A method for real-time tracking of transition resistance and fault phase selection in single-phase grounding faults in distribution networks

Abstract

This invention discloses a method for real-time tracking of transition resistance and fault phase selection in single-phase ground faults in distribution networks. Applicable to the field of distribution network protection and control technology, the method includes the following steps: measuring the zero-sequence voltage of the distribution network and calculating the instantaneous value of the fault current in real time; constructing a single-phase ground fault initiation criterion and determining whether a single-phase ground fault has occurred; measuring the voltages of the three phases A, B, and C to ground and plotting the volt-ampere characteristic curves between the fault current and the voltages of each phase to ground; determining the fault phase based on the distribution characteristics of the volt-ampere characteristic curves; and calculating the transition resistance in real time. This invention considers the influence of nonlinear arc resistance instability and distribution network parameter asymmetry, quickly and accurately determining the fault phase and tracking the development of the transition resistance in real time, providing theoretical guidance for correct fault handling and reliable arc suppression.

Description

Technical Field

[0001] This invention relates to the field of power distribution network fault detection and protection technology, specifically a method for real-time tracking of transition resistance and fault phase selection in a single-phase grounding fault in a power distribution network. Background Technology

[0002] Single-phase grounding faults account for over 80% of all faults in my country's distribution networks, and 80% of these are unstable arcing faults or transient faults. Therefore, the transition resistance is often not a fixed value. The requirement is "rapid isolation of permanent faults and safe arc suppression of transient faults." For permanent faults, the fault point should be quickly disconnected to ensure the safe operation of the power grid; for transient faults, arc suppression devices should be quickly activated to prevent the fault from worsening and reduce power outage time. Therefore, the prerequisite for fault handling is the rapid and accurate identification of the fault type. The fault type and its development stage are directly characterized by the transition resistance, and real-time tracking of the dynamic changes in the transition resistance is a key technology for determining the fault type. With the widespread application of active flexible arc suppression technology, the rapid and accurate activation of arc suppression devices depends on the accurate identification of the faulty phase. Incorrect phase selection can lead to fault escalation. Therefore, research on real-time tracking of the transition resistance and fault phase selection methods for single-phase grounding faults in distribution networks is of great significance for the normal and safe operation of the power grid.

[0003] Existing transition resistance measurement techniques primarily utilize steady-state information and are suitable for identifying transition resistance in permanent, stable faults. However, when transition resistance fluctuates randomly, existing methods struggle to track changes in transition resistance in real time. Therefore, a real-time transition resistance tracking technology applicable to unstable arcing faults is urgently needed. Traditional phase selection methods rely on strictly symmetrical distributed parameters. However, the distributed parameters of distribution networks are typically asymmetrical, causing traditional phase selection criteria to fail in high-resistance grounding faults. Furthermore, the rapid deployment of arc-suppression devices requires rapid fault phase selection. Existing phase selection methods often rely on steady-state information such as the variation of zero-sequence voltage trajectories and the changes in phase-to-ground voltage amplitude and phase angle before and after the fault. This requires navigating a lengthy transient transition process, resulting in poor speed of fault phase selection. Therefore, research is urgently needed on rapid fault phase selection techniques that consider the asymmetry of distributed parameters to gain time for arc suppression.

[0004] The Chinese patent application number is CN202011509050.4, the publication number is CN112946414B, and the patent title is: "Identification Method of Grounded Phase and Transition Resistance in Distribution Network Based on Zero-Sequence Residual Voltage Suppression". This patent uses the neutral point voltage suppression of 0 as the control target. By comparing the changes in the injected current of the active flexible device during normal operation of the distribution network and after a single-phase ground fault, it achieves fault phase selection and transition resistance identification. This method still has good sensitivity for high-resistance faults, but it is only applicable to pure resistance faults. The fault phase selection method lacks speed and requires additional equipment investment. Chinese patent application number CN201710360981.4, publication number CN107192883B, patent title: A method for identifying the transition resistance of a high-resistance grounding fault in a resonant grounding system. This patent extracts the transient zero-sequence voltage and calculates the transient zero-sequence current at the fault point. The transition resistance is determined by the ratio of the transient zero-sequence voltage to the transient zero-sequence current at the fault point. This method utilizes transient data and has good speed, but it is still not applicable to situations where the transition resistance changes randomly, and it also has the problem of difficulty in extracting transient features. Summary of the Invention

[0005] Technical issues: With economic and social development and the continuous expansion of the power distribution network, the demand for and quality requirements of electricity are constantly increasing. The power distribution network is required to be able to respond to faults instantly and provide fault handling solutions quickly. However, when a fault occurs in the power distribution network, the transition resistance has random fluctuations, and most fault type identification and detection methods fail, making it difficult to identify and detect arc faults, which poses operational risks to the power distribution network.

