Short-circuit reverse-sequence protection method for three-phase alternating current and related equipment

Abstract

The invention provides a short-circuit reverse-sequence protection method for three-phase alternating current and related equipment, and relates to the technical field of new fields. Complex three-phase current information is converted into positive, negative and zero-sequence components which are easier to analyze through symmetric component decomposition. By calculating the anti-sequence component ratio and the zero-sequence component ratio, the ratios are kept relatively stable during normal load change, so that the influence of load change on fault judgment can be effectively eliminated. By introducing a first-order derivative and a second-order derivative, not only can the instantaneous characteristic change when the fault occurs be reflected, but also the dynamic process of fault development can be reflected, which is essentially different from a method which purely depends on a fixed threshold. According to the multi-dimensional feature analysis method, load fluctuation, harmonic interference and real faults can be effectively distinguished, the accuracy of fault recognition is improved, and misoperation of a protection device is avoided.

Description

Technical Field

[0001] The present application relates to the new technical field, and in particular to a short-circuit reverse sequence protection method and related equipment for three-phase alternating current. Background Art

[0002] In three-phase AC transmission systems, various short-circuit faults can endanger the safe and stable operation of the power system. To ensure power supply reliability, it is necessary to detect and identify fault types in a timely and accurate manner and take corresponding protective measures. As the scale of power systems continues to expand, the types of loads in the system are becoming more diverse, and a large number of power electronic equipment are connected, making the fault characteristics more complex.

[0003] At present, the fault detection methods used in engineering practice are mainly based on the amplitude and phase characteristics of three-phase current. This type of method collects three-phase current signals through online monitoring devices and determines the characteristic thresholds of different types of faults based on historical statistical data. In actual applications, the monitoring device continuously compares the relationship between the amplitude and phase of the measured current and the preset threshold. When it is detected that the current characteristic value exceeds the corresponding threshold, the corresponding fault type signal is output to control the circuit breaker to operate and isolate the fault.

[0004] However, due to the drastic dynamic changes of loads in the power system and the large amount of harmonics generated by power electronic equipment, the current characteristics in the system show the characteristics of rapid fluctuations. In this case, the judgment method based on fixed thresholds is prone to false operation. Especially when the system is disturbed, the current characteristics in the transient process are similar to those under fault conditions, making it difficult for the protection device to accurately distinguish whether a fault has actually occurred. Summary of the invention

[0005] The present application provides a short-circuit reverse sequence protection method and related equipment for three-phase alternating current, which are used to improve the accuracy of fault identification and avoid malfunction of the protection device.

[0006] In a first aspect, the present application provides a short-circuit reverse-sequence protection method for three-phase alternating current, comprising: collecting three-phase current of the three-phase alternating current; performing symmetrical component decomposition on the three-phase current to obtain positive-sequence component, reverse-sequence component and zero-sequence component of the three-phase current; calculating the ratio of the amplitude of the reverse-sequence component to the amplitude of the positive-sequence component to obtain the reverse-sequence component ratio; calculating the ratio of the amplitude of the zero-sequence component to the amplitude of the positive-sequence component to obtain the zero-sequence component ratio; calculating the rate of change of the positive-sequence component, the rate of change of the reverse-sequence component and the rate of change of the zero-sequence component to obtain the first-order derivative; calculating the change acceleration of the positive-sequence component, the change acceleration of the reverse-sequence component and the change acceleration of the zero-sequence component to obtain the second-order derivative; judging the fault type according to the reverse-sequence component ratio, the zero-sequence component ratio, the first-order derivative and the second-order derivative; predicting the fault development trend based on the second-order derivative; and outputting the fault type result and the fault development trend result.

[0007] By adopting the above technical solution, the complex three-phase current information is converted into positive, negative, and zero-sequence components that are easier to analyze through symmetrical component decomposition. By calculating the reverse-sequence component ratio and the zero-sequence component ratio, because these ratios remain relatively stable during normal load changes, the impact of load changes on fault judgment can be effectively eliminated. By introducing first-order derivatives and second-order derivatives, it can not only reflect the instantaneous characteristic changes when a fault occurs, but also reflect the dynamic process of fault development, which is essentially different from the method that simply relies on fixed thresholds. This multi-dimensional feature analysis method can effectively distinguish between load fluctuations, harmonic interference and real faults, improve the accuracy of fault identification, and avoid false operation of protection devices.

[0008] In combination with some embodiments of the first aspect, in some embodiments, the step of judging the fault type according to the reverse-sequence component ratio, the zero-sequence component ratio, the first-order derivative and the second-order derivative specifically includes: when the zero-sequence component ratio is greater than the zero-sequence ratio threshold, and the zero-sequence component change rate is greater than the zero-sequence change rate threshold, it is determined to be a single-phase grounding fault; when the reverse-sequence component ratio is greater than the reverse-sequence ratio threshold, and the reverse-sequence component change rate is greater than the reverse-sequence change rate threshold, it is determined to be a two-phase short-circuit fault; when the zero-sequence component ratio is greater than the zero-sequence grounding ratio threshold and the reverse-sequence component ratio is greater than the reverse-sequence grounding ratio threshold, and the zero-sequence component change rate is greater than the zero-sequence grounding change rate threshold and the reverse-sequence component change rate is greater than the reverse-sequence grounding change rate threshold, it is determined to be a two-phase grounding fault.

[0009] By adopting the above technical solution, the combination of zero-sequence component ratio and zero-sequence component change rate can accurately identify the characteristics of single-phase grounding faults; the combination of reverse-sequence component ratio and reverse-sequence component change rate can effectively detect two-phase short-circuit faults; and the simultaneous monitoring of the changes in the two sets of zero-sequence and reverse-sequence parameters can reliably indicate the occurrence of two-phase grounding faults. Through the dual verification of sequence component ratio and change rate, not only can different types of faults be accurately distinguished, but also misjudgment caused by transient processes can be effectively avoided, making the identification of fault types more accurate and reliable.

[0010] In combination with some embodiments of the first aspect, in some embodiments, the step of predicting the fault development trend based on the second-order derivative specifically includes: when the zero-sequence component change acceleration is greater than the zero-sequence acceleration threshold, it is determined that the single-phase grounding fault is in an aggravated development state; when the reverse-sequence component change acceleration is greater than the reverse-sequence acceleration threshold, it is determined that the two-phase short-circuit fault is in an aggravated development state; when the zero-sequence component change acceleration is greater than the zero-sequence grounding acceleration threshold and the reverse-sequence component change acceleration is greater than the reverse-sequence grounding acceleration threshold, it is determined that the two-phase grounding fault is in an aggravated development state.

[0011] By adopting the above technical solution, a fault development trend prediction mechanism based on the second-order derivative is established. The second-order derivative reflects the acceleration of the change of the fault quantity, and its physical meaning intuitively characterizes the dynamic characteristics of the fault development. By monitoring the change acceleration of the zero-sequence component and the reverse-sequence component respectively and comparing them with the corresponding acceleration threshold, the deterioration trend of the fault can be discovered in time. This prediction mechanism can not only warn of the development trend of the fault in advance, but also distinguish the evolution process of different types of faults, providing sufficient time margin for the system to take corresponding protection measures, and effectively improving the preventive protection capability of the power system.

