Method and system for low frequency protection of a generator motor, method for dynamic protection of a unit

Abstract

The application discloses a power generation motor low-frequency protection method and system and a unit dynamic protection method. The power generation motor low-frequency protection method comprises the following steps: obtaining a discrete sampling sequence of a motor, performing conversion iteration to obtain an actual operation frequency of a unit, if the frequency is within a preset range, obtaining a corresponding digital filter dynamic adjustment parameter and a dynamic sampling window length of a Fourier algorithm, and performing asynchronous correction on the discrete sampling sequence; obtaining initial electrical characteristics and corresponding compensation information based on the asynchronous corrected discrete sampling sequence corresponding to the dynamic sampling window length; compensating the initial electrical characteristics according to the compensation information to obtain calibrated electrical characteristics, and obtaining relay protection electrical characteristics compensated by frequency offset error according to the calibrated electrical characteristics; and analyzing the characteristics and preset conditions of power generation motor relay protection, and if the preset conditions are not met, triggering an alarm signal. The method can accurately identify potential faults in the low-frequency operation process of equipment.

Description

Technical Field

[0001] This disclosure relates to the field of power system relay protection technology, and in particular to a low-frequency protection method and system for generator motors and a dynamic protection method for generator units. Background Technology

[0002] Pumped storage power station generators have the unique characteristic of bidirectional operation, generating electricity and pumping water. During actual operation, the units frequently perform operations such as variable frequency start-up and electric braking shutdown. During the transition phases of speed increase and decrease, the unit's electrical frequency remains in the low-frequency range of 2Hz to 10Hz for extended periods. Currently, various relay protection systems for generators generally employ a full-cycle Fourier algorithm with a fixed sampling window length, and the accompanying digital filters are designed according to 50Hz power frequency parameters. This algorithm and filtering scheme, under rated power frequency conditions, possess advantages such as high accuracy in electrical quantity amplitude and phase measurement, and good protection action speed. It can meet the relay protection requirements of the unit under conventional power frequency operation and is widely used in various generator protection systems.

[0003] However, existing power frequency-adaptive relay protection algorithms and schemes suffer from severe electrical quantity measurement distortions under low-frequency dynamic operating conditions (2Hz–10Hz) due to insufficient sampling points, spectrum leakage, and the inability to balance accuracy and speed. This can easily lead to protection maloperation. To mitigate the risk of protection maloperation, current technologies generally employ a full low-frequency protection blocking strategy, directly shutting down all relay protection functions in the low-frequency range. While this passive protection method eliminates protection maloperation, it creates more serious safety hazards: various faults such as winding short circuits, stator grounding, and demagnetization occurring during low-frequency startup and braking of the unit cannot be detected and responded to by the protection system in real time, and the fault state persists. These latent faults cannot be automatically monitored and identified by the equipment and can only be discovered through manual inspection. By the time operators discover the fault, the unit has usually already suffered substantial and irreversible equipment damage, which not only significantly increases equipment maintenance costs and shortens the unit's service life but also seriously affects the safe, stable, continuous, and reliable operation of pumped storage power station units. Summary of the Invention

[0004] In view of this, the present disclosure provides a low-frequency protection method and system for generator motors and a dynamic protection method for generator units, which can solve the problems in the prior art where various potential faults such as winding short circuits, stator grounding, and loss of excitation during low-frequency operation of equipment cannot be detected and responded to in a timely manner, and can only be discovered manually afterward, ultimately causing irreversible damage to the generator unit and seriously affecting the safe and stable operation of the generator unit.

[0005] In a first aspect, embodiments of this disclosure provide a low-frequency protection method for a generator motor, comprising: Based on a preset sampling window length, the three-phase voltage and current analog quantities of the generator motor are collected to obtain a discrete sampling sequence; The actual operating frequency of the unit is obtained by transforming and iterating the discrete sampling sequence. If the actual operating frequency is within the preset frequency range, obtain the dynamic adjustment parameters of the digital filter and the dynamic sampling window length of the full-cycle Fourier algorithm corresponding to the actual operating frequency, and perform asynchronous sampling correction on the discrete sampling sequence; Based on the discrete sampling sequence after asynchronous sampling correction corresponding to the dynamic sampling window length, the initial electrical characteristics and the compensation information corresponding to the actual operating frequency are obtained. The initial electrical characteristics are corrected and compensated according to the compensation information to obtain calibrated electrical characteristics, which include the fundamental voltage calibration amplitude, fundamental voltage calibration phase, fundamental current calibration amplitude, and fundamental current calibration phase. Based on the calibration electrical characteristics, the relay protection electrical characteristics after frequency offset error compensation are obtained; The electrical characteristics of the relay protection are analyzed in conjunction with the preset conditions of the generator motor relay protection. If any preset condition is not met, the corresponding alarm signal is triggered.

[0006] Secondly, this disclosure also provides a low-frequency protection system for a generator motor, comprising: The actual operating frequency acquisition unit is used to collect the three-phase voltage and current analog quantities of the generator motor based on a preset sampling window length to obtain a discrete sampling sequence; and to perform transformation and iteration on the discrete sampling sequence to obtain the actual operating frequency corresponding to the unit at present. The dynamic analysis unit is used to obtain the dynamic adjustment parameters of the digital filter and the dynamic sampling window length of the full-cycle Fourier algorithm corresponding to the actual operating frequency if the actual operating frequency is within a preset frequency range, and to perform asynchronous sampling correction on the discrete sampling sequence. The compensation information acquisition unit is used to obtain the initial electrical characteristics and the compensation information corresponding to the actual operating frequency based on the discrete sampling sequence after asynchronous sampling correction corresponding to the dynamic sampling window length. An electrical characteristic calibration unit is used to correct and compensate the initial electrical characteristic according to the compensation information to obtain a calibrated electrical characteristic; A relay protection electrical characteristic compensation unit is used to obtain the relay protection electrical characteristics after frequency offset error compensation based on the calibrated electrical characteristics; The anomaly analysis unit is used to analyze the electrical characteristics of the relay protection and the preset conditions of the generator motor relay protection. If any preset condition is not met, the corresponding alarm signal is triggered.

[0007] Thirdly, this disclosure also provides a method for dynamic protection of a generator unit, including: Based on the collected three-phase voltage and three-phase current analog quantities of the generator motor, the actual operating frequency of the unit is obtained. Obtain the frequency range of the actual operating frequency, dynamically call the corresponding hold strategy and execute it.

