Method for diagnosing rotor inter-turn short circuit fault of synchronous condenser and calculating number of short-circuit turns

Abstract

The application provides a synchronous phase modifier rotor inter-turn short-circuit fault diagnosis and short-circuit turn number calculation method, comprising: obtaining a stator same-phase parallel branch circulating current signal of a rotating motor, extracting a 2nd harmonic amplitude and a 4th harmonic amplitude in the stator same-phase parallel branch circulating current signal; if the 2nd harmonic amplitude is greater than a first preset diagnosis threshold and the 4th harmonic amplitude is greater than a second preset diagnosis threshold, determining that the rotating motor has a rotor inter-turn short-circuit fault; determining a harmonic amplitude ratio according to the 2nd harmonic amplitude and the 4th harmonic amplitude; determining a fault slot position according to the harmonic amplitude ratio and a pre-constructed slot mapping relationship table; obtaining a current excitation current of the rotating motor, determining an excitation current relative increment according to the current excitation current and a preset excitation current reference value; determining a short-circuit turn number estimated value according to the excitation current relative increment and a magnetic circuit saturation coefficient corresponding to the fault slot position.

Description

Technical Field

[0001] This invention relates to the field of information technology, and in particular to a method for diagnosing inter-turn short-circuit faults and calculating the number of short-circuit turns in a synchronous condenser rotor. Background Technology

[0002] Synchronous condensers have been widely adopted in ultra-high voltage direct current (UHVDC) transmission projects due to their advantages such as large reactive power capacity, strong overexcitation capability, and fast response speed. As the core reactive power compensation equipment at both the sending and receiving ends of UHVDC transmission, synchronous condensers can dynamically adjust their excitation state according to the real-time operating conditions of the power grid, flexibly completing the absorption and generation of reactive power, playing a key role in stabilizing grid voltage and ensuring stable and efficient power transmission. However, under grid disturbances and fault conditions, synchronous condensers need to continuously bear the task of voltage support and are frequently subjected to inrush currents. Long-term operation can easily lead to problems such as excessive local temperature rise, aging and damage of winding insulation, and increased machine vibration. Inter-turn short circuits in rotor windings are a typical electrical fault of synchronous condensers that are frequent and seriously harmful. After the fault occurs, it will directly cause distortion of the air gap magnetic field of the motor and deterioration of operating performance, while also causing derivative problems such as increased unit vibration, disordered air gap magnetic flux distribution, and local magnetization of the shaft. Continued development of the fault can lead to local overheating of the windings, mechanical damage to components, and in extreme cases, even equipment burnout, seriously threatening the operational safety of the entire power system. Therefore, conducting research on the accurate diagnosis, fault location, and fault severity quantification of inter-turn short-circuit faults in the rotor windings of synchronous condensers is of significant engineering value and practical importance for improving equipment reliability and ensuring the stable operation of ultra-high voltage power grids.

[0003] Currently, detection methods for inter-turn short circuits in synchronous condenser rotor windings are mainly divided into two categories: offline detection methods and online detection methods. Both methods have significant shortcomings. Offline detection methods generally have high diagnostic reliability, but their application limitations are prominent: the DC resistance method requires the equipment to be shut down, a DC current to be applied to the rotor winding, and the winding resistance to be measured. The fault is then determined by comparing it with historical data. This method has extremely low sensitivity in identifying early, minor inter-turn short circuit faults. The distributed voltage method requires applying AC voltage to the rotor slip rings and measuring the voltage at each coil terminal segment. The short circuit location is determined by the abnormal voltage characteristics, which results in a cumbersome operation process and long detection time. The AC impedance method completes fault identification by applying AC voltage and measuring the AC impedance and loss of the winding. The detection steps are complicated and require multiple repeated measurements, resulting in low work efficiency. The repetitive pulse method relies on injecting low-voltage pulses into the winding and analyzing the reflected waveform to identify the fault, which cannot achieve online monitoring without shutting down the equipment. In addition, various invasive offline detection methods also generally suffer from problems such as difficult sensor installation, lack of field test data, and poor engineering implementation.

[0004] To overcome the shortcomings of offline detection technology, online fault diagnosis technology has become the mainstream development direction. Currently, the mainstream online methods include finite element simulation, multi-loop theoretical analysis, field chain analysis, stator branch even-harmonic circulation current method, and deep learning diagnostic method. The finite element method relies on a refined motor model to simulate the characteristics of magnetic field changes; multi-loop theory analyzes the fault by constructing a set of stator and rotor circuit equations; field chain analysis integrates both magnetic field and circuit dimensions to analyze faults; the even-harmonic circulation current method uses the harmonic characteristics of the circulating current in the stator's in-phase parallel branches to identify faults; and deep learning technology relies on massive amounts of operating data to train models and complete fault mode recognition.

[0005] While the aforementioned online diagnostic methods each have their own technical advantages, they still share common technical bottlenecks: most existing solutions focus only on a single aspect of fault identification, fault slot location, and short-circuit severity assessment, making it difficult to form an integrated diagnostic system. Especially in engineering applications, where the number of rotor slots can reach dozens or even hundreds, inter-turn short circuits in different rotor slots generate differentiated second and fourth harmonic signals on the stator side. The amplitude ratio of these two harmonics contains precise slot spatial information. Traditional methods only focus on changes in the amplitude of a single harmonic, ignoring the mapping relationship between the harmonic ratio and the fault slot, thus failing to achieve accurate location. Simultaneously, although the increase in excitation current can reflect the magnetomotive force loss caused by the short circuit, the magnetic circuit saturation degree varies in different rotor slots, and the relationship between the number of short-circuited turns and the increase in excitation current is not a simple linear one. Existing technologies do not incorporate corrections based on the magnetic circuit characteristics of the slots, making it difficult to quantitatively estimate the number of short-circuited turns, resulting in significant bias in the assessment results. In summary, the industry urgently needs an integrated diagnostic solution that can simultaneously complete fault identification, precise slot location, and quantitative estimation of the number of short-circuited turns. Summary of the Invention

[0006] This invention provides a method for diagnosing inter-turn short-circuit faults and calculating the number of short-circuit turns in a synchronous condenser rotor, mainly including:

[0007] Obtain the circulating current signal of the stator parallel branch of the rotating electric machine, and extract the amplitude of the second harmonic and the amplitude of the fourth harmonic from the circulating current signal of the stator parallel branch.

[0008] If the amplitude of the second harmonic is greater than the first preset diagnostic threshold and the amplitude of the fourth harmonic is greater than the second preset diagnostic threshold, it is determined that the rotating motor has a rotor inter-turn short circuit fault.

[0009] The harmonic amplitude ratio is determined based on the amplitude of the second harmonic and the amplitude of the fourth harmonic;

[0010] The location of the faulty slot is determined based on the harmonic amplitude ratio and the pre-constructed slot mapping table.

[0011] Obtain the current excitation current of the rotating motor, and determine the relative increment of the excitation current based on the current excitation current and the preset excitation current reference value;

[0012] The estimated number of short-circuit turns is determined based on the relative increment of the excitation current and the magnetic saturation coefficient corresponding to the location of the fault slot.

[0013] Furthermore, the step of acquiring the circulating current signal of the stator parallel branch of the rotating electric machine, and extracting the second and fourth harmonic amplitudes from the circulating current signal of the stator parallel branch, includes:

[0014] Collect the stator current signal of the first in-phase branch and the stator current signal of the second in-phase branch of the rotating motor;

[0015] The circulating current signal of the stator in-phase parallel branch is determined based on the difference between the stator in-phase first branch current signal and the stator in-phase second branch current signal.

[0016] Frequency domain analysis was performed on the circulating current signal of the stator in-phase parallel branch to extract the amplitude of the second harmonic and the amplitude of the fourth harmonic.

[0017] Furthermore, determining that the rotating motor has a rotor inter-turn short circuit fault if the amplitude of the second harmonic is greater than a first preset diagnostic threshold and the amplitude of the fourth harmonic is greater than a second preset diagnostic threshold includes:

[0018] Acquire the historical stator in-phase parallel branch circulating current signal of the rotating motor under fault-free operation;

[0019] Extract the historical second harmonic amplitude and the historical fourth harmonic amplitude from the historical stator in-phase parallel branch circulating current signal;

[0020] The first preset diagnostic threshold is determined by multiplying the maximum value of the historical second harmonic amplitude with a preset multiple.

[0021] The second preset diagnostic threshold is determined by multiplying the maximum value of the historical four harmonic amplitudes with the preset multiple.

[0022] If the amplitude of the second harmonic is greater than the first preset diagnostic threshold and the amplitude of the fourth harmonic is greater than the second preset diagnostic threshold, a diagnostic signal is generated to indicate that the rotating motor has a rotor turn-to-turn short circuit fault.

[0023] Furthermore, determining the location of the faulty slot based on the harmonic amplitude ratio and a pre-built slot mapping table includes:

[0024] Obtain the total number of rotor slots of the rotating electric motor and the spatial position information corresponding to each rotor slot;

[0025] For each rotor slot, the second harmonic modulation amount and the fourth harmonic modulation amount when a short circuit occurs in the rotor slot are determined based on the spatial position information of the rotor slot.

[0026] The harmonic amplitude ratio corresponding to the rotor slot is determined based on the ratio of the second harmonic modulation amount to the fourth harmonic modulation amount.

[0027] Based on the harmonic amplitude ratio corresponding to each rotor slot and the preset margin, the harmonic amplitude ratio interval corresponding to each rotor slot is divided, and the slot mapping relationship table is generated.

[0028] Determine the target harmonic amplitude ratio range to which the harmonic amplitude ratio belongs;

[0029] Obtain the target rotor slot corresponding to the target harmonic amplitude ratio interval from the slot mapping table, and determine the target rotor slot as the location of the fault slot.

[0030] Furthermore, the step of obtaining the current excitation current of the rotating motor and determining the relative increment of the excitation current based on the current excitation current and a preset excitation current reference value includes:

[0031] Obtain multiple sets of historical excitation current data of the rotating motor under typical fault-free operating conditions;

[0032] Extract the stable segment data from each set of historical excitation current data;

[0033] The preset excitation current reference value is obtained by averaging all stable segment data.

[0034] The current excitation current of the rotating motor in its current operating state is collected;

[0035] Calculate the difference between the current excitation current and the preset excitation current reference value to obtain the absolute increment of the excitation current;

[0036] The ratio of the absolute increment of the excitation current to the preset excitation current reference value is calculated to obtain the relative increment of the excitation current.

[0037] Furthermore, determining the estimated number of short-circuit turns based on the relative increment of the excitation current and the magnetic circuit saturation coefficient corresponding to the fault slot location includes:

[0038] Obtain the total number of winding turns of the rotary motor;

[0039] The magnetic circuit saturation coefficient corresponding to the fault slot location is obtained by querying a preset saturation coefficient database based on the fault slot location.

[0040] The corrected excitation current increment is determined by multiplying the relative increment of the excitation current by the magnetic circuit saturation coefficient.

[0041] The estimated number of short-circuit turns is determined by multiplying the modified excitation current increment by the total number of winding turns.

[0042] Furthermore, the step of dividing the harmonic amplitude ratio interval for each rotor slot according to the theoretical harmonic amplitude ratio and preset margin, and generating the slot mapping table, includes:

[0043] Obtain the difference between the theoretical harmonic amplitude ratios of two adjacent rotor slots;

[0044] The preset margin is determined based on the difference;

[0045] Taking the harmonic amplitude ratio corresponding to each rotor slot as the center, and combining the preset margin, determine the upper and lower threshold values ​​corresponding to that rotor slot.

[0046] The harmonic amplitude ratio range corresponding to the rotor slot is formed by the upper limit threshold and the lower limit threshold.

[0047] Establish a mapping relationship between all rotor slots and their corresponding harmonic amplitude ratio intervals to obtain the slot mapping relationship table.

