0052] When at the same time point (U- U ) and (U1- U 1) When both voltage peaks exist and the ratio of the difference between the two voltage peaks to the maximum value is within the preset value N1, C1 = 1, otherwise C1 = 0;

[0053] when U The amplitude change rate is less than the preset value N1, U 2 decreases in magnitude, U 1 increases, through U , U 1 and U 2 phase analysis to determine whether the oil film has broken down: U and U1 The phase change rate is less than the preset value N1, U When the phase of 2 lags behind the phase of the amplitude change time point by 85 to 90 degrees, C2 = 1, otherwise C2 = 0;

[0054] When (C1+C2)≥1, it is determined that the oil film has been broken down.

[0055] The bearing is in a stationary state while the rotor shaft rotates at high speed. The probability of voltage spikes caused by poor contact and interference of the monitoring units occurring at the same time to a similar degree is extremely low.

[0056] At the same time, the oil system of large motors such as generators is complex, and the lubricating oil is in a circulating rather than static state. Oil film oscillation, sealing bearing wear and other conditions will not only change the operating state of the oil film, but may also directly cause the rotor shaft vibration to increase. It is easy to misjudge whether the oil film is broken down by only judging the amplitude ratio or size relationship of the oil film voltage and the bearing voltage to the ground. The oil film is capacitive under the action of a sinusoidal voltage and exhibits a low resistance characteristic after breakdown. The bearing insulation to the ground maintains capacitance unchanged, and the phase change can be used to more accurately judge that the oil film has broken down.

[0057] When the overall waveform of the shaft voltage U meets the second situation, when the amplitude change rate of the shaft voltage U is less than the preset value N1, the amplitude of the equivalent oil film voltage U2 decreases, and the amplitude of the bearing-to-ground voltage U1 increases, the phase analysis of the shaft voltage U, the bearing-to-ground voltage U1 and the equivalent oil film voltage U2 is used to determine whether the oil film has broken down: when the phase change rate of the shaft voltage U and the bearing-to-ground voltage U1 is less than the preset value N1, and the phase of the equivalent oil film voltage U2 lags by 85 to 90 degrees compared to the phase at the time point when the amplitude change occurs, it is determined that the oil film has broken down.

[0058] When the overall waveform of the shaft voltage U meets the third condition, correlation analysis is used to determine whether the oil film has a breakdown fault:

[0059] Select the starting time points of the rising and falling edges of the bearing-to-ground voltage U1 waveform to form a set T u1 , select the starting time points of the rising and falling edges of the equivalent oil film voltage U2 waveform to form a set T u2 , select the starting time points of the rising and falling edges of the shaft voltage U waveform to form a set T u3 , T = T u1 ∪(T u2 ∩T u3 ), the interval between adjacent time points in T is taken as a time interval.

[0060] For motors with typical shaft voltages that are non-sinusoidal waveforms, such as variable-frequency drive motors with insulation at the bearing shells, there are rising and falling edges of the voltage in the shaft voltage waveform. Taking the bearing shell-to-ground voltage as an example, due to the existence of bearing shell insulation, the bearing shell is capacitive to the ground. The rising and falling edges of the bearing shell-to-ground voltage can be used to analyze whether there are charging and discharging currents at both ends of the bearing shell. The rising and falling edge characteristics of the bearing shell-to-ground voltage, shaft voltage, and oil film voltage are used to obtain the time interval required for correlation analysis, that is, the time interval is divided by analyzing whether there are charging and discharging currents.

[0061] For each time interval obtained, the correlation X1 between the shaft voltage U and the bearing-to-ground voltage U1, and the correlation X2 between the shaft voltage U and the equivalent oil film voltage U2 are calculated in each time interval; X1 and X2 are compared, and when X1>X2, it is determined that the oil film has broken down.

[0062] In the obtained time interval, when the oil film has not broken down, the shaft voltage mainly acts on the oil film, and the shaft voltage and the oil film characteristics are similar. The correlation analysis result should be X2>X1. When X1>X2, the bearing-to-ground voltage and the shaft voltage characteristics are similar. The shaft voltage mainly acts on the bearing-to-ground insulation rather than the oil film, and it is judged that the oil film insulation has failed.

