Motor winding early fault diagnosis method and system based on voltage balance

Abstract

The invention discloses an early fault diagnosis method and system for a motor winding based on voltage balance. The early fault diagnosis method for the motor winding comprises the following steps: acquiring a three-phase terminal voltage instantaneous value of a motor stator side in real time; respectively applying sliding window discrete Fourier transform to the three-phase terminal voltage instantaneous values so as to extract a complex phasor only containing power supply fundamental frequency; performing symmetric zero phasor operation on the complex phasor to obtain a three-phase zero-axis voltage instantaneous value; when the three-phase zero-axis voltage instantaneous value is larger than or equal to the working condition self-adaptive threshold voltage and lasts for exceeding the preset delay time, it is judged that an insulation failure risk exists, and a micro-short-circuit early warning signal is output; the working condition self-adaptive threshold voltage is corrected along with load step or asymmetric disturbance of the power grid. According to the invention, based on the three-phase zero-axis voltage, high-sensitivity and advanced early warning of early insulation faults such as motor winding turn-to-turn short circuit is realized; and the diagnosis reliability and robustness are greatly improved by introducing the working condition self-adaptive threshold voltage.

Description

Technical Field

[0001] This invention relates to electrical equipment condition detection and fault diagnosis, specifically to a method and system for early fault diagnosis of motor windings based on voltage balance. Background Technology

[0002] Three-phase rotating electric motors are core power equipment in the industrial field, and their operational reliability directly affects production safety and efficiency. Stator winding faults are one of the main causes of motor shutdowns, and insulation failure between strands within the winding is an early manifestation of this type of fault. If these defects are not detected early, they can quickly evolve into catastrophic failures, causing huge economic losses. Existing diagnostic methods based on current spectrum analysis have significant limitations: this method is extremely sensitive to changes in motor load and is prone to misdiagnosis under unbalanced supply voltage conditions. Furthermore, with the development of power electronics technology, motors are often driven by voltage source inverters, whose wideband, non-stationary voltage signals pose a serious challenge to traditional diagnostic methods, resulting in insufficient reliability, accuracy, and robustness in complex industrial environments. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a method and system for early fault diagnosis of motor windings based on voltage balance, so as to solve one or more problems existing in the prior art.

[0004] Technical solution: The present invention provides a method for early fault diagnosis of motor windings based on voltage balance, comprising:

[0005] (1) Real-time acquisition of instantaneous values ​​of the three-phase terminal voltage on the stator side of the motor;

[0006] (2) Apply a sliding window discrete Fourier transform to the instantaneous values ​​of the three-phase terminal voltages to extract complex phasors containing only the fundamental frequency of the power supply;

[0007] (3) Perform symmetrical zero-phasor operations on the complex phasors to obtain the instantaneous values ​​of the three-phase zero-axis voltages. ;

[0008] (4) When the instantaneous value of the three-phase zero-axis voltage Greater than or equal to the adaptive threshold voltage under operating conditions Furthermore, if the delay exceeds the preset time, an insulation failure risk is identified, and a micro-short circuit warning signal is output; the operating condition adaptive threshold voltage... It is corrected for load step changes or grid asymmetric disturbances.

[0009] Furthermore, the instantaneous value of the three-phase zero-axis voltage , , The fundamental frequency voltage phasor at terminal U. The fundamental frequency voltage phasor at terminal V. The fundamental frequency voltage phasor at terminal W. It is the sum of the three-phase fundamental frequency voltage phasors.

[0010] Furthermore, the operating condition adaptive threshold voltage , Based on the basic threshold voltage, and The preset weighting coefficients are, where Indicates sensitivity to load mutations. This indicates tolerance for fluctuations in grid voltage. It is the absolute value of the rate of change of the load current. It refers to the voltage imbalance of the power grid.

[0011] The present invention provides a voltage balance-based early fault diagnosis system for motor windings, comprising:

[0012] The three-phase voltage acquisition module is used to acquire the instantaneous values ​​of the three-phase terminal voltages on the stator side of the motor in real time.

[0013] The single-frequency phasor extraction module is used to apply a sliding window discrete Fourier transform to the instantaneous values ​​of the three-phase terminal voltages to extract complex phasors containing only the power supply fundamental frequency.

