A method and system for selecting phases in a distribution network based on transient phase voltage for single-phase grounding faults.

Abstract

The method and system for selecting phases for single-phase grounding faults in distribution networks based on transient phase voltages calculates the integral of the squares of the analytical values ​​of the three-phase voltages after the fault in the first cycle, using this integral as the first-dimensional criterion. Based on the zero-sequence equivalent network parameters of the distribution network, second-dimensional and third-dimensional criters are established. Among the three surfaces constructed using the first, second, and third-dimensional criters, the phase corresponding to the lowest-level surface is selected as the phase selection result for the single-phase grounding fault in the distribution network. The first and second distance differences between the lowest-level surface and the other two surfaces are calculated respectively. When both the first and second distance differences are negative, the phase selection result is deemed correct, enabling phase selection for single-phase grounding faults in the distribution network within one cycle.

Description

Technical Field

[0001] This invention belongs to the field of power system technology, specifically, it relates to a method and system for selecting phases for single-phase grounding faults in distribution networks based on transient phase voltage variation characteristics. Background Technology

[0002] Accurate identification of the faulty phase provides information for fault detection, fault line inspection, and repair. Phase selection for ground faults has become the foundation of emerging arc suppression technologies. Failure to select the correct phase not only affects the arc suppression effect but may also trigger a two-phase ground fault, expanding the nature and scope of the accident. Distribution networks have wide coverage and complex structures. The asymmetry of three-phase ground admittance caused by factors such as lack of line transposition has long existed, and high-resistance ground faults, such as those caused by tree obstructions, conductors falling onto roads, or grasslands, frequently occur in distribution networks. Currently, traditional fault phase identification methods mostly use metallic or transition-resistance grounding analysis models. Distribution network fault phase selection primarily utilizes three-phase voltage information at the busbar for fault phase identification. In the analysis and derivation, a stable resistance grounding model is often used, neglecting the influence of power system asymmetry and the nonlinear change of transition resistance over time. However, intermittent arc faults frequently occur in actual power grids, exhibiting significant transient information during the fault process. Existing technologies rely on steady-state information as the criterion, failing to rapidly identify faulty phases based on transient information. They also neglect the impact of power system asymmetry and do not consider arc grounding scenarios, leading to low accuracy and a high risk of misjudgment. In distribution networks, faulty phases are generally determined based on phase voltage amplitude and phase angle. Existing technologies analyze phase voltage changes during single-phase grounding faults, using the characteristics of the faulty phase voltage compared to the other two phase voltages to identify the faulty phase, but this requires amplitude and phase sequence information. The traditional phase voltage amplitude comparison method assumes that in an ungrounded system, the phase with the smallest voltage amplitude is the faulty phase. However, in high-resistance grounding faults, the three-phase voltage amplitudes are similar, and the existence of a high-resistance dead zone prevents existing technologies from accurately identifying the faulty phase. Existing technologies also analyze the failure of traditional criteria under power grid asymmetry by constructing a "phase vector" for zero-sequence voltage trajectory tracking to determine the grounding fault phase. However, this method is computationally complex and cumbersome, making it difficult to apply directly in practice. When a high-resistance ground fault occurs, the changes in the three-phase voltage and neutral point voltage are relatively small, making it difficult to obtain an accurate phase relationship. In this situation, determining the faulty phase based solely on the amplitude and phase angle relationship is challenging. In practice, from the perspective of quickly identifying the faulty phase, the fewer characteristic quantities involved in fault phase selection, the better. Because existing phase selection techniques lack universality, timeliness, and accuracy, there is an urgent need to develop a fault phase selection technique for low-current grounding systems applicable to various fault conditions, including both low-resistance and high-resistance grounding. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a method and system for selecting phases of single-phase grounding faults in distribution networks based on transient phase voltage. This solves the technical problem of being unable to promptly identify the faulty phase when a high-resistance grounding fault occurs under asymmetrical grid conditions, and enables phase selection of single-phase grounding faults in distribution networks within one cycle even under high-resistance dead zones.

[0004] The present invention adopts the following technical solution.

[0005] This invention proposes a phase selection method for single-phase grounding faults in distribution networks based on transient phase voltage, wherein the neutral point of the distribution network is grounded using an arc suppression coil; including:

[0006] Obtain the zero-sequence equivalent network parameters of the distribution network; establish the constraints on the zero-sequence equivalent network parameters of the distribution network based on the fact that the distribution network operates in an underdamped state under a high-resistance ground fault; and determine the attenuation factor and the transient main resonant frequency after the fault based on the constraints on the zero-sequence equivalent network parameters of the distribution network.

[0007] The phase voltage amplitude and phase angle before the fault are obtained. Using the zero-sequence equivalent network parameters of the distribution network, and based on the zero-sequence current model of the neutral point after the fault, the phase voltage phase angle after the fault and the zero-sequence voltage model of the bus after the fault are determined. Using the zero-sequence voltage model of the bus after the fault and the virtual fault potential, the analytical values ​​of the three-phase voltage after the fault are determined.

[0008] Starting from the moment of the fault occurrence, the integral of the square of the three-phase voltage analytical value after the fault is calculated in the first cycle and used as the first criterion; based on the zero-sequence equivalent network parameters of the distribution network, the second and third criters are established; among the three surfaces constructed by the first, second and third criteria, the phase corresponding to the bottommost surface is selected as the phase selection result for single-phase grounding fault in the distribution network.

[0009] Calculate the first distance difference and the second distance difference between the bottom surface and the other two surfaces respectively. When both the first distance difference and the second distance difference are negative, the fault phase selection result is determined to be correct.

