Synchronous phase modifier typical rotor fault non-intrusive diagnosis method

Abstract

The invention provides a non-intrusive diagnosis method for typical rotor faults of a synchronous phase modifier, and the method comprises the steps: carrying out finite element modeling and fault working condition setting, carrying out simulation to obtain magnetic field distribution data under each working condition, carrying out the extraction and feature analysis of stray magnetic field signals, extracting time domain and frequency domain signals of a stray magnetic field under healthy and various fault working conditions, and carrying out the diagnosis of the typical rotor faults of the synchronous phase modifier. Fundamental wave, odd-even harmonic components and signal change trends are compared and analyzed, stray magnetic field characteristics corresponding to faults are extracted and recognized, diagnosis criterion establishment and fault recognition are carried out, diagnosis criteria and threshold values of rotor turn-to-turn short circuit, dynamic eccentricity and shaft-diameter composite eccentricity faults are established according to the stray magnetic field characteristics, and the fault diagnosis accuracy is improved. And when the specific harmonic amplitude or change characteristic of the stray magnetic field signal exceeds the criterion threshold, determining the rotor fault of the corresponding type and degree. Equipment dismounting or structure reconstruction is not needed, the detection system is simple in structure, internal fault characteristics of the phase modifier can be reflected in real time, and high sensitivity and practicability are achieved.

Description

Technical Field

[0001] This invention relates to the field of synchronous motor and large power equipment operation status monitoring and fault diagnosis technology, and in particular to a non-invasive diagnostic method for typical rotor faults of synchronous condensers. Background Technology

[0002] Synchronous condensers, as crucial dynamic reactive power compensation devices in large power systems, are widely used in ultra-high voltage direct current (UHVDC) transmission and regional power grid stabilization. With the rapid development of UHVDC projects in my country, higher demands are placed on the health monitoring and fault diagnosis of synchronous condensers. Under long-term high-load and high-speed operation, synchronous condensers are highly susceptible to typical faults such as inter-turn short circuits and air gap eccentricity in their rotor windings. Inter-turn short circuits can lead to localized rotor overheating and insulation damage, potentially causing equipment shutdown or even complete failure in severe cases. Eccentricity faults cause distortion of the air gap magnetic field, resulting in increased vibration and noise, reduced bearing life, and in extreme cases, even rotor rubbing accidents, endangering the safe operation of the power grid.

[0003] Currently, traditional methods for detecting rotor faults in synchronous condensers mainly include AC impedance analysis, DC resistance analysis, open transformer analysis, detection coil analysis, and vibration diagnosis. These methods have limitations in practical applications, such as being highly invasive, requiring certain modifications to the equipment structure, having limited detection sensitivity, and being difficult to implement online monitoring. In particular, traditional detection methods often fail to identify early, weak inter-turn short circuits and slight eccentricity faults in a timely and accurate manner, increasing the risk of equipment operating with defects and the escalation of faults.

[0004] Stray magnetic fields are weak magnetic fields formed in the stator core and surrounding air domain when the internal air gap magnetic field of a synchronous condenser is transmitted to the outside. Changes in these fields can reflect the internal electromagnetic state and fault characteristics of the condenser. In recent years, with the development of high-sensitivity magnetic sensor technology, non-invasive online detection and fault diagnosis methods based on stray magnetic fields have received widespread attention. This method requires no disassembly or structural alteration of the equipment and can achieve real-time monitoring and early warning of faults such as rotor turn-to-turn short circuits and eccentricity under normal operating conditions, providing a new technical means to improve the reliability and safety of synchronous condenser operation.

[0005] However, there is currently a lack of a dedicated system for stray magnetic field modeling, signal feature extraction, and diagnostic criteria for typical rotor faults in synchronous condensers. Given the complex operating environment of synchronous condensers in actual conditions, there is an urgent need to propose a novel, highly sensitive, and practical non-invasive rotor fault diagnosis method to achieve accurate identification and online early warning of inter-turn short circuits and eccentricity faults.

[0006] Therefore, it is essential to design a non-invasive diagnostic method for typical rotor faults of synchronous condensers. Summary of the Invention

[0007] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a non-invasive diagnostic method for typical rotor faults of synchronous condensers.

[0008] To achieve the above objectives, the present invention provides the following solution:

[0009] This invention provides a non-invasive diagnostic method for typical rotor faults in synchronous condensers, comprising:

[0010] Step 1: Perform finite element modeling and fault condition setting. Based on the structural parameters and electromagnetic characteristics of the synchronous condenser, use finite element simulation software to establish a two-dimensional or three-dimensional electromagnetic field model of the condenser, and set the healthy state, rotor inter-turn short circuit, dynamic eccentricity and shaft diameter combined eccentricity fault conditions respectively, and simulate to obtain magnetic field distribution data under each condition.