[0006] Technical Solution: To solve the above-mentioned technical problems, this invention proposes a method for real-time tracking of transition resistance and fault phase selection in single-phase grounding faults in distribution networks, specifically including the following steps:

[0007] Step a: Construct a single-phase ground fault initiation criterion, collect the zero-sequence voltage of the distribution network in real time, and calculate the fault current in real time. When the absolute value of the fault current at a certain moment is greater than the fault judgment threshold M, it indicates that a single-phase ground fault has occurred in the distribution network, and continue to step b; otherwise, continue to monitor the distribution network.

[0008] Step b: Measure the phase-to-ground voltage of each phase in the distribution network, and plot the volt-ampere characteristic curves of phases A, B, and C with the fault current as the abscissa and the three-phase-to-ground voltage as the ordinate.

[0009] Step c: Determine the fault phase based on the quadrant in which the volt-ampere characteristic curve is located;

[0010] Step d: Calculate the transition resistance R in real time based on the fault phase-to-ground voltage and fault current. E (t), the specific expression is:

[0011]

[0012] Among them, u δ (t) represents the fault-to-ground voltage, δ = A, B, C, i E (t) represents the fault current.

[0013] The single-phase ground fault initiation criterion in step a can be determined by the following steps:

[0014] Step a1: Real-time acquisition of the zero-sequence voltage u0(t) of the distribution network, and substitution of the zero-sequence voltage into the fault current calculation expression to solve for the fault current i in real time. E (t), the specific expression for calculating the fault current is:

[0015]

[0016] Among them, G Σ and C Σ These are the total conductance to ground and the total capacitance to ground of the distribution network, i bd (t) represents the total unbalanced current of the distribution network;

[0017] Step a2: Determine the fault judgment threshold M, and take M = 0.1A. If the absolute value of the fault current at any time is less than the fault judgment threshold M, it indicates that there is no single-phase grounding fault in the distribution network. If the absolute value of the fault current at a certain time is greater than the fault judgment threshold M, it indicates that there is a single-phase grounding fault in the distribution network. The time corresponding to the first time when the absolute value of the fault current is greater than the fault judgment threshold is determined as the fault initial time t0.

[0018] The plotting of the current-voltage characteristic curve in step b can be determined by the following steps:

[0019] Step b1: Starting from the initial fault time t0, collect the phase-to-ground voltages and fault currents of distribution network A, B, and C at every sampling period T, for a total of N samplings, to obtain the three-phase-to-ground voltage sequence U. A (n), U B (n), U C (n) and the fault current sequence I(n), where n represents the nth sampling point;

[0020] Step b2: Using the fault current sequence as the abscissa and the three-phase-to-ground voltage sequence as the ordinate, obtain three sets of coordinates (I(n), U... A (n)), (I(n),U B (n)), (I(n),U C (n)) Place each set of coordinates in a plane rectangular coordinate system, and connect each set of coordinates with a smooth curve. The resulting smooth curve is the three-phase volt-ampere characteristic curve.

[0021] The fault phase selection method in step c can be determined by the following steps:

[0022] Step c1: Multiply the x-coordinate of each point on the current-voltage characteristic curves of phases A, B, and C by its corresponding y-coordinate to obtain the instantaneous power P at each point. δ (n):

[0023] P δ (n)=I(n)U δ (n) Equation 3

[0024] Where δ = A, B, C;

[0025] Step c2: Record the number of points in the current-voltage characteristic curves of phases A, B, and C where the instantaneous power is greater than 0, denoted as Q. A Q B Q C ;

[0026] Step c3: Compare Q A Q B Q C The largest number of these indicates that the phase's current-voltage characteristic curve is generally located in the first and third quadrants, thus identifying this phase as a faulty phase.