[0010] Preferably, the zero-sequence equivalent network parameters of the distribution network are obtained, including: the zero-sequence inductance of the arc suppression coil, the sum of the zero-sequence capacitances of each feeder to ground in the distribution network, and the zero-sequence equivalent resistance.

[0011] Preferably, based on the fact that the distribution network operates in an underdamped state under a high-resistance ground fault, the constraints of the zero-sequence equivalent network parameters of the distribution network are established, satisfying the following relationship:

[0012]

[0013] In the formula, L p C is the zero-sequence inductance of the arc suppression coil. 0sumR is the sum of the zero-sequence capacitances of each feeder to ground in the distribution network, and R is the zero-sequence equivalent resistance.

[0014] Based on the constraints of the zero-sequence equivalent network parameters of the distribution network, the transient main resonant frequency after a fault is determined, satisfying the following relationship:

[0015]

[0016] In the formula, ω f δ is the transient principal resonant frequency after the fault. s It is the attenuation factor;

[0017] Attenuation factor satisfies

[0018] Preferably, the phase voltage amplitude and phase angle before the fault are obtained; using the zero-sequence equivalent network parameters of the distribution network, and based on the zero-sequence current model of the neutral point after the fault, the phase voltage phase angle after the fault and the zero-sequence voltage model of the bus after the fault are determined; using the zero-sequence voltage model of the bus after the fault and the virtual fault potential, the analytical values ​​of the three-phase voltage after the fault are determined, including:

[0019] Based on the fact that the distribution network operates in an underdamped state under a high-resistance grounding fault, a neutral point zero-sequence current model is established after the fault.

[0020] Based on the post-fault neutral point zero-sequence current model, the phase voltage phase angle after the fault occurs is determined.

[0021] Based on the neutral point zero-sequence current model after the fault and the phase voltage phase angle after the fault, a bus zero-sequence voltage model after the fault is established.

[0022] A three-phase voltage model after a fault is established using the zero-sequence voltage model of the bus after the fault and the virtual fault potential.

[0023] Preferably, the neutral point zero-sequence current model after a fault satisfies the following relationship:

[0024]

[0025] In the formula, i 0fs The zero-sequence current at the neutral point after the fault, ω0 is the power frequency angular frequency, and θ s The phase angle of the phase voltage before the fault occurred. t1 is the phase angle of the phase voltage after the fault occurs, t1 is the fault time, and A1, A2, and B are the first coefficient, the second coefficient, and the third coefficient, respectively.

[0026] The first coefficient satisfies the following relationship:

[0027]

[0028] The second coefficient satisfies the following relationship:

[0029]

[0030] The third coefficient satisfies the following relationship:

[0031]

[0032] In the formula, U ms This represents the phase voltage amplitude before the fault occurred.

[0033] Preferably, let the phase angle of the phase voltage before the fault occurs be θ. s When t1 = 0, the phase voltage phase angle after the fault occurs is determined to satisfy the following relationship:

[0034]

[0035] Preferably, starting from the moment of the fault occurrence, the integral of the square of the analytical value of the three-phase voltage after the fault is calculated within the first cycle, serving as the first-dimensional criterion; based on the zero-sequence equivalent network parameters of the distribution network, second-dimensional and third-dimensional criters are established; among the three surfaces constructed by the first, second, and third-dimensional criters, the phase corresponding to the lowest-level surface is selected as the phase selection result for single-phase grounding faults in the distribution network, including:

[0036] The fault occurrence time is determined by using the transient traveling wave signal energy extremum method;

[0037] The integral of the square of the analytical value of the three-phase voltage after the fault is calculated in the first cycle and used as the first criterion.

[0038] Based on the zero-sequence equivalent network parameters of the distribution network, a second-dimensional criterion and a third-dimensional criterion are established, including:

[0039] Using zero-sequence equivalent resistance as the second criterion,

[0040] Based on the inductance current corresponding to the detuning degree of the distribution network system, the zero-sequence inductance of the arc suppression coil, and the sum of the zero-sequence capacitances of each feeder to ground in the distribution network, the capacitance current corresponding to the detuning degree of the distribution network system is determined as the third criterion.

[0041] Among the three surfaces constructed using the first, second, and third criters, the phase corresponding to the lowest-level surface is selected as the phase selection result for single-phase grounding faults in the distribution network.

[0042] Preferably, the Z-axis values ​​of the bottom surface are subtracted from the Z-axis values ​​of the other two surfaces to obtain the first distance difference and the second distance difference, respectively.

[0043] This invention also proposes a phase selection system for single-phase grounding faults in distribution networks based on transient phase voltage, comprising: a phase selection parameter calculation module, a three-phase voltage analytical value calculation module after the fault, a fault phase selection module, and a fault phase selection verification module;

[0044] The phase selection parameter calculation module is used to obtain the zero-sequence equivalent network parameters of the distribution network; based on the fact that the distribution network operates in an underdamped state under a high-resistance ground fault, the constraints of the zero-sequence equivalent network parameters of the distribution network are established; based on the constraints of the zero-sequence equivalent network parameters of the distribution network, the attenuation factor and the transient main resonant frequency after the fault are determined.

[0045] The three-phase voltage analytical value calculation module after the fault is used to obtain the phase voltage amplitude and phase angle before the fault occurs. Using the zero-sequence equivalent network parameters of the distribution network, and based on the zero-sequence current model of the neutral point after the fault, it determines the phase voltage phase angle after the fault and the zero-sequence voltage model of the bus after the fault. Using the zero-sequence voltage model of the bus after the fault and the virtual fault potential, it determines the analytical value of the three-phase voltage after the fault.