[0048] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

[0049] 1. This application relies on the circulating current signal of the stator in-phase parallel branch for analysis, and adaptively sets the 2nd and 4th harmonic diagnostic thresholds based on the historical fault-free operating data of the motor, using a dual-harmonic joint criterion to identify faults. Compared with offline detection methods such as DC resistance method and distributed voltage method, it does not require equipment shutdown and can be continuously monitored online throughout the process; at the same time, it effectively avoids the problems of single harmonic detection being susceptible to interference and having a high false judgment rate, and can accurately capture early minor inter-turn short circuit faults, greatly improving the sensitivity and reliability of fault identification.

[0050] 2. This application utilizes the unique correspondence between the amplitude ratios of the second and fourth harmonics of the circulating current when short-circuited in different rotor slots. A standardized slot mapping table is pre-built, combining the rotor's spatial location, harmonic modulation patterns, and measurement error margin. By looking up the table using the measured harmonic amplitude ratios, the faulty rotor slot number can be quickly located, fully leveraging the spatial location information contained in the harmonic ratios. This solves the problems of traditional diagnostic methods failing to distinguish faulty slots and providing ambiguous location information. The location results are accurate, with minimal computational load, meeting the needs of real-time on-site diagnosis.

[0051] 3. This application fully considers the actual working condition of uneven magnetic circuit saturation in different slots of the rotor, and introduces the magnetic circuit saturation coefficient of the corresponding slot to correct the relative increment of the excitation current, eliminating the calculation deviation caused by magnetic circuit nonlinearity, and establishing a linear correspondence between the corrected current increment and the number of short-circuit turns. Compared with the traditional method of directly estimating the number of turns by relying on the excitation current increment, this effectively reduces the estimation error, can accurately quantify the severity of short-circuit faults, and makes up for the shortcomings of existing technologies that cannot quantitatively assess the fault level.

[0052] 4. In this application, the threshold calibration, slot mapping table, and magnetic circuit saturation coefficient database can all be completed offline before the equipment is put into operation. The online diagnostic stage only requires signal acquisition, spectrum analysis, and simple table lookup and calculation, which has low hardware computing power requirements and is easy to integrate and deploy in existing monitoring systems. At the same time, the algorithm is not affected by changes in unit load or fluctuations in normal operating conditions, and is compatible with synchronous condensers of different numbers and capacities and various rotating motors, with strong versatility and scalability.

[0053] 5. This application can provide complete diagnostic information on three core aspects: whether a fault has occurred, the specific fault location, and the number of short-circuited turns. This provides maintenance personnel with quantitative and reliable data to differentiate the severity of faults and formulate maintenance plans. For minor faults, planned maintenance can be arranged; for serious faults, timely shutdown warnings can be triggered, preventing the fault from escalating and causing serious accidents such as winding overheating, equipment burnout, and grid voltage instability. This significantly improves the operational safety of synchronous condensers and UHV transmission systems, and reduces equipment maintenance costs and accident losses. Attached Figure Description

[0054] Figure 1 This is a flowchart of the method for diagnosing inter-turn short-circuit faults and calculating the number of short-circuit turns of a synchronous condenser rotor according to the present invention.

[0055] Figure 2 A two-dimensional finite element simulation model of the TTS-300-2 type hidden pole synchronous modulator;

[0056] Figure 3 A three-phase star-connected double-branch circuit model for the stator winding of a synchronous condenser;

[0057] Figure 4 This is the equivalent circuit model for inter-turn short circuits in the rotor windings.

[0058] Figure 5 This is a stator in-phase dual-branch circulating current analysis model;

[0059] Figure 6 The diagram shows the current in each branch and its circulation under healthy conditions.

[0060] Figure 7 The stator current and circulating current waveforms under a short-circuit fault in the 3 turns of rotor slot 1;

[0061] Figure 8 Comparison of the amplitude values ​​of the second and fourth harmonics of the circulating current in the branch before and after the fault;

[0062] Figure 9 The waveforms show the changes in excitation current before and after the fault. Detailed Implementation

[0063] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0064] like Figures 1 to 9 As shown in the figure, the method for diagnosing inter-turn short-circuit faults and calculating the number of short-circuit turns of a synchronous condenser rotor in this embodiment may specifically include:

[0065] Step S1: Obtain the circulating current signal of the stator parallel branch of the rotating electric machine, and extract the amplitude values ​​of the second and fourth harmonics from the circulating current signal of the stator parallel branch. This includes:

[0066] Step S11: Collect the stator current signal of the first in-phase branch and the stator current signal of the second in-phase branch of the rotating motor.

[0067] In the in-phase parallel double-branch structure of the stator winding of a rotating electric machine, the first and second branches are symmetrical during normal operation, with equal current amplitudes and consistent phases. The stator of a synchronous condenser adopts a three-phase star-connected double-parallel branch structure, and the winding circuit model is as follows: Figure 3 As shown; Figure 3 This diagram illustrates a three-phase star-connected double-branch structure of the stator winding of a synchronous condenser. Y represents the star connection point, and the three-phase windings are labeled A, B, and C, with each phase consisting of two parallel branches. Taking phase A as an example, the currents in branches a1 and a2 are i... a1 and i a2 The total current i in phase A A = i a1 + i a2 Phase B and Phase C have the same structure. When an inter-turn short circuit occurs in the rotor winding, the induced electromotive force of the two branches in the same phase differs, thus generating circulating current. This model is the basis for analyzing the circulating current of the two branches in the same phase of the stator. The equivalent analysis model of the circulating current of the two branches of stator A phase is shown in Figure 5; Figure 5 The stator A-phase dual-branch circulating current analysis model is shown. In the figure, R... a1 R a2 The winding resistances of branches a1 and a2 are respectively, i az Indicates the circulation between two branches, e a1 e a2 Let Z be the instantaneous induced electromotive force of the two branches, and Z be the load impedance. During normal operation, the parameters of the two branches are symmetrical. a1 =e a2 Circulation iaz = 0. When the rotor turns are short-circuited, the air gap magnetic field generates even harmonics, leading to an induced electromotive force e in both branches. a1 ≠e a2 This generates even-order harmonic circulating currents. Current sensors are installed on two parallel branches in phase with the stator to collect the current signals of the first and second branches in real time. Hall effect current sensors or Rogowski coils are selected and installed at appropriate locations on the branch conductors, ensuring a stable relative position between the sensor and the conductor. The sampling frequency is set to an integer multiple of the power frequency, typically not lower than 2 kHz, to meet the Nyquist sampling theorem requirements for subsequent harmonic analysis. The collected first branch current signal is denoted as... The current signal of the second branch is denoted as The two signals are sampled synchronously to ensure a strict correspondence between the sampling times and avoid errors in the circulation current calculation caused by time deviation.

[0068] Step S12: Determine the circulating current signal of the stator in-phase parallel branch based on the difference between the stator in-phase first branch current signal and the stator in-phase second branch current signal.

[0069] Step S121, for the first branch current signal Second branch current signal Time alignment calibration is performed. Since there may be slight differences in transmission delay between the two signal acquisition channels, the time offset between the two signals is first calculated through cross-correlation analysis. Specifically, the calculation method involves... and Perform cross-correlation calculations to find the time offset corresponding to the maximum value of the cross-correlation function. Then, time-shift compensation is applied to one of the signals to ensure strict alignment of the two signals on the time axis. The time alignment accuracy is required to be within one-tenth of the sampling period to ensure the accuracy of subsequent difference calculations.

[0070] Step S122 involves low-pass filtering preprocessing of the aligned two current signals. A Butterworth low-pass filter with a cutoff frequency ten times the power frequency is used to filter out high-frequency noise and interference components in the acquired signal. The Butterworth filter has the advantage of a flat amplitude-frequency response within the passband, which can preserve the fundamental and low-order harmonic components of the signal, while effectively suppressing the influence of high-frequency noise on the circulating current calculation. The filter order is selected as fourth order to achieve a balance between filtering effect and phase distortion.

[0071] Step S123: Calculate the instantaneous difference between the current signals of the first and second branches to obtain the circulating current signal of the stator in-phase parallel branches. Circulating current signal The calculation expression is: Under normal operating conditions, due to the symmetrical parameters of the two branches, and Equal amplitude and same phase, circulation It is close to zero or contains only a tiny noise component. When an inter-turn short-circuit fault occurs in the rotor winding, even-order harmonic magnetomotive force is generated in the air gap magnetic field, causing a difference in the induced electromotive force between the two branches. and No longer equal, circulation The circuit exhibits significant even-order harmonic components. The amplitude and frequency characteristics of the circulating current signal directly reflect the presence and extent of inter-turn short-circuit faults in the rotor winding.

[0072] Step S124: Perform data validity verification on the calculated circulating current signal. Check for any abnormal abrupt changes or data saturation in the circulating current signal. If the instantaneous value of the circulating current signal exceeds 95% of the sensor's range, the data segment is deemed invalid and needs to be re-acquired. Simultaneously, calculate the effective value of the circulating current signal. If the effective value is lower than the preset minimum detection threshold, it is considered to be in normal operating condition, as the circulating current signal mainly consists of measurement noise. This validity verification ensures the authenticity and reliability of the circulating current signal data used in subsequent frequency domain analysis.

[0073] In specific implementation, the expression for the stator in-phase dual-branch circulating current is:

[0074]

[0075] In the formula, Δi represents the branch circulation; w s Number of faulty turns; I f1 N is the magnetizing current after a short circuit; c Λ is the total number of turns in the winding; l is the air gap length; v is the magnetic flux density cutting speed of the winding; k ωn X represents the winding factor of the nth harmonic; n Let γ be the equivalent reactance of the nth harmonic of the branch, where n = 2 or 4; γ be the circumferential angle corresponding to the rotor tooth; y represent the y-th slot; β be the angle between adjacent rotor slots; α be the initial electrical angle of the rotor; ω be the electrical angular velocity of the rotor; and t be time.

[0076] Step S13: Perform frequency domain analysis on the circulating current signal of the stator in-phase parallel branch to extract the amplitude of the second harmonic and the amplitude of the fourth harmonic.

[0077] Step S131: Select a frequency domain analysis method to perform spectral transformation on the circulating current signal. The Fast Fourier Transform (FFT) is used to convert the time-domain circulating current signal into a frequency-domain spectrum. The FFT is a highly efficient Discrete Fourier Transform algorithm that can quickly calculate the frequency components of a signal. Before performing the FFT, the circulating current signal is windowed using a Hanning window function. The Hanning window function effectively suppresses spectral leakage and improves the frequency resolution of the frequency domain analysis. The windowed circulating current signal is denoted as... , where the window function The length is consistent with the number of sampling points.

[0078] Step S132: Perform a Fast Fourier Transform (FFT) operation on the windowed circulating current signal to obtain its frequency domain spectrum. The output of the FFT is a complex-form spectrum function containing amplitude and phase information. The horizontal axis of the spectrum function represents frequency, and the vertical axis represents the complex amplitude of the corresponding frequency component. Based on the rated operating frequency of the rotating electric motor... Locate the second harmonic frequency point in the spectrum. and the 4th harmonic frequency point The air gap magnetic field distortion caused by the inter-turn short circuit in the rotor winding mainly generates even harmonics, and the spectrum of the circulating current signal is in... and The location will show a significant peak.

[0079] Step S133: Extract the complex amplitude values ​​corresponding to the second and fourth harmonic frequency points in the spectrum. For the second harmonic, at the frequency point... Read the spectral function value at the location, and denote it as a complex number. For the fourth harmonic, at the frequency point Read the spectral function value at the location, and denote it as a complex number. Considering the impact of spectral leakage, the actual peak may occur at several frequency points near the target frequency. and Select a window containing three frequency points nearby, and take the complex value corresponding to the frequency point with the largest amplitude within the window as the complex amplitude of that harmonic.

