On-line monitoring method of variable frequency motor insulation to ground based on time domain characteristics of leakage current
Through a three-stage monitoring method based on the time domain characteristics of leakage current, the problem of difficult monitoring of the stator insulation degradation position and severity of the variable frequency motor is solved, real-time monitoring of the degradation phase, position and severity of the ground insulation degradation phase, and improving the maintenance efficiency and reliability of the motor.
Patent Information
- Application Number
- CN202210047014.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-01-14
- Publication Date
- 2025-04-25
- Estimated Expiration
- 2042-01-14
AI Technical Summary
The prior art is difficult to effectively monitor and locate the position and severity of the stator insulation degradation of frequency converter motors, resulting in the inability to perform timely maintenance and preventive maintenance.
A three-stage monitoring method based on the leakage current time domain characteristics is adopted, including online monitoring of the ground insulation degradation phase, location and severity. By establishing an expression of the initial oscillation amplitude of the step voltage excited by the degradation monitoring phase and the healthy phase, the difference between the two is compared to determine the degradation phase, and the degradation position and severity are determined by the initial oscillation amplitude and the degradation time of the leakage current.
Real-time monitoring of the degraded phase, position and severity of the ground insulation degraded phase, position and severity of the variable frequency motor, providing a favorable basis and basis for maintenance and use, and improving the reliability and service life of the motor.
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Figure CN114355126B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of variable frequency motor online monitoring, in particular to an online monitoring method for the insulation of a variable frequency motor to the ground based on the time domain characteristics of leakage current. Background Art
[0002] Variable frequency motors have been widely used in industrial applications, and their failures may lead to huge economic losses and safety issues. It is well known that the most common failures of AC motors are stator insulation failure, bearing failure, and rotor failure. According to survey statistics, about 30%-40% of motor failures are related to stator insulation. For variable frequency motors, high du / dt and repetitive pulse voltage greatly accelerate insulation degradation. Therefore, it is crucial to monitor the stator winding insulation to ground in this case.
[0003] Typically, insulation degradation is a long-term development process that may last for many years. Insulation degradation caused by thermal, mechanical and environmental stresses always results in continuous changes in insulation resistance and capacitance. Traditional offline testing can monitor the insulation condition to ground by measuring insulation resistance, insulation capacitance and polarization index. Insulation breakdown may be caused not only by reduced insulation electrical strength, but also by transient voltage or current applied to the insulation. The stator insulation condition can be evaluated by offline partial discharge testing or impulse voltage testing. Traditional offline testing requires the motor to be decommissioned, which is very time-consuming and can only evaluate the insulation condition of the offline motor.
[0004] In order to solve the above technical problems, technicians in this field have proposed various online monitoring technologies to evaluate the stator insulation condition of the motor during operation, such as online monitoring of partial discharge, online monitoring of capacitance and loss factor (C / DF), and online monitoring of switching transients.
[0005] First, the stator insulation condition is mainly evaluated by online partial discharge monitoring. About half of the typical stator insulation failures are caused by partial discharge. Online partial discharge monitoring methods are often used for high-voltage motor insulation evaluation and are rarely used for low-voltage motors. The main limitation of online partial discharge monitoring is that the technology is sensitive to noise and has poor reliability in some cases. To solve this problem, the noise can be separated by analyzing the pulse shape or by the time difference between the PD signals transmitted between PD sensors. Various wavelet-based methods have been proposed in the prior art to remove white noise or accurately extract PD features. If the online partial discharge monitoring method is applied to variable frequency motors, its reliability cannot meet the requirements.
[0006] Secondly, online C / DF monitoring evaluates C / DF by measuring differential mode (DM) leakage current and common mode (CM) leakage current online, and evaluates the overall state of insulation to ground and between phases. However, the C / DF method based on CM and DM leakage current can only monitor the overall state of stator insulation, while the capacitance to ground and between phases can be decoupled and evaluated through the multi-frequency domain information of relative ground voltage and DM leakage current. Therefore, the online C / DF monitoring method based on DM or CM leakage current has the problem of being unable to locate the most serious location of stator insulation degradation.