[0046] The fault phase selection module is used to calculate the integral of the square of the analytical value of the three-phase voltage after the fault occurs within the first cycle, starting from the time of the fault occurrence, as the first-dimensional criterion; based on the zero-sequence equivalent network parameters of the distribution network, the second-dimensional criterion and the third-dimensional criterion are established; among the three surfaces constructed by the first-dimensional criterion, the second-dimensional criterion, and the third-dimensional criterion, the phase corresponding to the bottommost surface is selected as the phase selection result for single-phase grounding fault in the distribution network.

[0047] The fault phase selection verification module is used to calculate the first distance difference and the second distance difference between the bottom surface and the other two surfaces. When both the first distance difference and the second distance difference are negative, the fault phase selection result is determined to be correct.

[0048] Preferably, the fault phase selection module includes: a fault occurrence time determination unit, a first-dimensional criterion establishment unit, a second-dimensional criterion establishment unit, a third-dimensional criterion establishment unit, and a fault phase selection unit;

[0049] The fault occurrence time determination unit is used to determine the fault occurrence time using the transient traveling wave signal energy extremum method.

[0050] The first-dimensional criterion establishment unit is used to calculate the integral of the square of the three-phase voltage analytical value after the fault in the first cycle, which serves as the first-dimensional criterion.

[0051] The second-dimensional criterion establishment unit is used to establish the zero-sequence equivalent resistance as the second-dimensional criterion.

[0052] The third-dimensional criterion establishment unit is used to determine the capacitive current corresponding to the detuning degree of the distribution network system based on the inductor current corresponding to the detuning degree of the distribution network system, the zero-sequence inductance of the arc suppression coil, and the sum of the zero-sequence capacitances of each feeder to ground in the distribution network, and to serve as the third-dimensional criterion.

[0053] The fault phase selection unit is used to select the phase corresponding to the lowest-level surface from the three surfaces constructed by the first-dimensional criterion, the second-dimensional criterion, and the third-dimensional criterion, as the phase selection result for single-phase grounding faults in the distribution network.

[0054] The beneficial effects of the present invention are that, compared with the prior art, the method proposed in this invention can quickly identify the faulty phase by utilizing only the transient change characteristics of the three-phase voltage after the fault occurs, thereby improving the accuracy of fault phase selection in a neutral point grounded system via an arc suppression coil, and can effectively avoid misjudgment, especially when a single-phase ground fault occurs in a high-resistance grounding system.

[0055] The method proposed in this invention has a wide range of applications and can be applied to various grounding systems, including high-resistance grounding systems. It can quickly identify the fault phase within the first cycle after a fault occurs without requiring any equipment modification to the system, making it suitable for practical engineering projects. Attached Figure Description

[0056] Figure 1 This is a flowchart of the single-phase grounding fault selection method for distribution networks based on transient phase voltage proposed in this invention;

[0057] Figure 2 This is the zero-order equivalent network in the embodiments of the present invention;

[0058] Figure 3 This is a three-dimensional surface diagram used for fault phase identification in an embodiment of the present invention;

[0059] Figure 4 This is a three-dimensional surface plot used for fault phase verification in an embodiment of the present invention. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0061] In low-current grounding systems, there is a lack of fault phase selection methods with high accuracy and wide applicability. Therefore, this invention proposes a single-phase grounding fault phase selection method for distribution networks based on transient phase voltage, such as... Figure 1 As shown, the method includes:

[0062] Step 1: Obtain the zero-sequence equivalent network parameters of the distribution network; establish the constraints on the zero-sequence equivalent network parameters of the distribution network based on the fact that the distribution network operates in an underdamped state under a high-resistance ground fault; and determine the attenuation factor and the transient main resonant frequency after the fault based on the constraints on the zero-sequence equivalent network parameters of the distribution network.

[0063] Specifically, in a non-limiting preferred embodiment, a lumped-parameter π-type equivalent circuit model is constructed for a neutral-point grounded system via an arc-suppression coil; after a single-phase ground fault occurs in the distribution network, a model is established as follows: Figure 2 The zero-sequence equivalent network shown is analyzed. A second-order differential equation is established for the transient process to calculate the zero-sequence current flowing through the neutral point arc suppression coil and the zero-sequence voltage of the bus.

[0064] When a single-phase ground fault occurs in a high-resistance grounding system, the feeder inductance, feeder resistance, and arc suppression coil resistance R... aL The zero-sequence inductance L of the arc suppression coil can be ignored. p Equal to 3 times the inductance of the arc suppression coil L ap The overcompensation of the arc suppression coil ranges from 5% to 15%. The system has n feeders, where the nth feeder is assumed to be the faulty feeder. C 0k (k = 1, 2, ..., n) represents the zero-sequence capacitance to ground of the k-th feeder, and the zero-sequence equivalent resistance R is equal to 3 times the fault transition resistance R. g i 0ks Let i be the zero-sequence current of the k-th feeder. 0fs This is the zero-sequence current at the fault point.

[0065] Specifically, step 1 includes:

[0066] Step 1.1: Obtain the parameters of the zero-sequence equivalent network of the distribution network, including: the zero-sequence inductance of the arc suppression coil, the sum of the zero-sequence capacitances of each feeder to ground in the distribution network, and the zero-sequence equivalent resistance.