[0027] Beneficial effects: This invention proposes a method for real-time tracking of transition resistance and fault phase selection in single-phase ground fault distribution networks. By using the phase-to-ground characteristic curves plotted from the fault current and phase-to-ground voltage of each phase, the method achieves real-time tracking of transition resistance and rapid and accurate fault phase selection after a fault occurs, providing theoretical guidance for subsequent fault handling schemes. This method is not affected by nonlinear transition resistance and parameter asymmetry, and can sensitively initiate faults, effectively avoiding the risks caused by long-term operation of distribution networks with faults. Attached Figure Description

[0028] Figure 1 Flowchart for real-time tracking of transition resistance and fault phase selection in single-phase grounding faults;

[0029] Figure 2 This is a schematic diagram of the simulation system for an example embodiment;

[0030] Figure 3 This is a diagram illustrating the fault-based startup process;

[0031] Figure 4 The three-phase current-voltage characteristic curve;

[0032] Figure 5 This is a real-time tracking graph of the transition resistance. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention proposes a method for real-time tracking of transition resistance and fault phase selection in single-phase grounding faults in distribution networks, such as... Figure 1 As shown, the specific steps include:

[0035] Step a: Construct a single-phase ground fault initiation criterion, collect the zero-sequence voltage of the distribution network in real time, and calculate the fault current in real time. When the absolute value of the fault current at a certain moment is greater than the fault judgment threshold M, it indicates that a single-phase ground fault has occurred in the distribution network, and continue to step b; otherwise, continue to monitor the distribution network.

[0036] Step b: Measure the phase-to-ground voltage of each phase in the distribution network, and plot the volt-ampere characteristic curves of phases A, B, and C with the fault current as the abscissa and the three-phase-to-ground voltage as the ordinate.

[0037] Step c: Determine the fault phase based on the quadrant in which the volt-ampere characteristic curve is located;

[0038] Step d: Calculate the transition resistance R in real time based on the fault phase-to-ground voltage and fault current. E (t), the specific expression is:

[0039]

[0040] Among them, u δ (t) represents the fault-to-ground voltage, δ = A, B, C, i E (t) represents the fault current.

[0041] The single-phase ground fault initiation criterion in step a can be determined by the following steps:

[0042] Step a1: Real-time acquisition of the zero-sequence voltage u0(t) of the distribution network, and substitution of the zero-sequence voltage into the fault current calculation expression to solve for the fault current i in real time. E (t), the specific expression for calculating the fault current is:

[0043]

[0044] Among them, G Σ and C Σ These are the total conductance to ground and the total capacitance to ground of the distribution network, i bd (t) represents the total unbalanced current of the distribution network;

[0045] Step a2: Determine the fault judgment threshold M, and take M = 0.1A. If the absolute value of the fault current at any time is less than the fault judgment threshold M, it indicates that there is no single-phase grounding fault in the distribution network. If the absolute value of the fault current at a certain time is greater than the fault judgment threshold M, it indicates that there is a single-phase grounding fault in the distribution network. The time corresponding to the first time when the absolute value of the fault current is greater than the fault judgment threshold is determined as the fault initial time t0.

[0046] The plotting of the current-voltage characteristic curve in step b can be determined by the following steps:

[0047] Step b1: Starting from the initial fault time t0, collect the phase-to-ground voltages and fault currents of distribution network A, B, and C at every sampling period T, for a total of N samplings, to obtain the three-phase-to-ground voltage sequence U. A (n), U B (n), U C (n) and the fault current sequence I(n), where n represents the nth sampling point;

[0048] Step b2: Using the fault current sequence as the abscissa and the three-phase-to-ground voltage sequence as the ordinate, obtain three sets of coordinates (I(n), U... A (n)), (I(n),U B (n)), (I(n),U C (n)) Place each set of coordinates in a plane rectangular coordinate system, and connect each set of coordinates with a smooth curve. The resulting smooth curve is the three-phase volt-ampere characteristic curve.

[0049] The fault phase selection method in step c can be determined by the following steps:

[0050] Step c1: Multiply the x-coordinate of each point on the current-voltage characteristic curves of phases A, B, and C by its corresponding y-coordinate to obtain the instantaneous power P at each point. δ (n):

[0051] P δ (n)=I(n)U δ (n) Equation 3

[0052] Where δ = A, B, C;

[0053] Step c2: Record the number of points in the current-voltage characteristic curves of phases A, B, and C where the instantaneous power is greater than 0, denoted as Q. A Q B Q C ;

[0054] Step c3: Compare Q A Q B Q CThe largest number of these indicates that the phase's current-voltage characteristic curve is generally located in the first and third quadrants, thus identifying this phase as a faulty phase.