[0080] Step S134: Calculate the amplitudes of the second and fourth harmonics. Based on the complex amplitude values... and The magnitude is calculated to obtain the harmonic amplitude. Second harmonic amplitude. equal The modulus is calculated as a complex number. The square root of the sum of the squares of the real and imaginary parts. Fourth harmonic amplitude. equal The magnitude is calculated in the same way. Since the output of the Fast Fourier Transform is related to the number of sampling points and the window function, the calculated amplitude is normalized by dividing the amplitude by half the number of sampling points to obtain the harmonic amplitude values ​​corresponding to the actual signal amplitude. The normalized second and fourth harmonic amplitudes are the feature quantities to be extracted.

[0081] In specific implementation, the expressions for the amplitudes of the second and fourth harmonics of the stator in-phase dual-branch circulating current are as follows:

[0082]

[0083] In the formula, P c2 and P c4 These are the amplitudes of the second and fourth harmonics of the circulation, respectively.

[0084] Preferably, the method for setting the preset diagnostic threshold of the present invention involves continuously collecting branch current data a preset number of times when the synchronous condenser is in a healthy and stable operating state, and calculating the amplitude values ​​P of the 2nd and 4th harmonics obtained from each sampling. c2 and P c4 The values ​​are calculated, and the maximum value among the results of the preset number of calculations is taken, and twice that value is used as the corresponding diagnostic thresholds τ1 and τ2.

[0085] In one possible implementation, for power systems with frequency fluctuations or non-stationary signals, a Short-Time Fourier Transform (SFT) is used instead of a Fast Fourier Transform (FFT) for frequency domain analysis. The SFT performs a piecewise Fourier transform on the signal using a sliding time window, simultaneously obtaining both time and frequency information, making it suitable for analyzing time-varying signals. Specifically, the circulating current signal is segmented into fixed-length time windows, each segment's length being an integer multiple of the power frequency cycle, with 50% overlap between adjacent windows. Windowing and FFT are applied to the signal segment within each time window to obtain the spectrum for that time period. The amplitudes of the second and fourth harmonics are extracted from the spectrum, and the average of the harmonic amplitudes obtained from all time windows is taken as the final second harmonic amplitude. and the amplitude of the fourth harmonic The short-time Fourier transform method can adapt to frequency fluctuations and signal non-stationarity, improving the robustness of harmonic extraction.

[0086] In another embodiment, the Hilbert-Huang transform is used for frequency domain analysis of the circulating current signal. The Hilbert-Huang transform includes two steps: empirical mode decomposition (EMD) and Hilbert spectral analysis. First, EMD is performed on the circulating current signal, decomposing it into several intrinsic mode function (EMF) components and a residual component. Each EMF component is an oscillation mode with a single frequency characteristic, corresponding to a characteristic frequency in the signal. By identifying the instantaneous frequencies of the EMF components, EMF components with instantaneous frequencies close to 2 and 4 times the power frequency are found, denoted as _____. and Then to and Perform a Hilbert transform, calculate its analytic signal, and extract the instantaneous amplitude from the analytic signal. The instantaneous amplitude is averaged over one power frequency cycle to obtain the second harmonic amplitude. .right The instantaneous amplitude is averaged over one power frequency cycle to obtain the amplitude of the fourth harmonic. The Hilbert-Huang transform method does not require preset basis functions, can adaptively decompose signals, and has good analytical effects on nonlinear and non-stationary signals. It is particularly suitable for the analysis of complex circulating current signals caused by rotor turn-to-turn short-circuit faults.

[0087] It should be noted that, in practical applications, to improve the accuracy of harmonic extraction, the DC component of the circulating current signal can be removed before frequency domain analysis. The average value of the circulating current signal over one complete power frequency cycle is calculated, and this average value is taken as the DC component. Subtracting the DC component from the original signal yields the circulating current signal. The presence of a DC component can affect the accuracy of spectrum analysis, especially in the low-frequency range where it can cause spectral leakage and interfere with the extraction of the second harmonic. After removing the DC component, the spectrum of the circulating signal is more concentrated on the AC components, and the peaks of the second and fourth harmonics are more pronounced, thus improving the extraction accuracy.

[0088] Specifically, the amplitude of the second harmonic and the amplitude of the fourth harmonic The magnitude of the fault directly reflects the severity of the inter-turn short-circuit fault in the rotor winding. Under normal operating conditions, due to the symmetry of the stator's two in-phase branches, the circulating current signal contains only a very small amount of measurement noise and inherent system imbalance components; the amplitudes of the second and fourth harmonics are typically less than one-thousandth of the rated current. When an inter-turn short circuit occurs in a slot of the rotor winding, the reverse current generated by the short-circuited turns forms a pulsating magnetomotive force in the air gap. This magnetomotive force exhibits a non-sinusoidal distribution in space and contains abundant even-order harmonic components. When these even-order harmonic magnetomotive forces cut the stator winding, they induce different even-order harmonic electromotive forces in the two in-phase branches, leading to a difference in the currents of the two branches and a significant increase in the amplitudes of the second and fourth harmonics in the circulating current signal. The more faulty turns there are, the stronger the even-order harmonic magnetomotive force, and the larger the amplitudes of the second and fourth harmonics in the circulating current. By monitoring... and The numerical changes can be detected in a timely manner to detect the occurrence of short circuit faults between rotor winding turns.

[0089] In one embodiment, taking a salient-pole synchronous condenser with a rated power of 300 MVA as an example, this simulation is based on a two-dimensional finite element model of the TTS-300-2 type salient-pole synchronous condenser. The model structure and rotor slot numbering are as follows: Figure 2 As shown; Figure 2 A two-dimensional finite element simulation model based on the actual parameters of a TTS-300-2 salient-pole synchronous condenser is presented. In the figure, the rotor slots are numbered sequentially from 1 to 16 (1 to 8 under the same magnetic pole), with slot 1 being the slot closest to the large tooth, and the slots numbered sequentially away from the large tooth. This model is used for field-circuit coupling simulation. The effectiveness of the method is verified by setting short-circuit faults with different slot positions and different numbers of turns. The stator winding adopts a star-connected dual-branch structure with a rated power frequency of 50 Hz. Before a 3-turn short-circuit fault occurs in the rotor's slot 1, the current signals of the two branches of stator phase A are collected. and Both signals have an amplitude of 2100 amperes and are perfectly synchronized in phase. Calculate the circulating current signal. The obtained circulating current signal amplitude is 9 amperes, mainly composed of measurement noise and inherent system imbalance. A Fast Fourier Transform (FFT) is performed on the circulating current signal to extract the second harmonic amplitude at 100 Hz (2 times the power frequency). The amplitude is 2.34 amperes, and the fourth harmonic amplitude is extracted at 200 Hz, which is four times the power frequency. The current is 0.63 amperes. The second harmonic diagnostic threshold is set. The threshold for 4th harmonic diagnosis is 4.683 amperes. It is 1.26 amperes, at this time and The synchronous condenser is determined to be in normal operating condition. After a 3-turn short-circuit fault occurs in rotor slot 1, the stator A-phase current signals are re-acquired. The amplitude becomes 2150 amperes. The amplitude changed to 2050 amperes, and a significant difference appeared in the currents of the two branches. After a 3-turn inter-turn short-circuit fault occurred in rotor slot 1, the time-domain waveforms of the stator currents in the two in-phase branches and the corresponding circulating currents are as follows: Figure 7 As shown; Figure 7 The simulated waveforms of the stator currents and circulating currents in the two in-phase branches after a 3-turn short-circuit fault in slot 1 are shown. The figure shows that before the fault, the currents in the two branches were completely overlapping; after the fault, the currents in the two branches showed significant differences, with their amplitudes no longer equal and their phases no longer perfectly aligned. The circulating current waveform exhibits periodic distortion, indicating the generation of harmonic components. This figure visually verifies that a rotor inter-turn short circuit leads to circulating currents in the two in-phase stator branches. The circulating current signal was calculated. The effective value rose to 35 amperes. A Fast Fourier Transform was performed on the post-fault circulating current signal, and the second harmonic amplitude was extracted at 100 Hz. The amplitude is 221.3 amperes, and the fourth harmonic amplitude is extracted at 200 Hz. The value is 48.13 amperes. The amplitudes of the second and fourth harmonics of the circulating current before and after the fault are compared as follows: Figure 8 As shown, Figure 8 The diagram illustrates the changes in the amplitudes of the 2nd and 4th harmonics in the branch circulating current before and after a short-circuit fault in the 3-turn section of slot 1. The left side of the diagram represents the harmonic amplitudes under healthy conditions, while the right side represents the harmonic amplitudes after the fault. The amplitude of the 2nd harmonic after the fault is P. c2 and the amplitude of the 4th harmonic P c4 Both are significantly greater than the thresholds τ1 and τ2 set under healthy conditions (twice the maximum value under healthy conditions), indicating that these two features can be used for fault detection; at this time and The system determined that a short-circuit fault had occurred in the rotor winding of the synchronous condenser. The amplitude of the second harmonic increased by approximately 95 times compared to before the fault, and the amplitude of the fourth harmonic increased by approximately 76 times compared to before the fault, indicating that the even-order harmonic components in the circulating current have extremely high sensitivity to short-circuit faults.

[0090] For example, in practical engineering applications, to ensure the real-time and continuous nature of harmonic extraction, a rolling window approach is used for online frequency domain analysis of the circulating current signal. The time window length is set to 1 second, corresponding to 50 power frequency cycles. The window data is updated every 0.1 seconds, and a Fast Fourier Transform is performed on the circulating current signal within the new window to extract the amplitudes of the 2nd and 4th harmonics. By using the rolling window approach, it is possible to achieve... and Continuous monitoring allows for timely detection of the moment when an inter-turn short-circuit fault occurs in the rotor winding. This is achieved within five consecutive windows. and When all values ​​exceed the diagnostic threshold, a fault is confirmed, triggering the fault location procedure. The scrolling window method balances the frequency and time resolution of frequency domain analysis, accurately extracting harmonic amplitudes while rapidly responding to fault occurrences, meeting the real-time requirements of online monitoring.

[0091] Understandably, the ratio of the second harmonic amplitude to the fourth harmonic amplitude has significant value in fault location. The second harmonic amplitude in the circulating current... and the amplitude of the fourth harmonic Each contains the second harmonic modulation amount and 4th harmonic modulation amount These two modulation quantities are only related to the spatial location of the faulty slot and not to the number of short-circuited turns. Therefore, the harmonic amplitude ratio Its value depends only on the position angle of the fault slot on the rotor circumference and is not affected by changes in the number of short-circuited turns. Through calculation... and with the pre-built fault slot number By comparing the mapping table of intervals, the rotor slot number where the inter-turn short circuit occurred can be accurately located. This characteristic enables the fault diagnosis method based on even harmonics of the circulating current to not only detect the existence of the fault, but also accurately locate the fault position, providing a clear target slot for subsequent short-circuit turn estimation and equipment maintenance.

[0092] Preferably, a digital signal processor (DSP) or field-programmable gate array (FPGA) is used for real-time calculation during the acquisition of circulating current signals and harmonic extraction. The analog signal output from the current sensor is converted into a digital signal by an analog-to-digital converter (ADC), and then input into the DSP for difference calculation, filtering, and fast Fourier transform (FFT) operations. The DSP has powerful parallel computing capabilities and a rich mathematical function library, enabling it to efficiently perform complex number operations and spectrum analysis with millisecond-level latency. The calculated second and fourth harmonic amplitudes are transmitted to a host computer monitoring system via a communication interface for fault diagnosis and result display. This hardware implementation ensures the real-time performance and reliability of harmonic extraction, meeting the engineering application requirements for online monitoring of synchronous condensers.