[0067] Step 1.2: Based on the fact that the distribution network operates in an underdamped state under a high-resistance ground fault, establish the constraints for the zero-sequence equivalent network parameters of the distribution network, which satisfy the following relationship:

[0068]

[0069] In the formula, L p C is the zero-sequence inductance of the arc suppression coil. 0sum R is the sum of the zero-sequence capacitances of each feeder to ground in the distribution network, and R is the zero-sequence equivalent resistance.

[0070] Step 1.3: Based on the constraints of the zero-sequence equivalent network parameters of the distribution network, determine the attenuation factor and the transient main resonant frequency after the fault.

[0071] Specifically, the neutral point of the distribution network is grounded using an arc suppression coil. The transient process of a single-phase high-resistance ground fault is equivalent to a second-order transient equivalent circuit. The established fault zero-sequence voltage model satisfies the following relationship:

[0072]

[0073] In the formula, u0fs and u0(t1) are the neutral point zero-sequence voltage after the fault and the bus zero-sequence voltage at the moment of the fault, respectively. p C is the zero-sequence inductance of the arc suppression coil. 0sum i is the sum of the zero-sequence capacitances to ground of each feeder in the distribution network. 0ps Let t1 be the zero-sequence current at the neutral point, t1 be the time of fault occurrence, R be the zero-sequence equivalent resistance, and i be the zero-sequence current. 0fs This is the zero-sequence current at the neutral point after the fault.

[0074] The second-order differential equation of the zero-sequence voltage model at the fault point satisfies the following relationship:

[0075]

[0076] u 0fs =U ms sin(ω0t1+θ s )

[0077] In the formula, U ms With θ s These are the phase voltage amplitude and phase angle before the fault occurred, respectively, and ω0 is the power frequency angular frequency.

[0078] Specifically, when a single-phase ground fault occurs in a high-resistance grounding system, and the fault transition resistance is large, the system operates in an underdamped state. At this time, the characteristic roots are a pair of conjugate complex roots. In a non-limiting preferred embodiment, the phase voltage phase angle before the fault occurs is set to zero. Solving the second-order differential equation yields two characteristic roots that satisfy the following relationship:

[0079]

[0080] Therefore, the transient principal resonant frequency after the fault satisfies the following relationship:

[0081]

[0082] In the formula, δ s ω is the attenuation factor. f This is the transient main resonant frequency after the fault.

[0083] The attenuation factor is defined, satisfying the following relationship:

[0084]

[0085] Step 2: Obtain the phase voltage amplitude and phase angle before the fault occurs. Using the zero-sequence equivalent network parameters of the distribution network, and based on the zero-sequence current model of the neutral point after the fault, determine the phase voltage and phase angle after the fault, as well as the zero-sequence voltage model of the bus after the fault. Using the zero-sequence voltage model of the bus after the fault and the virtual fault potential, determine the analytical values ​​of the three-phase voltage after the fault.

[0086] Specifically, step 2 includes:

[0087] Step 2.1: Based on the fact that the distribution network operates in an underdamped state under a high-resistance grounding fault, establish a neutral point zero-sequence current model after the fault.

[0088] When the system is in an underdamped state, the zero-sequence current flowing through the neutral point arc suppression coil is the same as the zero-sequence current flowing through the neutral point. Therefore, the neutral point zero-sequence current model after a fault satisfies the following relationship:

[0089]

[0090] In the formula, Let A1, A2, and B be the phase angle of the phase voltage after the fault occurs, and let A1, A2, and B be the first, second, and third coefficients, respectively, satisfying the following relationship:

[0091]

[0092] The first and second derivatives of the neutral point current are derived, and the specific results are as follows:

[0093]

[0094] Step 2.2: Based on the post-fault neutral point zero-sequence current model, determine the phase voltage phase angle after the fault occurs.

[0095] In a non-limiting preferred embodiment, to simplify the fault phase selection process during ground fault phase selection, the phase angle of the phase voltage before the fault occurs is set to θ. s When t1 = 0, the above equations can be combined to obtain the phase voltage and phase angle after the fault occurs, which satisfies the following relationship:

[0096]

[0097] Step 2.3: Based on the neutral point zero-sequence current model after the fault and the phase voltage phase angle after the fault, establish the bus zero-sequence voltage model after the fault.

[0098] The zero-sequence voltage model of the bus after a fault satisfies the following relationship:

[0099]

[0100] Step 2.4: Using the post-fault bus zero-sequence voltage model and virtual fault potential, determine the analytical values ​​of the three-phase voltages after the fault.

[0101] Specifically, in order to improve the identification of faulty phases, a virtual fault potential is set. In a non-limiting preferred embodiment, the virtual fault potential is the rated phase voltage.

[0102] The analytical values ​​of the three-phase voltages after a fault satisfy the following relationship:

[0103] u A =u0(t1)+e A

[0104] u B =u0(t1)+e B

[0105] u C =u0(t1)+e C

[0106] In the formula, e A e B and e C These are the three-phase virtual fault potentials, and u0(t1) is the bus zero-sequence voltage at time t1 after the fault occurs.

[0107] When a high-resistance ground fault occurs in a distribution network, the electrical quantity signals are weak due to the large transition resistance at the fault point. The electrical quantity characteristics of this type of fault are not obvious, making effective detection and protection difficult. When a single-phase high-resistance ground fault occurs in a distribution line, the three-phase voltage amplitude changes are small, and accurate phase relationships are difficult to obtain. In this case, the phase determination method based on voltage amplitude and phase relationships in the distribution network may result in misjudgment or failure.