[0055] Example.

[0056] The proposed real-time tracking of transition resistance and fault phase selection method for single-phase ground faults in distribution networks was verified using MATLAB / Simulink simulation. The simulation model is a 10kV medium-voltage distribution network with three feeders, and the topology is as follows: Figure 2 As shown in Table 1, the zero-sequence parameters to ground for each feeder are as follows. The capacitance current of the simulation model is 72.77A, the active current is 1.316A, the asymmetry is 1.75%, and the damping rate is 1.809%.

[0057] Table 1 Zero-sequence ground parameters of each feeder in the distribution network

[0058] Simulation analysis.

[0059] Assume a 3000Ω high-resistance ground fault occurs in phase A of feeder 1 at 0.13s, and a Cassie arc model is connected in series with the grounding resistor. The time constant of the arc column is 0.255ms, and the voltage gradient is 800V. Let the sampling period T = 0.08ms. According to the method of this invention, the zero-sequence voltage of the distribution network is measured in real time, and the fault current is calculated in real time and its absolute value is taken, such as... Figure 3 As shown, before 0.13s, the absolute value of the fault current was always less than the fault initiation criterion of 0.1. At 0.13s, the value first exceeded the fault initiation criterion, therefore, a single-phase ground fault was determined, and the fault time was set at 0.13s. Then, the phase-to-ground voltages of phases A, B, and C in the distribution network were measured, and combined with the fault current, the volt-ampere characteristic curves of phases A, B, and C were plotted, as shown below. Figure 4 As shown in the figure, the characteristic curves reveal that the phase A's volt-ampere characteristic curve is mainly distributed in the first and third quadrants, while the phases B and C's volt-ampere characteristic curves are distributed in all four quadrants. The graph clearly shows that the number of points on the phase A's volt-ampere characteristic curve located in the first and third quadrants is significantly greater than that of the other two phases, allowing direct identification of the faulty phase as phase A. Finally, dividing the phase A's voltage to ground by the fault current yields the real-time calculated value of the transition resistance, as shown below. Figure 5 As shown, the transition resistance fluctuates over time, and the distribution network is in a state of alternating arc extinction and arc ignition.

[0060] The results show that the method proposed in this invention is not affected by the asymmetry of distribution network parameters and the random fluctuation of transition resistance. It can accurately and quickly identify the faulty phase and track the transition resistance in real time, providing theoretical guidance for subsequent fault handling.

[0061] The working principle of this invention.

[0062] Figure 2 In the middle, e a e b e c These are the three-phase power supply potentials, C A C B C C G represents the sum of the distributed capacitances of each of the lines A, B, and C relative to ground. A G B G C G represents the sum of the distributed conductivities of all lines A, B, and C relative to ground. E (t) represents the random conductance of a single-phase ground fault, R E (t) represents the transition resistance. When switch K is closed, it indicates that a single-phase ground fault has occurred in the distribution network.

[0063] Taking a single-phase ground fault in phase A of a distribution network as an example, after the single-phase ground fault occurs, according to Kirchhoff's current law:

[0064]

[0065] in, The sum of these three is denoted as the total unbalanced current i of the system. bd (t).

[0066] In Equation 4, after the system topology is determined, the only unknown quantities are the fault current and the zero-sequence voltage. The zero-sequence voltage can be directly measured; substituting it into Equation 4 yields the instantaneous value of the fault current. Furthermore, the fault current also satisfies:

[0067]

[0068] The fault current equals the fault phase-to-ground voltage divided by the transition resistance. However, in Equation 5, both the fault phase-to-ground voltage and the transition resistance are unknown. Therefore, real-time tracking of the transition resistance requires fault phase selection. Although the transition resistance is time-varying, it is always positive in nature. Thus, the fault current and the fault phase-to-ground voltage always maintain the same sign and have the same zero point. That is, when the fault current is plotted on the x-axis and the fault phase-to-ground voltage is plotted on the y-axis, the volt-ampere characteristic curve always falls on the origin, the first quadrant, and the third quadrant.

