A method for characterizing single-phase grounding faults in distribution networks taking into account nonlinear arc resistance

Abstract

A method for characterizing single-phase grounding faults in a distribution network that takes into account nonlinear arc resistance includes: constructing a discretized computer simulation model of the arc model; determining fault arc model parameters for the discretized computer simulation model constructed under different conditions based on measured data of arcs generated when a distribution conductor passes through concrete, asphalt pads, gravel patches, or grassy areas when a single-phase grounding fault occurs; inputting the fault arc model parameters into the discretized computer simulation model of the arc model, integrating them with the normal operation model of the distribution network to form a discretized computer simulation model of the distribution network single-phase grounding fault; and performing characterization analysis of the distribution network single-phase grounding fault characteristics including nonlinear arc resistance based on zero-sequence current harmonic extraction and distortion analysis. The present invention implements electromagnetic transient simulation of arc faults occurring on distribution lines on grass, gravel, concrete, asphalt roads, or trees, meeting the needs of arc fault detection for single-phase grounding faults in distribution networks.

Description

Technical Field

[0001] The present invention belongs to the field of power system relay protection, and in particular relates to a method for characterizing single-phase grounding faults in a distribution network taking into account nonlinear arc resistance. Background Art

[0002] Fault line selection methods for low-current grounding distribution networks can be broadly divided into two categories based on the information they utilize. The first is based on external disturbances; the second utilizes the characteristics of electrical quantity changes during single-phase grounding faults. These methods can be further categorized into methods based on the steady-state component of the fault, methods based on the transient component of the fault, and comprehensive methods.

[0003] With the development of power electronics, artificial intelligence, and signal processing, fault line selection in low-current grounded distribution networks has made significant progress in recent years. Before discussing the optimization of fault line selection technology using these methods, a single-phase grounding arc model for distribution networks is constructed to accurately characterize the arc generation, development, and extinction process. This allows for more effective research on the transient process of arc-fault grounding in distribution systems. This foundation allows for the application of signal processing and artificial intelligence technologies in fault line selection and provides fundamental support for the development of fast, adjustable arc suppression compensation devices.

[0004] Currently, scholars have proposed a variety of arc models, which can be broadly categorized as switch arc models and fault arc models. Existing arc models used for fault characteristic analysis fall into two main categories: 1) arc theoretical models based on parameter fitting; and 2) arc numerical simulation models based on operating characteristics. Existing methods provide an important foundation for analyzing the electrical characteristics of non-effectively grounded distribution networks under single-phase-to-ground arc faults. However, these characteristic analyses are often based on a specific type of single-phase arc fault, such as those occurring on grass, gravel, concrete, asphalt roads, or trees. These methods fail to reveal the universal characteristics of arc faults and fall short of the research needs of arc fault detection. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for characterizing single-phase grounding faults in distribution networks taking into account nonlinear arc resistance, construct a universal electromagnetic transient nonlinear arc model, and seamlessly integrate it into a distribution system model containing multiple feeders, revealing the universal arc characteristics of single-phase grounding faults in distribution networks, and by changing the parameter settings in the module program, realizing electromagnetic transient simulation of arc faults occurring in distribution lines on grass, gravel, concrete, asphalt roads or trees, thereby meeting the needs of arc fault detection for single-phase grounding faults in distribution networks.

[0006] A method for characterizing a single-phase grounding fault in a distribution network taking into account nonlinear arc resistance comprises the following steps:

[0007] Step 1: Construct a discretized computer simulation model of the arc model;

[0008] Step 2: Based on the measured data of arc gap voltage and arc current generated when the distribution conductor passes through concrete, asphalt pad, gravel patch, and green grass for single-phase grounding fault, determine the fault arc model parameters of the discretized computer simulation model of the arc model constructed in step 1 under different conditions;

[0009] Step 3: Input the fault arc model parameters determined in step 2 into the discretized computer simulation model of the arc model formed in step 1, and integrate it with the normal operation model of the distribution network to form a discretized computer simulation model of the distribution network single-phase grounding fault. Carry out the characterization analysis of the distribution network single-phase grounding fault characteristics containing nonlinear arc resistance based on zero-sequence current harmonic extraction and distortion analysis.