[0008] The low-frequency protection method for generator motors provided in this disclosure can adaptively adjust filter parameters and full-cycle Fourier algorithm window length in real time, and, in conjunction with asynchronous sampling correction technology, effectively suppress transient DC components, high-order harmonic interference, and spectral leakage under low-frequency operating conditions. It also eliminates sampling synchronization deviation caused by frequency fluctuations, thereby improving the accuracy of low-frequency electrical sampling data from the source. This application relies on a preset frequency and error correction coefficient database to accurately compensate and correct the amplitude and phase calculation results of fundamental voltage and current in the low-frequency range, thus obtaining high-precision calibrated fundamental electrical quantities. Based on the calibrated electrical quantities, it calculates protection characteristic quantities such as differential current, negative sequence current, and measurement impedance, which can effectively eliminate false over-limits of characteristic quantities caused by frequency offset, avoid protection maloperation, and enable normal protection operation throughout the low-frequency start-up, shutdown, and braking process of the unit. It can accurately identify various real potential faults and respond in a timely manner, preventing the continuous development of faults and irreversible damage to equipment.

[0009] The above description is merely an overview of the technical solution disclosed herein. In order to better understand the technical means of this disclosure and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this disclosure more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a schematic flowchart of a low-frequency protection method for a generator motor provided in an embodiment of this disclosure.

[0012] Figure 2 This is a flowchart illustrating a method for obtaining the actual operating frequency of a generator unit as provided in an embodiment of this disclosure.

[0013] Figure 3 This is a flowchart illustrating a method for obtaining initial electrical characteristics and compensation information provided in an embodiment of this disclosure.

[0014] Figure 4This is a flowchart illustrating a method for obtaining frequency offset error compensated relay protection electrical characteristics based on calibrated electrical characteristics, as provided in an embodiment of this disclosure.

[0015] Figure 5 A flowchart illustrating the dynamic protection method for generating units provided in this embodiment of the present disclosure. Detailed Implementation

[0016] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings.

[0017] It should be understood that the following specific examples illustrate the implementation of this disclosure, and those skilled in the art can easily understand other advantages and effects of this disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. This disclosure can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this disclosure. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0018] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this disclosure, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0019] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this disclosure. The drawings only show the components related to this disclosure and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0020] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0021] Reference Figure 1 This application discloses a low-frequency protection method for a generator motor, comprising: S100 collects analog quantities of three-phase voltage and current of the generator motor based on a preset sampling window length to obtain a discrete sampling sequence; the discrete sampling sequence is transformed and iterated to obtain the actual operating frequency of the unit at present.

[0022] S200: If the actual operating frequency is within the preset frequency range, obtain the dynamic adjustment parameters of the digital filter corresponding to the actual operating frequency, the dynamic sampling window length of the full-cycle Fourier algorithm, and perform asynchronous sampling correction on the discrete sampling sequence.

[0023] The preset frequency range is preferably the low-frequency range of 2Hz to 10Hz.

[0024] S300 obtains the initial electrical characteristics and compensation information corresponding to the actual operating frequency based on the discrete sampling sequence after asynchronous sampling correction corresponding to the dynamic sampling window length.

[0025] S400 corrects and compensates the initial electrical characteristics based on the compensation information to obtain calibrated electrical characteristics.

[0026] The calibration electrical characteristics include the calibration amplitude of the fundamental voltage, the calibration phase of the fundamental voltage, the calibration amplitude of the fundamental current, and the calibration phase of the fundamental current.

[0027] S500 obtains the relay protection electrical characteristics after frequency offset error compensation based on the calibrated electrical characteristics.

[0028] Among them, the electrical characteristics of the relay protection after frequency offset error compensation include the differential current after compensation, the negative sequence current after compensation, and the measurement impedance after compensation.

[0029] S600 analyzes the electrical characteristics of the relay protection and the preset conditions of the generator motor relay protection. If any preset condition is not met, the corresponding alarm signal is triggered.

[0030] The low-frequency protection method for generator motors disclosed in this invention is specifically for relay protection of generator motors in pumped storage power stations under low-frequency operating conditions. It dynamically adjusts filter parameters and sampling window length according to the actual operating frequency of the unit, abandoning the use of fixed power frequency parameters, and can adapt to the waveform characteristics of a preset low-frequency range. Simultaneously, asynchronous sampling correction solves the sampling asynchrony problem caused by dynamic fluctuations in the unit's frequency, making the sampling data under low-frequency conditions more accurate, complete, and closely matching the real electrical waveform. Through offline calibration, a frequency and error correction database is established, and precise compensation is performed on the fundamental amplitude and phase calculated by Fourier transform for different low-frequency points. This corrects the inherent amplitude attenuation and phase shift problems of traditional algorithms at low frequencies, obtaining high-precision calibrated fundamental electrical quantities and completely solving the problem of severe distortion of electrical quantities under low-frequency operating conditions.

[0031] Based on the precisely calibrated fundamental voltage and current amplitude and phase, the core protection characteristics such as differential current, negative sequence current, and measured impedance are recalculated, eliminating false over-limit problems caused by frequency offset. For false fault characteristics caused by algorithm errors, the corrected characteristics can automatically return to the normal range, ensuring reliable protection without false tripping under low-frequency conditions, eliminating the need for overall blocking of protection in the low-frequency range.

[0032] Furthermore, this application eliminates the full low-frequency protection interlocking logic. During the entire startup and braking process within the preset range, all relay protections are always in an effective state. Once a potential fault exists in the unit during the low-frequency transition, the protection can accurately identify the actual fault characteristics and trigger alarms and tripping actions in a timely manner, realizing real-time fault monitoring and timely handling, avoiding the continuous expansion of the fault and causing permanent damage to the equipment, reducing the unit's operation and maintenance costs, and improving the safety and reliability of the pumped storage unit's startup and shutdown process and full-condition operation.

[0033] Reference Figure 2 The methods for obtaining the actual operating frequency of the S100 unit include: S110 collects the analog three-phase voltage and analog three-phase current at the generator terminals, and obtains a discrete sampling sequence after pre-amplifier low-pass filtering and analog-to-digital conversion.

[0034] The discrete sampling sequence includes voltage discrete sampling sequence and current discrete sampling sequence.