[0012] In combination with some embodiments of the first aspect, in some embodiments, after the step of predicting the fault development trend based on the second-order derivative, the method also includes: selecting corresponding components according to the fault type result to perform S transform time-frequency analysis, selecting zero-sequence components when the fault type result is a single-phase grounding fault, selecting reverse-sequence components when the fault type result is a two-phase short-circuit fault, and selecting zero-sequence components and reverse-sequence components when the fault type result is a two-phase grounding fault, to obtain S transform time-frequency analysis results, the S transform time-frequency analysis results including fault characteristic frequency and energy distribution; determining a high-frequency component threshold according to the fault development trend result, the high-frequency component threshold is positively correlated with the fault development trend result, when the proportion of high-frequency components in the energy distribution is greater than the high-frequency component threshold, substituting the fault characteristic frequency and energy distribution into a pre-established network equivalent impedance matrix to obtain impedance characteristics; establishing a group of fault current propagation equations according to the impedance characteristics, and using the least squares method to fit the error between the calculated current value and the theoretical calculated value to obtain the fault current propagation characteristics; calculating the fault point location coordinates according to the fault current propagation characteristics; calculating the fault current shunt value of adjacent loads according to the fault point location coordinates; determining the degree of load impact according to the fault current shunt value and the fault development trend result.

[0013] By adopting the above technical solution, the corresponding sequence components are intelligently selected for S transform analysis according to different fault types, ensuring the pertinence of the analysis object. The S transform can simultaneously obtain time domain and frequency domain characteristics, where the fault characteristic frequency reflects the essential characteristics of the fault, and the energy distribution reflects the severity of the fault. In particular, the high-frequency component threshold is dynamically adjusted according to the fault development trend, which effectively adapts to the differences in charging characteristics of different models in the charging station. Combined with the analysis of the network equivalent impedance matrix and the fault current propagation characteristics, it can not only accurately locate the fault point, but also evaluate the degree of impact on each load, thereby realizing accurate fault identification and differentiated protection, and effectively avoiding the problem of false tripping caused by the shared grounding grid.

[0014] In combination with some embodiments of the first aspect, in some embodiments, the step of substituting the fault characteristic frequency and energy distribution into a pre-established network equivalent impedance matrix to obtain the impedance characteristics specifically includes: dividing the fault characteristic frequency by the reference frequency to obtain the frequency correction coefficient; dividing the energy value of each frequency component in the energy distribution by the total energy value of the energy distribution to obtain the weight coefficient; and multiplying the impedance value of each node in the network equivalent impedance matrix by the corresponding frequency correction coefficient and weight coefficient to obtain the impedance characteristics.

[0015] By adopting the above technical solution, the reference frequency is corrected using the frequency correction coefficient, eliminating the influence of frequency deviation. By introducing the weight coefficient based on energy distribution, the contribution of different frequency components to the impedance characteristics corresponds to their energy size. This weighted correction mechanism ensures that the network equivalent impedance matrix can accurately reflect the network characteristics under fault conditions, especially when multiple charging piles in the charging station work at the same time and the charging characteristics vary greatly. The calculated impedance characteristics are more in line with the actual network status, providing a reliable basis for subsequent fault location and protection strategy formulation.

[0016] In combination with some embodiments of the first aspect, in some embodiments, the steps of calculating the location coordinates of the fault point according to the fault current propagation characteristics specifically include: obtaining the topological structure of the power system and the location coordinate information of each monitoring point; calculating the distance value from each monitoring point to the fault point based on the fault current propagation characteristics; establishing a group of distance equations between the location coordinates of each monitoring point and the location coordinates of the fault point based on the distance values; selecting three monitoring points as reference points; constructing a triangulation positioning equation based on the location coordinates of the three reference points and the corresponding distance values, and calculating the initial solution of the location coordinates of the fault point; and using the data of the remaining monitoring points to correct the initial solution to obtain the location coordinates of the fault point.

[0017] By adopting the above technical solutions, a complete spatial positioning framework is first established based on the topological structure of the power system. The distance value calculated by the fault current propagation characteristics, combined with the triangulation positioning method, can quickly obtain the initial solution of the fault point location. The mechanism of using the remaining monitoring point data for correction effectively improves the positioning accuracy. This multi-point collaborative positioning method makes full use of the information of all monitoring points in the system, and can still maintain a high positioning accuracy in the complex power supply environment of the charging station, laying the foundation for subsequent differentiated protection control.

[0018] In combination with some embodiments of the first aspect, in some embodiments, the step of calculating the fault current shunt value of adjacent loads based on the fault point location coordinates specifically includes: determining the adjacent load nodes directly connected to the fault point based on the fault point location coordinates and the topological structure of the power system, and establishing an electrical connection path from the fault point to each adjacent load node; establishing a current balance equation for the fault point and each adjacent load node based on Kirchhoff's current law to form a node current equation group; setting the fault point as a current source injection point, and determining the fault point injection current according to the fault type; determining the impedance value of each branch according to the impedance characteristics, and using the node voltage method to solve the node current equation group to obtain the fault current shunt value flowing through each adjacent load node; wherein the fault current shunt value satisfies: the sum of the fault current shunt values ​​of each adjacent load node is equal to the fault point injection current.

[0019] By adopting the above technical solution, combined with Kirchhoff's current law and node voltage method, the fault current shunt value of each adjacent load node can be accurately calculated. In particular, by considering the impedance characteristics to determine the impedance value of each branch, the shunt calculation is more in line with the actual network status. This shunt calculation method based on the physical model can accurately evaluate the impact of the fault on each load, provide a reliable criterion for achieving precise protection control, and effectively avoid the misoperation of the protection device.

[0020] In a second aspect, the present application provides a short-circuit reverse-sequence protection system for three-phase alternating current, and the short-circuit reverse-sequence protection system for three-phase alternating current includes: one or more processors and a memory; the memory is coupled to the one or more processors, the memory is used to store computer program code, the computer program code includes computer instructions, and one or more processors call the computer instructions to enable the short-circuit reverse-sequence protection system for three-phase alternating current to execute the method described in the first aspect and any possible implementation method of the first aspect.

[0021] In a third aspect, the present application provides a computer program product comprising instructions. When the computer program product is run on a short-circuit reverse-sequence protection system for three-phase alternating current power, the short-circuit reverse-sequence protection system for three-phase alternating current power executes the method described in the first aspect and any possible implementation method of the first aspect.

[0022] In a fourth aspect, the present application provides a computer-readable storage medium comprising instructions, which, when executed on a short-circuit reverse-sequence protection system for three-phase alternating current power, causes the short-circuit reverse-sequence protection system for three-phase alternating current power to execute the method described in the first aspect and any possible implementation method of the first aspect.

[0023] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages: 1. Through symmetrical component decomposition, the complex three-phase current information is converted into positive, negative, and zero-sequence components that are easier to analyze. By calculating the reverse-sequence component ratio and the zero-sequence component ratio, because these ratios remain relatively stable during normal load changes, the impact of load changes on fault judgment can be effectively eliminated. By introducing first-order derivatives and second-order derivatives, it can not only reflect the instantaneous characteristic changes when a fault occurs, but also reflect the dynamic process of fault development, which is fundamentally different from the method that simply relies on fixed thresholds. This multi-dimensional feature analysis method can effectively distinguish between load fluctuations, harmonic interference and real faults, improve the accuracy of fault identification, and avoid false operation of protection devices.