[0093] Step S2: If the amplitude of the second harmonic is greater than a first preset diagnostic threshold and the amplitude of the fourth harmonic is greater than a second preset diagnostic threshold, it is determined that the rotating motor has a rotor inter-turn short circuit fault. This includes:

[0094] Step S21: Obtain the historical stator in-phase parallel branch circulating current signal of the rotating motor under fault-free operation.

[0095] During stable operation of the rotating electric motor, circulating current signals are collected using current sensors installed on the parallel branches of the stator windings in phase. The data acquisition process ensures that the rotating electric motor is in a fault-free, healthy operating state, with stable load conditions and ambient temperature and humidity meeting normal operating requirements. The data acquisition span covers multiple typical operating conditions of the rotating electric motor, including steady-state operation phases under different load levels, to obtain representative historical circulating current data. The collected circulating current signals are then converted from analog to digital and stored in the historical database of the monitoring system. The sampling frequency is... Set to at least ten times the frequency required for harmonic analysis, i.e. ( (To analyze the harmonic frequencies), ensuring that the harmonic components in the circulating signal can be accurately captured.

[0096] Step S22: Extract the historical second harmonic amplitude and the historical fourth harmonic amplitude from the historical stator in-phase parallel branch circulating current signal.

[0097] A Fast Fourier Transform (FFT) is performed on the acquired historical circulation signals to convert the time-domain signal into a frequency-domain signal, yielding the spectral distribution of the circulation signal. The fundamental frequency is then identified from the spectrum. The corresponding frequency position is used to locate the frequency points corresponding to the second and fourth harmonics. Among them, the second harmonic frequency... 4th harmonic frequency Extract the amplitude values ​​at these two frequency points and record them as the historical second harmonic amplitude values. And the amplitude of the 4th harmonic in history ( , (This represents the total number of historical samples). For each acquired circulating signal sample, the above harmonic extraction operation is performed to form a historical second harmonic amplitude sequence. and the historical fourth harmonic amplitude sequence These sequences reflect the natural fluctuation range of even harmonics in the circulating signal of a rotating electrical machine under healthy conditions.

[0098] Step S23: Determine the first preset diagnostic threshold based on the product of the maximum value of the historical second harmonic amplitude and a preset multiple.

[0099] Step S231: Traverse the historical second harmonic amplitude sequence Find the maximum value in the sequence. ,satisfy This maximum value represents the highest possible level of the second harmonic amplitude in the circulating current signal when the rotating electric motor is operating healthily. Since the even-order harmonic amplitude in the circulating current signal should be extremely small, close to zero, the actual measured second-order harmonic amplitude will exhibit some non-zero fluctuations due to factors such as measurement noise, sensor accuracy, and power grid harmonic interference. Finding the maximum value in historical data allows us to determine the upper limit of this normal fluctuation.

[0100] Step S232: Select a preset multiple. The maximum amplitude of the second harmonic in history Multiply by the product to obtain the first preset diagnostic threshold. The calculation formula is: Preset multiplier The selection of is based on a large amount of experimental data and engineering experience, and the range of values ​​is . A balance needs to be struck between the sensitivity and anti-interference capability of fault detection. If a preset multiplier is used... If the threshold is too small, the diagnostic threshold will be close to the historical maximum, which may cause normal fluctuations to be misjudged as faults, resulting in false alarms. If a preset multiple is used... If the threshold is too high, the increase in harmonic amplitude caused by early minor faults may not exceed the threshold, leading to missed detection.

[0101] In one embodiment, a preset multiple is used. That is, the first preset diagnostic threshold is satisfied. This method of value determination can effectively distinguish between the maximum fluctuation under healthy conditions and the significant increment after a fault occurs, thus ensuring detection sensitivity while avoiding false alarms.

[0102] Step S233: Calculate the first preset diagnostic threshold. The diagnostic thresholds are stored in the diagnostic module of the monitoring system and serve as the basis for subsequent real-time fault detection. The determination of diagnostic thresholds can be periodically updated based on the accumulated operating time of the rotating motor. Once new healthy operating data is accumulated, the maximum historical amplitude of the second harmonic is recalculated. And update This allows diagnostic criteria to be dynamically adjusted as the equipment status evolves, maintaining diagnostic accuracy.

[0103] For example, suppose that during the healthy operation of a synchronous condenser, continuous data acquisition is performed. The circulating current signal of the stator in-phase parallel branch was subjected to Fast Fourier Transform (FFT) to extract 100 historical second harmonic amplitude values, with values ​​ranging from... Fluctuations between these ranges. Traversing the sequence yields... Select a preset multiple Substituting into the formula, we can obtain During subsequent online monitoring, if the amplitude of the second harmonic in the real-time collected circulating signal exceeds... If the value is positive, it indicates a possible rotor inter-turn short circuit fault. This adaptive threshold setting method based on the maximum value of historical data can adapt to individual differences in rotating motors and differences in field operating environments, avoiding the problem of poor universality of fixed thresholds on different devices.

[0104] Step S24: Determine the second preset diagnostic threshold based on the product of the maximum value of the historical four harmonic amplitudes and the preset multiple.

[0105] Step S241: Traverse the historical 4th harmonic amplitude sequence Find the maximum value in the sequence. ,satisfy Similar to the second harmonic, the amplitude of the fourth harmonic in a healthy state should also be extremely small, but in actual measurements, it will fluctuate to some extent due to various interference factors. Find the maximum historical amplitude of the fourth harmonic to determine the upper limit of normal fluctuation of the fourth harmonic in a healthy state.

[0106] Step S242, using the same preset multiple as used to determine the first preset diagnostic threshold. The maximum amplitude of the fourth harmonic in history Multiply by this to obtain the second preset diagnostic threshold. The calculation formula is: Keep both diagnostic thresholds at the same preset multiple. This ensures that the judgment criteria for the second and fourth harmonics in fault detection have a consistent sensitivity level, avoiding misjudgment or missed judgment due to inconsistent threshold settings.

[0107] Step S243, set the second preset diagnostic threshold. Stored in the diagnostic module of the monitoring system, and compared with the first preset diagnostic threshold. When used together, they form a dual-harmonic collaborative judgment mechanism. By simultaneously monitoring the amplitude changes of the 2nd and 4th harmonics, and requiring both to exceed their respective diagnostic thresholds before a fault is determined, the reliability of fault detection can be significantly improved, and the false alarm rate that may result from single-harmonic judgment can be reduced.

[0108] In one embodiment, for the same synchronous condenser, the historical fourth harmonic amplitude is extracted from 100 sets of historical circulation signals. Fluctuations between them can be obtained Using a preset multiple Calculated When the amplitude of the fourth harmonic in the real-time monitored circulating signal exceeds... At that time, the fault status is determined by combining the judgment results of the second harmonic amplitude.

[0109] It should be noted that the historical maximum values ​​of the second and fourth harmonics are... , There are usually orders of magnitude differences due to the varying levels of background interference for different harmonic orders under healthy conditions. Diagnostic thresholds are set separately for each harmonic's historical maximum value. , Instead of using a uniform absolute threshold, this method can more accurately reflect the degree of abnormality of each harmonic component and improve the accuracy of fault detection.

[0110] Step S25: If the amplitude of the second harmonic is greater than the first preset diagnostic threshold and the amplitude of the fourth harmonic is greater than the second preset diagnostic threshold, a diagnostic signal is generated to characterize the rotor inter-turn short circuit fault of the rotating motor.

[0111] During real-time monitoring, the circulating current signal of the stator in-phase parallel branch is continuously acquired, and the real-time second harmonic amplitude of the current circulating current signal is extracted in real time. and real-time 4th harmonic amplitude Real-time extraction Compared with the first preset diagnostic threshold Compare and extract in real time. Compared with the second preset diagnostic threshold Compare them. When both conditions are met... and Under two conditions, the monitoring system generates a diagnostic signal. This signal can trigger an alarm device to send a fault notification to maintenance personnel, or automatically record the time of the fault and related parameters, providing a basis for subsequent fault location and severity assessment. The dual-threshold collaborative judgment mechanism ensures that a fault is only determined when both independent harmonic characteristic quantities are abnormal, effectively avoiding misjudgments caused by occasional interference from a single harmonic.

[0112] In one embodiment, when the circulating signal at a certain moment is monitored in real time... ,satisfy ,at the same time ,satisfy Upon receiving the alarm, the monitoring system immediately generates a fault diagnosis signal, triggers an audible and visual alarm, and displays fault information on the monitoring interface. Maintenance personnel, after receiving the alarm, can then determine the specific location of the faulty slot and the number of short-circuited turns using the subsequent fault location process, and formulate a corresponding maintenance plan. This adaptive threshold-based dual-harmonic collaborative judgment method can detect anomalies in the early stages of a fault, providing strong support for preventative maintenance and preventing further escalation of the fault, which could lead to equipment damage or power grid safety accidents.

[0113] Step S3: Determine the harmonic amplitude ratio based on the second and fourth harmonic amplitudes; determine the location of the faulty slot based on the harmonic amplitude ratio and a pre-built slot mapping table. This includes:

[0114] Step S31: Obtain the total number of rotor slots of the rotating motor and the spatial position information corresponding to each rotor slot.

[0115] Based on the rotor structure parameters of the synchronous condenser, the total number of rotor slots N is obtained. For salient-pole rotors, several rotor slots are typically evenly distributed under each magnetic pole. The spatial position information of each rotor slot relative to the rotor magnetic pole axis is collected, including the circumferential angle position corresponding to the center line of the slot. Taking the center line of the large tooth of a certain magnetic pole as the angle zero point, the slot numbers of each rotor slot are sequentially marked along the rotor rotation direction, and the spatial angle coordinates corresponding to each slot number are recorded. For symmetrically distributed multi-pole rotors, only the spatial position of each rotor slot under a single magnetic pole needs to be recorded; the positions of the rotor slots under other magnetic poles can be derived through periodic symmetry.

[0116] Step S32: For each rotor slot, determine the second harmonic modulation amount and the fourth harmonic modulation amount when the rotor slot is short-circuited based on the spatial position information of the rotor slot.

[0117] Step S321: Based on the circumferential angular position of the rotor slot, establish the spatial distribution function of the air gap magnetomotive force when an inter-turn short circuit occurs in that slot. The equivalent circuit model of the rotor winding inter-turn short circuit is as follows: Figure 4 As shown, Figure 4 The equivalent circuit model of an inter-turn short circuit in the rotor winding is shown. (Figure e) f As the excitation DC voltage source, I f0 R represents the instantaneous value of the excitation current. SC For short-circuit transition resistance, L f For the excitation winding inductance, I sc This represents the short-circuit loop current. According to the superposition principle, an inter-turn short circuit in the rotor winding can be equivalent to applying an additional short-circuit current of the same amplitude but opposite direction to the short-circuit coil portion on top of the normal operating conditions. This model is used to analyze the changes in excitation current and the distortion of the air gap magnetomotive force after a fault; the fault can be equivalent to superimposing a reverse short-circuit current on top of the normal excitation loop, which causes distortion of the air gap magnetomotive force. When an inter-turn short circuit occurs in rotor slot y, the additional magnetomotive force generated by the short-circuit current in the air gap exhibits a non-sinusoidal distribution along the circumferential direction. This magnetomotive force can be expanded into a Fourier series, containing the fundamental component and various harmonic components. Due to the discrete spatial distribution characteristics of the rotor slots, the spatial distribution function of the air gap magnetomotive force generated by short-circuit faults in different slots exhibits phase differences, which directly depend on the spatial angular position of the rotor slot.

[0118] Step S322 involves coupling the spatial distribution function of the air gap magnetomotive force (EMF) with the spatial distribution function of the stator windings to extract the even-order harmonic components of the induced electromotive force (EMF) in the two in-phase branches of the stator. The stator windings are sinusoidally distributed in space, and their winding factor has different attenuation effects on different harmonics. When the even-order harmonic components in the air gap MMF cut the stator windings, they induce even-order harmonic EMFs with equal amplitude and opposite phase in the two in-phase branches. This EMF difference drives the two branches to generate even-order harmonic circulating currents.