[0011] Step 2: Extract and analyze stray magnetic field signals. Select sampling points in the air domain outside the stator core, and extract the time and frequency domain signals of stray magnetic fields under healthy and various fault conditions. Compare and analyze the fundamental wave, odd and even harmonic components and signal change trends, and extract and identify the stray magnetic field characteristics corresponding to the fault.

[0012] Step 3: Establish diagnostic criteria and identify faults. Based on the obtained stray magnetic field characteristics, establish diagnostic criteria and thresholds for rotor inter-turn short circuits, dynamic eccentricity, and shaft diameter composite eccentricity faults. When the specific harmonic amplitude or variation characteristics of the stray magnetic field signal exceed the criterion threshold, determine the corresponding type and degree of rotor fault, and realize non-invasive, online automatic diagnosis.

[0013] Preferably, in step 1, the established finite element model includes the stator, rotor, air gap, and key areas of the air domain on the back of the stator core, and is modeled in two or three dimensions according to actual needs.

[0014] Preferably, dynamic eccentricity faults are simulated by adjusting the relative offset between the rotor shaft center and the stator shaft center, and shaft-diameter combined eccentricity faults are simulated by jointly setting axial and radial eccentricity conditions.

[0015] Preferably, the stray magnetic field characteristics include the fundamental amplitude, even harmonic components, odd harmonic components, and time-domain peak value and frequency-domain distribution characteristics.

[0016] Preferably, in step 3, diagnostic criteria and thresholds for rotor inter-turn short circuits, dynamic eccentricity, and combined shaft diameter eccentricity faults are established, specifically as follows:

[0017] The percentage a% of the sum of the amplitudes of the collected radial stray magnetic flux density even harmonics relative to the fundamental amplitude is used as the threshold criterion:

[0018]

[0019] In the formula, A1, A2, A4, A6, and A8 represent the amplitudes of the fundamental wave, the second harmonic, the fourth harmonic, the sixth harmonic, and the eighth harmonic, respectively.

[0020] When the overexcitation and underexcitation thresholds for inter-turn short circuits are greater than 4.6% and 3.8% respectively, and the peak value of radial stray magnetic flux density decreases, it is determined to be an inter-turn short circuit fault in the rotor excitation winding.

[0021] When the thresholds for overexcitation and underexcitation of dynamic eccentricity are greater than 19.71% and 17.35% respectively, and the peak value of radial stray magnetic flux density increases, it is determined to be a rotor dynamic eccentricity fault.

[0022] Preferably, when the radial peak value of stray magnetic flux density at different positions along the axial direction on the back of the stator core of the synchronous condenser changes proportionally with the increase of the axial coordinate, it is determined to be a rotor shaft diameter composite eccentricity fault.

[0023] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0024] This invention provides a non-invasive diagnostic method for typical rotor faults of synchronous condensers, including finite element modeling and fault condition setting. Based on the structural parameters and electromagnetic characteristics of the synchronous condenser, a two-dimensional or three-dimensional electromagnetic field model of the condenser is established using finite element simulation software. Healthy state, rotor inter-turn short circuit, dynamic eccentricity, and shaft diameter combined eccentricity fault conditions are set respectively. Simulations are used to obtain magnetic field distribution data under each condition. Stray magnetic field signals are extracted and their characteristics are analyzed. Sampling points are selected in the air domain outside the stator core, and the time and frequency domain signals of stray magnetic fields under healthy and various fault conditions are extracted respectively. The fundamental wave, odd and even harmonic components, and signal variation trends are compared and analyzed. The stray magnetic field characteristics corresponding to the fault are extracted and identified. Diagnostic criteria are established and fault identification is performed. Based on the obtained stray magnetic field characteristics, diagnostic criteria and thresholds for rotor inter-turn short circuit, dynamic eccentricity, and shaft diameter combined eccentricity faults are established. When the specific harmonic amplitude or variation characteristics of the stray magnetic field signal exceed the criterion threshold, the corresponding type and degree of rotor fault are determined, achieving non-invasive, online automatic diagnosis. This invention requires no disassembly or structural modification of the equipment. The detection system has a simple structure and can reflect the internal fault characteristics of synchronous condensers in real time, exhibiting high sensitivity and practicality. Simulation and theoretical analysis results verify the effectiveness of the method, providing new ideas and technical support for online monitoring and health assessment of typical synchronous condenser faults. It is applicable to the field of fault diagnosis and condition monitoring of large-capacity synchronous condensers in power systems. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A two-dimensional simulation model diagram of the camera;