[0014] The three-phase zero-axis voltage generation module is used to perform symmetrical zero-phasor operations on complex phasors to obtain the instantaneous values ​​of the three-phase zero-axis voltage. ;

[0015] The fault determination module is used to determine the instantaneous value of the three-phase zero-axis voltage. Greater than or equal to the adaptive threshold voltage under operating conditions Furthermore, if the delay exceeds the preset time, an insulation failure risk is identified, and a micro-short circuit warning signal is output; the operating condition adaptive threshold voltage... Corrected for load step changes or grid asymmetric disturbances.

[0016] Furthermore, the three-phase voltage acquisition module employs a high-impedance isolation sampling circuit to achieve non-invasive voltage detection.

[0017] Furthermore, the sliding window length of the single-frequency phasor extraction module is set to the number of sampling points corresponding to the integer period of the power supply base frequency in order to reduce spectral leakage.

[0018] Furthermore, the three-phase zero-axis voltage generation module includes a phasor adder and a scaling factor;

[0019] Phasor adders are used to sum the phasors of three-phase fundamental frequency voltages: , It is the sum of the phasors of the three-phase fundamental frequency voltage. The fundamental frequency voltage phasor at terminal U. The fundamental frequency voltage phasor at terminal V. The fundamental frequency voltage phasor at terminal W;

[0020] The scaler is used to scale the summation result by one-third to generate the instantaneous three-phase zero-axis voltage values. .

[0021] Furthermore, the operating condition adaptive threshold voltage , Based on the basic threshold voltage, and The preset weighting coefficients are, where Indicates sensitivity to load mutations. This indicates tolerance for fluctuations in grid voltage. It is the absolute value of the rate of change of the load current. It refers to the voltage imbalance of the power grid.

[0022] Furthermore, the aforementioned voltage balance-based early fault diagnosis system for motor windings also includes a wideband power supply adaptation unit, which is used to synchronously adjust the sliding window length of the single-frequency phasor extraction module when the output frequency of the voltage source inverter changes, so as to maintain the amplitude accuracy of the instantaneous value of the three-phase zero-axis voltage.

[0023] This invention solves the problems of complex installation and high dependence on power quality in existing systems by using non-invasive voltage sampling and wideband power supply adaptation technology, thereby achieving the system's engineering applicability and ease of use.

[0024] Furthermore, the voltage balance-based early fault diagnosis system for motor windings also includes a communication interface unit for uploading micro short-circuit warning signals to a remote monitoring terminal or local protection device.

[0025] This invention solves the problems of isolated fault information and inability to participate in control in real time by integrating a communication interface unit, and realizes a complete automated closed loop from fault diagnosis to linkage protection.

[0026] From the perspective of fault mechanism, the essence of inter-turn short circuit is the disruption of the inherent symmetry of the three-phase windings of the motor. In a healthy and symmetrical three-phase system, the vector sum of the voltages of each phase at any given time (i.e., the common-mode voltage) should theoretically tend to zero. However, when a local short circuit occurs within any phase winding, the impedance of that phase will abnormally decrease, causing a small but measurable distortion in the amplitude and phase of its terminal voltage relative to other healthy phases. This three-phase asymmetry caused by the fault directly leads to the vector sum no longer canceling each other out, thus generating a characteristic signal in the common-mode voltage. Therefore, the three-phase zero-axis voltage can be regarded as an extremely sensitive "observation window" for system symmetry, capable of effectively capturing the subtle imbalances introduced by early inter-turn short circuits.

[0027] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention uses three-phase zero-axis voltage as the core detection index, which solves the problem that the traditional current spectrum analysis method is not sensitive to early weak faults, and realizes high sensitivity and early warning of early insulation faults such as inter-turn short circuits in motor windings; In addition, by introducing operating condition adaptive threshold voltage, the industry problem of false alarms caused by motors under complex operating conditions such as load changes and power grid fluctuations is solved, and the reliability and robustness of diagnosis are greatly improved. Attached Figure Description

[0028] Figure 1 This is a flowchart of an early fault diagnosis method for motor windings based on voltage balance provided by an embodiment of the present invention;

[0029] Figure 2 This invention provides an early fault diagnosis system architecture for motor windings based on voltage balance. Detailed Implementation

[0030] The invention will now be further described with reference to the accompanying drawings.

[0031] It adopts a 1.1kW three-phase squirrel-cage induction motor with 4 poles. The motor stator winding is a three-phase star connection with a rated line voltage of 400V, a rated phase current of 4.3A, and 396 turns per phase in series.

[0032] Example 1: As Figure 1 As shown, Example 1 provides a method for early fault diagnosis of motor windings based on voltage balance, including the following steps:

[0033] (1) Real-time acquisition of instantaneous values ​​of the three-phase terminal voltage on the stator side of the motor.