[0010] Furthermore, the step 1 specifically includes:

[0011] Step 1.1: Construct a discretized computer simulation model of the arc model from the perspective of energy balance; the general mathematical equation of the arc model is:

[0012]

[0013] Where g is the arc conductance per unit length, e is the arc voltage per unit length; p loss is the power dissipated per unit arc length; τ is the time coefficient of the arc; V arc is a voltage variable related to the arc dissipation power; i is the current flowing through the arc;

[0014] Let dt be represented by simulation compensation Δt, and dg be represented by g(t+Δt)-g(t). Then the real-time arc conductance at simulation time t+Δt is obtained by the arc time coefficient τ(t), the current i(t) flowing through the arc, and the arc conductance g(t) at the previous simulation time t. The mathematical expression of the discretized computer simulation model of the arc model is as follows:

[0015]

[0016] Where Δt is the simulation step size, based on which the arc conductance g(t+Δt) at time t+Δt can be obtained from the arc parameters at time t;

[0017] Step 1.2: Build a discretized computer simulation model of the arc model in the power system electromagnetic transient simulation software, convert the discretized simulation mechanism model of the nonlinear arc shown in formula (2) into the integration link and absolute value link in the power system electromagnetic transient simulation software, and realize the power system electromagnetic transient simulation through the TACS subroutine.

[0018] Furthermore, the step 2 specifically includes:

[0019] Step 2.1: Test the ground resistance of the distribution conductor in four conditions: single-phase grounding through concrete, asphalt pad, gravel patch, and grass;

[0020] Based on the ground resistance test results in step 2.1, determine the fault arc model parameters under four conditions.

[0021] Furthermore, the arc fault model parameters include the dissipated power voltage V arc , arc time constant τ=A×e B ×g Variable A and variable B in.

[0022] Furthermore, step 3 specifically includes: first, building discrete computer simulation models of the distribution network's overhead lines, cable lines, transformers, loads, etc., and connecting these discrete computer simulation models to form a normal operation model of the distribution network; then seamlessly embedding the discrete computer simulation model of the arc model established in step 1 into the normal operation model of the distribution network, and inputting the fault arc model parameters determined in step 2 into the discrete computer simulation model of the arc model to realize simulation analysis of single-phase grounding faults in the distribution network.

[0023] Furthermore, the single-phase grounding fault simulation analysis of the distribution network specifically includes:

[0024] Step 3.1: Characterize the single-phase grounding fault characteristics when the neutral point of the distribution network is ungrounded: Simulate and analyze the characteristics of single-phase grounding faults through trees and single-phase grounding faults through gravel / grass / concrete. Then, analyze and extract the harmonics of the zero-sequence current and analyze the distortion rate to extract the characteristics of the single-phase grounding fault in the distribution network.

[0025] Step 3.2: Conduct single-phase grounding arc fault characteristic analysis when the neutral point of the distribution network is grounded through an arc suppression coil: simulate and analyze to obtain the single-phase grounding fault characteristics through trees and single-phase grounding fault characteristics through gravel / grass / concrete respectively; analyze and extract each harmonic of the zero-sequence current and analyze the distortion rate to extract and form the characteristic representation of the single-phase grounding fault of the distribution network.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This paper proposes a method for characterizing single-phase ground faults in distribution networks that takes into account nonlinear arc resistance. A discretized computer simulation model for single-phase ground faults in distribution networks is constructed within general power system electromagnetic transient simulation software. This model describes the reignition and extinction of arcs based on the energy balance of the arc gap. Appropriate simplifications are then applied to infer arc simulation parameters from arc fault experimental data. The fault characterization is then generated based on the available experimental data. Compared to existing methods, the proposed method specifies arc fault parameters for several typical distribution network scenarios: single-phase grounding through trees, grass, gravel, and concrete. The proposed method can simulate the electrical characteristics of distribution networks under different types of ground arc faults, characterizing the characteristics of single-phase ground faults in distribution networks under different nonlinear arc resistances using the harmonics and distortion rate of the zero-sequence current. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural diagram of a digital simulation model of a single-phase grounding fault in a distribution network, which is a discretized computer simulation model including an arc model constructed by the present invention;