[0027] Figure 2 To adjust the 3D simulation model of the camera;

[0028] Figure 3 Diagrams showing the spatial angles of stray magnetic flux density along different short paths between turns;

[0029] Figure 4 Time-domain information diagram of stray magnetic flux density along different short-path directions between turns;

[0030] Figure 5 Frequency domain information diagram of stray magnetic flux density along different inter-turn short paths;

[0031] Figure 6 A time-domain diagram showing stray magnetic flux density along short paths between underexcited turns;

[0032] Figure 7 Frequency domain information diagram of stray magnetic flux density along short paths between underexcited turns;

[0033] Figure 8 Radial stray magnetic flux density maps for spatial angles with different degrees of eccentricity;

[0034] Figure 9 Time-domain information diagram of radial stray magnetic flux density at different degrees of eccentricity;

[0035] Figure 10 Frequency domain information diagram of radial stray magnetic flux density at different degrees of eccentricity;

[0036] Figure 11 Time-domain waveforms of radial stray magnetic flux density under different degrees of underexcitation;

[0037] Figure 12 Frequency domain information diagram of radial stray magnetic flux density under different degrees of eccentricity under underexcitation;

[0038] Figure 13 The stray magnetic flux density radial time-domain information diagram under different eccentricities;

[0039] Figure 14 Radial frequency domain information diagram of stray magnetic flux density under different eccentricities;

[0040] Figure 15 Time-domain information of radial stray magnetic flux density at different sampling points;

[0041] Figure 16 Frequency domain information diagram of radial stray magnetic flux density at different sampling points;

[0042] Figure 17 This is a schematic diagram of the non-invasive diagnostic method for typical rotor faults of a synchronous condenser according to an embodiment of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] The purpose of this invention is to provide a non-invasive diagnostic method for typical rotor faults of synchronous condensers, which solves the shortcomings of existing diagnostic methods for typical rotor faults of synchronous condensers, such as strong invasiveness, low detection sensitivity, and difficulty in achieving real-time online monitoring. This method can be used to identify typical faults such as inter-turn short circuits, dynamic eccentricity, and combined shaft diameter eccentricity of rotors online, so as to realize early warning and health status assessment of equipment.

[0045] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] like Figure 17 As shown, the present invention provides a non-invasive diagnostic method for typical rotor faults of synchronous condensers, comprising:

[0047] Step 1: Perform finite element modeling and fault condition setting. Based on the structural parameters and electromagnetic characteristics of the synchronous condenser, use finite element simulation software to establish a two-dimensional or three-dimensional electromagnetic field model of the condenser, and set the healthy state, rotor inter-turn short circuit, dynamic eccentricity and shaft diameter combined eccentricity fault conditions respectively, and simulate to obtain magnetic field distribution data under each condition.

[0048] Step 2: Extract and analyze stray magnetic field signals. Select sampling points in the air domain outside the stator core, and extract the time and frequency domain signals of stray magnetic fields under healthy and various fault conditions. Compare and analyze the fundamental wave, odd and even harmonic components and signal change trends, and extract and identify the stray magnetic field characteristics corresponding to the fault.

[0049] Step 3: Establish diagnostic criteria and identify faults. Based on the obtained stray magnetic field characteristics, establish diagnostic criteria and thresholds for rotor inter-turn short circuits, dynamic eccentricity, and shaft diameter composite eccentricity faults. When the specific harmonic amplitude or variation characteristics of the stray magnetic field signal exceed the criterion threshold, determine the corresponding type and degree of rotor fault, and realize non-invasive, online automatic diagnosis.

[0050] In step 1, finite element modeling and fault condition setting are performed. Based on the structural parameters and electromagnetic characteristics of the synchronous condenser, a two-dimensional or three-dimensional electromagnetic field model of the condenser is established using finite element simulation software. Fault conditions including healthy state, rotor inter-turn short circuit, dynamic eccentricity, and shaft-diameter combined eccentricity are set, and the magnetic field distribution data under each condition is obtained through simulation. Specifically:

[0051] Based on the structural parameters of the synchronous condenser (such as the dimensions of the stator and rotor, the number of pole pairs, the winding arrangement, the air gap length, etc.), a two-dimensional or three-dimensional electromagnetic field model of the synchronous condenser is established using Ansys Maxwell software. The model should include key areas such as the stator, rotor, air gap, and air domain on the back of the stator core.