[0108] Transient signals are characterized by randomness, locality, and non-stationarity, making them difficult to capture. Extracting electrical transients requires high-speed acquisition equipment, involving the capture and analysis of rapidly changing signals in the power system. These signals change very quickly, necessitating high-speed acquisition to ensure data accuracy and integrity. Therefore, existing high-resistance grounding fault phase selection methods require equipment modifications and increased construction investment in existing projects, resulting in poor economic efficiency. The method proposed in this invention, however, requires no additional primary equipment investment, utilizing existing measuring devices for phase selection. It is applicable to various neutral point connection methods in low-current grounding systems and leverages the transient characteristics of three-phase voltage to improve the accuracy and speed of phase selection, thereby enhancing the safety and reliability of the distribution network.

[0109] Step 3: Starting from the time of the fault occurrence, calculate the integral of the square of the three-phase voltage analytical value after the fault in the first cycle, and use it as the first-dimensional criterion; establish the second-dimensional criterion and the third-dimensional criterion according to the zero-sequence equivalent network parameters of the distribution network; select the phase corresponding to the bottommost surface from the three surfaces constructed by the first-dimensional criterion, the phase selection result of the single-phase grounding fault in the distribution network.

[0110] Specifically, step 3 includes:

[0111] Step 3.1: Use the transient traveling wave signal energy extremum method to determine the time of fault occurrence.

[0112] Specifically, using the transient traveling wave signal energy extremum method to determine the fault occurrence time is a non-limiting but preferred option. Those skilled in the art can choose different methods to determine the fault occurrence time according to the actual situation.

[0113] Specifically, after a single-phase ground fault occurs, the transient traveling wave signal flows through the fault detection device. At the moment the fault occurs, the energy of the transient traveling wave signal reaches its maximum value. Subsequently, due to the energy consumption of the transmission line impedance, the energy of the transient traveling wave signal gradually decays. Therefore, the moment corresponding to the sudden change in the energy of the transient traveling wave signal to the maximum extreme value is taken as the moment of fault occurrence. The moment of fault occurrence is the starting point of the integration interval of the square of the three-phase voltage analytical value.

[0114] Step 3.2: Calculate the integral of the square of the three-phase voltage analytical value after the fault within the first cycle, and use it as the first criterion.

[0115] Since the phase angle of the fault phase voltage cannot be determined at the instant of a short circuit, if the fault phase voltage is in the negative half-cycle at the instant of the fault, and at the same time a certain fault phase voltage is in the positive half-cycle with a positive instantaneous derivative, the integral value of the non-fault phase voltage may be greater than the non-fault phase voltage in the current half-cycle. A certain amount of time should be allowed for the transient voltage to transition. After multiple model simulations, it was found that if the length of the integration interval is adjusted to be greater than or equal to one cycle, the larger the integration interval, the more sufficient the fault phase voltage drops, and the higher the identification accuracy. However, this sacrifices the speed of phase selection and cannot meet the requirements for the fault phase selection action time limit when there is a high-resistance grounding fault in the distribution box. If the length of the integration interval is adjusted to be less than one cycle, the fault phase voltage drops insufficiently due to the three-phase asymmetry of the distribution network system. In this case, misjudgment may occur due to the influence of the three-phase asymmetry of the distribution network system. That is, when the drop in the normal phase voltage exceeds the drop in the fault phase voltage, it will be incorrectly judged that a grounding fault has occurred in the normal phase. This misjudgment often occurs in existing technologies that rely on the change in steady-state phase voltage as the phase selection criterion. This is a misjudgment caused by not considering the influence of the three-phase asymmetry of the distribution network system. Therefore, considering both speed and accuracy, this invention uses the first cycle as the integration time. In a non-limiting preferred embodiment, the length of the integration interval for the squares of the three-phase voltage analytical values ​​is 0.02 s. The determination of the above integration interval is a value obtained through extensive model simulation experiments and device simulation experiments, which can meet the requirements for the safe and stable operation of existing distribution network systems considering the influence of three-phase asymmetry, and has high universality.

[0116] When a single-phase ground fault occurs, the line voltage undergoes a transient change, resulting in unequal voltage integrals during the positive and negative half-cycles within the same period. Directly integrating the analytical values ​​of the three-phase voltages at this time will lead to discrepancies between the final result and the expected result. For example, due to the transient change, the integral value of the non-faulty phase voltage in the negative half-cycle may be greater than the integral value of the faulty phase voltage in the positive half-cycle, thus causing circuit breaker malfunction. Therefore, this invention proposes integrating the squares of the analytical values ​​of the three-phase voltages.

[0117] Step 3.3: Based on the zero-sequence equivalent network parameters of the distribution network, establish the second-dimensional criterion and the third-dimensional criterion, including:

[0118] 1) Zero-sequence equivalent resistance is used as the second criterion;

[0119] Using zero-sequence equivalent resistance as the second criterion, the value of the zero-sequence equivalent resistance has no impact on the value of the first criterion, thus it can be used as one of the coordinates for constructing a three-dimensional surface. Furthermore, the value of the zero-sequence equivalent resistance can intuitively reflect whether the current ground fault type is low-resistance grounding or high-resistance grounding.

[0120] 2) Based on the inductance current corresponding to the detuning degree of the distribution network system, the zero-sequence inductance of the arc suppression coil, and the sum of the zero-sequence capacitances of each feeder to ground in the distribution network, determine the capacitance current corresponding to the detuning degree of the distribution network system as the third criterion.