[0035] Specifically, a multi-channel synchronous acquisition system using a relay protection device is employed to simultaneously acquire the analog three-phase voltage and current signals corresponding to the generator motor terminals. These analog voltage and current signals are then fed into a pre-amplifier analog low-pass filter for anti-aliasing filtering, removing high-frequency interference components above the folding frequency and eliminating spectral aliasing during the analog-to-digital conversion stage. The cutoff frequency of the pre-amplifier analog low-pass filter is preferably configured to be below half the sampling rate. The anti-aliasing filtered analog electrical signals of each phase are then synchronously input to the analog-to-digital converter (ADC). The ADC synchronously samples and quantizes the multiple analog signals according to a preset fixed sampling rate, converting the continuous analog electrical signals into discrete digital signals and outputting discrete voltage and current sampling sequences in a three-phase stationary coordinate system.

[0036] S120, transforms and iterates the discrete sampled sequence to obtain the actual operating frequency of the unit.

[0037] This step includes: transforming the discrete voltage sampling sequence and the discrete current sampling sequence to the dq synchronous rotating coordinate system using Parker transformation to obtain the dq-axis components, which include the d-axis voltage component, the q-axis voltage component, the d-axis current component, and the q-axis current component. A phase-locked loop algorithm is then used to perform real-time iterative calculations on the dq-axis components to obtain the unit's current actual operating frequency.

[0038] The method for obtaining the four components includes: acquiring the real-time electrical angle of the generator motor rotor in real time; using the real-time electrical angle as the transformation reference, performing Park coordinate rotation transformation operation on the voltage discrete sampling sequence and the current discrete sampling sequence point by point, and calculating the corresponding d-axis voltage component, q-axis voltage component, d-axis current component and q-axis current component in the dq synchronous rotating coordinate system respectively.

[0039] The iterative calculation specifically includes: performing hierarchical closed-loop real-time iterative processing on the four input vectors of d-axis voltage component, q-axis voltage component, d-axis current component, and q-axis current component through a phase-locked loop iterative calculation model to obtain real-time angular velocity parameters; converting the real-time angular velocity parameters by dividing them by 2π to obtain the actual operating frequency of the generator set at the current moment, thereby achieving high-precision and real-time detection of the generator set's operating frequency.

[0040] The method for obtaining real-time angular velocity parameters includes: relying on the orthogonal steady-state characteristics of the dq-axis, constructing voltage orthogonal constraint equations using the d-axis and q-axis voltage components, and constructing current orthogonal constraint equations using the d-axis and q-axis current components; bidirectionally verifying the orthogonality deviation of the voltage and current vectors to accurately capture the unit's operating phase offset. The four dq-axis vectors are synchronously connected to the phase-locked loop closed-loop iterative circuit, using the voltage dq-component as the phase reference quantity and the current dq-component as the auxiliary correction quantity; the difference between the theoretical orthogonal steady-state vector and the actual acquired conversion vector is compared in real time, iteratively eliminating phase deviation, amplitude deviation, and operating condition disturbance deviation during the calculation process. Based on the accurate dq-axis components after deviation correction, the instantaneous rotational angular velocity of the synchronous rotating coordinate system is solved in real time, and the angular velocity parameters are continuously iteratively updated until the calculation converges, obtaining stable and accurate real-time angular velocity parameters.

[0041] For S200, the dynamic adjustment parameters of the digital filter corresponding to the actual operating frequency and the dynamic sampling window length of the full-cycle Fourier algorithm are obtained, including: S210, determine the number of single-cycle sampling points corresponding to the actual operating frequency, and use the number of single-cycle sampling points as the dynamic sampling window length of the full-cycle Fourier algorithm.

[0042] The dynamic sampling window length is N: N = sampling rate Fs / actual operating frequency f. In this step, the sliding sampling window length of the Fourier operation can be dynamically modified. The window length is equal to N points, ensuring that the window exactly contains one complete electrical cycle.

[0043] S220 obtains the dynamic adjustment parameters of the digital filter corresponding to the actual operating frequency from the preset mapping library of unit operating frequency and digital filter parameters.

[0044] Among them, the dynamic adjustment parameters of the digital filter are the filtering operation coefficients, which specifically include the cutoff frequency and the order.

[0045] The asynchronous sampling correction of the discrete sampling sequence in S200 specifically includes: obtaining the number of pre-approved fractional sampling points in a single cycle based on the fixed hardware sampling frequency and the actual operating frequency; obtaining the fractional deviation between the number of pre-approved fractional sampling points in a single cycle and the number of sampling points in a single cycle; and interpolating and correcting the discrete sampling sequence based on the fractional deviation to obtain an equivalent sampling sequence aligned with the current electrical cycle boundary.

[0046] In existing technologies, the slight dynamic shift in the operating frequency of electrical equipment such as power grids and motors in power electrical sampling scenarios can cause the number of sampling points actually collected by the hardware within each complete electrical cycle to be non-fixed integers, resulting in a decimal part deviation. Over a long period of time, this can cause the sampling sequence to shift cycle by cycle, leading to problems such as cycle boundary misalignment and phase distortion of the sampled data. In other words, the fixed sampling frequency of the hardware is mismatched with the actual operating frequency of the electrical signal, and may even cause problems such as sampling point phase shift, cycle misalignment, and data inaccuracy. This step can eliminate the asynchronous deviation between the inherent sampling clock of the hardware and the dynamic electrical cycle, so that the cycle boundary of the final sampling sequence is completely aligned with the real-time electrical signal cycle. It fully takes into account the inherent characteristics of the hardware sampling clock and the dynamic frequency characteristics of the electrical signal, and can truly reflect the theoretically accurate number of samples under the current electrical cycle.

[0047] Based on the decimal deviation obtained from the solution, the original discrete sampling sequence is corrected by high-precision interpolation. Through interpolation algorithms such as linear interpolation and spline interpolation adapted to the characteristics of electrical signals, the number and position of sampling points in the original sampling sequence are finely adjusted and compensated to accurately offset the period offset problem caused by the decimal deviation. The value and phase of each sampling moment are recalibrated, and the final output equivalent sampling sequence can perfectly match the periodic variation law of the real-time electrical signal.

[0048] Reference Figure 3 The methods for obtaining the initial electrical characteristics and compensation information of the S300 specifically include: S310: Obtain the asynchronously sampled and corrected discrete voltage and discrete current sampling sequences corresponding to the dynamic sampling window length, denoted as the target voltage sampling sequence and the target current sampling sequence.

[0049] Specifically, to address the asynchronous sampling deviation problem of the field sampling equipment, point-by-point deviation calibration, timing alignment, and data compensation are performed on the original discrete voltage and current sampling data. Sampling distortion data caused by clock deviation, frequency drift, and hardware sampling delay during the sampling process are eliminated, and finally, the calibrated voltage target sampling sequence and current target sampling sequence are output.