[0029] Figure 2 This is a flow chart of arc simulation of single-phase ground fault in distribution network in the present invention;

[0030] Figure 3 A distribution network simulation model diagram;

[0031] Figure 4 Characteristics of grounding faults through trees when the neutral point of the distribution network is not grounded;

[0032] Figure 5 Characteristics of grounding faults through gravel / grass / concrete when the neutral point of the distribution network is not grounded;

[0033] Figure 6 Harmonic analysis of grounding fault waveforms through trees when the neutral point of the distribution network is not grounded;

[0034] Figure 7 Characteristics of the fault when the neutral point of the distribution network is grounded through arc suppression coils and then grounded through trees;

[0035] Figure 8 Fault characteristics of distribution network neutral point grounded through gravel / grass / concrete when grounded through arc suppression coil. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0037] See also Figure 1-8 The embodiment of the present invention provides a method for characterizing a single-phase grounding fault in a distribution network taking into account nonlinear arc resistance, comprising the following steps:

[0038] Step 1: Construct a discretized computer simulation model of the arc model, such as Figure 1 The specific steps of step 1 are as follows:

[0039] Step 1.1: Construct a discretized computer simulation model of the arc model from the perspective of energy balance.

[0040] The general mathematical equation for the arc model is:

[0041]

[0042] In the above formula, g is the arc conductance per unit length, e is the arc voltage per unit length; p loss is the power dissipated per unit arc length; τ is the time coefficient of the arc; V arc is a voltage variable related to the arc dissipation power; i is the current flowing through the arc, which can generally be calculated using the observed arc current and arc conductance when the experimental data dg / dt=0.

[0043] The general mathematical equation (1) of the arc model is a theoretical equation and cannot be implemented using a computer discretization simulation program. Representing dt with the simulation compensation Δt and dg with g(t+Δt)-g(t), the real-time arc conductance at the simulation time t+Δt can be obtained using the arc time coefficient τ(t), the arc current i(t), and the arc conductance g(t) at the previous simulation time t. The mathematical expression of the discretization computer simulation model of the arc model is as follows:

[0044]

[0045] In the above formula, Δt is the simulation step size, based on which the arc conductance g(t+Δt) at time t+Δt can be obtained from the arc parameters at time t.

[0046] Step 1.2: Build a discretized computer simulation model of the arc model in the power system electromagnetic transient simulation software.

[0047] The discretized simulation mechanism model of the nonlinear arc shown in Equation (2) is converted into the integration and absolute value calculation steps in the power system electromagnetic transient simulation software, which mainly relies on the TACS subroutine (Transient Analysis of Control Systems) to realize the power system electromagnetic transient simulation. The control system, device, and phenomenon simulated by TACS are solved separately from the electrical network in the electromagnetic transient simulation software. The output of the electrical network solution is used as the input of TACS in the same time step, but the output of TACS can only be used as the input of the network solution in the next time step. That is, the simulation steps of the electrical network containing TACS are generally as follows: first, assume that TACS does not exist, solve the electrical network from t-△t to t, then use the electrical network monitoring quantity at t-△t as the input of TACS, calculate the output of TACS, and input it into the electrical network at t after a delay of △t, thereby realizing the indirect connection between TACS and the electrical network.

[0048] When solving the arc dynamic equation, the CTR and RES signals are also set for its output. CTR is a control signal. When CTR>0, the integral link will take effect. At this time, it means that the arc is in the arcing period, that is, the CTR signal is used to control the arc duration. At this time, the arc equation solution is used to control the corresponding arc resistance; when CTR<=0, the output of this link is equal to the RES value, which means that the arc is in the arc extinction period. At this time, the arc resistance change rate when the arc is extinguished needs to be set. Based on the integration, absolute value calculation, and control modular program, a discrete computer simulation model of the arc model is constructed, such as Figure 2 shown.