[0119] Step S323: Based on the equivalent circuit parameters of the stator in-phase dual-branch circuit, calculate the amplitudes of the second and fourth harmonic components in the even-order harmonic circulating current. The circulating current between the two branches is limited by both branch resistance and branch leakage reactance; the equivalent impedance of the branch varies for different harmonics. The amplitude of the second harmonic circulating current is proportional to the quotient of the second harmonic electromotive force divided by the second harmonic equivalent impedance, and the amplitude of the fourth harmonic circulating current is proportional to the quotient of the fourth harmonic electromotive force divided by the fourth harmonic equivalent impedance.

[0120] Step S324: Extract the modulation factor related to the spatial position of the rotor slot from the amplitude of the second harmonic circulating current, and record it as the second harmonic modulation amount corresponding to the rotor slot. This modulation amount reflects the weight of the rotor slot spatial position on the amplitude of the second harmonic circulating current. Its value depends on the cosine value of the circumferential angle corresponding to the slot in the spatial distribution function of the second harmonic magnetomotive force. For different slot numbers, the second harmonic modulation amount exhibits a periodic variation due to the different spatial angles.

[0121] Step S325: Using the same method as in step S324, extract the modulation factor related to the spatial position of the rotor slot from the amplitude of the fourth harmonic circulating current, and record it as the fourth harmonic modulation amount corresponding to that rotor slot. This modulation amount reflects the weight of the rotor slot spatial position on the amplitude of the fourth harmonic circulating current. Its value depends on the cosine value of the circumferential angle corresponding to the slot in the spatial distribution function of the fourth harmonic magnetomotive force. Since the spatial period of the fourth harmonic is half that of the second harmonic, the spatial variation patterns of the fourth harmonic modulation amount and the second harmonic modulation amount corresponding to the same slot number are significantly different.

[0122] In one possible implementation, for the case of a salient-pole synchronous condenser with 8 rotor slots uniformly distributed under a single magnetic pole, the circumferential angular interval between adjacent rotor slots is: Taking slot 1 as an example, let its corresponding initial angle be... The second harmonic modulation amount of the slot is:

[0123] 4th harmonic modulation amount:

[0124]

[0125] in, This is the circumferential angle of the tooth corresponding to the slot. For slot number 2, the initial angle is... The corresponding second harmonic modulation amount is The 4th harmonic modulation amount is By analogy, the second and fourth harmonic modulation quantities corresponding to each rotor slot can be calculated.

[0126] For example, for slot 1, which is close to the center of the magnetic pole tooth, since its spatial position is close to the magnetic pole axis, the corresponding initial angle is... The second harmonic modulation amount is relatively small. Achieving a large positive value, while the 4th harmonic modulation amount The value is relatively small. For slot 8, which is far from the center of the large tooth, its initial angle The magnitude is relatively large, close to the edge of the magnetic pole, at which point the second harmonic modulation amount is... The value decreases or even becomes negative, while the 4th harmonic modulation amount The value of the modulation increases relatively. This variation in modulation caused by spatial location differences provides a theoretical basis for distinguishing different slot numbers by harmonic amplitude ratio.

[0127] It should be noted that the attenuation effect of the winding factor on different harmonics needs to be considered in the calculation of harmonic modulation. Second harmonic winding factor. With the 4th harmonic winding factor The different values ​​of these factors lead to differences in the induced intensity of the second and fourth harmonic circulating currents, even under the same air gap magnetomotive force. When extracting the modulation amount, the influence of the winding factor needs to be removed from the circulating current amplitude expression, so that the modulation amount reflects only the effect of the rotor slot spatial position and is independent of the winding parameters. This ensures that the modulation amount is universal and applicable to synchronous condensers with different winding configurations.

[0128] In another possible implementation, taking slot 1 as an example, let its corresponding initial angle be... The second harmonic modulation amount of the slot is:

[0129] 4th harmonic modulation amount:

[0130]

[0131] Step S33: Determine the harmonic amplitude ratio corresponding to the rotor slot based on the ratio of the second harmonic modulation amount to the fourth harmonic modulation amount.

[0132] The second harmonic modulation amount of the rotor slot With the 4th harmonic modulation amount Dividing them yields the modulation ratio. This is due to the amplitude of the second harmonic circulating current. With the second harmonic modulation amount Proportional to the amplitude of the fourth harmonic circulation With the 4th harmonic modulation amount They are directly proportional, therefore the amplitudes of the second and fourth harmonics of the circulation are proportional. Equal to the modulation ratio The harmonic amplitude is higher than It depends solely on the spatial location of the rotor slots and is independent of factors such as the number of short-circuit turns, the magnitude of the excitation current, and the load conditions, thus possessing the unique characteristic of fault location.

[0133] In specific implementation, the amplitude ratio of the second and fourth harmonics of the stator in-phase dual-branch circulating current is:

[0134]

[0135] In the formula, P 24 S1 represents the amplitude ratio of the second and fourth harmonics of the circulating current; S2 and S4 represent the modulation amounts of the second and fourth harmonics, respectively. Indicates the second harmonic winding factor. Indicates the 4th harmonic winding factor. For the second harmonic equivalent reactance of the branch, The equivalent reactance for the fourth harmonic of the branch is given.

[0136] Preferably, the specific method of obtaining the fault slot location based on the harmonic amplitude ratio and the pre-constructed mapping table of the present invention is as follows: extract the second and fourth harmonic components in the branch circulation after the fault occurs, and calculate their harmonic amplitude ratio P. 24 Match P by looking up a table 24 The interval in which the faulty slot is located is used to pinpoint the faulty slot number; where, in the mapping table, each slot number corresponds to P. 24 The intervals do not overlap and there is a margin between adjacent intervals.

[0137] Step S34: Based on the harmonic amplitude ratio corresponding to each rotor slot and the preset margin, divide the harmonic amplitude ratio interval corresponding to each rotor slot and generate the slot mapping relationship table.

[0138] In this embodiment, the slot mapping relationship table is shown in Table 1:

[0139] Table 1 Slot Mapping Relationship Table

[0140]

[0141] Step S341: Obtain the difference between the theoretical harmonic amplitude ratios of two adjacent rotor slots.

[0142] For a salient-pole synchronous condenser with 16 rotor slots, the theoretical harmonic amplitude ratio for each rotor slot is extracted according to the slot numbering order. The theoretical harmonic amplitude ratio is obtained through field-circuit coupling simulation, reflecting the relative intensity relationship of the second and fourth harmonic components of the air gap magnetic field when an inter-turn short circuit occurs in different slot positions. The calculation of the... Slot No. and No. The difference in the theoretical harmonic amplitude ratio between slots is denoted as: ,in The value ranges from 1 to 15. This difference reflects the distinguishability of adjacent slots in terms of harmonic characteristics. The larger the difference, the easier it is to distinguish adjacent slots. The smaller the difference, the closer the harmonic characteristics of adjacent slots are, requiring a more refined interval division strategy.

[0143] In addition, in practical implementation, due to the structural symmetry and harmonic characteristics, it is also possible to analyze only the 8 slots with obvious distinguishing features.

[0144] Step S342: Determine the preset margin based on the difference.

[0145] Step S3421: Calculate the theoretical harmonic amplitude ratio difference for all adjacent rotor slots and obtain the minimum value of the difference. .

[0146] Iterate through all harmonic amplitude ratio differences between adjacent slot pairs, and find the smallest value among the 15 difference data. The slot pair corresponding to the smallest difference is the most difficult to distinguish between adjacent slots. The size of the smallest difference directly affects the resolution of the mapping table. If the smallest difference is too small, the harmonic characteristics of adjacent slots will highly overlap, and a stricter margin value needs to be set to avoid misjudgment.

[0147] Step S3422: Calculate the baseline value of the preset margin based on the minimum difference.

[0148] Minimum difference Multiply by the preset scaling factor To obtain the baseline value with the preset margin. The calculation formula is:

[0149]

[0150] Preset ratio coefficient The value ranges from 0.2 to 0.4, and is used to reserve sufficient recognition margin for each slot while ensuring that adjacent intervals do not overlap. If the proportional coefficient is too large, the interval range will be too wide, which may cause adjacent intervals to overlap; if the proportional coefficient is too small, the interval range will be too narrow, reducing the anti-interference ability and making it easy to miss detection when there are errors in actual measurement.

[0151] Step S3423: Based on the theoretical harmonic amplitude ratio of each rotor slot and the difference between adjacent slots, the reference value is corrected to obtain the preset margin corresponding to the rotor slot.

[0152] Regarding the first For rotor slot number 1, calculate its relationship with the previous slot number 2. Slot number 1 and the next slot number 2 The difference in harmonic amplitude ratio of slot number 1 is denoted as . and Take the smaller of the two differences and multiply it by the correction factor. , obtained the Preset margin of slot number The calculation formula is:

[0153]

[0154] The correction factor ζ ranges from 0.25 to 0.35 and is used for personalized adjustments based on the specific location of each slot and the difficulty of distinguishing adjacent slots. For slot sections where the theoretical harmonic amplitude ratio changes relatively smoothly, the adjacent differences are small, and the corresponding preset margin is reduced accordingly to ensure that the intervals do not overlap; for slot sections where the theoretical harmonic amplitude ratio changes drastically, the adjacent differences are large, and the corresponding preset margin can be appropriately increased to improve the anti-interference capability.

[0155] Step S343: Taking the harmonic amplitude ratio corresponding to each rotor slot as the center, and combining it with the preset margin, determine the upper limit threshold and lower limit threshold corresponding to the rotor slot.

[0156] Step S3431: Obtain the theoretical harmonic amplitude ratio corresponding to the y-th rotor slot. and the preset margin corresponding to this slot. .

[0157] Extract the theoretical harmonic amplitude ratio of slot y from the simulation database. This value is the ratio of the second harmonic amplitude to the fourth harmonic amplitude of the stator in-phase dual-branch circulating current, calculated through finite element simulation under the condition that a single-turn short-circuit fault occurs in slot y of the rotor and the synchronous condenser is operating under rated conditions. Simultaneously, extract the preset margin value corresponding to this slot, calculated according to step S3431.

[0158] Step S3432, compare the theoretical harmonic amplitude with... Subtract the preset margin , obtained the The lower threshold corresponding to rotor slot number 1 .

[0159] The formula for calculating the lower threshold is:

[0160] = -

[0161] The lower threshold defines the first The left boundary of the harmonic amplitude ratio interval for slot #1; when the actually measured harmonic amplitude ratio is lower than this lower threshold, it is no longer considered as slot #2. If the fault is in slot number 1, the possibility of a fault in the previous slot or other slots should be considered.

[0162] Step S3433, compare the theoretical harmonic amplitude with... Plus preset margin , obtained the The upper limit threshold corresponding to rotor slot number 1 .

[0163] The formula for calculating the upper limit threshold is:

[0164] =

[0165] The upper limit threshold defines the first The right boundary of the harmonic amplitude ratio interval for slot #1; when the actually measured harmonic amplitude ratio is higher than this upper threshold, it is no longer considered as slot #2. If the fault is in slot number 1, the possibility of a faulty slot in the next slot or other slots should be considered.

[0166] Step S3434, check the first Upper limit threshold of rotor slot number Is it less than the first? The lower threshold of rotor slot number 1 If yes, then keep the current threshold; otherwise, adjust the preset margin and recalculate.