[0050] In this step, the dynamic window length can adapt to the frequent frequency deviation of the power system, effectively solving the problems of spectrum leakage and sampling out-of-synchronization that occur when the system frequency deviates from the rated value when the fixed sampling window length is used. Asynchronous sampling correction can eliminate the inherent error of the hardware sampling link, so that the final target sampling sequence can fully match the real instantaneous change law of electrical quantity.

[0051] S320 performs a full-cycle Fourier transform on the voltage target sampling sequence and the current target sampling sequence to obtain the initial electrical characteristics.

[0052] The initial electrical characteristics include the initial amplitude of the fundamental voltage, the initial amplitude of the fundamental current, and the initial phase.

[0053] Specifically, using the complete power frequency cycle as the transformation window, full-cycle discrete Fourier operations are performed on the time-regulated and error-corrected voltage target sampling sequence and current target sampling sequence, respectively. The amplitude and phase information of the fundamental components of the voltage and current signals are calculated through orthogonal decomposition, and the core initial electrical characteristic parameters are screened and solidified, mainly including the initial amplitude of the fundamental voltage, the initial amplitude of the fundamental current, and the initial phase of the voltage and current.

[0054] In this step, the full-cycle Fourier transform has excellent harmonic suppression capabilities, effectively filtering out interference from high-order harmonics, pulse interference, and noise clutter in the power system on the fundamental electrical quantities, and avoiding calculation errors caused by periodic truncation.

[0055] S330 retrieves compensation information corresponding to the actual operating frequency from a database of frequencies and error correction coefficients pre-built through offline simulation and field test calibration.

[0056] The compensation information includes electrical amplitude correction coefficient, current amplitude correction coefficient, and phase offset compensation amount.

[0057] Specifically, in the early stages, a large number of offline simulations can be used to simulate the sampling error characteristics under different frequencies and operating conditions. Combined with the test calibration data of various loads, faults, and steady-state operation scenarios on site, a dedicated database of frequency and error correction coefficients can be pre-built. Using the actual operating frequency as the search keyword, the system accurately matches the corresponding compensation parameters in the database and retrieves three types of core compensation information: voltage electrical amplitude correction coefficient, current amplitude correction coefficient, and phase offset compensation amount.

[0058] In this step, the offline calibration database can integrate error patterns across all operating conditions and frequency ranges, avoiding the drawbacks of a single theoretical correction model being unable to adapt to complex field conditions. By precisely retrieving compensation parameters one-to-one with the frequency, it can specifically offset the inherent errors of amplitude attenuation and phase shift caused by different frequency offset downsampling algorithms and hardware devices, achieving dynamic and accurate compensation of electrical characteristic parameters and significantly improving the accuracy and adaptability of power parameter detection.

[0059] Meanwhile, this solution also allows the final voltage, current amplitude, and phase parameters to accurately reflect the actual operating status of the system, meeting the needs of high-precision power services such as relay protection, power quality analysis, and condition monitoring.

[0060] For S400, the initial electrical characteristics are corrected and compensated according to the compensation information to obtain calibrated electrical characteristics. This includes: correcting and compensating the initial electrical characteristics, namely the initial amplitude of the fundamental voltage, the initial amplitude of the fundamental current, the initial phase of the fundamental voltage, and the initial phase of the fundamental current, according to the amplitude correction coefficient and the phase offset compensation amount to obtain calibrated electrical characteristics. The calibrated electrical characteristics include the calibrated amplitude of the fundamental voltage, the calibrated phase of the fundamental voltage, the calibrated amplitude of the fundamental current, and the calibrated phase of the fundamental current.

[0061] Specifically, amplitude correction is achieved by multiplying the initial amplitude of the fundamental frequency of each phase voltage and current by the corresponding amplitude correction factor, thus obtaining accurate fundamental frequency voltage and fundamental frequency current for each of the three phases without frequency deviation error. Phase correction is achieved by superimposing the initial phase of each phase voltage and the initial phase of each phase current with the corresponding phase offset compensation, thus obtaining the calibrated phase of the fundamental frequency voltage and the calibrated phase of the fundamental frequency current.

[0062] Reference Figure 4 The method for obtaining the frequency offset error compensated relay protection electrical characteristics based on the calibration electrical characteristics of S500 specifically includes: S510 constructs a three-phase corrected voltage complex phasor based on the fundamental voltage calibration amplitude and fundamental voltage calibration phase; constructs a three-phase corrected current complex phasor based on the fundamental current calibration amplitude and fundamental current calibration phase.

[0063] Specifically, the calibration phase, measured in degrees, is uniformly converted into the radian value required for trigonometric function calculations. Then, based on Euler's formula, complex decomposition is performed on each phase. The real part of the phasor is obtained by multiplying the amplitude of the single-phase calibration voltage by the cosine value of the corresponding phase, and the imaginary part of the phasor is obtained by multiplying the amplitude by the sine value of the corresponding phase. The real and imaginary parts are combined to form a single-phase equivalent complex phasor. After completing the corresponding calculations of the three-phase voltages in sequence, the complete set of three-phase corrected voltage complex phasors is obtained.

[0064] The preferred method for constructing the three-phase corrected complex current phasors is the same as above. Specifically, the calibration amplitude and calibration phase of the three-phase fundamental current are read. First, the calibration phase of each phase current is converted from angle to radian. Then, the complex real part and imaginary part are solved for each phase using the calibration amplitude and the converted radian phase. The complex current phasors of each phase are then combined to generate the complex current phasors of each phase. After all three phases are calculated, they are integrated into the three-phase corrected complex current phasors.

[0065] S520 obtains differential current based on the three-phase corrected voltage complex phasor and the three-phase corrected current complex phasor.

[0066] Specifically, the complex phasors of the three-phase corrected currents on both sides of the generator motor protection zone are collected. The complex phasors of the same phase currents on the same side and the opposite side are superimposed to obtain the complex phasors of the differential currents of each phase. The magnitude of the complex phasors of the differential currents of each phase is then calculated as the differential current after compensation.

[0067] The complete set of three-phase current complex phasors, after amplitude and phase calibration processing, is collected from the local and opposite sides of the generator protection zone. The three-phase corrected current complex phasors of the local and opposite sides are then processed to obtain the three-phase corrected current complex phasors of the local and opposite sides. According to the principle of matching, the complex phasors of the same phase on the local and opposite sides are vector superimposed.

[0068] During the calculation, the real part of the differential current phasor is obtained by directly adding the real part of the two phasors and the imaginary part of the differential current phasor by adding the imaginary part of the two phasors. The real part and the imaginary part are paired to form the complex phasor of the differential current of that phase. The three independent in-phase vector superposition calculations are completed in sequence to obtain the complex phasor of the differential current of each of the three phases.