[0034] (2) Apply a sliding window discrete Fourier transform to the instantaneous values ​​of the three-phase terminal voltages to extract complex phasors containing only the fundamental frequency of the power supply.

[0035] (3) Perform symmetrical zero-phasor operations on the complex phasors to obtain the instantaneous values ​​of the three-phase zero-axis voltages. .

[0036] Instantaneous value of three-phase zero-axis voltage , , The fundamental frequency voltage phasor at terminal U. The fundamental frequency voltage phasor at terminal V. The fundamental frequency voltage phasor at terminal W. It is the sum of the three-phase fundamental frequency voltage phasors.

[0037] (4) When the instantaneous value of the three-phase zero-axis voltage Greater than or equal to the adaptive threshold voltage under operating conditions Furthermore, if the delay exceeds a preset time (e.g., 100ms), an insulation failure risk is identified, and a micro-short circuit warning signal is output; operating condition adaptive threshold voltage. It is corrected for load step changes or grid asymmetric disturbances. The reason for considering the delay time is that there are many instantaneous disturbances during motor operation, such as device switching noise and voltage sags.

[0038] Operating condition adaptive threshold voltage , Based on the basic threshold voltage, and The preset weighting coefficients are, where Indicates sensitivity to load mutations. This indicates tolerance for fluctuations in grid voltage. It is the absolute value of the rate of change of the load current. It refers to the voltage imbalance of the power grid.

[0039] Example 2: Figure 2 As shown, Embodiment 2 provides a motor winding early fault diagnosis system based on voltage balance, including a three-phase voltage acquisition module, a single-frequency phasor extraction module, a three-phase zero-axis voltage generation module, a fault determination module, a wideband power supply adaptation unit, and a communication interface unit.

[0040] The three-phase voltage acquisition module is used to acquire the instantaneous values ​​of the three-phase terminal voltages on the stator side of the motor in real time. Specifically, the three-phase voltage acquisition module adopts a high-impedance isolation sampling circuit with an input impedance ≥10MΩ and a common-mode impulse voltage tolerance ≥2.5kV.

[0041] In this embodiment, the three-phase voltage acquisition module uses three independent high-impedance differential isolation amplifiers (AMC1300) as the core sensing units. The input terminals of these three channels are connected to the U, V, and W three-phase power terminals in the motor junction box via shielded cables, respectively, for parallel measurement. The amplifier has an input impedance of 22kΩ and an electrical isolation strength of 5000Vrms conforming to UL 1577 standards, enabling non-invasive voltage detection of the motor's three-phase power terminals.

[0042] It establishes a barrier between the measuring circuit and the power supply line of the motor under test, effectively blocking high voltage and large current in the circuit and ensuring equipment safety. Moreover, it has extremely high input impedance, which means that while acquiring voltage signals, it will only draw extremely weak current, which will hardly have any impact on the normal faults of the motor itself, and can truly capture the original voltage waveform of the motor during operation.

[0043] The voltage signals from the three channels are isolated and amplified, and then digitized using a set of high-precision analog-to-digital converters with synchronous sampling. The sampling frequency is fixed at 10kHz to ensure that the three voltage values ​​are strictly synchronized in time.

[0044] The single-frequency phasor extraction module applies a sliding window Discrete Fourier Transform to the instantaneous values ​​of the three-phase terminal voltages to extract complex phasors containing only the power supply fundamental frequency. Specifically, the sliding window length of the single-frequency phasor extraction module is set to the number of sampling points corresponding to an integer period of the power supply fundamental frequency to reduce spectral leakage.

[0045] The digitized signal is fed into a single-frequency phasor extraction module, where it is first tracked in real time via a software phase-locked loop to determine the fundamental frequency of the power supply. The length of the Hanning window is dynamically set according to the fundamental frequency. Calculate the window length in multiples of integer periods:

[0046]

[0047] in, The system sampling frequency, This is the current power supply base frequency. Represents the length of the sliding window; the reload window coefficient, each analysis window contains 5 complete power cycles. A Discrete Fourier Transform is applied to the voltage sequence of each channel under the window function. Through precise frequency tracking and integer cycle truncation, spectral leakage is suppressed to below -31dB, thereby extracting complex phasors containing only the fundamental component with high precision, effectively filtering out grid harmonics and random noise interference.