[0063] For variable frequency drive motors with insulation at the bearing, since their typical shaft voltage waveform is non-sinusoidal and has complex characteristics, the peak comparison method after harmonic analysis is prone to misjudgment, and the phase judgment method is difficult to apply. Correlation analysis can solve these problems well.

[0064] Example 2

[0065] This embodiment provides a shaft voltage monitoring device, such as Figure 3 As shown, it consists of a bearing voltage monitoring unit, a shaft voltage monitoring unit, an oil film voltage calculation unit, a waveform feature judgment unit and an oil film breakdown judgment unit.

[0066] The bearing voltage monitoring unit: Figure 4 As shown, a metal lead-out point is added to the bearing on the excitation side of the generator, and the voltage difference between this lead-out point and the ground potential, that is, the bearing-to-ground voltage U1, is monitored.

[0067] The shaft voltage monitoring unit monitors the voltage of the rotor shaft to the ground, that is, the shaft voltage U. The ground potential of the shaft voltage U is consistent with the ground potential of the bearing shell to the ground voltage U1.

[0068] The oil film voltage calculation unit calculates the difference between the shaft voltage U and the bearing-to-ground voltage U1, that is, the equivalent oil film voltage U2 = (U-U1).

[0069] The waveform characteristic judgment unit judges the overall waveform characteristic of the shaft voltage U.

[0070] The oil film breakdown judgment unit is composed of one or more subunits of a harmonic analysis subunit, a peak comparison subunit, a phase judgment subunit, a time interval selection subunit, and a correlation calculation subunit, and identifies the oil film breakdown fault according to the judgment result of the waveform feature judgment unit.

[0071] In the waveform characteristic judgment unit, the overall waveform characteristics of the shaft voltage U are divided into the following three situations: situation one, the overall waveform of the shaft voltage U is a sine wave and there is an obvious pulse-type peak value; situation two, the overall waveform of the shaft voltage U is a sine wave and there is no obvious pulse-type peak value; situation three, the overall waveform of the shaft voltage U is a non-sinusoidal wave.

[0072] Specifically, when the overall waveform of the shaft voltage U meets the condition 1, the oil film breakdown fault is diagnosed by the harmonic analysis, peak comparison and phase analysis subunits: the shaft voltage U is subjected to harmonic analysis, and the sum of the voltage components in the shaft voltage U that are lower than the preset frequency N is U , using (U- U ) to obtain the pulse peak value waveform in U; ​​the same method as above is used to carry out harmonic analysis of U1 and U2, and the following are obtained respectively: U 1 and U 2;

[0073] When at the same time point (U- U ) and (U1- U 1) When both voltage peaks exist and the ratio of the difference between the two voltage peaks to the maximum value is within the preset value N1, C1 = 1, otherwise C1 = 0;

[0074] when U The amplitude change rate is less than the preset value N1, U 2 decreases in magnitude, U 1 increases, through U , U 1 and U 2 phase analysis to determine whether the oil film has broken down: U and U 1 is less than the preset value N1, U When the phase of 2 lags behind the phase of the amplitude change time point by 85 to 90 degrees, C2 = 1, otherwise C2 = 0;

[0075] When (C1+C2)≥1, it is determined that the oil film has been broken down.

[0076] Specifically, when the overall waveform of the shaft voltage U meets the second situation, when the amplitude change rate of the shaft voltage U is less than the preset value N1, the amplitude of the equivalent oil film voltage U2 decreases, and the amplitude of the bearing-to-ground voltage U1 increases, the phase of the shaft voltage U, the bearing-to-ground voltage U1 and the equivalent oil film voltage U2 is analyzed by the phase judgment subunit to determine whether the oil film has broken down: when the phase change rate of the shaft voltage U and the bearing-to-ground voltage U1 is less than the preset value N1, and the phase of the equivalent oil film voltage U2 lags by 85 to 90 degrees compared to the phase at the time point when the amplitude change occurs, it is determined that the oil film has broken down.