[0024] 2. Intelligently select the corresponding sequence components for S transform analysis according to different fault types to ensure the pertinence of the analysis object. S transform can simultaneously obtain time domain and frequency domain characteristics, among which the fault characteristic frequency reflects the essential characteristics of the fault, and the energy distribution reflects the severity of the fault. In particular, the high-frequency component threshold is dynamically adjusted according to the fault development trend, which effectively adapts to the differences in charging characteristics of different models in the charging station. Combined with the analysis of the network equivalent impedance matrix and the fault current propagation characteristics, it can not only accurately locate the fault point, but also evaluate the degree of impact on each load, thereby realizing accurate fault identification and differentiated protection, and effectively avoiding the problem of false tripping caused by the shared grounding grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart of a short circuit reverse sequence protection method for three-phase alternating current in an embodiment of the present application; Figure 2 is another flow chart of a short-circuit reverse sequence protection method for three-phase alternating current in an embodiment of the present application; Figure 3 It is an exemplary hardware structure diagram of a short-circuit reverse sequence protection device for three-phase alternating current in an embodiment of the present application. DETAILED DESCRIPTION

[0026] The terms used in the following embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to be used as limitations to the present application. As used in the specification and appended claims of the present application, the singular expressions one, a kind, described, described, the above, the and this are intended to also include plural expressions unless the context clearly indicates otherwise. It should also be understood that the terms and / or used in the present application refer to and include any or all possible combinations of one or more of the listed items.

[0027] In the following, the terms first and second are used for descriptive purposes only and are not to be understood as suggesting or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as first and second may explicitly or implicitly include one or more of the features, and in the description of the embodiments of the present application, unless otherwise specified, the meaning of multiple is two or more.

[0028] See also Figure 1 , Figure 1 It is a flow chart of a short circuit reverse sequence protection method for three-phase alternating current in an embodiment of the present application; S101, collecting three-phase current of three-phase alternating current; Among them, three-phase alternating current refers to an electric power system composed of three sinusoidal alternating currents with a phase difference of 120 degrees, including phase A, phase B and phase C.

[0029] S102, performing symmetrical component decomposition on the three-phase current to obtain a positive sequence component, a reverse sequence component, and a zero sequence component of the three-phase current; Among them, the positive sequence component represents a symmetrical component with three phases of equal size and the same phase sequence as the power supply, which is used to indicate the normal operating state of the system; the negative sequence component represents a symmetrical component with three phases of equal size and opposite phase sequence as the power supply, which is used to indicate an asymmetrical fault state; the zero sequence component represents a symmetrical component with three phases of equal size and the same phase, which is used to indicate a ground fault state.

[0030] In some embodiments, the asymmetrical three-phase current is decomposed into positive sequence, negative sequence and zero sequence components by using a symmetrical component method. Specifically, a symmetrical component transformation matrix is ​​constructed, and each phase current is multiplied by the transformation matrix to obtain three sequence components.

[0031] In some specific embodiments, three groups of digital filters are first designed; then the three-phase current signals are respectively input into the corresponding filters; and finally, each sequence component is obtained through the output of the filter, which is not limited here.

[0032] S103, calculating the ratio of the amplitude of the reverse sequence component to the amplitude of the positive sequence component to obtain a reverse sequence component ratio; Among them, the amplitude represents the maximum value of the AC current and is used to indicate the intensity of the current; the reverse sequence component ratio refers to the ratio of the reverse sequence component amplitude to the positive sequence component amplitude and is used to indicate the degree of system asymmetry.

[0033] In some embodiments, a standardized index is obtained by calculating the amplitude ratio of the reverse sequence component to the positive sequence component, which can eliminate the influence of the system load level and more accurately reflect the fault characteristics.

[0034] In some specific embodiments, the instantaneous values ​​of the positive sequence and reverse sequence components are first obtained; then the effective values ​​of each are calculated; and finally a division operation is performed to obtain a ratio, which is not limited here.

[0035] S104, calculating the ratio of the amplitude of the zero-sequence component to the amplitude of the positive-sequence component to obtain a zero-sequence component ratio; The zero-sequence component ratio refers to the ratio of the zero-sequence component amplitude to the positive-sequence component amplitude, which is used to indicate the degree of system grounding fault.

[0036] This step is similar to step S103 and is used to quantitatively evaluate the degree of ground fault in the system. In some embodiments, by calculating the amplitude ratio of the zero-sequence component to the positive-sequence component, a standardized index reflecting the characteristics of the ground fault is obtained. This index is not affected by the operating power of the system and can accurately reflect the severity of the ground fault.

[0037] S105, calculating the rate of change of the positive sequence component, the rate of change of the reverse sequence component and the rate of change of the zero sequence component to obtain a first-order derivative; The rate of change indicates how fast the electrical quantity changes over time and is used to indicate the speed at which a fault develops.

[0038] In some embodiments, the instantaneous change rates of the three sequence components are calculated respectively, and the speed characteristics of each sequence component changing with time are obtained by numerical differentiation method. These change rate information can reflect the development process and change trend of the fault.

[0039] S106, calculating the change acceleration of the positive sequence component, the change acceleration of the reverse sequence component and the change acceleration of the zero sequence component to obtain a second-order derivative; The change acceleration indicates how fast the rate of change changes, and is used to indicate the acceleration characteristics of fault development.

[0040] In some embodiments, the first-order derivative is further differentiated to obtain the changing acceleration of each sequence component. These second-order derivative information can more deeply reflect the dynamic characteristics of fault development and provide an important basis for predicting the fault development trend.

[0041] S107, judging the fault type according to the reverse sequence component ratio, the zero sequence component ratio, the first order derivative and the second order derivative; In some embodiments, by establishing judgment rules, characteristic quantities such as reverse sequence component ratio, zero sequence component ratio, first-order derivative and second-order derivative are compared with preset thresholds, and the characteristic combination of various indicators is comprehensively analyzed to ultimately determine the specific type of fault.

[0042] In some specific embodiments, step S107 specifically includes: When the zero-sequence component ratio is greater than the zero-sequence ratio threshold, and the zero-sequence component change rate is greater than the zero-sequence change rate threshold, it is determined to be a single-phase grounding fault; It should be noted that when a ground fault occurs in one phase, a zero-sequence loop will be formed at the fault point, resulting in a significant increase in the zero-sequence component. The zero-sequence component ratio exceeds the threshold, indicating that there is an obvious zero-sequence current, indicating that a ground fault has occurred in the system. At this time, the reverse-sequence component is relatively small and does not meet the reverse-sequence related criterion, so the possibility of a two-phase fault can be ruled out.

[0043] When the reverse sequence component ratio is greater than the reverse sequence ratio threshold, and the reverse sequence component change rate is greater than the reverse sequence change rate threshold, it is determined to be a two-phase short circuit fault; It should be noted that when two phases are short-circuited, the currents between the faulty phases cancel each other out, resulting in significant phase sequence asymmetry. The reverse sequence component ratio exceeds the threshold, indicating that the system has serious phase sequence imbalance. Since there is no grounding, the zero sequence component is very small and does not meet the zero sequence related criteria, so the grounding fault can be ruled out.