[0069] For each phase, the magnitude of the complex phasor of the corresponding differential current is calculated by summing the squares of the real and imaginary parts of the differential phasor of that phase and then taking the second square root. The resulting scalar value is the differential current after compensation for that phase. By repeating this calculation process for all phases, the complete amplitude of the three-phase differential current after compensation can be obtained.

[0070] S530, based on the constructed three-phase corrected current complex phasor, uses symmetrical component transformation operation to solve the negative sequence current complex phasor, and obtains the magnitude of the negative sequence current complex phasor as the compensated negative sequence current.

[0071] Specifically, the real and imaginary values ​​of the three-phase correction current phasors are obtained, and complex domain operations are performed based on the standard transformation matrix of the symmetrical components. First, the rotation operator is substituted, and then the complex weighted sum of the three-phase current phasors is completed according to the calculation formula of the negative sequence components and then divided by the coefficient. At the same time, the real and imaginary parts of each phasor are weighted and superimposed respectively, and the real and imaginary parts of the negative sequence current complex phasor are combined to obtain the real and imaginary parts of the negative sequence current complex phasor, and the combination forms the complete negative sequence current complex phasor.

[0072] To obtain the magnitude of the negative-sequence complex phasor, square the real and imaginary parts of the phasor respectively, add them together, and then take the second square root of the sum. The resulting scalar value is the compensated negative-sequence current.

[0073] S540 performs complex division operations on the corrected voltage complex phasors and the corrected current complex phasors of each phase to obtain the three-phase measurement impedance complex phasors. The magnitude and impedance angle of the measurement impedance complex phasors of each phase are extracted as the compensated measurement impedance.

[0074] Specifically, based on the independent voltage complex phasors of the three phases obtained from the previous correction process and the corrected current complex phasors that are matched one-to-one with each phase, the complex phasors of the corrected voltage and the complex phasors of the corrected current of each phase are divided phase by phase to solve for the complex phases of the measurement impedance of the three phases respectively.

[0075] During the calculation, either polar coordinates can be used to divide the magnitude and subtract the phase, or rectangular coordinates can be used to convert the denominator to real numbers and then decompose the real part of the impedance and the imaginary part of the reactance. The two calculation methods can be selected as needed.

[0076] After solving the complex impedance phasors for each phase, the magnitude and impedance angle are extracted for each set of complex impedance phasors. The magnitude is obtained by taking the square root of the real and imaginary parts of the impedance. The impedance angle is solved by combining the arctangent function with the values ​​of the real and imaginary parts, or directly obtained from the phase difference between the voltage and current phasors. The finally extracted phase impedance magnitude and corresponding impedance angle are the compensated measured impedance after error correction.

[0077] The method for S600 to analyze the electrical characteristics of relay protection and the preset conditions of relay protection for generator motors includes: inputting the electrical characteristics of relay protection into various relay protection criteria of generator motors for logical judgment; if the characteristics meet the protection action setting value and delay conditions, the protection device outputs a trip control signal or an alarm signal.

[0078] Among them, the relay protection criteria include: 1) longitudinal differential protection criteria, that is, comparing the ratio of the differential current amplitude to the braking current amplitude with the preset ratio braking setting to determine whether the differential protection operation conditions are met.

[0079] 2) Negative sequence current protection criterion, that is, comparing the negative sequence current amplitude with the preset negative sequence current setting to determine whether the negative sequence overcurrent protection action conditions are met.

[0080] 3) Impedance protection criterion, which is to compare the position of the complex value of the measured impedance on the impedance plane with the preset impedance action area to determine whether the distance protection action conditions are met.

[0081] 4) Overvoltage / undervoltage protection criteria, which compare the amplitude of the corrected and compensated fundamental voltage with the preset overvoltage or undervoltage setting to determine whether the voltage protection operation conditions are met.

[0082] 5) Overcurrent protection criterion: The amplitude of the fundamental current after correction and compensation is compared with the preset overcurrent setting to determine whether the overcurrent protection operation conditions are met.

[0083] The analysis method for determining whether a feature meets the protection action setting and delay conditions includes: performing a delay count on the logical judgment results of each relay protection criterion; and confirming that the protection action condition is met only when the feature quantity continuously meets the protection action setting and the cumulative satisfaction time reaches the preset delay setting.

[0084] For differential protection of the same speed type, the delay setting is set to zero, and the trip is triggered immediately after the operating conditions are met.

[0085] For time-delay protections such as negative sequence current protection and impedance protection, the output is completed after timing according to the preset delay setting.

[0086] According to the type of action criterion, the protection device outputs the corresponding trip control signal to the circuit breaker trip circuit or outputs an alarm signal to the monitoring system. At the same time, it records the time of protection action, the type of action criterion, and the value of characteristic quantities to form a protection action report.

[0087] Example 1: Implementation process of low-frequency protection during the start-up of SFC variable frequency water pump in pumped storage unit.

[0088] This embodiment addresses the special operating condition of a pumped storage generator's static frequency converter (SFC) starting from zero speed. In this condition, the unit has no initial speed and relies on the SFC's output frequency converter to accelerate, exhibiting a smooth, continuous frequency increase from 2Hz to 50Hz. The 2Hz to 10Hz low-frequency range is a common failure zone for traditional relay protection, easily leading to malfunctions in ratio differential protection due to frequency shifts and sampling mismatches. Simultaneously, fault identification sensitivity decreases significantly. This invention's protection method operates throughout this low-frequency range, achieving precise protection adaptation.

[0089] Specifically, a preset high-precision sampling window length is used to continuously acquire analog signals of three-phase voltage and three-phase current at the generator terminals in real time. The continuous analog signals are converted into discrete sampling sequences through an analog-to-digital conversion module, thus completing the real-time acquisition and storage of the original electrical data. The sampling accuracy meets the requirements for identifying low-frequency weak electrical signals of the unit.

[0090] The collected discrete sampling sequence is transformed and iterated. At the same time, combined with the Parker transformation algorithm of the generator terminal electrical quantity, the discrete voltage and current quantities in the three-phase stationary coordinate system are converted into DC components in the dq rotating coordinate system. The built-in phase-locked loop module tracks and refreshes the current actual operating frequency of the unit in real time, so as to achieve accurate frequency measurement in the low frequency range of 2Hz~10Hz without dead angles, and the frequency measurement error is controlled within ±0.05Hz.