[0007] Again, the switching transient monitoring method is used to predict the remaining useful life (RUL) of the stator insulation. The RUL can be predicted by applying a pulse voltage with a high rate of change and monitoring the overshoot of the variable frequency motor leakage current. These transient current responses are mainly affected by the insulation capacitance, and the insulation capacitance can be used to indicate the state of the stator insulation. There are obvious differences between the transient current response spectra of healthy motors and aging motors. In order to better characterize the insulation state, it is necessary to quantify the high-frequency differences, and the switching transient monitoring method also cannot provide degradation location information.
[0008] Therefore, those skilled in the art need a method for locating stator insulation degradation. Summary of the invention
[0009] The purpose of the present invention is to solve the above problems and to design an online monitoring method for the insulation of a variable frequency motor to the ground based on the time domain characteristics of the leakage current.
[0010] An online monitoring method for the insulation of a variable frequency motor to ground based on the time domain characteristics of leakage current, the method includes three levels of monitoring, the first level of monitoring is the online monitoring of the phase of insulation degradation of the variable frequency motor to ground, the second level of monitoring is the online monitoring of the position of insulation degradation of the variable frequency motor to ground, and the third level of monitoring is the online monitoring of the severity of insulation degradation of the variable frequency motor to ground;
[0011] The first level is the online monitoring of the insulation degradation phase of the variable frequency motor to the ground. The monitoring process includes:
[0012] Step 1: Establish the initial oscillation amplitude A of the leakage current excited by the step voltage of the degradation monitoring phase ini-d The expression is:
[0013]
[0014] Where: ΔU d represents the step voltage applied to the degenerate phase, R g is the insulation resistance to ground, C g is the insulation capacitance to ground, L s is the stator inductance, R s is the stator resistance, x is the location of insulation degradation to ground;
[0015] Step 2: Establish the initial oscillation amplitude A of the leakage current excited by the healthy phase step voltage ini-h The expression is:
[0016]
[0017] Where: ΔU h represents the step voltage applied to the healthy phase, R g is the insulation resistance to ground, C g is the insulation capacitance to ground, L s is the stator inductance, R s is the stator resistance, x is the location of insulation degradation to ground;
[0018] Step 3: Set the initial oscillation amplitude A of the leakage current excited by the step voltage of the degradation monitoring phase ini-d The initial oscillation amplitude A of the leakage current excited by the step voltage of the healthy phase ini-h Compare them, if the amplitudes of the two are different, it is determined that the degradation monitoring phase has been degraded;
[0019] The second level is online monitoring of the location of insulation degradation of the variable frequency motor to the ground. The monitoring process includes:
[0020] Select the initial oscillation amplitude A of the leakage current excited by the step voltage of the degradation monitoring phase ini-d The expression is used as the basis for monitoring the location of insulation degradation to ground, with A ini-d From the expression, the insulation degradation position to ground is x, A ini-d The larger the value of is, the closer the insulation degradation position x is to the motor input terminal;
[0021] Level 3: Monitoring of the severity of insulation degradation of variable frequency motor to ground. The monitoring process includes: insulation resistance to ground R g Monitoring and ground insulation capacitance C g The severity of insulation degradation to ground depends on the insulation resistance R g And the insulation capacitance to ground C g Therefore, by constructing a circuit with an insulation resistance R g And the insulation capacitance to ground C g The expression can monitor the severity of insulation degradation to ground and establish the leakage current decay time T s The expression is:
[0022]
[0023] In the formula, R g is the insulation resistance to ground, C g is the insulation capacitance to ground, L s is the stator inductance, R s is the stator resistance. From the above formula, we can know that Ts With R g and C g is proportional to the product of g and C g The larger the value of is, the less severe the insulation degradation of the variable frequency motor to the ground is. s The higher the value, the less severe the insulation degradation of the variable frequency motor to ground, and vice versa.