[0044] When the zero-sequence component ratio is greater than the zero-sequence grounding ratio threshold and the reverse-sequence component ratio is greater than the reverse-sequence grounding ratio threshold, and the zero-sequence component change rate is greater than the zero-sequence grounding change rate threshold and the reverse-sequence component change rate is greater than the reverse-sequence grounding change rate threshold, it is determined to be a two-phase grounding fault.

[0045] It should be noted that two-phase grounding has the characteristics of both phase-to-phase short circuit and grounding fault; both zero-sequence and reverse-sequence characteristics are required to meet their respective threshold requirements at the same time; this dual criterion can effectively distinguish between single-phase grounding or two-phase short circuit faults.

[0046] It can be seen that the combination of zero-sequence component ratio and zero-sequence component change rate can accurately identify the characteristics of single-phase grounding faults; the combination of reverse-sequence component ratio and reverse-sequence component change rate can effectively detect two-phase short-circuit faults; and the simultaneous monitoring of the changes in the two sets of zero-sequence and reverse-sequence parameters can reliably indicate the occurrence of two-phase grounding faults. Through the dual verification of sequence component ratio and change rate, not only can different types of faults be accurately distinguished, but also misjudgment caused by transient processes can be effectively avoided, making the identification of fault types more accurate and reliable.

[0047] S108. Predicting fault development trend based on second-order derivatives; Among them, the fault development trend indicates the possible future change direction and degree of the fault.

[0048] In some embodiments, by analyzing the sign and size of the second-order derivative, it is determined whether the fault is in an accelerated development stage and whether the fault will further deteriorate, thereby providing a decision-making basis for taking protective measures in a timely manner.

[0049] In some specific embodiments, step S108 specifically includes: When the zero-sequence component change acceleration is greater than the zero-sequence acceleration threshold, it is determined that the single-phase grounding fault is in an aggravated development state; It should be noted that the acceleration of the zero-sequence component change reflects the change in the rate of change of the ground current; when the acceleration exceeds the threshold, it indicates that the zero-sequence current is not only increasing, but also increasing at an accelerating rate.

[0050] When the reverse sequence component change acceleration is greater than the reverse sequence acceleration threshold, it is determined that the two-phase short circuit fault is in an aggravated development state; It should be noted that the acceleration of the reverse-sequence component change reflects the change in the rate of change of the degree of phase-to-phase short-circuit current imbalance; if the acceleration exceeds the threshold, it means that the short-circuit current imbalance is increasing at an accelerated rate.

[0051] When the zero-sequence component change acceleration is greater than the zero-sequence grounding acceleration threshold and the reverse-sequence component change acceleration is greater than the reverse-sequence grounding acceleration threshold, it is determined that the two-phase grounding fault is in an aggravated development state.

[0052] It should be noted that it is necessary to monitor the acceleration characteristics in both the zero-sequence and reverse-sequence directions simultaneously; if both accelerations exceed the threshold at the same time, it means that both the grounding and short-circuit fault characteristics are intensifying.

[0053] It can be seen that the combination of zero-sequence component ratio and zero-sequence component change rate can accurately identify the characteristics of single-phase grounding faults; the combination of reverse-sequence component ratio and reverse-sequence component change rate can effectively detect two-phase short-circuit faults; and the simultaneous monitoring of the changes in the two sets of zero-sequence and reverse-sequence parameters can reliably indicate the occurrence of two-phase grounding faults. Through the dual verification of sequence component ratio and change rate, not only can different types of faults be accurately distinguished, but also misjudgment caused by transient processes can be effectively avoided, making the identification of fault types more accurate and reliable.

[0054] S109. Output the fault type result and the fault development trend result.

[0055] It should be noted that outputting the fault type results and fault development trend results enables the external system to obtain these results and use them as a reference for decision-making, thereby achieving rapid fault isolation and differentiated protection.

[0056] It can be seen that the complex three-phase current information is converted into positive, negative, and zero-sequence components that are easier to analyze through symmetrical component decomposition. By calculating the reverse-sequence component ratio and the zero-sequence component ratio, the influence of load changes on fault judgment can be effectively eliminated because these ratios remain relatively stable during normal load changes. By introducing first-order derivatives and second-order derivatives, it can not only reflect the instantaneous characteristic changes when a fault occurs, but also reflect the dynamic process of fault development, which is essentially different from the method that simply relies on fixed thresholds. This multi-dimensional feature analysis method can effectively distinguish between load fluctuations, harmonic interference and real faults, improve the accuracy of fault identification, and avoid false operation of protection devices.

[0057] In actual use, in complex power supply environments of charging stations, there are problems of false tripping, which affects the operational efficiency of charging stations. For example, charging piles are powered by multiple distribution circuits and share the same grounding grid. Due to differences in new energy vehicle models, there are large differences in the current characteristics during the charging process: some models require large currents at the beginning of charging, while others require large currents at the end; some models have stable charging curves, while others have large fluctuations. When multiple charging piles are working at the same time, if a charging pile has a ground short circuit, the shared grounding grid may cause the protection device to misjudge, causing the normal charging pile to trip, affecting the operational efficiency of the charging station.

[0058] See also Figure 2 , Figure 2 is another flow chart of a short-circuit reverse sequence protection method for three-phase alternating current in an embodiment of the present application; Therefore, in some embodiments, after step S108, the following steps are further included: S201, select corresponding components according to the fault type result to perform S transform time-frequency analysis, select zero-sequence component when the fault type result is a single-phase grounding fault, select reverse-sequence component when the fault type result is a two-phase short-circuit fault, select zero-sequence component and reverse-sequence component when the fault type result is a two-phase grounding fault, and obtain S transform time-frequency analysis results, which include fault characteristic frequency and energy distribution; Among them, S transform time-frequency analysis refers to an improved short-time Fourier transform method, which is used to analyze the time-frequency characteristics of the signal; the fault characteristic frequency refers to the main frequency component when the fault occurs; the energy distribution represents the energy proportion of each frequency component.

[0059] In some embodiments, the S-transform time-frequency analysis includes: inputting a selected sequence component signal; window segmenting the signal; performing Fourier transform on the signal in each time window; and obtaining a three-dimensional representation of time-frequency-amplitude.

[0060] In some specific embodiments, it is necessary to obtain three-phase current signals (ia, ib, ic), and calculate the zero-sequence, positive-sequence, and reverse-sequence components through the symmetrical component transformation matrix: zero-sequence component i0 = (ia + ib + ic) / 3; positive-sequence component i1 = (ia + a×ib + a²×ic) / 3; reverse-sequence component i2 = (ia + a²×ib + a×ic) / 3; where: a = e^(j2π / 3). The analysis component is selected according to the fault type. When a single-phase grounding fault occurs, the zero-sequence component i0 is used; when a two-phase short-circuit fault occurs, the reverse-sequence component i2 is used; when a two-phase grounding fault occurs, both the zero-sequence component i0 and the reverse-sequence component i2 are used. Perform S transform analysis on the selected sequence components: first perform discrete Fourier transform (DFT) on the signal; for each frequency point, construct a Gaussian window function; calculate the S transform coefficients: S(τ, f) = ∫x(t)w(t-τ, f)e^(-j2πft)dt; where w(t, f) is a frequency-dependent Gaussian window.