[0167] For two adjacent slots, their harmonic amplitude ratio intervals must satisfy the condition that they do not overlap, i.e. The testing method is comparative. and The size relationship, if This indicates that there is a safe gap between the two intervals, meeting the non-overlap requirement, and the current threshold setting is reasonable. If This indicates that the two intervals overlap or are adjacent, and the correction factor needs to be reduced. The value of is recalculated. Slot No. and the The preset margin of slot number is adjusted until the non-overlap condition is met. Through iterative adjustments, the harmonic amplitude ratio intervals of all adjacent slots are ultimately made so that they neither overlap nor retain an appropriate safety margin, ensuring the accuracy and reliability of fault location.

[0168] Step S344: The harmonic amplitude ratio range corresponding to the rotor slot is constructed based on the upper limit threshold and the lower limit threshold.

[0169] Regarding the first Rotor slot number, lower limit threshold As the left endpoint of the interval, with the upper threshold The right endpoint of the interval constitutes the harmonic amplitude ratio identification interval for this slot, denoted as . This interval indicates that when the calculated ratio of the 2nd to 4th harmonic amplitudes after harmonic extraction of the actual collected stator in-phase dual-branch circulating current falls within this interval, the fault is determined to have occurred in the 4th harmonic. Rotor slot number 1. The width of the interval is equal to... A wider range allows for greater tolerance to measurement errors and signal fluctuations, but an excessively wide range may cause adjacent ranges to overlap; a smaller range results in higher positioning accuracy, but reduces the ability to resist interference. A balance needs to be struck between the two.

[0170] Step S345: Establish the mapping relationship between all rotor slots and their corresponding harmonic amplitude ratio intervals to obtain the slot mapping relationship table.

[0171] A mapping table was created by assigning the numbers of the 16 rotor slots to their corresponding harmonic amplitude ratio intervals. Each row in the table records a slot number and its corresponding upper and lower limits for the interval. The mapping table is arranged in ascending order of slot number for easy lookup later. All intervals in the table satisfy the constraints of non-overlapping intervals and sufficient margin between adjacent intervals, ensuring that any measured harmonic amplitude ratio can fall into at most one interval, thus achieving unique identification of the faulty slot. The slot mapping table is stored in the synchronous condenser monitoring system as a basis for online fault location.

[0172] It should be noted that the method for determining the preset margin directly affects the performance of the slot mapping table. If the preset margin is too large, although it can improve the anti-interference capability, it will easily lead to the overlap of adjacent intervals, especially in slot sections where the theoretical harmonic amplitude ratio changes relatively smoothly, which may result in the intersection of intervals of multiple slots, causing positioning ambiguity. If the preset margin is too small, although it can ensure that the intervals do not overlap strictly, it will reduce the tolerance for measurement errors. In actual working conditions, when the signal is affected by noise interference or load fluctuations, the actual harmonic amplitude ratio may fall into the interval gap, leading to missed detection. This invention dynamically determines the benchmark margin based on the minimum difference between adjacent slots, and then makes personalized corrections based on the specific location of each slot and the adjacent difference, achieving an optimized balance between positioning accuracy and anti-interference capability. This adaptive margin setting method not only ensures that all adjacent intervals do not overlap, but also reserves sufficient recognition margin for each slot, making the slot mapping table have high accuracy and robustness in practical applications.

[0173] Preferably, after constructing the slot mapping table, the effectiveness of the table is verified through simulation or experiment. Specifically, in the finite element simulation model, a short-circuit fault with a different number of turns is set for each slot. The stator in-phase dual-branch circulating current signal is collected, the actual harmonic amplitude ratio is calculated, the faulty slot is determined by looking up the table, and the location accuracy is statistically analyzed. If the location accuracy is lower than a preset threshold, such as 95%, it indicates that the current preset margin setting is unreasonable, and the correction coefficient needs to be readjusted. The mapping table is then reconstructed until the positioning accuracy meets the requirements. This iterative optimization method yields an optimal slot mapping table suitable for specific synchronous condenser models and operating conditions, providing reliable technical support for online fault diagnosis.

[0174] The slot mapping table constructed in this invention has the following technical advantages: First, by dynamically determining the preset margin, an adaptive balance between positioning accuracy and anti-interference capability is achieved, avoiding the problems of insufficient accuracy or poor robustness in the fixed margin method; Second, by individually correcting the margin of each slot, the differences in harmonic characteristics of different slot sections are fully considered, making the mapping table more in line with actual physical laws; Third, through strict non-overlapping constraints and iterative adjustment mechanisms, the uniqueness and reliability of fault location are ensured; Finally, the construction process of the mapping table is based on theoretical harmonic amplitude ratio data, eliminating the need for a large number of field fault samples, reducing the difficulty of engineering implementation, and improving the practicality and scalability of the method.

[0175] This method effectively addresses measurement uncertainties in practical engineering by introducing a preset margin.

[0176] It should be noted that the specific value of the preset margin can be optimized and adjusted based on the on-site measurement conditions and historical statistical data. In situations with complex electromagnetic environments or low measurement accuracy, the preset margin can be appropriately increased to improve fault tolerance. In situations with good measurement conditions and high accuracy of the harmonic extraction algorithm, the preset margin can be appropriately decreased to improve the precision of slot number differentiation. By flexibly setting the preset margin, this method can adapt to the fault location requirements in different application scenarios.

[0177] Specifically, the construction of the slot mapping table can be completed offline, pre-calculated and stored based on the motor design parameters before the synchronous condenser is put into operation. Once generated, the table remains unchanged throughout the entire operating cycle. Fault diagnosis only requires table lookup and matching, resulting in minimal computation and fast response. This strategy of offline construction and online table lookup ensures both the theoretical accuracy of fault location and meets the engineering practicality requirements of real-time diagnosis.

[0178] Step S35: Determine the target harmonic amplitude ratio range to which the harmonic amplitude ratio belongs.

[0179] The harmonic amplitude ratio calculated in step S33 under the fault condition is... The harmonic amplitude ratio is compared one by one with the harmonic amplitude ratio intervals corresponding to each rotor slot in the slot mapping table. It is determined whether the harmonic amplitude ratio value falls within the valid interval corresponding to a certain rotor slot, that is, whether the value is greater than the lower limit of the interval and less than the upper limit of the interval. If the condition is met, the target harmonic amplitude ratio interval to which the harmonic amplitude ratio belongs is determined.

[0180] Step S36: Obtain the target rotor slot corresponding to the target harmonic amplitude ratio interval from the slot mapping table, and determine the target rotor slot as the fault slot location.

[0181] Based on the mapping relationship in the slot mapping table, the rotor slot number corresponding to the target harmonic amplitude ratio interval is read, and this slot number is used as the target rotor slot, which is the location of the rotor slot where the inter-turn short circuit fault has occurred. The fault slot number information is output to complete the precise fault location.

[0182] In one embodiment, assuming that the harmonic amplitude ratio under fault conditions is calculated to be 1.40 through step S33, and the value is found to fall within the effective range corresponding to slot 3 by querying the slot mapping table. If the fault occurs between these values, it is determined that the fault is in slot 3. The system outputs the fault slot location as rotor slot 3, providing an accurate basis for subsequent short-circuit turn count calculation and maintenance decisions. This method utilizes the harmonic amplitude ratio, a characteristic quantity insensitive to the number of short-circuit turns, to achieve precise slot location independent of the fault severity, solving the technical challenge of coupling fault location and severity assessment in traditional methods.

[0183] Step S4: Obtain the current excitation current of the rotating motor, and determine the relative increment of the excitation current based on the current excitation current and a preset excitation current reference value. This includes:

[0184] Step S41: Obtain multiple sets of historical excitation current data of the rotating motor under typical fault-free operating conditions.

[0185] During normal operation of the rotating electric motor, continuous time-series records of the excitation current are collected under different load rates to form multiple sets of historical excitation current datasets. A typical operating condition refers to a stable operating state where the synchronous condenser is within its rated power factor range and the grid voltage fluctuates around its rated value, excluding data during start-up / shutdown transitions and grid disturbances. The collection of multiple data sets should cover different load rate ranges, including light load, medium load, and full load, to ensure the representativeness of subsequent baseline values.

[0186] Step S42: Extract the stable segment data from each group of historical excitation current data.

[0187] A stable segment refers to a continuous time interval in the excitation current time series curve where the fluctuation amplitude is consistently below a predetermined threshold. The specific determination method is as follows: for each set of historical excitation current time series data, the standard deviation is calculated segment by segment using a fixed sliding window. When the standard deviation within several consecutive windows is lower than the predetermined fluctuation threshold, this continuous interval is marked as a stable segment, and valid data for subsequent averaging calculations is extracted from it.

[0188] For example, for a TTS-300-2 type synchronous condenser, a set of historical excitation current data was collected for a duration of 600 seconds. The standard deviation of the data was calculated segment by segment using a 10-second sliding window and a 1-second step. When the standard deviation was below 0.5 amperes for 20 consecutive windows, the interval was determined to be a stable segment. In this set of data, the data within approximately the first 60 seconds of the startup phase and approximately 30 seconds after load switching were excluded because the standard deviation exceeded the threshold; the remaining portion was marked as a stable segment and included in subsequent calculations. This determination process ensures that the extracted data accurately reflects the level of the excitation current under steady-state conditions, eliminating the influence of transient disturbances on the baseline value.

[0189] In one possible implementation, the fluctuation threshold can be set based on the statistical distribution of historical data. For example, the 95th percentile of the absolute value of the first-order difference of the excitation current at all sampling points can be taken as the fluctuation threshold, so that the threshold adapts to the actual operating characteristics of the equipment.

[0190] Step S43: Calculate the average value of all stable segment data to obtain the preset excitation current reference value.

[0191] All stable segment data extracted from each group of historical data in step S42 are merged, and the arithmetic mean of the merged dataset is calculated. The result is the preset excitation current reference value. This benchmark value comprehensively reflects the typical steady-state level of the excitation current of the synchronous condenser under multiple load conditions, and can be used as a reference benchmark for calculating the change in excitation current in subsequent fault diagnosis.

[0192] Step S44: Collect the current excitation current of the rotating motor in its current operating state.

[0193] After establishing the baseline value, the instantaneous value of the excitation current under the current operating state of the synchronous condenser is acquired in real time through the existing excitation current acquisition circuit. After low-pass filtering, the average value of the stable section is taken as the current excitation current I. f1 The representative value.

[0194] Step S45: Calculate the difference between the current excitation current and the preset excitation current reference value to obtain the absolute increment of the excitation current.

[0195] The difference between the current excitation current value collected in step S44 and the preset excitation current reference value obtained in step S43 is the absolute increment of the excitation current. This absolute increment directly reflects the additional component of the excitation current caused by the short circuit between rotor winding turns, and its magnitude is positively correlated with the number of short-circuited turns.

[0196] Step S46: Calculate the ratio of the absolute increment of the excitation current to the preset excitation current reference value to obtain the relative increment of the excitation current.

[0197] The relative increment of the excitation current is calculated by dividing the absolute increment of the excitation current obtained in step S45 by the preset excitation current reference value obtained in step S43. This normalization process is the core of this step.

[0198] In this embodiment, the expression for calculating the relative increment of the excitation current is:

[0199] In the formula, Δi f K represents the relative increment of the excitation current. b k1 and k2 are saturation coefficients; k1 and k2 are positive constants; I f0 I f1 These are the excitation currents before and after the short circuit, respectively; w s For the number of faulty turns, N c This represents the total number of turns in the winding.

[0200] Preferably, the steady-state reference value I of the excitation current during normal operation of the present invention f0 The data was taken from the stable period of historical data under typical fault-free operating conditions of the generator, and the average value was obtained by taking multiple measurements under multiple loads.