[0048] The three-phase zero-axis voltage generation module is used to perform symmetrical zero-phasor operations on complex phasors to obtain the instantaneous values ​​of the three-phase zero-axis voltage. Specifically, the three-phase zero-axis voltage generation module includes a phasor adder and a scaling factor.

[0049] Phasor adders are used to sum the phasors of three-phase fundamental frequency voltages:

[0050]

[0051] in, It is the sum of the phasors of the three-phase fundamental frequency voltage. The fundamental frequency voltage phasor at terminal U. The fundamental frequency voltage phasor at terminal V. The fundamental frequency voltage phasor at terminal W.

[0052] The scaler is used to scale the summation result by one-third to generate the instantaneous three-phase zero-axis voltage values. :

[0053]

[0054] In an ideal three-phase symmetrical system The theoretical value should be zero.

[0055] The fault determination module is used to determine the instantaneous value of the three-phase zero-axis voltage. Greater than or equal to the adaptive threshold voltage under operating conditions Furthermore, if the delay exceeds the preset time, an insulation failure risk is identified, and a micro-short circuit warning signal is output; the operating condition adaptive threshold voltage... Corrected for load step changes or grid asymmetric disturbances.

[0056] The core of the fault judgment module is the adaptive threshold voltage for operating conditions. In response to the problem that motors are prone to false alarms when the load changes suddenly or the power grid fluctuates, the system detects the three-phase zero-axis voltage while simultaneously detecting the rate of change of the load current and the imbalance of the power grid voltage. When these strong interference conditions are identified, the system will automatically and in real time raise the fault judgment threshold according to the preset algorithm.

[0057] Operating condition adaptive threshold voltage It consists of a basic threshold value and two dynamic adjustment terms, and its calculation formula is as follows:

[0058]

[0059] in, This is the basic threshold voltage (e.g., 1.5V), which corresponds to the upper limit of normal common-mode voltage fluctuation that the motor can tolerate under stable and balanced operating conditions. and These are the preset weighting coefficients (0.05 and 0.5 respectively). This determines the system's sensitivity to sudden load changes. This determines the system's tolerance to grid voltage fluctuations. It is the absolute value of the rate of change of the load current. This refers to the voltage imbalance of the power grid. All parameters above are derived based on the normal operating conditions of this motor.

[0060] The fault diagnosis module will continuously compare the instantaneous values ​​of the three-phase zero-axis voltage calculated in real time. With dynamically calculated adaptive threshold voltage for operating conditions If and only if If the signal persists for more than a preset delay time of 100ms (excluding instantaneous spike interference), the fault determination module determines that there is a risk of insulation failure and outputs a micro short circuit warning signal, which is a continuous high-level digital signal.

[0061] The fault detection module continuously monitors and analyzes the motor's operating parameters, identifying characteristic signals of inter-turn short circuits in the windings through the three-phase zero-axis voltage, and can capture extremely weak fault signs. In this embodiment, an insulation failure warning signal can still be triggered when the number of short-circuited turns accounts for less than 1% of the total number of winding turns.

[0062] The wideband power supply adaptation unit mainly uses a phase-locked loop circuit to accurately track the real-time frequency of the voltage source inverter output. Whenever the frequency changes, the system immediately recalculates and adjusts the sampling window length in digital signal processing according to the new frequency value, ensuring that each analysis window always accurately contains an integer number of complete cycles of the power supply.

[0063] The communication interface unit is used to upload micro short-circuit warning signals to remote monitoring terminals or local protection devices via the MODBUS TCP protocol.

[0064] The communication interface unit primarily transmits the insulation fault early warning signals generated internally by the system to external devices via the MODBUS TCP protocol. These signals are sent to locally installed automated protection equipment and relay protection devices. Upon receiving the early warning signal, the device can activate an audible and visual alarm, simultaneously recording the timestamp of the fault occurrence and collecting relevant electrical parameters, which are then stored in the EEPROM. Based on preset safety policies, it can also initiate protective operations such as load reduction or orderly shutdown, thus forming a complete early warning and protection closed loop.

[0065] In summary, this invention acquires three-phase voltage non-invasively, extracts the fundamental phasor through an integer-cycle sliding window, and calculates the three-phase zero-axis voltage as a fault characteristic. It employs an adaptive threshold voltage to compensate for load fluctuations and grid imbalances in real time, reducing the false alarm rate by more than four times. The wideband power supply adaptation unit automatically tracks inverter frequency changes, maintaining integer-cycle analysis, and is suitable for both power frequency and frequency converter power supplies. This invention can detect ≤1% inter-turn short circuits, outputs a warning after debouncing, supports MODBUS TCP protocol upload, and achieves a closed-loop diagnostic protection system.