[0024] The R s and L s The values were obtained by measuring with an impedance analyzer.
[0025] During the online monitoring of the insulation degradation phase of the variable frequency motor to the ground, A ini-d Greater than A ini-h During the online monitoring of the position of insulation degradation of the variable frequency motor to the ground, x=0 corresponds to the line input end of the variable frequency motor, and x=1 corresponds to the neutral point of the variable frequency motor.
[0026] Beneficial Effects
[0027] The on-line monitoring method for the ground insulation of a variable frequency motor based on the leakage current time domain characteristics produced by the technical solution of the present invention has the following advantages:
[0028] This method monitors the degradation of the insulation of the variable frequency motor to the ground based on the time domain characteristics of the leakage current, namely the initial oscillation amplitude, oscillation period and attenuation time. This method can not only monitor the phase and position of the insulation degradation to the ground, but also monitor the severity of the insulation degradation to the ground, thus providing a favorable basis and basis for the maintenance and use of the variable frequency motor. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Figure 1 is the initial amplitude A when the degradation position is different in the present invention ini The simulation result diagram of
[0030] Figure 2 is the decay time T under different insulation resistance and insulation capacitance of the present invention s The simulation result diagram of
[0031] Figure 3 is a schematic diagram of the test platform configuration of the present invention;
[0032] Figure 4 It is a result diagram of the leakage current and step voltage of the degraded phase and the healthy phase under the conditions of DC240V bus voltage, 3.3nF insulation capacitance, 1MΩ insulation resistance and x=0.5 according to the present invention;
[0033] Figure 5It is a result diagram of leakage current and degraded phase step voltage when the degradation position is different under the conditions of DC240V bus voltage, 3.3nF insulation capacitance, and 1MΩ insulation resistance according to the present invention;
[0034] Figure 6 is a result diagram of the decay time under different insulation capacitances according to the present invention;
[0035] Figure 7 is a result diagram of the decay time under different insulation resistances according to the present invention;
[0036] Figure 8 It is a table of the conditions and main parameters required for the test platform of the present invention;
[0037] Fig. 9 is the oscillation period T when the degradation position is different in Embodiment 2 of the present invention c The simulation result diagram of DETAILED DESCRIPTION
[0038] The present invention will be described in detail below in conjunction with the accompanying drawings. Figure 1-9 As shown;
[0039] The electronic devices used in this technical solution are all existing products. The technical solution of this application has no special requirements or changes to the structure of the above-mentioned electronic devices. The above-mentioned electronic devices are all conventional electronic devices.
[0040] During the implementation of this technical solution, personnel in this field need to connect all electrical components in this case with their corresponding power supplies through wires, and should select a suitable controller according to actual conditions to meet control requirements. The specific connection and control sequence should refer to the following working principle, and the electrical connection between each electrical component is completed in the order of working in sequence. The detailed connection means are well-known technologies in this field. The following mainly introduces the working principle and process, and does not explain the electrical control.
[0041] Example 1
[0042] The test platform built to verify the proposed method is as follows Figure 3 The test motor used in this test platform is a 3kW variable frequency motor, and the inverter is controlled by dSPACE. In order to simulate the insulation degradation to the ground, an RC adjustment circuit with different impedances is connected between the stator winding and the ground. The test conditions and motor parameters are shown in Figure 8 , where the insulation resistance and insulation capacitance are the parameters of the RC regulation circuit. During the test, the test conditions of the variable frequency motor system remain unchanged.
[0043] The test platform setup diagram is as follows: Figure 3As shown. A current transformer is installed at the motor input terminal to measure the ground leakage current, and three sets of voltage transformers are installed to measure the phase voltage. In order to eliminate the error caused by noise and DC bus voltage fluctuation, the initial oscillation amplitude A is used. ini-d , Oscillation period T c and decay time T s The statistical average value of the insulation degradation to ground is used to monitor the insulation degradation to ground.