[0061] Extract characteristic frequencies from the S-transform result matrix, analyze the spectrum at each time point, and find the frequency points where the energy value exceeds the set threshold. The typical threshold is set to 2-3 times the average energy. For example, the identification of the main characteristic frequencies includes: the amplitude change of the fundamental frequency (50Hz / 60Hz), the sudden change of the harmonic frequency (100Hz, 150Hz, etc.), the appearance time and duration of the transient high-frequency component, and the identification and recording of the fault-specific frequency. At the same time, the energy distribution calculation is performed, and the frequency band is divided into a low frequency band (0-100Hz, mainly including the fundamental and low-order harmonics), a medium frequency band (100-500Hz, including medium and high-order harmonics) and a high frequency band (above 500Hz, including transient and interference components). Energy calculation is performed for each frequency band, including calculating the total energy in the frequency band, determining the percentage of each frequency band's energy in the total energy, and recording the change of energy distribution over time.

[0062] S202, determining a high-frequency component threshold according to the fault development trend result, the high-frequency component threshold is positively correlated with the fault development trend result, when the proportion of high-frequency components in the energy distribution is greater than the high-frequency component threshold, substituting the fault characteristic frequency and energy distribution into a pre-established network equivalent impedance matrix to obtain impedance characteristics; Among them, the high-frequency component threshold represents the standard value for judging the severity of high-frequency interference; the high-frequency component ratio refers to the ratio of high-frequency energy to total energy; the network equivalent impedance matrix refers to the matrix that describes the impedance relationship between power grid nodes; and the impedance characteristic represents the equivalent impedance after considering the frequency characteristics.

[0063] In some embodiments, the high-frequency component threshold is dynamically adjusted according to the fault development trend. When the high-frequency interference exceeds the threshold, the frequency and energy characteristic information is used to correct the network impedance to obtain a more accurate impedance characteristic.

[0064] The fault development trend result reflects the severity of the fault, which is calculated based on the acceleration of the sequence component change. The greater the sequence component change acceleration, the faster the fault develops, and the larger the corresponding fault development trend result. The high-frequency component usually reflects the transient characteristics of the fault. The more serious the fault, the larger the amplitude of the high-frequency component. Therefore, the high-frequency component threshold should be positively correlated with the fault development trend result, that is, the larger the fault development trend result, the larger the corresponding high-frequency component threshold should be, so as to accurately capture the high-frequency characteristics of the fault process.

[0065] In some embodiments, step S202 specifically includes: S2021. Divide the fault characteristic frequency by the reference frequency to obtain a frequency correction coefficient; Among them, the fault characteristic frequency refers to the main fault frequency component identified in the S-transform time-frequency analysis; the reference frequency refers to the nominal operating frequency of the system, usually 50Hz or 60Hz.

[0066] After a system fault occurs and the S-transform time-frequency analysis is completed, the fault characteristic frequency needs to be standardized. In some embodiments, by dividing the fault characteristic frequency by the reference frequency, a dimensionless frequency correction coefficient can be obtained, which reflects the degree of deviation of the fault frequency from the normal operating frequency of the system, providing a correction basis for subsequent impedance characteristic calculations.

[0067] S2022, dividing the energy value of each frequency component in the energy distribution by the total energy value of the energy distribution to obtain a weight coefficient; The total energy value refers to the cumulative sum of the energy values ​​of all frequency components; the weight coefficient represents the proportion of the energy of each frequency component in the total energy, and is used to indicate the importance of different frequency components.

[0068] After obtaining the energy distribution result of the S transform, it is necessary to quantify the importance of each frequency component. In some embodiments, by calculating the proportion of the energy value of each frequency component to the total energy, a weight coefficient reflecting the relative importance of each frequency component is obtained. These coefficients will be used in the subsequent impedance characteristic calculation to ensure that more important frequency components have greater influence.

[0069] S2023. Multiply the impedance value of each node in the network equivalent impedance matrix by the corresponding frequency correction coefficient and weight coefficient to obtain impedance characteristics.

[0070] Among them, the network equivalent impedance matrix represents the impedance relationship between all nodes in the power system (such as generator access points, transformer connection points, busbar connection points, etc.), which is an n×n complex matrix, where n is the number of system nodes; the node impedance value includes self-impedance (matrix diagonal elements Zii, representing the impedance from node i to the reference node) and mutual impedance (non-diagonal elements Zij, representing the impedance from node i to j); the frequency correction coefficient reflects the influence of the fault frequency on the impedance, because the node impedance value will change with the frequency; the weight coefficient reflects the importance of each frequency component in the fault characteristics, which is used to highlight the influence of the main fault characteristics; the impedance characteristic refers to the corrected impedance matrix, which more accurately reflects the electrical characteristics of the system under the fault state.

[0071] In some embodiments, the correction process takes into account two key factors: one is the variation characteristics of the impedance value with frequency, and the other is the importance of different frequency components. For each impedance element Zij in the matrix, the frequency correction coefficient is first used for correction. This is because the impedance values ​​of the inductor and capacitor are related to the frequency and need to be adjusted accordingly at the fault frequency; then it is multiplied by the weight coefficient to ensure that the frequency component with a large energy share contributes more to the final impedance characteristics. This double correction ensures that the corrected impedance matrix reflects both the impact of the fault frequency and the main components of the fault characteristics. The entire correction process needs to process the real and imaginary parts of the impedance separately because their dependence on frequency may be different.

[0072] In some specific embodiments, the complex impedance in the matrix is ​​decomposed into a resistive component and a reactive component; Apply a frequency correction factor to the reactance component (because it is directly related to frequency); keep the resistance component basically unchanged (because it has little relationship with frequency); apply weight coefficients to the corrected resistance and reactance components respectively; consider the superposition effect of multiple frequency components and calculate the weighted average; synthesize a new complex impedance value.

[0073] It can be seen that the reference frequency is corrected by the frequency correction coefficient, eliminating the influence of frequency deviation. By introducing the weight coefficient based on energy distribution, the contribution of different frequency components to the impedance characteristics corresponds to their energy size. This weighted correction mechanism ensures that the network equivalent impedance matrix can accurately reflect the network characteristics under fault conditions, especially when multiple charging piles in the charging station work at the same time and the charging characteristics vary greatly. The calculated impedance characteristics are more in line with the actual network status, providing a reliable basis for subsequent fault location and protection strategy formulation.

[0074] S203, establishing a fault current propagation equation group according to the impedance characteristics, using the least squares method to fit the error between the calculated current value and the theoretical calculated value, and obtaining the fault current propagation characteristics; Among them, the fault current propagation equation group represents the mathematical description of the fault current distribution in the system, which is constructed by Kirchhoff's law and Ohm's law; the least squares method refers to a mathematical method to obtain the optimal solution by minimizing the sum of squares of errors between the measured value and the theoretical value; the theoretical calculated value refers to the current value calculated according to circuit theory; the calculated current value refers to the actual measured or estimated current value; the fault current propagation characteristics refer to the set of characteristic parameters that describe the propagation law of the fault current in the system, including the propagation path, attenuation characteristics and distribution law.