[0077] Specifically, when the overall waveform of the shaft voltage U meets the third condition, the time interval selection subunit and the correlation calculation subunit are used to perform correlation analysis to determine whether the oil film has a breakdown fault:

[0078] The time interval selection subunit selects the starting time points of the rising edge and the falling edge of the bearing-to-ground voltage U1 waveform to form a set T u1 , select the starting time points of the rising and falling edges of the equivalent oil film voltage U2 waveform to form a set T u2 , select the starting time points of the rising and falling edges of the shaft voltage U waveform to form a set T u3 , T = T u1 ∪(T u2 ∩T u3 ), the interval between adjacent time points in T is a time interval;

[0079] The correlation calculation subunit: for each obtained time interval, calculates the correlation X1 between the shaft voltage U and the bearing-to-ground voltage U1, and the correlation X2 between the shaft voltage U and the equivalent oil film voltage U2 in each time interval; compares X1 and X2, and when X1>X2, it is determined that the oil film has undergone a breakdown failure.

[0080] Example 3

[0081] This embodiment provides a shaft voltage monitoring method, the steps of which are as follows:

[0082] 1. By adding a metal lead-out point on the bearing on the excitation side of the generator and monitoring the voltage difference between this lead-out point and the ground potential, that is, the bearing-to-ground voltage, recorded as U1.

[0083] 2. Monitor the voltage of the rotor shaft to the ground, that is, the shaft voltage U. The ground potential of U is consistent with the ground potential of the bearing voltage U1. Since the two ends of the oil film are the bearing and the rotor shaft respectively, calculate U2=(U-U1) to obtain the equivalent oil film voltage.

[0084] 3. Judging the waveform characteristics of the shaft voltage U, the overall waveform of U is a sine wave with an obvious pulse-type spike value.

[0085] 4. Perform harmonic analysis on U. The sum of the voltage components in U that are lower than the preset frequency of 350Hz is U , using (U- U ) to obtain the pulse peak value waveform in U, and the harmonic analysis of U1 and U2 is carried out in the same way as above to obtain U 1. U 2.

[0086] 5. At the same time point (U- U ) and (U1- U1 ) both have voltage peaks, and the ratio of the difference between the two voltage peaks to the maximum value is 3%, which is less than the preset value of 5%, C1=1, (C1+C2)≥1, and it is judged that there is an oil film breakdown discharge fault.

[0087] Example 4

[0088] This embodiment provides a shaft voltage monitoring method, the steps of which are as follows:

[0089] 1. By adding a metal lead-out point on the bearing on the excitation side of the generator and monitoring the voltage difference between this lead-out point and the ground potential, that is, the bearing-to-ground voltage, recorded as U1.

[0090] 2. Monitor the voltage of the rotor shaft to the ground, that is, the shaft voltage U. The ground potential of U is consistent with the ground potential of the bearing voltage U1. Since the two ends of the oil film are the bearing and the rotor shaft respectively, calculate U2=(U-U1) to obtain the equivalent oil film voltage.

[0091] 3. Judging the waveform characteristics of the shaft voltage U, the overall waveform of U is a sine wave and there is no obvious pulse-type spike value.

[0092] 4. The amplitude change rate of U is 4%, which is less than the preset value of 5%. The amplitude of U2 decreases and the amplitude of U1 increases. Through the phase analysis of U, U1 and U2, it is determined whether the oil film has broken down.

[0093] 5. The phase change rate of U and U1 is less than the preset value of 5%, and the phase of U2 lags 86 degrees compared to the phase at the time point when the amplitude change occurs, indicating that the oil film has been broken down.

[0094] Example 5

[0095] This embodiment provides a shaft voltage monitoring method, the steps of which are as follows:

[0096] 1. By adding a metal lead-out point on the bearing on the excitation side of the generator and monitoring the voltage difference between this lead-out point and the ground potential, that is, the bearing-to-ground voltage, recorded as U1.