[0044] Monitoring the degraded phase of variable frequency motors
[0045] Since the structure and parameters of the stator winding are three-phase balanced, if the insulation to the ground is not degraded, the leakage current excited by the three-phase voltage is the same. When one phase has insulation degradation to the ground, the three-phase winding is no longer balanced, and the leakage current excited by the degraded phase voltage will be different from the leakage current excited by the healthy phase voltage. The difference is reflected in the initial oscillation amplitude A. ini Therefore, the insulation degradation of the variable frequency motor to the ground can be calculated based on A ini-d and A ini-h The difference is monitored online, such as Figure 1 As shown in Figure 1, the leakage current amplitude of the degraded phase and the healthy phase is compared to verify whether the degraded phase has degraded. The experimental waveforms of the leakage current and step voltage of the degraded phase and the healthy phase are shown in Figure 1. Figure 4 As shown in the figure, the upper and lower waveforms are leakage current and step voltage, respectively. It can be seen that the initial oscillation amplitude of the leakage current excited by voltage in the degraded phase and the healthy phase is different. ini-d and A ini-h They are approximately 410mA and 100mA respectively. There is a large difference between the amplitudes of the two. Therefore, it can be determined that the monitored phase of the variable frequency motor has been degraded.
[0046] Monitor the location of insulation degradation of variable frequency motors to the ground
[0047] The leakage current amplitude A of the degraded insulation position of the variable frequency motor through the voltage excitation of the degraded phase ini-d The position corresponding to x=0 is the motor input terminal, and the leakage current amplitude A excited by the voltage of the degenerated phase ini-d The expression of x and A can be obtained ini-d The relationship between the leakage current amplitude and the degraded phase step voltage at different locations of insulation degradation to ground is as follows: Figure 5 As shown, when x = 0.5, A ini-d About 410mA; when the degenerate position x changes from 0.5 to 0.2, A ini-d It can be seen from the above changes that those skilled in the art can determine the leakage current amplitude A of the voltage excitation of the degenerate phase. ini-d The changes in the insulation degradation position of the variable frequency motor to the ground can be monitored online.
[0048] Monitor the severity of insulation degradation of variable frequency motors
[0049] like Figure 2 As shown in the figure, the severity of the insulation degradation of the variable frequency motor to the ground is determined by the leakage current decay time T s Carry out online monitoring. Under different conditions of insulation capacitance and insulation resistance, T s The changes are as follows Figure 6 and Figure 7 As shown. Figure 6 It can be seen that T s Follow C g increases with the increase of Figure 7 It can be seen that with the increase of R g The increase of T s For the variable frequency test motor used in this application, the T s The severity of the insulation degradation to the ground is predicted online based on the changes in the ground insulation degradation. When the severity of the insulation degradation to the ground reaches the maximum, the ground insulation of the variable frequency motor is broken down.
[0050] Example 2
[0051] The leakage current oscillation period T can also be used c To achieve online monitoring of the insulation degradation position of the variable frequency motor to the ground, the monitoring process includes:
[0052] Step 1: Establish the periodic component P of the leakage current c The expression is:
[0053] Where, t is the test time of the leakage current signal, R g is the insulation resistance to ground, C g is the insulation capacitance to ground, L s is the stator inductance, R s is the stator resistance, x is the location of insulation degradation to ground;
[0054] Step 2: Establish the leakage current oscillation period T based on the periodic component Pc c The expression is:
[0055] In the formula, R g is the insulation resistance to ground, C g is the insulation capacitance to ground, L s is the stator inductance, R s is the stator resistance, x is the location of insulation degradation to ground;
[0056] By T c It can be seen from the expression that T cThe relationship with x is a parabolic relationship. As the degenerate position moves toward the neutral point, T c Increase first and then decrease slightly, such as Fig. 9 shown.
[0057] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions. The sentence "includes an element defined by ... does not exclude the existence of other identical elements in the process, method, article or device including the element".