[0075] In some specific embodiments, a fault current propagation equation group is established: Based on the node admittance equation [Y][V] = [I], where:

Y

V

I

[0076] S204, calculating the coordinates of the fault point location according to the fault current propagation characteristics; Among them, the fault point location coordinates refer to the specific location of the fault in two-dimensional or three-dimensional space; the power system topology structure represents the connection relationship and spatial layout of the electrical components in the system; the monitoring point refers to the system node where the measuring equipment is installed; the location coordinate information includes the x, y, and z coordinate values ​​of the monitoring point in space.

[0077] After obtaining the fault current propagation characteristics, it is necessary to determine the specific location of the fault. In some embodiments, the spatial location information and measurement data of all monitoring points in the system are first collected; then the distance from each monitoring point to the fault point is calculated based on the fault current propagation characteristics; the three monitoring points with the best signal quality are selected to construct the basic positioning equation; finally, the data of other monitoring points are used to optimize the preliminary calculation results to improve the positioning accuracy.

[0078] In some embodiments, step S204 specifically includes: S2041. Obtain the topological structure of the power system and the location coordinate information of each monitoring point; Among them, the power system topology structure represents the connection relationship and layout of each component in the power network; the monitoring point refers to the network node location where the fault monitoring device is installed; the location coordinate information is used to represent the specific location data of the monitoring point in space; the network node represents the key connection point in the power system; the spatial coordinate system refers to the reference coordinate system used for positioning.

[0079] This step is performed first when fault location begins. In some embodiments, it is necessary to extract the latest network topology information from the power system management database, including the connection relationship of substations, lines, switches and other equipment. At the same time, the precise geographic coordinates of all monitoring points where fault monitoring devices have been installed are obtained. These coordinates usually include longitude, latitude or x, y, and z values ​​in a local coordinate system. These data will provide basic information for subsequent fault location calculations.

[0080] S2042, calculating the distance value from each monitoring point to the fault point according to the fault current propagation characteristics; Among them, the fault current propagation characteristics represent the physical laws of fault current propagation in the power grid; the distance value refers to the electrical or physical distance from the monitoring point to the fault point; the propagation speed is used to represent the propagation rate of the fault current in the line; the propagation delay represents the time required for the fault signal to reach the monitoring point from the fault point; and the wavefront arrival time refers to the moment when the fault wave first arrives at the monitoring point.

[0081] This step is performed after obtaining system information. In some embodiments, it is necessary to analyze the time difference of the fault wave arriving at each monitoring point based on the propagation characteristics of the fault current. By measuring the arrival time of the fault wave and combining the propagation speed of the electromagnetic wave in the power line, the actual distance from the fault point to each monitoring point is calculated. This calculation process needs to consider the influencing factors such as line characteristics and propagation medium.

[0082] S2043, establishing a distance equation group between the position coordinates of each monitoring point and the position coordinates of the fault point based on the distance value; Among them, the distance equation group represents a set of mathematical equations that describe the relationship between the coordinates of the monitoring point and the coordinates of the fault point; the position coordinate refers to the specific position of the point in the coordinate system; the spatial distance is used to represent the geometric distance between two points; the equation group represents a set of multiple related equations; the coordinate relationship refers to the position correspondence between different points.

[0083] This step is performed after obtaining the distance value. In some embodiments, it is necessary to establish a distance equation for each monitoring point, which expresses the Euclidean distance relationship between the coordinates of the monitoring point and the unknown coordinates of the fault point. Each equation contains the coordinates of the fault point to be determined as unknown quantities, and the coordinates of the monitoring point and the calculated distance value as known quantities. In this way, a complete system of nonlinear equations can be formed.

[0084] S2044, select three monitoring points as reference points; Among them, the reference point represents the benchmark monitoring point used for initial positioning calculation; the selection rule refers to the standard and method for selecting the reference point; the geometric distribution is used to represent the distribution characteristics of the monitoring point in space; the signal quality represents the reliability of the monitoring data; and the spatial layout refers to the spatial arrangement of the monitoring points.

[0085] This step is performed after establishing the distance equation group. In some embodiments, it is necessary to select three most suitable points from all monitoring points as reference points. The selection criteria usually include factors such as good signal quality, reasonable spatial distribution, and moderate distance from the fault point. These reference points will be used to preliminarily determine the location of the fault point, so their selection directly affects the positioning accuracy.

[0086] S2045, constructing a triangulated positioning equation according to the position coordinates of the three reference points and the corresponding distance values, and calculating an initial solution of the position coordinates of the fault point; Among them, the triangulation positioning equation represents a mathematical equation for spatial positioning based on three reference points; the initial solution refers to the first calculation result of the fault point location; the positioning algorithm is used to represent the calculation method for solving the position coordinates; the iterative calculation represents the process of gradually approaching the exact solution through multiple operations; the convergence of the solution refers to the stability of the calculation results.

[0087] This step is performed after selecting the reference point. In some embodiments, it is necessary to use the known coordinates of the three reference points and the measured distance values ​​to construct an equation system based on the triangulation positioning principle. By solving this nonlinear equation system, a preliminary estimate of the coordinates of the fault point location can be obtained. The solution process may require the use of specific numerical methods, such as the Newton iteration method.

[0088] S2046. Correct the initial solution using the data of the remaining monitoring points to obtain the coordinates of the fault point location.

[0089] Among them, correction refers to the correction and optimization of the initial calculation results; remaining monitoring points refer to other monitoring points that are not used for initial positioning; position accuracy is used to indicate the accuracy of the positioning results; error analysis refers to the evaluation of the deviation of the positioning results; and optimization algorithm refers to the calculation method used to improve positioning accuracy.

[0090] This step is performed after the initial solution is obtained. In some embodiments, it is necessary to optimize and correct the initial solution using the data of monitoring points that are not involved in the initial calculation. By comparing the difference between the actual measured values ​​of these monitoring points and the theoretical calculated values, an error correction model is established to adjust the initial solution to improve the positioning accuracy. The correction process may require multiple iterations until the result meets the accuracy requirements.

[0091] It can be seen that first, a complete spatial positioning framework is established based on the topological structure of the power system. The distance value calculated by the fault current propagation characteristics, combined with the triangulation positioning method, can quickly obtain the initial solution of the fault point location. The mechanism of using the remaining monitoring point data for correction effectively improves the positioning accuracy. This multi-point collaborative positioning method makes full use of the information of all monitoring points in the system, and can still maintain a high positioning accuracy in the complex power supply environment of the charging station, laying the foundation for subsequent differentiated protection control.

[0092] S205, calculating the fault current shunt value of the adjacent load according to the position coordinates of the fault point; In some embodiments, step S205 specifically includes: S2051. Determine the adjacent load nodes directly connected to the fault point according to the coordinates of the fault point location and the topological structure of the power system, and establish an electrical connection path from the fault point to each adjacent load node; Among them, the coordinates of the fault point position represent the spatial positioning information of the fault location; the power system topology structure refers to the connection relationship diagram between the components of the power network; the adjacent load nodes are used to represent the connection points of electrical equipment directly electrically connected to the fault point; the electrical connection path represents the specific electrical path between the fault point and the load node; direct connection means that there is no other intermediate node connection relationship between the two nodes.

[0093] In some embodiments, it is first necessary to locate the fault point in the power system topology map, and then scan all load nodes directly connected to the point. For each adjacent load node, it is necessary to determine the specific connection method between it and the fault point, including the type of connection line, connection distance and other information. This information will be used for subsequent current analysis and calculation.