[0069] Assume e b (t)+u0(t) and i E If (t) has the same sign, then we can obtain e. b (t)+u0(t) and e a (t)+u0(t) have the same sign, i.e., 2u0(t)-e c (t) is always non-positive or always non-negative. (This is related to 2u0(t)-e) cSince (t) is an alternating quantity, the non-faulty phases do not always share the same sign as the fault current. Therefore, the volt-ampere characteristic curves plotted by the non-faulty phase-to-ground voltage and the fault current will lie in the second and fourth quadrants. After plotting the three-phase volt-ampere characteristic curves, it is only necessary to determine the number of points on the curves located in the first and third quadrants, and identify the phase with the largest number as the faulty phase. After determining the faulty phase, only the transition resistance remains unknown in Equation 5. Dividing the faulty phase-to-ground voltage by the fault current yields the instantaneous value of the transition resistance.

Claims

1. A method for real-time tracking of transition resistance and fault phase selection in a single-phase grounding fault in a distribution network, characterized in that, The fault current is calculated in real time, the volt-ampere characteristic curves between each phase-to-ground voltage and the fault current are plotted, and the fault phase is determined based on the distribution characteristics of the volt-ampere characteristic curves. The transition resistance is tracked in real time. The steps include the following: Step a: Construct a single-phase ground fault initiation criterion, collect the zero-sequence voltage of the distribution network in real time, and calculate the fault current in real time. When the absolute value of the fault current at a certain moment is greater than the fault judgment threshold M, it indicates that a single-phase ground fault has occurred in the distribution network, and continue to step b; otherwise, continue to monitor the distribution network. Step b: Measure the phase-to-ground voltage of each phase in the distribution network, and plot the volt-ampere characteristic curves of phases A, B, and C with the fault current as the abscissa and the three-phase-to-ground voltage as the ordinate. Step c: Determine the fault phase based on the quadrant of the volt-ampere characteristic curve, specifically through the following steps: Step c1: Multiply the x-coordinate of each point on the current-voltage characteristic curves of phases A, B, and C by its corresponding y-coordinate to obtain the instantaneous power at each point. : Formula 3 in, ; Step c2: Record the number of points in the current-voltage characteristic curves of phases A, B, and C where the instantaneous power is greater than 0, denoted as . , , ; Step c3: Comparison , , The largest number of these indicates that the phase's current-voltage characteristic curve is generally located in the first and third quadrants, thus identifying this phase as a faulty phase. Step d: Calculate the transition resistance in real time based on the fault phase-to-ground voltage and fault current. The specific expression is: Formula 1 in, The voltage to ground of the faulty phase. , This is the fault current.

2. The method for real-time tracking of transition resistance and fault phase selection in a distribution network for single-phase grounding faults according to claim 1, characterized in that, The single-phase ground fault initiation criterion in step a can be determined by the following steps: Step a1: Real-time acquisition of zero-sequence voltage in the distribution network The zero-sequence voltage is substituted into the fault current calculation expression to solve the fault current in real time. The specific expression for calculating the fault current is as follows: Formula 2 in, and These are the total ground conductance and total ground capacitance of the distribution network, respectively. This refers to the total unbalanced current in the distribution network. Step a2: Determine the fault judgment threshold M, taking M=0.1A. If the absolute value of the fault current at any given time is always less than the fault judgment threshold M, it indicates that no single-phase grounding fault has occurred in the distribution network. If the absolute value of the fault current at a certain time is greater than the fault judgment threshold M, it indicates that a single-phase grounding fault has occurred in the distribution network. The time corresponding to the first time the absolute value of the fault current exceeds the fault judgment threshold is determined as the fault initial moment. .

3. The method for real-time tracking of transition resistance and fault phase selection in a single-phase grounding fault in a distribution network according to claim 1, characterized in that, The plotting of the current-voltage characteristic curve in step b can be determined by the following steps: Step b1: From the initial moment of the fault Initially, every sampling period T, the phase-to-ground voltages and fault currents of distribution networks A, B, and C are collected, for a total of N samplings, to obtain the three-phase-to-ground voltage sequence. , , and fault current sequence ,in Indicates the first One sampling point; Step b2: Using the fault current sequence as the x-axis and the three-phase-to-ground voltage sequence as the y-axis, obtain three sets of coordinates. , , Each set of coordinates is placed in a Cartesian coordinate system, and a smooth curve is used to connect each set of coordinates. The resulting smooth curve is the three-phase volt-ampere characteristic curve.

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