[0097] 2. Monitor the voltage of the rotor shaft to the ground, that is, the shaft voltage U. The ground potential of U is consistent with the ground potential of the bearing voltage U1. Since the two ends of the oil film are the bearing and the rotor shaft respectively, calculate U2=(U-U1) to obtain the equivalent oil film voltage.

[0098] 3. Determine the waveform characteristics of the shaft voltage U. The overall waveform of U is a non-sinusoidal wave.

[0099] 4. Select the starting time points of the rising and falling edges of the bearing-to-ground voltage U1 waveform to form a set T u1 , select the starting time points of the rising and falling edges of the equivalent oil film voltage U2 waveform to form a set T u2 , select the starting time points of the rising and falling edges of the shaft voltage U waveform to form a set T u3 , T = T u1 ∪(T u2 ∩T u3 ), the interval between adjacent time points in T is taken as a time interval.

[0100] 5. In the second time interval in T, the correlation between the shaft voltage U and the bearing-to-ground voltage U1 is 0.99, and the correlation between the shaft voltage U and the equivalent oil film voltage U2 is 0.1. 0.99>0.1, which indicates that the oil film has undergone a breakdown failure.

[0101] Example 6

[0102] This embodiment provides a shaft voltage monitoring method, the steps of which are as follows:

[0103] 1. By adding a metal lead-out point on the bearing on the excitation side of the generator and monitoring the voltage difference between this lead-out point and the ground potential, that is, the bearing-to-ground voltage, recorded as U1.

[0104] 2. Monitor the voltage of the rotor shaft to the ground, that is, the shaft voltage U. The ground potential of U is consistent with the ground potential of the bearing voltage U1. Since the two ends of the oil film are the bearing and the rotor shaft respectively, calculate U2=(U-U1) to obtain the equivalent oil film voltage.

[0105] 3. Judging the waveform characteristics of the shaft voltage U, the overall waveform of U is a sine wave with an obvious pulse-type spike value.

[0106] 4. Perform harmonic analysis on U. The sum of the voltage components in U that are lower than the preset frequency of 350Hz is U , using (U- U ) to obtain the pulse peak value waveform in U, and the harmonic analysis of U1 and U2 is carried out in the same way as above to obtain U 1. U 2.

[0107] 5. U The amplitude change rate is 4%, which is less than the preset value of 5%. U 2 decreases in magnitude, U 1 increases, through U , U 1 and U 2 phase analysis to determine whether the oil film has been broken down.

[0108] 6. U and U 1 The phase change rate is less than the preset value 5%, U The phase of 2 lags behind the phase of the amplitude change time point by 86 degrees, C2=1, (C1+C2)≥1, and it is judged that the oil film has been broken down.

[0109] Compared with traditional technologies, the present invention adds metal lead-out points at the bearing and monitors the voltage between the bearing and the ground. The difference between the shaft voltage and the voltage between the bearing and the ground is used to analyze the relationship between the difference and the shaft voltage in terms of amplitude, phase, peak value, correlation, etc., so that it can directly determine whether the oil film has broken down without relying on shaft current monitoring. The scope of application covers large hidden-pole synchronous motors such as generators, phase regulators and variable-frequency drive motors. Different typical shaft voltage waveforms can be analyzed and diagnosed, thereby improving the function of the monitoring device and omitting the shaft current monitoring link to save device costs.

[0110] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A shaft voltage monitoring method, characterized in that: include: Step 1), add a metal lead point on the bearing on the excitation side of the generator, and monitor the voltage difference between the lead point and the ground potential, that is, the bearing-to-ground voltage U1; Step 2), monitoring the voltage of the rotor shaft to the ground, that is, the shaft voltage U, the ground potential of the shaft voltage U is consistent with the ground potential of the bearing shell to the ground voltage U1; Step 3), calculate the difference between the shaft voltage U and the bearing-to-ground voltage U1, that is, the equivalent oil film voltage U2 = (U-U1); Step 4), judging the overall waveform characteristics of the shaft voltage U; Step 5), based on the result of the overall waveform feature judgment, one or more methods including harmonic analysis, peak value comparison, phase analysis and judgment, and correlation analysis are combined to identify the oil film breakdown fault.