[0121] The capacitive current is the capacitive current at the fault point after a fault, and its magnitude is an empirical value. In this invention, it is proposed that the capacitive current be calculated by the sum of the detuning degree-related inductance current, the zero-sequence inductance of the arc suppression coil, and the zero-sequence capacitance to ground of each feeder in the distribution network. Based on the calculation method of phase voltage and phase angle after a fault proposed in this invention, the third criterion is the calculated capacitive current, which actually includes the changes in the zero-sequence inductance of the arc suppression coil and the sum of the zero-sequence capacitance to ground of each feeder in the distribution network. Therefore, the third criterion can also characterize the changes in phase voltage and phase angle after a fault.

[0122] Moreover, in practice, based on a large number of model simulation experiments and device simulation experiments, this invention proposes that the fewer feature quantities involved in fault phase selection, the better, from the perspective of quickly and accurately judging the fault phase. Therefore, these three dimensions of criteria are the preferred results.

[0123] Step 3.4: Among the three surfaces constructed by the first-dimensional criterion, the second-dimensional criterion, and the third-dimensional criterion, select the phase corresponding to the bottommost surface as the phase selection result for single-phase grounding faults in the distribution network.

[0124] The information in the three surfaces constructed based on the first, second, and third criters includes: the first criterion characterizes the easily identifiable phase voltage amplitude after a fault occurs; the second criterion characterizes the current ground fault type; and the third criterion characterizes the change in phase voltage phase angle after a fault occurs.

[0125] Using the method proposed in this invention, a three-dimensional surface layer is drawn by sampling large amounts of data in Matlab, such as... Figure 3 As shown, Figure 3 In this model, the first criterion is plotted on the X-axis (rk / Φhms), with the zero-sequence equivalent resistance ranging from 500 to 5000 Ω. The second criterion is plotted on the Y-axis (ic / A), with the calculated capacitance current ranging from 10 to 150 A at a detuning degree of +5%. The third criterion is plotted on the Z-axis, representing the integrals AF, BF, and CF of the squared analytical values ​​of the three-phase voltages after the fault, calculated within the first cycle. By comparing the hierarchical relationships of the three surfaces, phase A corresponding to the bottommost surface is selected as the phase selection result for single-phase grounding faults in the distribution network, thus achieving phase identification of single-phase grounding faults. Furthermore, from... Figure 3As can be seen, the curved surface in the middle corresponds to phase B. Before the fault occurred, there was a three-phase asymmetry in the distribution network, resulting in a more significant voltage drop in phase B than in phase A after the fault. This demonstrates that the impact of the three-phase asymmetry on the electrical characteristics after the fault cannot be ignored. This makes the detection and handling of high-resistance grounding faults more difficult with existing technologies, leading to the long-term existence of high-resistance grounding faults that cannot be detected, endangering the distribution network and personal safety. Furthermore, in the case of neutral point grounding via an arc suppression coil, the three-phase voltage imbalance caused by the asymmetry of three-phase ground admittances is further amplified into unbalanced overvoltages. Severe unbalanced overvoltages can cause zero-sequence voltage relays to malfunction, affecting the stable operation of the distribution network to some extent. If high-resistance faults in the distribution network are not handled promptly, they may pose safety hazards such as electric shock and fire. Therefore, the method proposed in this invention can accurately select the fault phase from grounding faults occurring in a three-phase asymmetrical distribution network system.

[0126] Step 4: Calculate the first distance difference and the second distance difference between the bottom surface and the other two surfaces respectively. When both the first distance difference and the second distance difference are negative, the fault phase selection result is determined to be correct.

[0127] The first distance difference and the second distance difference are obtained by subtracting the Z-axis values ​​of the other two surfaces from the Z-axis value of the bottom surface.

[0128] To avoid the impact of three-phase asymmetry in the distribution network system on phase selection results, a method based on a drawn 3D surface layer is proposed. The surface corresponding to A is paired with the surfaces corresponding to B and C, and the differences between them are calculated pairwise. Both results are negative. Figure 4 As shown, the first criterion is plotted on the X-axis (rk / Φhms), the second criterion on the Y-axis (ic / A), and the difference between the two is plotted on the Z-axis. It can be seen that, starting from the time of the fault occurrence, the integral of the square of the analytical value of phase A voltage after the fault is minimized in the first cycle, thus verifying that phase A is the faulty phase.

[0129] This invention also proposes a phase selection system for single-phase grounding faults in distribution networks based on transient phase voltage, comprising: a phase selection parameter calculation module, a three-phase voltage analytical value calculation module after the fault, a fault phase selection module, and a fault phase selection verification module;

[0130] The phase selection parameter calculation module is used to obtain the zero-sequence equivalent network parameters of the distribution network; based on the fact that the distribution network operates in an underdamped state under a high-resistance ground fault, the constraints of the zero-sequence equivalent network parameters of the distribution network are established; based on the constraints of the zero-sequence equivalent network parameters of the distribution network, the attenuation factor and the transient main resonant frequency after the fault are determined.

[0131] The three-phase voltage analytical value calculation module after the fault is used to obtain the phase voltage amplitude and phase angle before the fault occurs. Using the zero-sequence equivalent network parameters of the distribution network, and based on the zero-sequence current model of the neutral point after the fault, it determines the phase voltage phase angle after the fault and the zero-sequence voltage model of the bus after the fault. Using the zero-sequence voltage model of the bus after the fault and the virtual fault potential, it determines the analytical value of the three-phase voltage after the fault.