[0094] S2052, establishing a current balance equation between the fault point and each adjacent load node based on Kirchhoff's current law to form a node current equation group; Among them, Kirchhoff's current law represents the basic law that the algebraic sum of node currents is zero; the current balance equation refers to the mathematical expression that describes the conservation relationship of node currents; the node current equation group is used to represent the system of simultaneous equations of the relationship between multiple node currents; the node represents the convergence point of current in the circuit; current conservation means that the current flowing into the node is equal to the current flowing out of the node.

[0095] In some embodiments, current balance equations need to be established for each node, including the fault point and all adjacent load nodes. These equations need to take into account all currents flowing into and out of the node to ensure that Kirchhoff's current law is satisfied. The number of equations is equal to the number of nodes minus one, forming a complete solution system.

[0096] S2053, setting the fault point as a current source injection point, and determining the fault point injection current according to the fault type; Among them, the current source injection point indicates the location where the fault current is injected into the system; the fault type refers to the specific fault form occurring in the system; the injected current is used to indicate the fault current introduced at the fault point; the current source model indicates the equivalent model used to describe the fault current characteristics; and the fault characteristics refer to the typical electrical characteristics of different types of faults.

[0097] This step is performed after the current equations are established. In some embodiments, the current source characteristics at the fault point need to be determined based on the identified fault type (such as single-phase grounding, two-phase short circuit, etc.). Different types of faults will result in different current injection characteristics, which need to be accurately reflected in the current source model. The amplitude and phase angle of the injected current need to be set accordingly according to the fault type.

[0098] S2054. Determine the impedance value of each branch according to the impedance characteristics, and use the node voltage method to solve the node current equation group to obtain the fault current shunt value flowing through each adjacent load node; wherein the fault current shunt value satisfies: the sum of the fault current shunt values ​​of each adjacent load node is equal to the fault point injection current.

[0099] Among them, the impedance characteristic represents the impedance parameters and characteristics of each part of the circuit; the branch impedance value refers to the impedance size of each connected branch in the circuit; the node voltage method is used to represent the analysis method of solving the network current through the node voltage; the fault current shunt value represents the distribution of the fault current among each adjacent load; current conservation means that the distribution of the current injected at the fault point among each load satisfies the law of conservation of current.

[0100] This step is performed after the fault current source is determined. In some embodiments, the impedance values ​​of each branch need to be determined based on the system impedance characteristics, and these values ​​may change with frequency. Then, the node voltage method is applied to convert the node current equations into node voltage equations for solution. The solution needs to satisfy the law of conservation of current, that is, the sum of the shunt values ​​of each load node is equal to the total current injected at the fault point.

[0101] It can be seen that the fault current shunt value of each adjacent load node can be accurately calculated by combining Kirchhoff's current law and the node voltage method. In particular, by considering the impedance characteristics to determine the impedance value of each branch, the shunt calculation is more in line with the actual network status. This shunt calculation method based on the physical model can accurately evaluate the impact of the fault on each load, provide a reliable criterion for achieving precise protection control, and effectively avoid the misoperation of the protection device.

[0102] S206. Determine the load impact degree according to the fault current shunt value and the fault development trend result.

[0103] Among them, the fault current shunt value indicates the magnitude of the fault current shared by each adjacent load; the fault development trend result refers to the development law of the fault evolution over time; the load impact degree is used to indicate the severity of the impact of the fault on the load; the impact assessment index refers to the quantitative index for assessing the load impact degree; the impact degree threshold refers to the critical value for distinguishing different impact levels.

[0104] In some specific embodiments, the current splitting characteristic value is calculated: Calculate the deviation rate of load branch current from the nominal value: δI = (I measured - I nominal) / I nominal × 100% Calculate the fault current split coefficient in this branch: K = Ifault component / Itotal fault The deviation rate reflects the degree to which the load current deviates from the normal operating value, and the shunt coefficient indicates the distribution ratio of the fault current in the branch.

[0105] Determine the characteristics of fault development trends: Calculate the rate of change of current (first-order derivative): dI / dt = (Icurrent - Iprevious) / Δt Calculate the current change acceleration (second-order derivative): d²I / dt² = (dI / dt current - dI / dt previous) / Δt Among them, the first-order derivative reflects the speed of current change and characterizes the speed of fault development; the second-order derivative reflects the acceleration of current change and characterizes the degree of change in the fault development trend. Establish an impact assessment function: Impact degree = f(δI, K, dI / dt, d²I / dt²) This function takes into account four parameters: the deviation rate reflects the current impact, the shunt coefficient represents the strength of the fault, the change rate represents the development speed, and the acceleration represents the development trend. The specific form of the evaluation function is: Degree of influence = w1·δI + w2·K + w3·|dI / dt| + w4·|d²I / dt²| The evaluation function integrates the influence of various parameters by weighted summation, where w1~w4 are weight coefficients, which need to be determined based on system characteristics and engineering experience. The absolute values ​​of |dI / dt| and |d²I / dt²| are taken to unify the positive and negative nature of the parameters.

[0106] It can be seen that the S transform analysis is performed by intelligently selecting the corresponding sequence components according to different fault types, which ensures the pertinence of the analysis object. The S transform can simultaneously obtain time domain and frequency domain features, where the fault characteristic frequency reflects the essential characteristics of the fault, and the energy distribution reflects the severity of the fault. In particular, the high-frequency component threshold is dynamically adjusted according to the fault development trend, which effectively adapts to the differences in charging characteristics of different models in the charging station. Combined with the analysis of the network equivalent impedance matrix and the fault current propagation characteristics, it can not only accurately locate the fault point, but also evaluate the degree of impact on each load, thereby realizing accurate fault identification and differentiated protection, and effectively avoiding the problem of false tripping caused by the shared grounding grid.

[0107] An exemplary short-circuit reverse sequence protection system 300 for three-phase alternating current provided in an embodiment of the present application is introduced below. Figure 3 Schematic diagram of an exemplary hardware structure of a short-circuit reverse sequence protection system 300 for three-phase alternating current provided in an embodiment of the present application.

[0108] In some embodiments, the short-circuit reverse sequence protection system 300 for three-phase alternating current is a computer device or the short-circuit reverse sequence protection system 300 for three-phase alternating current includes a computer device. The computer device includes a processor, a memory and a network interface connected via a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store data. The network interface of the computer device is used to communicate with other external terminals or servers through a network connection. In some embodiments, the network interface can be a wired network interface, and in some embodiments, the network interface can also be a wireless network interface. When the computer program is executed by the processor, the method in the embodiment of the present application is implemented.

[0109] Those skilled in the art will understand that Figure 3 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0110] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

[0111] As used in the above embodiments, depending on the context, the term when may be interpreted to mean if or after or in response to determining or in response to detecting. Similarly, depending on the context, the phrase upon determining or upon detecting (the stated condition or event) may be interpreted to mean if determining or in response to determining or upon detecting (the stated condition or event) or in response to detecting (the stated condition or event).

[0112] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from one website site, computer, server or data center to another website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium may be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated. The available medium may be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid-state hard disk), etc.