2. The shaft voltage monitoring method according to claim 1, characterized in that: In step 4), the overall waveform characteristics of the shaft voltage U are divided into the following three cases: Case 1, the overall waveform of the shaft voltage U is a sine wave and there is an obvious pulse-type peak value; Case 2, the overall waveform of the shaft voltage U is a sine wave and there is no obvious pulse-type peak value; Case 3, the overall waveform of the shaft voltage U is a non-sinusoidal wave.

3. The shaft voltage monitoring method according to claim 2, characterized in that: When the overall waveform of the shaft voltage U meets the condition 1, the oil film breakdown fault is diagnosed by harmonic analysis, peak comparison and phase analysis: Harmonic analysis is performed on the shaft voltage U, and the sum of the voltage components in the shaft voltage U that are lower than the preset frequency N is U , using (U- U ) to obtain the pulse peak value waveform in U; The same method as above is used to carry out harmonic analysis of U1 and U2, and the results are U 1 and U 2; When at the same time point (U- U ) and (U1- U 1) When both voltage peaks exist and the ratio of the difference between the two voltage peaks to the maximum value is within the preset value N1, C1 = 1, otherwise C1 = 0; when U The amplitude change rate is less than the preset value N1, U 2 decreases in magnitude, U 1 increases, through U , U 1 and U 2 phase analysis to determine whether the oil film has broken down: U and U 1 is less than the preset value N1. U When the phase of 2 lags behind the phase of the amplitude change time point by 85 to 90 degrees, C2 = 1, otherwise C2 = 0; When (C1+C2)≥1, it is determined that the oil film has been broken down.

4. The shaft voltage monitoring method according to claim 2, characterized in that: When the overall waveform of the shaft voltage U meets the second situation, when the amplitude change rate of the shaft voltage U is less than the preset value N1, the amplitude of the equivalent oil film voltage U2 decreases, and the amplitude of the bearing-to-ground voltage U1 increases, the phase analysis of the shaft voltage U, the bearing-to-ground voltage U1 and the equivalent oil film voltage U2 is used to determine whether the oil film has broken down: when the phase change rate of the shaft voltage U and the bearing-to-ground voltage U1 is less than the preset value N1, and the phase of the equivalent oil film voltage U2 lags by 85 to 90 degrees compared to the phase at the time point when the amplitude change occurs, it is determined that the oil film has broken down.

5. The shaft voltage monitoring method according to claim 2, characterized in that: When the overall waveform of the shaft voltage U meets the third condition, correlation analysis is used to determine whether the oil film has a breakdown fault: Select the starting time points of the rising and falling edges of the bearing-to-ground voltage U1 waveform to form a set T u1 , select the starting time points of the rising and falling edges of the equivalent oil film voltage U2 waveform to form a set T u2 , select the starting time points of the rising and falling edges of the shaft voltage U waveform to form a set T u3 , T=T u1 ∪(T u2 ∩T u3 ), the interval between adjacent time points in T is a time interval; For each time interval obtained, the correlation X1 between the shaft voltage U and the bearing-to-ground voltage U1, and the correlation X2 between the shaft voltage U and the equivalent oil film voltage U2 are calculated in each time interval; X1 and X2 are compared, and when X1>X2, it is determined that the oil film has broken down.

6. A shaft voltage monitoring device, characterized in that: It includes a bearing voltage monitoring unit, a shaft voltage monitoring unit, an oil film voltage calculation unit, a waveform feature judgment unit and an oil film breakdown judgment unit; The bearing voltage monitoring unit is as follows: a metal lead-out point is added to the bearing on the excitation side of the generator, and the voltage difference between the lead-out point and the ground potential is monitored, that is, the bearing voltage to ground U1; The shaft voltage monitoring unit: monitors the voltage of the rotor shaft to the ground, that is, the shaft voltage U, and the ground potential of the shaft voltage U is consistent with the ground potential of the bearing shell to the ground voltage U1; The oil film voltage calculation unit calculates the difference between the shaft voltage U and the bearing-to-ground voltage U1, that is, the equivalent oil film voltage U2=(U-U1); The waveform characteristic judgment unit judges the overall waveform characteristic of the shaft voltage U; The oil film breakdown judgment unit is composed of one or more subunits of a harmonic analysis subunit, a peak comparison subunit, a phase judgment subunit, a time interval selection subunit, and a correlation calculation subunit, and identifies the oil film breakdown fault according to the judgment result of the waveform feature judgment unit.