[0091] When the phase-locked loop detects that the actual operating frequency of the unit has dropped to 3Hz (within the preset low-frequency range of 2Hz~10Hz), it automatically retrieves the exclusive dynamic parameters corresponding to 3Hz: on the one hand, it automatically lowers the cutoff frequency of the digital filter to match the filtering requirements of low-frequency electrical signals and filter out low-frequency harmonics and sampling noise interference; on the other hand, it adaptively lengthens the sampling window of the full-cycle Fourier algorithm, adjusting the sampling window length to 16.7 times that of the standard sampling window at 50Hz power frequency, ensuring that a single complete electrical cycle can be fully covered and sampled under the 3Hz low-frequency condition, thus completely solving the waveform truncation and sampling distortion problems caused by traditional fixed window length sampling.

[0092] Simultaneously, based on this dynamic sampling window length, the original discrete sampling sequence is asynchronously sampled and corrected to eliminate sampling deviations caused by the asynchronous sampling clock and unit electrical frequency under variable frequency operation.

[0093] Based on the accurate discrete sampling sequence corrected by asynchronous sampling, the initial electrical characteristics of the unit are calculated by the full-cycle Fourier algorithm, including the amplitude and phase of the initial fundamental voltage and the amplitude and phase of the initial fundamental current.

[0094] Simultaneously, the system retrieves the amplitude and phase compensation information corresponding to the 3Hz frequency. For measurement errors caused by spectrum leakage and frequency shift under low-frequency conditions, it performs global correction and compensation on the initial electrical characteristics, and finally obtains high-precision calibrated electrical characteristics, namely, fundamental voltage calibration amplitude, fundamental voltage calibration phase, fundamental current calibration amplitude, and fundamental current calibration phase, completely eliminating false differential current and false current deviation caused by spectrum leakage.

[0095] Based on the calibrated electrical characteristics, the electrical characteristic parameters of the relay protection after full compensation of the frequency offset error are calculated, and they are compared and analyzed in real time with the preset relay protection conditions such as generator motor ratio differential protection and fault protection.

[0096] In this embodiment, during the entire process of the unit's SFC frequency converter speeding up from zero and starting at a low frequency of 2Hz to 10Hz, the adaptive low-frequency protection strategy of this application is continuously activated, and the ratio differential protection does not have any false tripping or false alarm phenomena, which can effectively avoid the problem of protection false tripping caused by false electrical quantities under low-frequency operating conditions.

[0097] Meanwhile, for the simulated stator phase-to-phase short circuit fault during unit startup, the protection device can accurately capture the electrical characteristics of the fault, complete fault identification and tripping within 25ms, and achieve rapid and reliable fault isolation, taking into account both the anti-maloperation performance of low-frequency steady-state operation and the speed and reliability of fault conditions.

[0098] Example 2: Implementation process of low-frequency protection under the electrical braking shutdown condition of generator motor.

[0099] This embodiment addresses the electrical braking condition during normal shutdown of a pumped-storage generator motor. During normal shutdown, the unit exits the generator / pumping operation mode and engages the electrical braking circuit to achieve rapid speed reduction. The unit's operating frequency smoothly and continuously decreases from the rated 10Hz to 2Hz, remaining in a low-frequency variable operating condition throughout. Under this condition, the amplitude of the unit's electrical signals attenuates and the frequency continuously shifts. Traditional fixed-parameter protection algorithms are prone to sampling failures and measurement deviations, leading to false alarms and trips in overcurrent protection and stator grounding protection, and failing to accurately identify hidden faults in the braking circuit. The method of this invention engages this frequency reduction range throughout the entire shutdown process, achieving effective protection coverage.

[0100] Specifically, after the unit is put into electric braking shutdown, the protection device immediately starts the low-frequency protection sampling logic, continuously collects the analog quantities of three-phase voltage and current at the generator terminal based on the preset sampling window length, and generates a real-time discrete sampling sequence.

[0101] By using an iterative conversion algorithm and a phase-locked loop to monitor the unit's operating frequency in real time, the dynamic frequency changes during the 10Hz~2Hz frequency reduction process are tracked throughout, and the unit is determined in real time to be in the preset low-frequency protection activation range.

[0102] Throughout the process of the unit frequency gradually decreasing from 10Hz to 2Hz, the parameters of the digital filter and the dynamic sampling window length of the full-cycle Fourier algorithm are dynamically adjusted frame by frame according to the real-time measured operating frequency. The lower the frequency, the lower the filter cutoff frequency and the longer the sampling window length are simultaneously adjusted to ensure complete sampling and accurate filtering of weak low-frequency electrical signals. At the same time, the discrete sampling sequence is asynchronously sampled and corrected in real time to adapt to the sampling requirements of the continuously decreasing frequency under changing operating conditions and avoid sampling mismatch problems caused by dynamic frequency shift.

[0103] Based on the corrected discrete sampling sequence, the initial fundamental voltage, current amplitude and phase parameters under the unit's electrical braking condition are extracted. Then, combined with the dedicated compensation information corresponding to the real-time frequency, the initial electrical measurement parameters are accurately corrected and compensated to eliminate measurement errors caused by harmonic interference, frequency drift and spectral leakage under the braking condition, and obtain high-precision calibrated electrical characteristics.

[0104] Throughout the entire process of the unit's electrical braking shutdown, the backup overcurrent protection and stator grounding protection continue to operate based on the compensated relay protection electrical characteristics of this invention, and compare and judge the electrical characteristic parameters with the preset protection action conditions in real time.

[0105] In this embodiment, during the entire process of the unit's 10Hz~2Hz electric braking frequency reduction shutdown, all sets of relay protection devices operate stably, with no false alarms or false trips caused by low-frequency conditions, thus ensuring the safety and stability of the unit's normal shutdown process.

[0106] Meanwhile, this method can accurately capture minor grounding faults and abnormal current fluctuations in the braking circuit, effectively identify hidden faults in the braking circuit that traditional protection cannot detect, solve the problem of blind spots in the protection of low-frequency shutdown conditions of the unit, and comprehensively improve the fault protection capability and operational reliability of the generator motor during shutdown.