[0113] Those skilled in the art can understand that to implement all or part of the processes in the above-mentioned embodiments, the processes can be completed by computer programs to instruct related hardware, and the programs can be stored in computer-readable storage media. When the programs are executed, they can include the processes of the above-mentioned method embodiments. The aforementioned storage media include: ROM or random access memory RAM, magnetic disk or optical disk and other media that can store program codes.

Claims

1. A short circuit reverse sequence protection method for three-phase alternating current, characterized in that: include: Collect three-phase current of three-phase alternating current; Decomposing the three-phase current into symmetrical components to obtain positive-sequence components, negative-sequence components and zero-sequence components of the three-phase current; Calculating the ratio of the amplitude of the reverse sequence component to the amplitude of the positive sequence component to obtain the reverse sequence component ratio; Calculating the ratio of the amplitude of the zero-sequence component to the amplitude of the positive-sequence component to obtain the zero-sequence component ratio; Calculating the rate of change of the positive sequence component, the rate of change of the reverse sequence component and the rate of change of the zero sequence component to obtain a first-order derivative; Calculating the changing acceleration of the positive sequence component, the changing acceleration of the reverse sequence component and the changing acceleration of the zero sequence component to obtain a second-order derivative; Determining a fault type according to the reverse-sequence component ratio, the zero-sequence component ratio, the first-order derivative, and the second-order derivative; Predicting the fault development trend based on the second-order derivative; Output the fault type result and the fault development trend result.

2. The method according to claim 1, characterized in that The step of judging the fault type according to the reverse sequence component ratio, the zero sequence component ratio, the first order derivative and the second order derivative specifically includes: When the zero-sequence component ratio is greater than the zero-sequence ratio threshold, and the zero-sequence component change rate is greater than the zero-sequence change rate threshold, it is determined to be a single-phase grounding fault; When the reverse sequence component ratio is greater than the reverse sequence ratio threshold, and the reverse sequence component change rate is greater than the reverse sequence change rate threshold, it is determined to be a two-phase short circuit fault; When the zero-sequence component ratio is greater than the zero-sequence grounding ratio threshold and the reverse-sequence component ratio is greater than the reverse-sequence grounding ratio threshold, and the zero-sequence component change rate is greater than the zero-sequence grounding change rate threshold and the reverse-sequence component change rate is greater than the reverse-sequence grounding change rate threshold, it is determined to be a two-phase grounding fault.

3. The method according to claim 2, characterized in that The step of predicting the fault development trend based on the second-order derivative specifically includes: When the zero-sequence component change acceleration is greater than the zero-sequence acceleration threshold, it is determined that the single-phase grounding fault is in an aggravated development state; When the reverse-sequence component change acceleration is greater than the reverse-sequence acceleration threshold, it is determined that the two-phase short-circuit fault is in an aggravated development state; When the zero-sequence component change acceleration is greater than the zero-sequence grounding acceleration threshold and the reverse-sequence component change acceleration is greater than the reverse-sequence grounding acceleration threshold, it is determined that the two-phase grounding fault is in an aggravated development state.

4. The method according to claim 3, characterized in that After the step of predicting the fault development trend based on the second-order derivative, the method further includes: Select corresponding components according to the fault type result to perform S transform time-frequency analysis, select the zero-sequence component when the fault type result is the single-phase grounding fault, select the reverse-sequence component when the fault type result is the two-phase short-circuit fault, and select the zero-sequence component and the reverse-sequence component when the fault type result is the two-phase grounding fault, and obtain an S transform time-frequency analysis result, wherein the S transform time-frequency analysis result includes a fault characteristic frequency and energy distribution; Determine a high-frequency component threshold value according to the fault development trend result, wherein the high-frequency component threshold value is positively correlated with the fault development trend result, and when the proportion of high-frequency components in the energy distribution is greater than the high-frequency component threshold value, substitute the fault characteristic frequency and the energy distribution into a pre-established network equivalent impedance matrix to obtain an impedance characteristic; Establishing a fault current propagation equation group according to the impedance characteristics, using the least squares method to fit the error between the calculated current value and the theoretical calculated value, and obtaining the fault current propagation characteristics; Calculating the coordinates of the fault point location according to the fault current propagation characteristics; Calculate the fault current shunting value of the adjacent load according to the fault point position coordinates; The degree of load impact is determined according to the fault current shunt value and the fault development trend result.

5. The method according to claim 4, characterized in that The step of substituting the fault characteristic frequency and the energy distribution into a pre-established network equivalent impedance matrix to obtain the impedance characteristic specifically includes: Dividing the fault characteristic frequency by the reference frequency to obtain a frequency correction coefficient; Dividing the energy value of each frequency component in the energy distribution by the total energy value of the energy distribution to obtain a weight coefficient; The impedance value of each node in the network equivalent impedance matrix is ​​multiplied by the corresponding frequency correction coefficient and the weight coefficient to obtain the impedance characteristic.

6. The method according to claim 4, characterized in that The step of calculating the coordinates of the fault point location according to the fault current propagation characteristics specifically includes: Obtain the topological structure of the power system and the location coordinate information of each monitoring point; Calculate the distance value from each monitoring point to the fault point according to the fault current propagation characteristic; Based on the distance value, a distance equation group between the position coordinates of each monitoring point and the position coordinates of the fault point is established; Three monitoring points were selected as reference points; Constructing a triangulated positioning equation according to the position coordinates of the three reference points and the corresponding distance values, and calculating an initial solution of the position coordinates of the fault point; The initial solution is corrected using the data of the remaining monitoring points to obtain the coordinates of the fault point location.

7. The method according to claim 4, characterized in that The step of calculating the fault current shunt value of the adjacent load according to the fault point position coordinates specifically includes: Determine the adjacent load nodes directly connected to the fault point according to the position coordinates of the fault point and the topological structure of the power system, and establish an electrical connection path from the fault point to each of the adjacent load nodes; Establishing a current balance equation between the fault point and each of the adjacent load nodes based on Kirchhoff's current law to form a node current equation group; The fault point is set as a current source injection point, and a fault point injection current is determined according to the fault type; The impedance value of each branch is determined according to the impedance characteristic, and the node current equation group is solved by the node voltage method to obtain the fault current shunt value flowing through each of the adjacent load nodes; wherein the fault current shunt value satisfies: the sum of the fault current shunt values ​​of each of the adjacent load nodes is equal to the injected current of the fault point.

8. A short circuit reverse sequence protection system for three-phase alternating current, characterized in that: The short-circuit reverse-sequence protection system for three-phase alternating current includes: one or more processors and a memory; the memory is coupled to the one or more processors, the memory is used to store computer program code, the computer program code includes computer instructions, and the one or more processors call the computer instructions to enable the short-circuit reverse-sequence protection system for three-phase alternating current to execute the method described in any one of claims 1-7.

9. A computer program product comprising instructions, characterized in that When the computer program product runs on a short-circuit reverse-sequence protection system for three-phase alternating current, the short-circuit reverse-sequence protection system for three-phase alternating current executes the method according to any one of claims 1 to 7.

10. A computer-readable storage medium comprising instructions, characterized in that: When the instruction is executed on a short-circuit reverse-sequence protection system for three-phase alternating current, the short-circuit reverse-sequence protection system for three-phase alternating current is caused to execute the method according to any one of claims 1 to 7.

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