7. The shaft voltage monitoring device according to claim 6, characterized in that: In the waveform characteristic judgment unit, the overall waveform characteristics of the shaft voltage U are divided into the following three situations: situation one, the overall waveform of the shaft voltage U is a sine wave and there is an obvious pulse-type peak value; situation two, the overall waveform of the shaft voltage U is a sine wave and there is no obvious pulse-type peak value; situation three, the overall waveform of the shaft voltage U is a non-sinusoidal wave.

8. The shaft voltage monitoring device according to claim 7, characterized in that: When the overall waveform of the shaft voltage U meets the condition 1, the oil film breakdown fault is diagnosed by harmonic analysis, peak comparison and phase judgment subunits: Harmonic analysis is performed on the shaft voltage U, and the sum of the voltage components in the shaft voltage U that are lower than the preset frequency N is U , using (U- U ) to obtain the pulse peak value waveform in U; The same method as above is used to carry out harmonic analysis of U1 and U2, and the results are U 1 and U 2; When at the same time point (U- U ) and (U1- U 1) When both voltage peaks exist and the ratio of the difference between the two voltage peaks to the maximum value is within the preset value N1, C1 = 1, otherwise C1 = 0; when U The amplitude change rate is less than the preset value N1, U 2 decreases in magnitude, U 1 increases, through U , U 1 and U 2 phase analysis to determine whether the oil film has broken down: U and U 1 is less than the preset value N1. U When the phase of 2 lags behind the phase of the amplitude change time point by 85 to 90 degrees, C2 = 1, otherwise C2 = 0; When (C1+C2)≥1, it is determined that the oil film has been broken down.

9. The shaft voltage monitoring device according to claim 7, characterized in that: When the overall waveform of the shaft voltage U meets the second situation, when the amplitude change rate of the shaft voltage U is less than the preset value N1, the amplitude of the equivalent oil film voltage U2 decreases, and the amplitude of the bearing-to-ground voltage U1 increases, the phase of the shaft voltage U, the bearing-to-ground voltage U1 and the equivalent oil film voltage U2 is analyzed by the phase judgment subunit to determine whether the oil film has broken down: when the phase change rate of the shaft voltage U and the bearing-to-ground voltage U1 is less than the preset value N1, and the phase of the equivalent oil film voltage U2 lags by 85 to 90 degrees compared to the phase at the time point when the amplitude change occurs, it is determined that the oil film has broken down.

10. The shaft voltage monitoring device according to claim 7, characterized in that: When the overall waveform of the shaft voltage U meets the third condition, the time interval selection subunit and the correlation calculation subunit are used to perform correlation analysis to determine whether the oil film has a breakdown fault: The time interval selection subunit selects the starting time points of the rising edge and the falling edge of the bearing-to-ground voltage U1 waveform to form a set T u1 , select the starting time points of the rising and falling edges of the equivalent oil film voltage U2 waveform to form a set T u2 , select the starting time points of the rising and falling edges of the shaft voltage U waveform to form a set T u3 , T=T u1 ∪(T u2 ∩T u3 ), the interval between adjacent time points in T is a time interval; The correlation calculation subunit: for each obtained time interval, calculates the correlation X1 between the shaft voltage U and the bearing-to-ground voltage U1, and the correlation X2 between the shaft voltage U and the equivalent oil film voltage U2 in each time interval; compares X1 and X2, and when X1>X2, it is determined that the oil film has undergone a breakdown failure.

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