[0132] The fault phase selection module is used to calculate the integral of the square of the analytical value of the three-phase voltage after the fault occurs within the first cycle, starting from the time of the fault occurrence, as the first-dimensional criterion; based on the zero-sequence equivalent network parameters of the distribution network, the second-dimensional criterion and the third-dimensional criterion are established; among the three surfaces constructed by the first-dimensional criterion, the second-dimensional criterion, and the third-dimensional criterion, the phase corresponding to the bottommost surface is selected as the phase selection result for single-phase grounding fault in the distribution network.

[0133] The fault phase selection verification module is used to calculate the first distance difference and the second distance difference between the bottom surface and the other two surfaces. When both the first distance difference and the second distance difference are negative, the fault phase selection result is determined to be correct.

[0134] Preferably, the fault phase selection module includes: a fault occurrence time determination unit, a first-dimensional criterion establishment unit, a second-dimensional criterion establishment unit, a third-dimensional criterion establishment unit, and a fault phase selection unit;

[0135] The fault occurrence time determination unit is used to determine the fault occurrence time using the transient traveling wave signal energy extremum method.

[0136] The first-dimensional criterion establishment unit is used to calculate the integral of the square of the three-phase voltage analytical value after the fault in the first cycle, which serves as the first-dimensional criterion.

[0137] The second-dimensional criterion establishment unit is used to establish the zero-sequence equivalent resistance as the second-dimensional criterion.

[0138] The third-dimensional criterion establishment unit is used to determine the capacitive current corresponding to the detuning degree of the distribution network system based on the inductor current corresponding to the detuning degree of the distribution network system, the zero-sequence inductance of the arc suppression coil, and the sum of the zero-sequence capacitances of each feeder to ground in the distribution network, and to serve as the third-dimensional criterion.

[0139] The fault phase selection unit is used to select the phase corresponding to the lowest-level surface from the three surfaces constructed by the first-dimensional criterion, the second-dimensional criterion, and the third-dimensional criterion, as the phase selection result for single-phase grounding faults in the distribution network.

[0140] Based on the traditional high-resistance grounding criterion, this invention proposes a fault phase selection method with strong universality and anti-interference capability. By analyzing the changes and magnitudes of the three-phase voltage amplitudes in the first cycle during a single-phase grounding fault, the fault phase is selected. This method can eliminate the influence of three-phase asymmetry in the distribution network system. The method is highly practical and effectively improves the real-time performance of fault phase selection. It can also quickly and accurately identify the faulty phase under complex conditions such as high-resistance faults.

[0141] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0142] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0143] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0144] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A single-phase grounding fault phase selection method based on transient phase voltage for a power distribution network, the neutral point of the power distribution network being grounded by an arc suppression coil; characterized in that, The method comprises the following steps: obtaining zero sequence equivalent network parameters of the power distribution network, including: arc suppression coil zero sequence inductance, the sum of zero sequence capacitances of each feeder in the power distribution network to ground, and zero sequence equivalent resistance; establishing a constraint condition of the zero sequence equivalent network parameters of the power distribution network according to the under-damped state of the power distribution network under high-resistance grounding fault; determining a damping factor and a transient main resonance frequency after the fault based on the constraint condition of the zero sequence equivalent network parameters of the power distribution network; obtaining the amplitude and phase angle of the phase voltage before the fault, determining the phase angle of the phase voltage after the fault and a bus zero sequence voltage model after the fault based on a neutral point zero sequence current model after the fault by using the zero sequence equivalent network parameters of the power distribution network; determining the analytical value of the three-phase voltage after the fault by using the bus zero sequence voltage model after the fault and a virtual fault potential; wherein the virtual fault potential comprises a rated phase voltage; determining the fault occurrence time by using a transient traveling wave signal energy extremum method; calculating the integral of the square of the analytical value of the three-phase voltage after the fault in the first cycle as a first-dimensional criterion with the fault occurrence time as the starting point; establishing a second-dimensional criterion and a third-dimensional criterion based on the zero sequence equivalent network parameters of the power distribution network, including: taking the zero sequence equivalent resistance as the second-dimensional criterion, determining a capacitance current corresponding to the power distribution network system detuning degree as the third-dimensional criterion based on the inductance current corresponding to the power distribution network system detuning degree, the arc suppression coil zero sequence inductance, and the sum of the zero sequence capacitances of each feeder in the power distribution network to ground; selecting the phase corresponding to the curve surface located at the bottom layer from the three curve surfaces constructed by the first-dimensional criterion, the second-dimensional criterion, and the third-dimensional criterion as the single-phase grounding fault selection result of the power distribution network; respectively calculating a first distance difference value and a second distance difference value between the curve surface at the bottom layer and the other two curve surfaces, and determining that the fault selection result is correct when the first distance difference value and the second distance difference value are both negative.