Claims

1. A method for early fault diagnosis of motor windings based on voltage balance, characterized in that, The method comprises: (1) collecting real-time three-phase terminal voltage instantaneous values of the motor stator side; (2) applying a sliding window discrete Fourier transform to the three-phase terminal voltage instantaneous values respectively to extract complex phasors containing only the power fundamental frequency. (3) Perform symmetrical zero sequence operation on the complex phasor to obtain three-phase zero-axis voltage instantaneous value ; (4) When the instantaneous value of the three-phase zero-axis voltage Greater than or equal to the adaptive threshold voltage under operating conditions Furthermore, if the delay time continues beyond the preset time, it is determined that there is a risk of insulation failure and a micro short circuit warning signal is output. Operating condition adaptive threshold voltage Corrected for load steps or grid asymmetry disturbances.

2. The voltage balance based motor winding incipient fault diagnosis method according to claim 1, characterized in that, Three-phase zero-sequence voltage instantaneous value , , is the U terminal fundamental voltage phasor, is the V terminal fundamental voltage phasor, is the W terminal fundamental voltage phasor, is the sum of the three-phase fundamental voltage phasors.

3. The voltage balance based motor winding incipient fault diagnosis method of claim 1, wherein, Operating condition adaptive threshold voltage , is a base threshold voltage, and are preset weighting coefficients, wherein represents a sensitivity to load mutation, represents a tolerance to grid voltage fluctuation, is an absolute value of a load current change rate, is a grid voltage unbalance degree.

4. A voltage balance based motor winding incipient fault diagnosis system, characterized in that, The method comprises: a three-phase voltage acquisition module, configured to collect real-time three-phase terminal voltage instantaneous values of the motor stator side; a single-frequency phasor extraction module, configured to apply a sliding window discrete Fourier transform to the three-phase terminal voltage instantaneous values respectively to extract complex phasors containing only the power fundamental frequency; The three-phase zero-axis voltage generation module is configured to perform a symmetric zero-sequence operation on the complex phasor to obtain a three-phase zero-axis voltage instantaneous value ; A fault determination module is configured to determine that there is a risk of insulation failure and output a micro-short circuit early warning signal when the instantaneous value of the three-phase zero-axis voltage is greater than or equal to an operating condition adaptive threshold voltage and lasts for more than a preset delay time. Operating condition adaptive threshold voltage Corrected with load step or grid asymmetry disturbance.

5. The voltage balance based motor winding incipient fault diagnosis system of claim 4, wherein, The three-phase voltage acquisition module adopts a high-resistance isolation sampling circuit to realize non-intrusive voltage detection.

6. The voltage balance based motor winding incipient fault diagnosis system of claim 4, wherein, The sliding window length of the single-frequency phasor extraction module is set to the number of sampling points corresponding to an integer period of the power fundamental frequency, so as to reduce spectral leakage.

7. The voltage balance based motor winding incipient fault diagnosis system of claim 4, wherein, The three-phase zero-axis voltage generation module comprises a phasor adder and a proportional scaler. A phasor adder is used to sum the three phase fundamental voltage phasors: , is the sum of the three phase fundamental voltage phasors, is the U terminal fundamental voltage phasor, is the V terminal fundamental voltage phasor, is the W terminal fundamental voltage phasor; A proportioner is used to scale the summation result by one third to generate a three-phase zero-sequence voltage instantaneous value .

8. The voltage balance based motor winding incipient fault diagnosis system of claim 4, wherein, Operating condition adaptive threshold voltage , is a base threshold voltage, and is a preset weighting coefficient, wherein represents a sensitivity to load mutation, represents a tolerance to grid voltage fluctuation, is an absolute value of a load current change rate, is a grid voltage unbalance degree.

9. The voltage balance based motor winding incipient fault diagnosis system of claim 6, wherein, Further comprising a wide-band power source adaptation unit, configured to synchronously adjust the sliding window length of the single-frequency phasor extraction module when the output frequency of the voltage source inverter changes, so as to maintain the amplitude accuracy of the three-phase zero-axis voltage instantaneous values.

10. The voltage balance based motor winding incipient fault diagnosis system of claim 4, wherein, Further comprising a communication interface unit, configured to upload the micro-short circuit early warning signal to a remote monitoring terminal or a local protection device.

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