[0058] The above technical solutions only reflect the preferred technical solutions of the technical solutions of the present invention. Some changes that may be made to certain parts thereof by technicians in this technical field all reflect the principles of the present invention and fall within the protection scope of the present invention.
Claims
1. A method for online monitoring of the insulation of a variable frequency motor to ground based on the time domain characteristics of leakage current, the method comprising three levels of monitoring, characterized in that: The first level of monitoring is the online monitoring of the phase of insulation degradation between the variable frequency motor and the ground, the second level of monitoring is the online monitoring of the position of insulation degradation between the variable frequency motor and the ground, and the third level of monitoring is the online monitoring of the severity of insulation degradation between the variable frequency motor and the ground; The first level is the online monitoring of the insulation degradation phase of the variable frequency motor to the ground. The monitoring process includes: Step 1: Establish the initial oscillation amplitude A of the leakage current excited by the step voltage of the degradation monitoring phase ini-d The expression is: Where: ΔU d represents the step voltage applied to the degenerate phase, R g is the insulation resistance to ground, C g is the insulation capacitance to ground, L s is the stator inductance, R s is the stator resistance, x is the location of insulation degradation to ground; Step 2: Establish the initial oscillation amplitude A of the leakage current excited by the healthy phase step voltage ini-h The expression is: Where: ΔU h represents the step voltage applied to the healthy phase, R g is the insulation resistance to ground, C g is the insulation capacitance to ground, L s is the stator inductance, R s is the stator resistance, x is the location of insulation degradation to ground; Step 3: Set the initial oscillation amplitude A of the leakage current excited by the step voltage of the degradation monitoring phase ini-d The initial oscillation amplitude A of the leakage current excited by the step voltage of the healthy phase ini-h Compare them, if the amplitudes of the two are different, it is determined that the degradation monitoring phase has been degraded; The second level is online monitoring of the location of insulation degradation of the variable frequency motor to the ground. The monitoring process includes: Select the initial oscillation amplitude A of the leakage current excited by the step voltage of the degradation monitoring phase ini-d The expression is used as the basis for monitoring the location of insulation degradation to ground, with A ini-d From the expression, the insulation degradation position to ground is x, A ini-d The larger the value of is, the closer the insulation degradation position x is to the motor input terminal; Level 3: Monitoring of the severity of insulation degradation of variable frequency motor to ground. The monitoring process includes: insulation resistance to ground R g Monitoring and ground insulation capacitance C g The severity of insulation degradation to ground depends on the insulation resistance R g And the insulation capacitance to ground C g Therefore, by constructing a circuit with an insulation resistance R g And the insulation capacitance to ground C g The expression can monitor the severity of insulation degradation to ground and establish the leakage current decay time T s The expression is: In the formula, R g is the insulation resistance to ground, C g is the insulation capacitance to ground, L s is the stator inductance, R s is the stator resistance. From the above formula, we can know that T s With R g and C g is proportional to the product of g and C g The larger the value of is, the less severe the insulation degradation of the variable frequency motor to the ground is. s The higher the value, the less severe the insulation degradation of the variable frequency motor to ground, and vice versa.
2. The method for online monitoring of the insulation of a variable frequency motor to ground based on the time domain characteristics of leakage current according to claim 1 is characterized in that: The R s , L s The values were obtained by measuring with an impedance analyzer.
3. The method for online monitoring of the insulation of a variable frequency motor to ground based on the time domain characteristics of leakage current according to claim 1 is characterized in that: During the online monitoring of the insulation degradation phase of the variable frequency motor to the ground, A ini-d Greater than A ini-h .
4. The method for online monitoring of the insulation of a variable frequency motor to ground based on the time domain characteristics of leakage current according to claim 1 is characterized in that: During the online monitoring of the position of the variable frequency motor's insulation degradation to the ground, x=0 corresponds to the line-in terminal of the variable frequency motor, and x=1 corresponds to the neutral point of the variable frequency motor.