[0052] In step 2, stray magnetic field signals are extracted and their features are analyzed. Sampling points are selected in the air domain outside the stator core, and the time and frequency domain signals of stray magnetic fields under healthy and various fault conditions are extracted respectively. The fundamental wave, odd and even harmonic components and signal variation trends are compared and analyzed, and the stray magnetic field characteristics corresponding to the fault are extracted and identified. Specifically:

[0053] The air gap magnetomotive force under healthy operation of the synchronous condenser can be expressed as:

[0054]

[0055] In the formula, F N ω is the amplitude of the nth harmonic of the air gap magnetomotive force; ω is the electric angular velocity; α is the stator circumferential mechanical angle; β n The angle between the air gap magnetomotive force and the excitation magnetomotive force;

[0056] Due to manufacturing precision and installation errors, the magnetic circuit structure of the synchronous condenser in operation cannot achieve an ideal symmetrical state, and a static slight eccentricity phenomenon usually exists. Therefore, the air gap magnetic permeability method is used to analyze the change in the magnetic field of the synchronous condenser caused by static eccentricity. The static eccentric air gap magnetic permeability model can be expressed as:

[0057]

[0058] In the formula, Λ s Λ0 is the static eccentric air gap permeability; δ is the air gap permeability constant; m β is the air gap permeability coefficient for the m-th harmonic; m The initial phase of the air gap magnetic permeability for the mth harmonic;

[0059] The expression for calculating the air gap magnetic flux density when the rotor winding is in normal condition is as follows:

[0060]

[0061] In the formula, The spectrum of the main magnetic field in the air gap of the camera is composed of the fundamental wave and odd harmonics.

[0062] and

[0063]

[0064] Based on different values ​​of nm, the following classification and discussion are conducted:

[0065] When nm≠0, the mechanical angular velocity of the rotating magnetic field is dα / dt=nω / (n±m), which differs from the mechanical angular velocity of the rotor, thus generating asynchronous torque;

[0066] When nm = 0, the expression for the rotating magnetic field component is:

[0067]

[0068] It can be seen that parameter α disappears, which means that the magnetic flux density of this magnetic field component is the same at all positions on the stator circumference. This phenomenon is obviously inconsistent with the theory. Therefore, it is inferred that the magnetic field component is distorted and a stray magnetic field is formed outside the condenser.

[0069] To obtain the distribution law of stray magnetic field after inter-turn short circuit of rotor winding, it is necessary to analyze the reverse magnetomotive force generated by the short-circuited turns, the expression of which is:

[0070]

[0071] The expression for the air gap magnetic flux density of the short-circuited turns after the rotor winding is short-circuited can be derived as follows:

[0072]

[0073] In the formula The reverse magnetomotive force of the main magnetic field in the air gap of the tuner is shown in its spectrum as the nth harmonic, where n = 1, 2, 3, ... It can be decomposed into:

[0074]

[0075] Based on different values ​​of nm, the following classification and discussion are conducted:

[0076] When nm≠0, the mechanical angular velocity of the rotating magnetic field is dα / dt=nω / (n±m), which differs from the mechanical angular velocity of the rotor, thus generating asynchronous torque;

[0077] When nm = 0, the expression for the rotating magnetic field component is:

[0078]

[0079] It can be seen that the mechanical angle α parameter of the stator circumference disappears, from which it can be inferred that the magnetic flux component of this part has been distorted, forming a reverse stray magnetic field outside the stator core of the condenser. Its path is the same as the stray magnetic field path of the rotor winding in a healthy state, and its spectrum shows the nth harmonic.

[0080] Since both the stator core and air have a decay effect on the diffusion of the radial air gap magnetic field, this invention introduces the attenuation coefficient method to theoretically analyze the radial stray magnetic field.

[0081] The diffusion of air gap magnetic flux density through the medium can be analyzed using Maxwell's equations, and the expression is as follows:

[0082]

[0083] In the formula, F is the magnetic vector potential; σ is the magnetic permeability of the medium; and μ is the electrical conductivity of the medium.

[0084] There is no eddy current effect in the stator core and air domain, so σ is 0. Therefore, the scalar form of the above equation in polar coordinates is:

[0085]

[0086] Since the above equation is independent of time, the scalar expression for the magnetic vector obtained by the method of separation of variables is:

[0087]

[0088] Once the magnetomotive force is calculated, the expression for the magnetic flux density can be derived:

[0089] B = Curl(A);

[0090] The radial component of the magnetic flux density B can then be calculated separately. and tangential components The expression is:

[0091]

[0092] In the medium encountered by the air gap magnetic flux density of the synchronous condenser as it propagates outward, the air medium and the stator core are considered as ideal media without eddy current losses. Such media only cause changes in the magnitude of the magnetic flux density without affecting the phase. Calculating the attenuation coefficient in the air domain is relatively simple; we first solve for it. At infinity outside the stator core of the synchronous condenser, i.e., when ρ→∞, the radial component of the magnetic field... and tangential components Both tend to zero, and these two components have the same order of magnitude, but there is a phase difference of π / 2m in their spatial distribution. Based on this, the attenuation coefficient in the air outside the stator core of the condenser is defined as the ratio of the tangential magnetic flux density at a radius of ρ to the tangential magnetic flux density on the outer surface of the stator core, and its expression is:

[0093]

[0094] Similarly, the stator core attenuation coefficient K can be calculated. s Its expression is:

[0095]

[0096] In the formula, μ r Represents relative permeability, where P is the number of pole pairs of the motor;

[0097] Since the number of pole pairs of the camera is 1, the above formula can be simplified as follows:

[0098]

[0099] Because the outer diameter R of the stator core in the formula sext Stator core inner diameter R sint Relative permeability μ r Since the distance ρ from a point outside the stator core to the center is constant, it is obvious that the attenuation coefficient is also constant. Because there are no eddy currents in the stator yoke and air section, only the amplitude changes. Since the attenuation coefficients of the stator core and air region are independent, multiplying the attenuation coefficients of the stator core and air region yields the total attenuation coefficient of the synchronous condenser, K. SC The expression is:

[0100]

[0101] Therefore, the expression for the stray magnetic flux density of the camera condenser can be obtained as follows:

[0102]

[0103] Therefore, there is a linear relationship between the stray magnetic flux density of the condenser and the air gap magnetic flux density;

[0104] When an eccentric fault occurs, the magnetomotive force of the condenser does not change because the excitation current of the condenser does not change. The distortion of the magnetic flux density is caused by the change in the air gap length. When an eccentric fault occurs, the air gap magnetic flux density and stray magnetic flux density are linearly related, that is, they have the same trend of change and their spectrum diagrams are consistent.

[0105] Dynamic eccentricity faults are simulated by adjusting the relative offset between the rotor shaft center and the stator shaft center, while shaft-diameter combined eccentricity faults are simulated by jointly setting axial and radial eccentricity conditions.

[0106] The stray magnetic field characteristics include the fundamental amplitude, even harmonic components, odd harmonic components, and time-domain peak value and frequency-domain distribution characteristics.

[0107] In step 3, diagnostic criteria and thresholds for rotor inter-turn short circuits, dynamic eccentricity, and combined shaft diameter eccentricity faults are established, specifically as follows:

[0108] To more intuitively reflect the degree of dynamic eccentricity and inter-turn short-circuit faults, the percentage 'a%' of the sum of the amplitudes of the collected radial stray magnetic flux density even harmonics relative to the fundamental amplitude is used as the threshold criterion, as follows:

[0109]

[0110] In the formula, A1, A2, A4, A6, and A8 represent the amplitudes of the fundamental wave, the second harmonic, the fourth harmonic, the sixth harmonic, and the eighth harmonic, respectively.

[0111] The calculation results of stray magnetic field a% under overexcitation condition in inter-turn short circuit are shown in Table 1;

[0112] Table 1. Calculation results of stray magnetic field a% under overexcitation conditions during inter-turn short circuit.

[0113]

[0114]

[0115] The calculation results of stray magnetic field a% under underexcitation conditions of inter-turn short circuit are shown in Table 2;

[0116] Table 2. Calculation results of stray magnetic field a% under underexcited conditions during inter-turn short circuit.

[0117]

[0118] Therefore, a% is proportional to the degree of inter-turn short circuit in the synchronous condenser rotor winding, with overexcitation and underexcitation thresholds of 4.6% and 3.8%, respectively. Combining the stray magnetic flux density time-domain signal, when the radial peak value of the stray magnetic flux density decreases below the healthy operating state and a% is greater than the threshold, it can be determined that the synchronous condenser has experienced an inter-turn short circuit fault in the rotor excitation winding.

[0119] The calculation results of stray magnetic field a% under overexcitation condition of dynamic eccentricity fault of synchronous condenser are shown in Table 3;

[0120] Table 3. Calculation results of stray magnetic field a% under overexcitation condition in the case of dynamic eccentricity fault of synchronous condenser.

[0121]

[0122]

[0123] The calculation results of stray magnetic field a% under underexcitation condition of dynamic eccentricity fault of synchronous condenser are shown in Table 4;

[0124] Table 4. Calculation results of stray magnetic field a% under under-excitation conditions in the case of dynamic eccentricity fault of synchronous condenser.

[0125]

[0126] Therefore, the degree of rotor eccentricity of the synchronous condenser is proportional to a%, and the overexcitation and underexcitation threshold criteria are 19.71% and 17.35%, respectively. Combining the stray magnetic flux density time-domain signal of the synchronous condenser, when the radial peak value of the stray magnetic flux density increases higher than that of the healthy operating state and a% is greater than the threshold, it can be judged that the synchronous condenser has a rotor eccentricity fault.