[0201] After the fault occurs, the excitation current will show a significant increase. A comparison of the excitation current waveforms before and after the short-circuit fault in the 3 turns of rotor slot 1 is shown below. Figure 9 As shown, Figure 9 The changes in excitation current before and after a short-circuit fault in three turns of slot 1 are shown. Before the fault, the excitation current was stable near its rated value; after the fault, the excitation current rapidly increased and stabilized at a higher level, with the difference being the increment Δi. f The increment and the number of short-circuit turns satisfy a quantitative relationship, and the number of short-circuit turns can be estimated by combining the saturation coefficient; the excitation current increment can be combined with the magnetic circuit saturation coefficient of the slot to complete the quantitative calculation of the number of short-circuit turns. By offline calibration of the magnetic circuit saturation coefficient of each rotor slot and the total number of winding turns of the motor, and then combining the relative increment of the excitation current to complete the correction calculation, the final output is an accurate estimate of the number of short-circuit turns, realizing the quantitative assessment of the fault degree.

[0202] It should be noted that the reference excitation current level of the synchronous condenser varies under different power grid operating conditions. If only the absolute increment is used as the input for subsequent short-circuit turns estimation, the actual short-circuit severity corresponding to the absolute increment caused by the same number of short-circuit turns will deviate under full-load conditions with a higher reference value compared to light-load conditions. By normalizing the absolute increment to a ratio relative to the reference value, i.e., the relative increment of the excitation current, the influence of operating condition differences on the magnitude of the increment can be eliminated. This ensures that the quantitative relationship between the relative increment of the excitation current and the number of short-circuit turns remains stable and consistent under different load conditions, thus providing a reliable input for accurate subsequent short-circuit turns estimation.

[0203] In one embodiment, the preset excitation current reference value of a synchronous condenser under medium load conditions is... The current excitation current is 1200 amperes. After a short circuit occurs between turns in the rotor winding, the current stabilizes at [current value missing]. Ampere, absolute increment Ampere, relative increment of excitation current Under another operating condition, the baseline value for the same synchronous condenser running at full load. The current is 1500 amperes. If a short circuit with the same number of turns occurs, the absolute increment is about 75 amperes, but the relative increment of the excitation current is also about 5%.

[0204] Understandably, although the absolute increment values ​​differ under the two operating conditions, the relative increments remain consistent, which reflects the normalization process's elimination of operating condition interference. Subsequent steps estimate the number of short-circuited turns in the fault slot based on the relationship between the relative increment of the excitation current and the saturation coefficient, thus completing a quantitative assessment of the degree of rotor inter-turn short-circuit faults.

[0205] Step S6: Determine the estimated number of short-circuit turns based on the relative increment of the excitation current and the magnetic circuit saturation coefficient corresponding to the fault slot location. This includes:

[0206] Step S61: Obtain the total number of turns of the rotating motor winding; Read the total number of turns parameter of the rotor winding from the synchronous condenser nameplate parameters or design file. This parameter represents the complete number of turns of the rotor winding under a single magnetic pole.

[0207] In the technical parameter document of the synchronous condenser, the total number of rotor winding turns is explicitly recorded as a basic design parameter. This parameter not only determines the electrical characteristics of the excitation winding but also directly affects the air gap magnetic field distribution and the motor's operating performance. After obtaining the total number of winding turns, the system stores this value as a constant Nc, which serves as the normalization benchmark for subsequent short-circuit turn estimation. For the TTS-300-2 synchronous condenser, its single-pole rotor winding has a total of 128 turns, a value that is fixed in the monitoring system parameter configuration file at the factory. The main parameters of the TTS-300-2 synchronous condenser are shown in Table 2:

[0208] Table 2 Main Parameters of TTS-300-2 Synchronous Condenser

[0209]

[0210] Step S62: Query a preset saturation coefficient database according to the location of the fault slot to obtain the magnetic circuit saturation coefficient corresponding to the location of the fault slot.

[0211] Step S621 establishes an offline calibration process for the saturation coefficient database. Before the synchronous condenser is put into operation, short-circuit faults with the same number of turns are set for each slot of the rotor using finite element simulation or experimental testing methods. For example, three turns of short circuit are set sequentially in slots 1 to 16, and the increase in excitation current under each fault condition is recorded. Due to the differences in the magnetic circuit structure at different slots of the rotor, slots closer to the large teeth have lower magnetic reluctance and higher magnetic flux density, resulting in more significant magnetic circuit saturation, while slots farther from the large teeth have higher magnetic reluctance and weaker saturation. By comparing the differences in the increase in excitation current at different slots with the same number of short-circuit turns, the magnetic circuit saturation characteristics of each slot can be extracted.

[0212] Step S622: Calculate the saturation coefficient value for each slot. The saturation coefficient is defined as a correction factor considering the magnetic circuit saturation effect; its physical meaning is to convert the actual measured excitation current increment into a proportional coefficient equivalent to the increment under linear magnetic circuit conditions. For the first... Slot number 1, its saturation coefficient The following relationship is used to determine the number of known turns in the slot: After a short-circuit fault, measure the increment of the excitation current. Simultaneously, the theoretical increment is calculated based on the linear magnetic circuit assumption. The ratio of the two is the saturation coefficient of the tank.

[0213] In this embodiment, the expression for the saturation coefficient is:

[0214]

[0215] Among them, K b is the saturation coefficient; k1 and k2 are positive constants; w s This represents the number of faulty turns.

[0216] Step S623: Construct the saturation coefficient database table structure. The database uses the slot number as the index key to store the corresponding saturation coefficient value. The table structure contains two columns: the first column is the slot number, with a value range of 1 to 16, corresponding to the 16 slots of the rotor; the second column is the saturation coefficient. The numerical value typically ranges from 1 to 2. This database is loaded into memory during the initialization of the camera condenser monitoring system to support the need for rapid online fault diagnosis.

[0217] Step S624: Perform a database query operation. After step S4 completes the fault slot location, the system obtains the fault slot number. Using this slot number as the query key, retrieve the corresponding saturation coefficient from the saturation coefficient database. The query process uses a direct index, with a constant time complexity, ensuring fast response times for real-time diagnostics. If the fault location result is slot 1, the query returns... The value; if the location is slot 5, then return the value. The value.

[0218] In one possible implementation, a detailed analysis is conducted on the differences in magnetic circuit saturation characteristics among the rotor slots of a salient-pole synchronous condenser. The magnetic reluctance distribution along the circumferential direction of the rotor core is not uniform, which is determined by both the slot structure and the distribution of the excitation windings. In slots near the large teeth, the magnetic flux density is usually higher, making the magnetic circuit more prone to saturation. Once an inter-turn short circuit occurs in the winding at this location, the saturation of the local magnetic circuit causes a nonlinear decrease in permeability, resulting in a reduction in the equivalent inductance of the short-circuit loop. Consequently, the induced short-circuit circulating current under the same main magnetic flux is actually larger. This short-circuit circulating current generates a strong demagnetizing magnetomotive force, further weakening the air gap magnetic field. To maintain the terminal voltage, the excitation system must add an additional compensating magnetomotive force. Therefore, when a short circuit occurs near the large teeth in the saturation region, the same number of short-circuit turns will result in a more significant increase in excitation current. Conversely, slots farther from the large teeth have a larger magnetic circuit cross-sectional area and a lower basic magnetic flux density. The magnetic circuit operates primarily in the linear segment, resulting in a weak saturation effect, a larger short-circuit inductance, and a much smaller circulating current. Consequently, the increase in excitation current during a short circuit with the same number of turns is relatively gradual. It is evident that the differences in saturation characteristics among different slots can lead to systematic biases when directly estimating the number of short-circuit turns using the increase in excitation current. For example, the number of turns is often overestimated in the saturation region. To address this issue, a saturation coefficient that varies with the slot position can be introduced for correction. This unifies the calculation of the excitation current increment measured for each slot to the same baseline, thus eliminating the nonlinear effects introduced by the slot position and significantly improving the accuracy of the turns estimation.

[0219] Step S63: Determine the corrected excitation current increment based on the product of the relative increment of the excitation current and the magnetic circuit saturation coefficient.

[0220] Step S631: Obtain the relative increment of the excitation current calculated in step S5. This increment represents the relative change in excitation current after a fault relative to the normal baseline value. It has been normalized and the value is typically in the range of 0.02 to 0.20. The relative increment of excitation current reflects the overall impact of a short-circuit fault on the excitation circuit. However, due to the magnetic circuit saturation effect, the relationship between this increment and the number of short-circuit turns is affected by slot-related nonlinear factors.

[0221] Step S632: Perform saturation effect correction calculation. The relative increment of the excitation current is... The saturation coefficient obtained in step S612 Perform a division operation to obtain the corrected excitation current increment. :

[0222]

[0223] The physical meaning of this correction process is to convert the actual measured increment into an increment value under equivalent linear magnetic circuit conditions. Since the saturation coefficient is greater than 1, the corrected increment value is smaller than the original increment, thus reducing the reinforcing effect of magnetic circuit saturation on the current increment.

[0224] Step S633: Analyze the physical meaning of the correction increment. Correct the excitation current increment. This method eliminates the differences in magnetic circuit saturation related to different slots, ensuring that faults in different slots correspond to the same correction increment value for the same number of short-circuited turns. This normalization process transforms complex nonlinear electromagnetic relationships into approximately linear correspondences, paving the way for subsequent turns estimation based on linear assumptions. The numerical range of the correction increment is typically between 0.01 and 0.15, depending on the number of short-circuited turns and the faulty slot.

[0225] In one possible implementation, the electromagnetic physical mechanism of saturation coefficient correction can be summarized as follows: When an inter-turn short circuit occurs in the rotor winding, the circulating current generated in the short-circuit loop will form a demagnetizing magnetomotive force in the air gap that is opposite to the normal excitation magnetomotive force, thereby causing distortion of the air gap composite magnetic field and a corresponding weakening of the main magnetic flux. If the fault point is located in a slot near the large tooth, the magnetic flux density in this area is already high, and the core material has entered the saturation segment of the BH curve, resulting in a significant reduction in local permeability. This state will have a dual effect: firstly, the decrease in permeability reduces the equivalent inductance of the short-circuit loop, increasing the induced short-circuit circulating current under the same rate of change of main magnetic flux, making the demagnetizing effect more intense; secondly, to compensate for this demagnetizing effect and maintain a constant terminal voltage, the excitation system needs to provide a current increment much higher than the linear magnetic circuit assumption at the current low permeability operating point in order to restore the air gap flux. Conversely, if the fault occurs in a slot far from the large tooth, the core is in the linear operating region, the permeability is approximately constant, the short-circuit inductance is large, the demagnetizing effect is weak, and the increase in excitation current matches the theoretical prediction of the linear model more closely. The difference in increment caused by the different saturation characteristics of the slots leads to a systematic overestimation tendency in the saturation region when the method of directly estimating the number of short-circuit turns based on the increase in excitation current. To address this problem, a saturation coefficient greater than 1 can be introduced to correct the measured increment. This coefficient is divided by the current increment value of each slot, mapping the electromagnetic response at different locations uniformly to a linear magnetic circuit reference, thereby establishing a stable linear mapping relationship between the corrected increment and the number of short-circuit turns.

[0226] It should be noted that the introduction of the saturation coefficient significantly improves the accuracy of short-circuit turn estimation. After the saturation coefficient correction is introduced, the correction increments calculated for the two slots tend to be consistent, and the turn estimation error is reduced to within 5%. This correction method does not rely on complex nonlinear magnetic circuit models; it only requires pre-calibrating the saturation coefficients of each slot and storing them in a database. During online diagnostics, correction can be achieved through simple multiplication and division operations, resulting in high computational efficiency and ease of engineering implementation.

[0227] In one embodiment, assuming that step S4 locates the fault in slot 3, step S5 calculates the relative increment of the excitation current. The value is 0.026. Step S612 queries the saturation coefficient database to obtain... Perform the correction calculation. This value indicates that if the magnetic circuit were perfectly linear, the excitation current increment corresponding to the current short-circuit fault in slot 3 should be 2.3%. Compared to the original increment of 2.6%, the correction value is approximately 15%, compensating for the increment suppression effect caused by slight magnetic circuit saturation. If the fault occurred in slot 1, the measured... The value is 0.024, query ,but The result is close to that of slot 3, indicating that the actual number of short-circuited turns in the two slots is similar, thus verifying the effectiveness of the correction method.