[0107] Secondly, this application discloses a low-frequency protection system for a generator motor, used to implement the low-frequency protection method for a generator motor disclosed in the first aspect of this application. The system includes: The actual operating frequency acquisition unit is used to collect the three-phase voltage and current analog quantities of the generator motor based on a preset sampling window length to obtain a discrete sampling sequence; and to convert and iterate the discrete sampling sequence to obtain the actual operating frequency of the unit at present. The dynamic analysis unit is used to obtain the dynamic adjustment parameters of the digital filter corresponding to the actual operating frequency and the dynamic sampling window length of the full-cycle Fourier algorithm if the actual operating frequency is within the preset frequency range, and to perform asynchronous sampling correction on the discrete sampling sequence. The compensation information acquisition unit is used to obtain the initial electrical characteristics and the compensation information corresponding to the actual operating frequency based on the discrete sampling sequence after asynchronous sampling correction corresponding to the dynamic sampling window length. An electrical characteristic calibration unit is used to correct and compensate the initial electrical characteristics based on the compensation information to obtain calibrated electrical characteristics; The relay protection electrical characteristic compensation unit is used to obtain the relay protection electrical characteristics after frequency offset error compensation based on the calibrated electrical characteristics; The anomaly analysis unit is used to analyze the electrical characteristics of the relay protection and the preset conditions of the generator motor relay protection. If any preset condition is not met, the corresponding alarm signal is triggered.

[0108] Reference Figure 5 The third aspect of this application discloses a dynamic protection method for a generator unit, comprising: S10: Based on the collected analog three-phase voltage and analog three-phase current of the generator motor, obtain the actual operating frequency of the unit at present. S20: Obtain the frequency range of the actual operating frequency, dynamically call the corresponding hold-up strategy and execute it.

[0109] Among them, the frequency range of the actual operating frequency is obtained, and the corresponding maintenance strategy is dynamically called and executed, including: if the actual operating frequency is greater than the preset frequency, switching to the power frequency fixed parameter protection algorithm; If the actual operating frequency is within the preset frequency range, obtain the dynamic adjustment parameters of the digital filter corresponding to the actual operating frequency, the dynamic sampling window length of the full-cycle Fourier algorithm, and perform asynchronous sampling correction on the discrete sampling sequence. Based on the discrete sampling sequence after asynchronous sampling correction corresponding to the dynamic sampling window length, the initial electrical characteristics and compensation information corresponding to the actual operating frequency are obtained.

[0110] The initial electrical characteristics are corrected and compensated based on the compensation information to obtain the calibrated electrical characteristics; The relay protection electrical characteristics after frequency offset error compensation are obtained based on the calibrated electrical characteristics; The electrical characteristics of the relay protection are analyzed in conjunction with the preset conditions of the generator motor relay protection. If any preset condition is not met, the corresponding alarm signal is triggered.

[0111] It should be noted that if the actual operating frequency is within the preset frequency range, the specific implementation method is consistent with the corresponding steps of the generator motor low-frequency protection method disclosed in the first aspect of this application, so it will not be described in detail here.

[0112] Furthermore, the preset frequency range is preferably 2Hz to 10Hz, with the preset frequency being 10Hz.

[0113] The dynamic protection method for generator units disclosed in the third aspect of this application can flexibly adjust the corresponding protection method according to different operating states, thereby achieving effective protection of the generator motor.

[0114] The basic principles of this disclosure have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this disclosure are merely examples and not limitations, and should not be considered as essential features of each embodiment of this disclosure. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the scope of this disclosure to the necessity of employing the aforementioned specific details for implementation.

[0115] In this disclosure, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. The block diagrams of devices, apparatuses, devices, and systems involved in this disclosure are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, devices, and systems can be connected, arranged, and configured in any manner. Words such as "comprising," "including," "having," etc., are open-ended terms meaning "including but not limited to," and are used interchangeably with them. The terms "or" and "and" as used herein refer to the terms "and / or," and are used interchangeably with them unless the context clearly indicates otherwise. The term "such as" as used herein refers to the phrase "such as but not limited to," and is used interchangeably with it.

[0116] Additionally, as used herein, the "or" used in a list of items beginning with "at least one" indicates a separate list, such that a list of, for example, "at least one of A, B, or C" means A or B or C, or AB or AC or BC, or ABC (i.e., A and B and C). Furthermore, the word "exemplary" does not imply that the described example is preferred or better than other examples.

[0117] It should also be noted that in the systems and methods of this disclosure, the components or steps can be decomposed and / or recombined. These decompositions and / or recombinations should be considered as equivalent solutions to this disclosure.

[0118] Various changes, substitutions, and modifications can be made to the technology described herein without departing from the teachings defined by the appended claims. Furthermore, the scope of the claims of this disclosure is not limited to the specific aspects of the processes, machines, manufactures, events, means, methods, and actions described above. Currently existing or later-developed processes, machines, manufactures, events, means, methods, or actions that perform substantially the same function or achieve substantially the same result as the corresponding aspects described herein can be utilized. Therefore, the appended claims include such processes, machines, manufactures, events, means, methods, or actions within their scope.

[0119] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use this disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of this disclosure. Therefore, this disclosure is not intended to be limited to the aspects shown herein, but rather to be carried out within the widest scope consistent with the principles and novel features disclosed herein.

[0120] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this disclosure to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

Claims

1. A method for low-frequency protection of a generator motor, characterized in that, include: Based on a preset sampling window length, the three-phase voltage and current analog quantities of the generator motor are collected to obtain a discrete sampling sequence; The actual operating frequency of the unit is obtained by transforming and iterating the discrete sampling sequence. If the actual operating frequency is within the preset frequency range, obtain the dynamic adjustment parameters of the digital filter and the dynamic sampling window length of the full-cycle Fourier algorithm corresponding to the actual operating frequency, and perform asynchronous sampling correction on the discrete sampling sequence; Based on the discrete sampling sequence after asynchronous sampling correction corresponding to the dynamic sampling window length, the initial electrical characteristics and the compensation information corresponding to the actual operating frequency are obtained. The initial electrical characteristics are corrected and compensated according to the compensation information to obtain calibrated electrical characteristics, which include the fundamental voltage calibration amplitude, fundamental voltage calibration phase, fundamental current calibration amplitude, and fundamental current calibration phase. Based on the calibration electrical characteristics, the relay protection electrical characteristics after frequency offset error compensation are obtained; The electrical characteristics of the relay protection are analyzed in conjunction with the preset conditions of the generator motor relay protection. If any preset condition is not met, the corresponding alarm signal is triggered.

2. The low-frequency protection method for generator motors according to claim 1, characterized in that, The process of obtaining the actual operating frequency of the unit based on the collected analog three-phase voltage and analog three-phase current of the generator motor includes: The analog three-phase voltage and analog three-phase current quantities corresponding to the generator motor terminals are collected, and discrete sampling sequences are obtained by pre-amplifier low-pass filtering and analog-to-digital conversion. The discrete sampling sequences include voltage discrete sampling sequences and current discrete sampling sequences. The actual operating frequency of the unit is obtained by transforming and iterating the discrete sampling sequence.