[0127] When the radial peak value of stray magnetic flux density at different positions along the axial direction on the back of the stator core of the synchronous condenser changes proportionally with the increase of the axial coordinate, it is determined to be a combined eccentricity fault of the rotor shaft diameter.

[0128] This invention also provides an embodiment, taking a 300MVar dual water-cooled synchronous condenser at a converter station as the research object. Its main parameters are shown in Table 5, and the two-dimensional finite element model of the condenser is shown below. Figure 1 As shown, the model includes several parts such as stator and rotor cores, windings, and air gap.

[0129] Table 5. Main parameters of a 300MVar dual water-cooled synchronous condenser at a converter station.

[0130]

[0131]

[0132] Because the distribution of the rotor shaft diameter and the composite eccentric air gap changes along the axial direction, axial data is required. Therefore, a three-dimensional simulation model of the synchronous condenser is established, such as... Figure 2 As shown;

[0133] Under rated operating conditions, i.e., overexcitation (excitation current of 1800A), short circuits occurred in turns 0, 2, 4, and 6 of rotor slot 1. The radial component of the stray magnetic flux density signal was extracted from the back of the stator core of the synchronous condenser. Figure 3 The radial magnetic flux density components are obtained at sampling points 1001 for different inter-turn short-circuit spatial angles. Figure 4 Time-domain plots of stray magnetic flux density along short paths between different turns. Figure 5 The spectrum obtained by performing a Fourier transform on the time-domain signal;

[0134] As can be seen from Figure 3, the stray magnetic flux density decreases with increasing fault severity. Figure 4It can be seen that the peak value of the radial stray magnetic flux density is 180.1 μT under healthy operating conditions, and 178.3 μT under short-circuit conditions (6 turns). The peak value decreases as the inter-turn short-circuit fault intensifies. Fourier transform analysis of the radial stray magnetic flux density time-domain signal waveform reveals that when the excitation winding is normal, the radial stray magnetic flux density is dominated by the 50Hz fundamental wave and odd-order harmonics. However, when short-circuit occurs in turns 2, 4, and 6 of the rotor winding in slot 1, even-order harmonics (2nd and 4th orders) appear, and their amplitude gradually increases with the depth of the inter-turn short-circuit fault. Therefore, the inter-turn short-circuit fault of the synchronous condenser rotor can be effectively identified based on the stray magnetic field time-domain signal and characteristic harmonics.

[0135] To investigate the influence of different operating modes of the synchronous condenser on the stray magnetic field characteristics extracted from inter-turn short-circuit faults, the excitation current was set to 600A, i.e., the synchronous condenser was operating under underexcitation conditions. The rotor inter-turn short-circuit conditions were consistent with those under overexcitation conditions, namely normal, short-circuited 2, 4, and 6 turns, respectively. The radial time-domain signal of the stray magnetic flux density was acquired and Fourier analysis was performed. The results are as follows: Figure 6 , Figure 7 As shown.

[0136] Figure 6 The time-domain waveform of radial stray magnetic flux density under underexcitation. Figure 7 The spectrum is obtained by performing a Fourier transform on the radial stray magnetic flux density time-domain signal. It can be found that the peak value of the radial stray magnetic flux density in the healthy operating state under the underexcited state of the synchronous condenser is 179.8 μT, and the peak value of the radial stray magnetic flux density in the 6-turn short-circuit state is 178.1 μT. As the degree of inter-turn short-circuit fault increases, the peak value of the radial stray magnetic flux density still shows a decreasing trend, and even harmonics of the stray magnetic flux density can still be extracted, but the amplitude of the even harmonic components is attenuated due to the decrease in excitation current.

[0137] Under rated operating conditions, i.e. overexcitation (excitation current is 1800A), four states are set: normal rotor, 10%, 15%, and 20% dynamic eccentricity. The radial component magnetic flux density signal of stray magnetic flux density is extracted from the back of the stator core of the synchronous condenser. Figure 8 The radial stray magnetic flux density is measured at 1001 sampling points with different degrees of eccentricity and spatial angles. Figure 9 Time-domain plots of radial stray magnetic flux density with different degrees of eccentricity. Figure 10 This is the spectrum obtained by performing a Fourier transform on the time-domain signal.