2. The single-phase grounding fault selection method of the power distribution network based on transient phase voltage according to claim 1, wherein the constraint condition of the zero sequence equivalent network parameters of the power distribution network is established according to the under-damped state of the power distribution network under high-resistance grounding fault, and satisfies the following relationship: the transient main resonance frequency after the fault is determined based on the constraint condition of the zero sequence equivalent network parameters of the power distribution network, and satisfies the following relationship: In the formula, is the zero sequence inductance of the arc suppression coil, is the sum of the zero sequence capacitances of the feeders in the distribution network, is the zero sequence equivalent resistance; 3. The single-phase grounding fault selection method of the power distribution network based on transient phase voltage according to claim 2, wherein the amplitude and phase angle of the phase voltage before the fault are obtained, the phase angle of the phase voltage after the fault and the bus zero sequence voltage model after the fault are determined based on the neutral point zero sequence current model after the fault by using the zero sequence equivalent network parameters of the power distribution network; the analytical value of the three-phase voltage after the fault is determined by using the bus zero sequence voltage model after the fault and the virtual fault potential, and comprises the following steps: wherein is the post-fault transient main resonance frequency, is the damping factor; The attenuation factor satisfies . the neutral point zero sequence current model after the fault is established according to the under-damped state of the power distribution network under high-resistance grounding fault; the phase angle of the phase voltage after the fault is determined based on the neutral point zero sequence current model after the fault; the bus zero sequence voltage model after the fault is established based on the neutral point zero sequence current model after the fault and the phase angle of the phase voltage after the fault; the three-phase voltage model after the fault is established by using the bus zero sequence voltage model after the fault and the virtual fault potential. ​ ​ 4. The single-phase grounding fault selection method based on transient phase voltage of the power distribution network according to claim 3, wherein, the post-fault neutral point zero sequence current model satisfies the following relationship: wherein, is the post-fault neutral zero sequence current, is the power frequency angular frequency, is the pre-fault phase voltage phase angle, is the post-fault phase voltage phase angle, is the fault time, , , are a first coefficient, a second coefficient and a third coefficient, respectively; the first coefficient satisfies the following relationship: the second coefficient satisfies the following relationship: the third coefficient satisfies the following relationship: In the formula, is the phase voltage amplitude before the fault occurs.

5. The single-phase grounding fault selection method based on transient phase voltage of the power distribution network according to claim 4, wherein, the phase angle of the phase voltage before the fault occurs is 0, the phase angle of the phase voltage after the fault occurs is determined to satisfy the following relationship: is 0, the phase angle of the phase voltage after the fault occurs is determined to satisfy the following relationship: 。 6. The single-phase grounding fault selection method based on transient phase voltage of the power distribution network according to claim 1, wherein, the Z-axis numerical value of the bottommost surface is subtracted from the Z-axis numerical values of the other two surfaces, respectively, as the first distance difference value and the second distance difference value.

7. A single phase to ground fault phase selection system for a power distribution network based on transient phase voltages characterised in that, comprising: a phase selection parameter calculation module, a post-fault three-phase voltage analytical value calculation module, a fault phase selection module, and a fault phase selection verification module; the phase selection parameter calculation module is configured to obtain zero sequence equivalent network parameters of the power distribution network, including: a Petersen coil zero sequence inductance, a sum of zero sequence capacitances of each feeder to ground in the power distribution network, and a zero sequence equivalent resistance; a constraint condition of the zero sequence equivalent network parameters of the power distribution network is established according to the fact that the power distribution network operates in an under-damped state under high-resistance grounding fault; and a decay factor and a post-fault transient main resonance frequency are determined based on the constraint condition of the zero sequence equivalent network parameters of the power distribution network; the post-fault three-phase voltage analytical value calculation module is configured to obtain a phase voltage amplitude and a phase angle before the fault occurs, determine a post-fault phase voltage phase angle and a post-fault bus zero sequence voltage model based on the post-fault neutral point zero sequence current model by using the zero sequence equivalent network parameters of the power distribution network, and determine post-fault three-phase voltage analytical values by using the post-fault bus zero sequence voltage model and a virtual fault potential; the virtual fault potential includes a rated phase voltage; the fault phase selection module is configured to determine a fault occurrence time by using a transient traveling wave signal energy extremum method, calculate an integral of squares of the post-fault three-phase voltage analytical values in the first cycle as a first dimension criterion, establish a second dimension criterion and a third dimension criterion based on the zero sequence equivalent network parameters of the power distribution network, including: taking the zero sequence equivalent resistance as the second dimension criterion, determining a capacitance current corresponding to a power distribution network system detuning degree as the third dimension criterion based on an inductance current corresponding to the power distribution network system detuning degree, the Petersen coil zero sequence inductance, and the sum of zero sequence capacitances of each feeder to ground in the power distribution network, and selecting a phase corresponding to a surface located at the bottommost layer among three surfaces constructed by the first dimension criterion, the second dimension criterion, and the third dimension criterion as a single-phase grounding fault selection result of the power distribution network; the fault phase selection verification module is configured to calculate a first distance difference value and a second distance difference value between the surface located at the bottommost layer and the other two surfaces, respectively, and determine that the fault phase selection result is correct when the first distance difference value and the second distance difference value are both negative.

8. The single-phase grounding fault selection system based on transient phase voltage of the power distribution network according to claim 7, wherein, the fault phase selection module comprises: a fault occurrence time determination unit, a first dimension criterion establishment unit, a second dimension criterion establishment unit, a third dimension criterion establishment unit, and a fault phase selection unit. The fault occurrence time determination unit is configured to determine the fault occurrence time by using a transient traveling wave signal energy extreme value method; The first dimension criterion establishment unit is configured to calculate the integral of the square of the analytic value of the three-phase voltage after the fault in the first cycle as the first dimension criterion; The second dimension criterion establishment unit is configured to use the zero sequence equivalent resistance as the second dimension criterion; The third dimension criterion establishment unit is configured to determine the capacitance current corresponding to the off-tuning degree of the distribution network system based on the inductance current corresponding to the off-tuning degree of the distribution network system, the zero sequence inductance of the arc suppression coil, and the sum of the zero sequence capacitances of each feeder in the distribution network, and use the capacitance current as the third dimension criterion; The fault phase selection unit is configured to select the phase corresponding to the curve surface located at the bottom layer from the three curve surfaces constructed by the first dimension criterion, the second dimension criterion, and the third dimension criterion, and use the phase as the single-phase ground fault phase selection result of the distribution network.

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