3. The low-frequency protection method for generator motors according to claim 2, characterized in that, The step of transforming and iterating the discrete sampling sequence to obtain the actual operating frequency of the unit includes: The voltage discrete sampling sequence and the current discrete sampling sequence are transformed into the dq synchronous rotating coordinate system through Park transformation to obtain the dq axis components; The phase-locked loop algorithm is used to perform real-time iterative calculations on the dq axis components to obtain the current actual operating frequency of the unit.

4. The low-frequency protection method for generator motors according to claim 1, characterized in that, The process of obtaining the dynamic adjustment parameters of the digital filter corresponding to the actual operating frequency and the dynamic sampling window length of the full-cycle Fourier algorithm includes: The number of single-cycle sampling points corresponding to the actual operating frequency is determined, and the number of single-cycle sampling points is used as the dynamic sampling window length of the full-cycle Fourier algorithm. The dynamic adjustment parameters of the digital filter corresponding to the actual operating frequency are obtained from the preset mapping library of unit operating frequency and digital filter parameters.

5. The low-frequency protection method for generator motors according to claim 4, characterized in that, The asynchronous sampling correction of the discrete sampling sequence includes: The number of fractional sampling points for a single-cycle pre-approval is obtained based on the fixed hardware sampling frequency and the actual operating frequency. The decimal deviation between the number of decimal sampling points in the single-cycle pre-approval process and the number of sampling points in the single cycle is obtained; The discrete sampling sequence is interpolated and corrected based on the fractional deviation to obtain an equivalent sampling sequence aligned with the current electrical cycle boundary.

6. The low-frequency protection method for generator motors according to claim 1, characterized in that, The process of obtaining initial electrical characteristics and compensation information corresponding to the actual operating frequency based on the discrete sampling sequence after asynchronous sampling correction corresponding to the dynamic sampling window length includes: Obtain the asynchronously sampled and corrected discrete voltage and discrete current sampling sequences corresponding to the dynamic sampling window length, and denot them as the target voltage sampling sequence and the target current sampling sequence. A full-cycle Fourier transform is performed on the voltage target sampling sequence and the current target sampling sequence to obtain initial electrical characteristics, which include the initial amplitude of the fundamental voltage, the initial amplitude of the fundamental current, and the initial phase. The compensation information corresponding to the actual operating frequency is retrieved from a database of frequencies and error correction coefficients pre-built through offline simulation and field test calibration; the compensation information includes electrical amplitude correction coefficient, current amplitude correction coefficient, and phase offset compensation amount.

7. The low-frequency protection method for generator motors according to claim 6, characterized in that, The process of obtaining the relay protection electrical characteristics after frequency offset error compensation based on the calibrated electrical characteristics includes: Construct three-phase corrected voltage complex phasors based on the fundamental voltage calibration amplitude and the fundamental voltage calibration phase; Construct three-phase corrected current complex phasors based on the fundamental current calibration amplitude and the fundamental current calibration phase; The differential current is obtained based on the three-phase corrected voltage complex phasor and the three-phase corrected current complex phasor; Based on the three-phase corrected current complex phasor, the negative sequence current complex phasor is obtained by symmetrical component transformation operation, and the magnitude of the negative sequence current complex phasor is used as the compensated negative sequence current. Based on the three-phase corrected voltage complex phasor and the three-phase corrected current complex phasor, the three-phase measurement impedance complex phasor is obtained, and the phasor magnitude and impedance angle corresponding to the three-phase measurement impedance complex phasor are used as the compensated measurement impedance. Among them, the electrical characteristics of the relay protection after frequency offset error compensation include the differential current after compensation, the negative sequence current after compensation, and the measurement impedance after compensation.

8. A low-frequency protection system for a generator motor, characterized in that, include: The actual operating frequency acquisition unit is used to acquire the three-phase voltage and current analog quantities of the generator motor based on the preset sampling window length to obtain a discrete sampling sequence; The actual operating frequency of the unit is obtained by transforming and iterating the discrete sampling sequence. The dynamic analysis unit is used to obtain the dynamic adjustment parameters of the digital filter and the dynamic sampling window length of the full-cycle Fourier algorithm corresponding to the actual operating frequency if the actual operating frequency is within a preset frequency range, and to perform asynchronous sampling correction on the discrete sampling sequence. The compensation information acquisition unit is used to obtain the initial electrical characteristics and the compensation information corresponding to the actual operating frequency based on the discrete sampling sequence after asynchronous sampling correction corresponding to the dynamic sampling window length. An electrical characteristic calibration unit is used to correct and compensate the initial electrical characteristic according to the compensation information to obtain a calibrated electrical characteristic; A relay protection electrical characteristic compensation unit is used to obtain the relay protection electrical characteristics after frequency offset error compensation based on the calibrated electrical characteristics; The anomaly analysis unit is used to analyze the electrical characteristics of the relay protection and the preset conditions of the generator motor relay protection. If any preset condition is not met, the corresponding alarm signal is triggered.

9. A method for dynamic protection of a generating unit, characterized in that, include: Based on the collected three-phase voltage and three-phase current analog quantities of the generator motor, the actual operating frequency of the unit is obtained. Obtain the frequency range of the actual operating frequency, dynamically call the corresponding hold strategy and execute it.

10. The unit dynamic protection method according to claim 9, characterized in that, The process of obtaining the frequency range of the actual operating frequency, dynamically invoking and executing the corresponding hold-up strategy includes: If the actual operating frequency is greater than the preset frequency, switch to the power frequency fixed parameter protection algorithm. If the actual operating frequency is within the preset frequency range, obtain the dynamic adjustment parameters of the digital filter and the dynamic sampling window length of the full-cycle Fourier algorithm corresponding to the actual operating frequency, and perform asynchronous sampling correction on the discrete sampling sequence; Based on the discrete sampling sequence after asynchronous sampling correction corresponding to the dynamic sampling window length, the initial electrical characteristics and the compensation information corresponding to the actual operating frequency are obtained. The initial electrical characteristics are corrected and compensated based on the compensation information to obtain calibrated electrical characteristics; Based on the calibration electrical characteristics, the relay protection electrical characteristics after frequency offset error compensation are obtained; The electrical characteristics of the relay protection are analyzed in conjunction with the preset conditions of the generator motor relay protection. If any preset condition is not met, the corresponding alarm signal is triggered.

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