[0138] Depend on Figure 8 , Figure 9It can be seen that the peak value of the radial stray magnetic flux density is 180.1 μT under healthy operating conditions, and 184 μT under a 20% eccentricity fault. The peak value of the radial stray magnetic flux density increases with the severity of the eccentricity fault. Fourier transform analysis of the time-domain signal waveform of the radial stray magnetic flux density reveals that without an eccentricity fault, the radial stray magnetic flux density is dominated by a 50Hz fundamental wave and odd-order harmonics. However, when the rotor experiences a dynamic eccentricity fault, even-order harmonics such as the 2nd and 4th orders appear, and their amplitude gradually increases with the severity of the eccentricity fault. Therefore, the stray magnetic field time-domain signal and characteristic harmonics can effectively identify dynamic eccentricity faults in the synchronous condenser rotor.

[0139] To investigate the influence of different operating modes of the synchronous condenser on the stray magnetic field characteristics extracted from a dynamic eccentricity fault, the excitation current of the synchronous condenser was set to 600A, i.e., the synchronous condenser was operating under under-excitation conditions. The radial time-domain signals of the stray magnetic flux density were extracted for rotor normal operation and dynamic eccentricity of 10%, 15%, and 20%, respectively. The results are as follows: Figure 11 As shown, the Fourier transform result of the obtained time-domain signal is as follows: Figure 12 As shown.

[0140] Figure 11 The time-domain waveforms of radial stray magnetic flux density under underexcitation with different degrees of eccentricity are shown. Figure 12 The image shows the spectrum obtained by performing a Fourier transform on the radial stray magnetic flux density time-domain signal. It can be observed that the peak value of the radial stray magnetic flux density in the healthy operating state under the underexcited state of the synchronous condenser is 179.8 μT, and the peak value is 182.6 μT under 20% dynamic eccentricity. As the degree of dynamic eccentricity fault increases, the peak value of the radial stray magnetic flux density and the amplitude of even harmonics still show an increasing trend, but the extracted even harmonic content is lower compared to the overexcited state.

[0141] When a combined rotor shaft diameter eccentricity occurs, the origin of the z-axis coordinate is set at the intersection of the rotor shaft and the stator shaft, with eccentricity rates of 5%, 7.5%, and 10%, respectively. To investigate the influence of the shaft diameter eccentricity angle on the stray magnetic field, radial time-domain signals of stray magnetic flux density with different eccentricity rates are extracted at z=0 on the back of the stator core.

[0142] Figure 13 The stray magnetic flux density radial time-domain waveforms under different shaft diameter eccentricities are shown. Figure 14 The image shows the spectrum obtained by performing a Fourier transform on the radial stray magnetic flux density time-domain signal. It can be observed that both the radial peak value and the second harmonic of the stray magnetic flux density increase with the increase of the eccentricity angle.

[0143] When a synchronous condenser experiences a combined rotor shaft diameter eccentricity fault, the stray magnetic flux density on the back of the stator core is unevenly distributed along the axial direction. This can be used as a basis for judging whether a combined rotor shaft diameter eccentricity fault has occurred in the synchronous condenser. With an eccentricity rate of 5%, the radial time-domain signals of stray magnetic flux density at z values ​​of 0, 1000 mm, and 2000 mm are extracted from the back of the stator core. 0, 1000, and 2000 correspond to sampling points 1, 2, and 3, respectively.

[0144] Figure 15 For the time-domain waveforms of radial stray magnetic flux density at different sampling points, Figure 16 The spectrum is obtained by performing a Fourier transform on the radial stray magnetic flux density time-domain signal.

[0145] Depend on Figure 15 It can be seen that the radial peak value of stray magnetic flux density at different axial positions on the back of the stator core is not the same, and the radial peak value of stray magnetic flux density increases with the increase of z. Figure 16 It can be seen that the amplitude of even harmonics increases with the increase of z. Therefore, when the radial peak value of stray magnetic flux density on the back of the stator core of the synchronous condenser is not equal and changes proportionally with the change of z, it can be determined that the synchronous condenser has a rotor shaft diameter composite eccentricity fault.

[0146] In order to more intuitively reflect the degree of dynamic eccentricity and inter-turn short circuit fault, the percentage content a% of the sum of the collected radial stray magnetic flux density even harmonic amplitudes relative to the fundamental amplitude is used as the threshold criterion.

[0147] Simulation results show that stray magnetic fields, as projections of the air gap magnetic field onto the outside of the synchronous condenser, can reflect fault information of the synchronous condenser in real time. Measurement can be performed simply by installing a sensor outside the synchronous condenser. Using stray magnetic fields, "external measurement and internal diagnosis" can be achieved, providing a new non-invasive online monitoring and diagnosis method for on-site operation and maintenance.