[0228] Step S64: Determine the estimated number of short-circuit turns based on the product of the corrected excitation current increment and the total number of winding turns.

[0229] Step S641: Establish a linear mapping relationship between the correction increment and the number of short-circuited turns. Under the linear magnetic circuit assumption, the increase in excitation current caused by an inter-turn short circuit in the rotor winding is proportional to the number of short-circuited turns, with the proportionality coefficient being the reciprocal of the total number of winding turns. This relationship can be expressed as: Number of short-circuited turns Equivalent to correcting the increment of excitation current With total number of winding turns The product of the two. The physical basis of this linear relationship is that an inter-turn short circuit is equivalent to inserting a reverse magnetomotive force source into the excitation circuit. Its strength is proportional to the number of short-circuited turns. In order to maintain the air gap flux constant, the excitation current needs to be increased accordingly, and the increment is linearly related to the number of short-circuited turns.

[0230] Step S642: Perform short-circuit turn estimation calculation. Use the corrected excitation current increment obtained in step S613. The total number of winding turns obtained in step S611 Multiply by this to obtain an estimated number of short-circuit turns. :

[0231]

[0232] Since the correction increment has eliminated the saturation effect, the calculation result directly reflects the actual number of short-circuit turns. The estimation accuracy depends on the measurement accuracy of the correction increment and the calibration accuracy of the saturation coefficient.

[0233] Step S643: Perform numerical processing on the estimation results. Since the number of short-circuit turns is an integer, while the calculated result may be a decimal, it is necessary to perform numerical processing. Rounding is performed. The specific rules are: if the decimal part is less than 0.5, round down to the nearest integer; if the decimal part is greater than or equal to 0.5, round up. This process yields the final integer value for the number of short-circuited turns. This value is output as the fault diagnosis result.

[0234] Step S644: Evaluate the reliability of the estimation results. Compare the correction increment with the preset reasonable range. If the correction increment is too small, for example, less than 0.01, it indicates that the fault severity is extremely minor or there may be measurement errors, and the reliability of the estimation results is low. If the correction increment is too large, for example, more than 0.20, it indicates that there are many short-circuited turns or multiple faults, and further verification is required. Within the normal estimation range, the accuracy of the turns estimation after correction with the saturation coefficient can usually reach within ±1 turn.

[0235] In one possible implementation, the theoretical basis for the linear relationship between the correction increment and the number of short-circuit turns is elaborated in detail. Based on the electromagnetic theory of motors, the magnetomotive force of the excitation winding... Proportional to excitation current With total number of turns The product of, i.e. .when When a short circuit occurs in the winding, the short-circuit loop generates a reverse magnetomotive force. Its amplitude is ,in This is the short-circuit current. It is used to maintain the main magnetic flux in the air gap. To ensure stable terminal voltage, the excitation winding needs to be increased with magnetomotive force. To compensate for the short-circuit reverse magnetomotive force, i.e. Assuming the magnetic path is linear, the excitation current increment... satisfy Due to short-circuit current With excitation current They are close in magnitude and can be approximated as... That is, the relative increment of the excitation current It equals the ratio of short-circuit turns to total turns. After saturation coefficient correction, the correction increment is... To more accurately satisfy this linear relationship, therefore This theoretical relationship has been verified through extensive simulations and experiments in practical applications, proving that when the number of short-circuited turns does not exceed 10% of the total number of turns, the error introduced by the linear assumption is less than 5%.

[0236] Specifically, the total number of winding turns This method serves as a normalization benchmark in short-circuit turns estimation. The number of turns in the excitation winding varies significantly between different types of synchronous condensers; small units may have only tens of turns, while large units can have hundreds. The same number of short-circuit turns corresponds to different proportions of excitation current increments in different units. However, by multiplying by the total number of turns for inverse normalization, the relative increment can be converted into an absolute number of turns, achieving a unified diagnostic method across different unit types. The applicability of this method is not limited by differences in unit capacity, number of poles, or winding structure; it only requires configuring the corresponding total turns parameter during system initialization.

[0237] It should be noted that the applicability of the short-circuit turns estimation method varies depending on the severity of the fault. When the number of short-circuit turns is small, such as 1 to 3 turns, the excitation current increment is small, the measurement signal-to-noise ratio is relatively low, and the estimation result may be affected by measurement noise and system disturbances, resulting in a relatively large error, possibly reaching ±1 turn. When the number of short-circuit turns is moderate, such as 4 to 10 turns, the excitation current increment is within a range that is easy to measure accurately, the saturation coefficient correction effect is significant, the estimation accuracy is the highest, and the error is usually within ±0.5 turns. When the number of short-circuit turns is large, such as more than 15 turns, the fault severity is severe, the applicability of the linear assumption decreases, and complex situations such as multi-point faults or complete insulation breakdown may occur. The estimation result needs to be combined with other diagnostic information for comprehensive judgment. Therefore, this method is most suitable for early to mid-stage inter-turn short-circuit faults, providing accurate quantitative diagnosis before the fault expands, and providing a basis for timely maintenance measures.

[0238] Preferably, after estimating the number of short-circuit turns, the system automatically generates a diagnostic report containing the faulty slot number and the number of short-circuit turns. The report includes: fault detection time, located faulty slot number, estimated number of short-circuit turns, current excitation current value, correction increment value, saturation coefficient used, and estimation reliability rating. This report is presented to maintenance personnel through the monitoring system interface and simultaneously archived to a historical database for subsequent analysis. The diagnostic report provides a quantitative basis for maintenance decisions. Maintenance personnel can determine the severity of the fault based on the number of short-circuit turns: if the number of turns is less than 5, continued monitoring and planned maintenance can be arranged; if the number of turns is between 5 and 10, it is recommended to arrange a shutdown for maintenance as soon as possible; if the number of turns exceeds 10, immediate shutdown is required to prevent the fault from escalating and causing equipment damage. This quantitative diagnostic result significantly improves the scientific nature and targeted nature of synchronous condenser maintenance management, effectively reducing the risk of over-maintenance or untimely maintenance due to inaccurate fault diagnosis.

[0239] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for diagnosing inter-turn short-circuit faults and calculating the number of short-circuit turns in a synchronous condenser rotor, characterized in that, include: Obtain the circulating current signal of the stator parallel branch of the rotating electric machine, and extract the amplitude of the second harmonic and the amplitude of the fourth harmonic from the circulating current signal of the stator parallel branch. If the amplitude of the second harmonic is greater than the first preset diagnostic threshold and the amplitude of the fourth harmonic is greater than the second preset diagnostic threshold, it is determined that the rotating motor has a rotor inter-turn short circuit fault. The harmonic amplitude ratio is determined based on the amplitude of the second harmonic and the amplitude of the fourth harmonic; The location of the faulty slot is determined based on the harmonic amplitude ratio and the pre-constructed slot mapping table. Obtain the current excitation current of the rotating motor, and determine the relative increment of the excitation current based on the current excitation current and the preset excitation current reference value; The estimated number of short-circuit turns is determined based on the relative increment of the excitation current and the magnetic saturation coefficient corresponding to the location of the fault slot.

2. The method as described in claim 1, characterized in that, The process of acquiring the circulating current signal of the stator parallel branch of the rotating electric machine and extracting the amplitude values ​​of the second and fourth harmonics from the circulating current signal of the stator parallel branch includes: Collect the stator current signal of the first in-phase branch and the stator current signal of the second in-phase branch of the rotating motor; The circulating current signal of the stator in-phase parallel branch is determined based on the difference between the stator in-phase first branch current signal and the stator in-phase second branch current signal. Frequency domain analysis was performed on the circulating current signal of the stator in-phase parallel branch to extract the amplitude of the second harmonic and the amplitude of the fourth harmonic.

3. The method as described in claim 1, characterized in that, If the amplitude of the second harmonic is greater than a first preset diagnostic threshold and the amplitude of the fourth harmonic is greater than a second preset diagnostic threshold, determining that the rotating motor has a rotor inter-turn short circuit fault includes: Acquire the historical stator in-phase parallel branch circulating current signal of the rotating motor under fault-free operation; Extract the historical second harmonic amplitude and the historical fourth harmonic amplitude from the historical stator in-phase parallel branch circulating current signal; The first preset diagnostic threshold is determined by multiplying the maximum value of the historical second harmonic amplitude with a preset multiple. The second preset diagnostic threshold is determined by multiplying the maximum value of the historical four harmonic amplitudes with the preset multiple. If the amplitude of the second harmonic is greater than the first preset diagnostic threshold and the amplitude of the fourth harmonic is greater than the second preset diagnostic threshold, a diagnostic signal is generated to indicate that the rotating motor has a rotor turn-to-turn short circuit fault.

4. The method as described in claim 1, characterized in that, The step of determining the location of the faulty slot based on the harmonic amplitude ratio and a pre-built slot mapping table includes: Obtain the total number of rotor slots of the rotating electric motor and the spatial position information corresponding to each rotor slot; For each rotor slot, the second harmonic modulation amount and the fourth harmonic modulation amount when a short circuit occurs in the rotor slot are determined based on the spatial position information of the rotor slot. The harmonic amplitude ratio corresponding to the rotor slot is determined based on the ratio of the second harmonic modulation amount to the fourth harmonic modulation amount. Based on the harmonic amplitude ratio corresponding to each rotor slot and the preset margin, the harmonic amplitude ratio interval corresponding to each rotor slot is divided, and the slot mapping relationship table is generated. Determine the target harmonic amplitude ratio range to which the harmonic amplitude ratio belongs; Obtain the target rotor slot corresponding to the target harmonic amplitude ratio interval from the slot mapping table, and determine the target rotor slot as the location of the fault slot.

5. The method as described in claim 1, characterized in that, The step of obtaining the current excitation current of the rotating motor and determining the relative increment of the excitation current based on the current excitation current and a preset excitation current reference value includes: Obtain multiple sets of historical excitation current data of the rotating motor under typical fault-free operating conditions; Extract the stable segment data from each set of historical excitation current data; The preset excitation current reference value is obtained by averaging all stable segment data. The current excitation current of the rotating motor in its current operating state is collected; Calculate the difference between the current excitation current and the preset excitation current reference value to obtain the absolute increment of the excitation current; The ratio of the absolute increment of the excitation current to the preset excitation current reference value is calculated to obtain the relative increment of the excitation current.

6. The method as described in claim 1, characterized in that, The step of determining the estimated number of short-circuit turns based on the relative increment of the excitation current and the magnetic circuit saturation coefficient corresponding to the fault slot location includes: Obtain the total number of winding turns of the rotary motor; The magnetic circuit saturation coefficient corresponding to the fault slot location is obtained by querying a preset saturation coefficient database based on the fault slot location. The corrected excitation current increment is determined by multiplying the relative increment of the excitation current by the magnetic circuit saturation coefficient. The estimated number of short-circuit turns is determined by multiplying the modified excitation current increment by the total number of winding turns.

7. The method as described in claim 4, characterized in that, The step of dividing the harmonic amplitude ratio interval for each rotor slot according to the theoretical harmonic amplitude ratio and preset margin, and generating the slot mapping table includes: Obtain the difference between the theoretical harmonic amplitude ratios of two adjacent rotor slots; The preset margin is determined based on the difference; Taking the harmonic amplitude ratio corresponding to each rotor slot as the center, and combining the preset margin, determine the upper and lower threshold values ​​corresponding to that rotor slot. The harmonic amplitude ratio range corresponding to the rotor slot is formed by the upper limit threshold and the lower limit threshold. Establish a mapping relationship between all rotor slots and their corresponding harmonic amplitude ratio intervals to obtain the slot mapping relationship table.

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