[0148] When a synchronous condenser rotor experiences an inter-turn short circuit, the radial peak value of stray magnetic flux density gradually decreases with increasing short-circuit severity. In addition to the fundamental and odd-order harmonics, the stray magnetic flux density spectrum also exhibits a second harmonic component, with the amplitude of the even-order harmonic increasing with the short-circuit severity. Conversely, when a synchronous condenser rotor experiences dynamic eccentricity, the radial peak value of stray magnetic flux density gradually increases with increasing eccentricity. In addition to the fundamental and odd-order harmonics, the stray magnetic flux density spectrum also shows a more pronounced second harmonic component than in the inter-turn short circuit, with its amplitude increasing with increasing eccentricity. Furthermore, the time-domain signal of the stray magnetic flux density radial peak value combined with the percentage of the radial stray magnetic flux density even-order harmonic amplitude can serve as a diagnostic criterion for rotor inter-turn short circuits and dynamic eccentricity faults. This criterion can effectively identify rotor faults and their severity.

[0149] After the synchronous condenser experiences rotor shaft diameter combined eccentricity, the stray magnetic field is unevenly distributed along the axial direction on the back of the stator core. Therefore, by monitoring the changes in the stray magnetic field at different axial positions, it can be determined whether a rotor shaft diameter combined eccentricity fault has occurred.

[0150] Under under excitation, the peak value of the radial component of stray magnetic flux density and the content of even harmonics decrease, but stray magnetic flux density signals and fault characteristic harmonics can still be extracted. Therefore, the system operation mode will not affect the diagnostic method.

[0151] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0152] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A non-invasive diagnostic method for typical rotor faults in synchronous condensers, characterized in that, include: Step 1: Perform finite element modeling and fault condition setting. Based on the structural parameters and electromagnetic characteristics of the synchronous condenser, use finite element simulation software to establish a two-dimensional or three-dimensional electromagnetic field model of the condenser, and set the healthy state, rotor inter-turn short circuit, dynamic eccentricity and shaft diameter combined eccentricity fault conditions respectively, and simulate to obtain magnetic field distribution data under each condition. Step 2: Extract and analyze stray magnetic field signals. Select sampling points in the air domain outside the stator core, and extract the time and frequency domain signals of stray magnetic fields under healthy and various fault conditions. Compare and analyze the fundamental wave, odd and even harmonic components and signal change trends, and extract and identify the stray magnetic field characteristics corresponding to the fault. Step 3: Establish diagnostic criteria and identify faults. Based on the obtained stray magnetic field characteristics, establish diagnostic criteria and thresholds for rotor inter-turn short circuits, dynamic eccentricity, and shaft diameter composite eccentricity faults. When the specific harmonic amplitude or variation characteristics of the stray magnetic field signal exceed the criterion threshold, determine the corresponding type and degree of rotor fault, and realize non-invasive, online automatic diagnosis.

2. The method according to claim 1, characterized in that, In step 1, the established finite element model includes the stator, rotor, air gap, and key areas of the air domain on the back of the stator core, and is modeled in two or three dimensions according to actual needs.

3. The method according to claim 2, characterized in that, Dynamic eccentricity faults are simulated by adjusting the relative offset between the rotor shaft center and the stator shaft center, while shaft-diameter combined eccentricity faults are simulated by jointly setting axial and radial eccentricity conditions.

4. The method according to claim 3, characterized in that, The stray magnetic field characteristics include the fundamental amplitude, even harmonic components, odd harmonic components, and time-domain peak value and frequency-domain distribution characteristics.

5. The method according to claim 4, characterized in that, In step 3, diagnostic criteria and thresholds for rotor inter-turn short circuits, dynamic eccentricity, and combined shaft diameter eccentricity faults are established, specifically as follows: The percentage a% of the sum of the amplitudes of the collected radial stray magnetic flux density even harmonics relative to the fundamental amplitude is used as the threshold criterion: In the formula, A1, A2, A4, A6, and A8 represent the amplitudes of the fundamental wave, the second harmonic, the fourth harmonic, the sixth harmonic, and the eighth harmonic, respectively. When the overexcitation and underexcitation thresholds for inter-turn short circuits are greater than 4.6% and 3.8% respectively, and the peak value of radial stray magnetic flux density decreases, it is determined to be an inter-turn short circuit fault in the rotor excitation winding. When the thresholds for overexcitation and underexcitation of dynamic eccentricity are greater than 19.71% and 17.35% respectively, and the peak value of radial stray magnetic flux density increases, it is determined to be a rotor dynamic eccentricity fault.

6. The method according to claim 5, characterized in that, When the radial peak value of stray magnetic flux density at different positions along the axial direction on the back of the stator core of the synchronous condenser changes proportionally with the increase of the axial coordinate, it is determined to be a combined eccentricity fault of the rotor shaft diameter.

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