[0049] Step 2: Based on the measured data of arc gap voltage and arc current generated when the distribution conductor passes through concrete, asphalt pad, gravel patch, and green grass for single-phase ground fault, determine the fault arc model parameters of the discretized computer simulation model of the arc model constructed in step 1 under different conditions. Step 2 specifically includes:

[0050] Step 2.1: Test the ground resistance of the distribution conductor in four conditions: single-phase grounding through concrete, asphalt mat, gravel patch, and grass. Based on the arc gap voltage and arc current results from the system test, the following can be calculated:

[0051] 1) For single-phase grounding through grass, the resistance during continuous arcing is approximately 110Ω to 340Ω;

[0052] 2) For single-phase gravel grounding, the resistance during continuous arcing is approximately 100Ω to 190Ω;

[0053] 3) For single-phase grounding via asphalt road or grounding via trees, the resistance during continuous arcing is greater than 10kΩ;

[0054] 4) For single-phase grounding through concrete, the resistance during continuous arcing is approximately 90Ω to 170Ω.

[0055] Step 2.2: In the discretized computer simulation model of the arc model constructed in step 1, the arc time τ and the dissipated power voltage V arc Determines the characteristics of the arc. Where arc time τ=A×e B×g Determined by variables A and B. According to the arc dynamic equation, as V arc As the variable A in the arc time decreases, the arc resistance decreases; as the variable B in the arc time decreases, the arc resistance decreases. Based on the results of step 2.1, the fault arc model parameters under the four conditions are determined, namely, the dissipated power voltage V arc , variables A and B in the arc time constant τ.

[0056] In order to match the four types of single-phase grounding of distribution networks: grounding through grass, grounding through gravel, grounding through trees, and grounding through concrete, four sets of arc parameters are determined by data fitting based on existing experimental results. For a nonlinear grounding arc passing through grass, the dissipated power voltage Varc is taken as 500, and the A and B in the arc time constant τ are taken as 9.0×10^(-7) and 12000, respectively. For a nonlinear grounding arc passing through gravel, the dissipated power voltage Varc is taken as 250, and the A and B in the arc time constant τ are taken as 9.0×10^(-7) and 12000, respectively. For a nonlinear grounding arc passing through trees, the dissipated power voltage Varc is taken as 2520, and the A and B in the arc time constant τ are taken as 5.6×10^(-7) and 400000, respectively. For a nonlinear grounding arc passing through concrete, the dissipated power voltage Varc is taken as 125, and the A and B in the arc time constant τ are taken as 9.0×10^(-7) and 12000, respectively.

[0057] Step 3: Input the fault arc model parameters determined in step 2 into the discretized computer simulation model of the arc model formed in step 1, and integrate it with the normal operation model of the distribution network to form a discretized computer simulation model of the distribution network single-phase grounding fault, and carry out the characterization analysis of the distribution network single-phase grounding fault characteristics containing nonlinear arc resistance based on zero-sequence current harmonic extraction and distortion analysis. Step 3 specifically includes: first, building discrete computer simulation models of the distribution network's overhead lines, cable lines, transformers, loads, etc., and connecting these discrete computer simulation models to form the normal operation model of the distribution network; then, seamlessly embedding the discretized computer simulation model of the arc model established in step 1 into the normal operation model of the distribution network, and inputting the fault arc model parameters Varc and A and B in the arc time constant τ determined in step 2 into the discretized computer simulation model of the arc model to realize the simulation analysis of the single-phase grounding fault of the distribution network. The simulation analysis of the single-phase grounding fault of the distribution network specifically includes:

[0058] Step 3.1: Carry out the characterization of single-phase grounding fault characteristics when the neutral point of the distribution network is not grounded, such as Figure 3 As shown, switch K is open. This model represents a 10kV distribution network feeder system consisting of overhead lines and cables. There are six outgoing lines, of which Line 1 is a hybrid overhead line-cable line consisting of 20km of overhead line and 10km of cable. Lines 2, 3, and 4 are cable lines, and the remaining lines are overhead lines. The transformer neutral point is grounded via an arc suppression coil. The system parameters are as follows:

[0059] 1) Overhead line parameters: r0 = 0.23Ω / km, r1 = 0.096Ω / km; l0 = 3.66mH / km, l1 = 1.22mH / km; c0 = 0.007μF / km, c1 = 0.011μF / km, g0 = 0.066×10 -6 S / km.

[0060] 2) Cable line parameters: r0 = 0.34Ω / km, r1 = 0.11Ω / km; l0 = 1.54mH / km, l1 = 0.52mH / km; c0 = 0.19μF / km, c1 = 0.29μF / km, g0 = 1.79×10 -6 S / km.

[0061] 3) Transformer parameters: Rated voltage ratio U N1 / U N2 =110kV / 10.5kV; rated capacity S N =50MVA; no-load loss P0=35kW; short-circuit loss P k =205kW; short-circuit voltage ratio is 10%.

[0062] 4) Load parameters: Actual system loads vary greatly, and the loads between phases of the same line are also different, making accurate simulation difficult. In the simulation of the embodiment of the present invention, a constant power load is used, with a load of 130kW + j60kW per phase, which is connected to the end of the line through a 630kVA distribution transformer.

[0063] The discretized computer simulation model of the arc model established in step 1 is connected to the fault point. The arc model parameters adopt the fault arc model parameters determined in step 2. The single-phase tree-grounding fault arc voltage is obtained by simulation analysis, such as Figure 4 As shown in the figure; Simulation analysis of single-phase grounding fault arc resistance through gravel / grass / concrete, as shown in the figure Figure 5 Then, the harmonics of the zero-sequence current are analyzed and extracted, and the distortion rate is analyzed to extract the characteristic representation of the single-phase grounding fault of the distribution network; Figure 4 The harmonics of the arc voltage of a single-phase tree-grounding fault are as follows: Figure 6 shown.

[0064] Step 3.2: Carry out single-phase grounding arc fault characteristic analysis when the neutral point of the distribution network is grounded through the arc suppression coil. Simulate and analyze the single-phase grounding fault current through trees, such as Figure 7 As shown; Single-phase ground fault arc voltage through gravel / grass / concrete, such as Figure 8 shown.

[0065] The arc current waveform when the arc resistance is relatively low after the arc suppression coil is grounded shows that after compensation by the arc suppression coil, not only is the single-phase ground fault current compensated to less than 10A during stable arcing, but the transient energy during the arcing phase is also effectively suppressed compared to the arc current waveform in the distribution network with an ungrounded neutral point. In the ungrounded system, during the arcing phase, the instantaneous arc current is very large, reaching 1.7kA, affected by the transient capacitance current of the distribution network. After grounding the arc suppression coil, except for the initial arcing phase, when the transient current value of the ground fault reached 250A, subsequent transient current values ​​are suppressed to less than 100A. After three cycles, the transient value of the ground current is even suppressed to around 20A, showing a significant suppression effect.

[0066] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for characterizing single-phase grounding faults in a distribution network taking into account nonlinear arc resistance, characterized by: The steps include: Step 1: Construct a discretized computer simulation model of the arc model; Step 2: Based on the measured data of arc gap voltage and arc current generated when the distribution conductor passes through concrete, asphalt pad, gravel patch, and green grass for single-phase grounding fault, determine the fault arc model parameters of the discretized computer simulation model of the arc model constructed in step 1 under different conditions; Step 3: Input the fault arc model parameters determined in step 2 into the discretized computer simulation model of the arc model formed in step 1 and integrate it with the normal operation model of the distribution network to form a discretized computer simulation model of the distribution network single-phase grounding fault. Conduct a characterization analysis of the distribution network single-phase grounding fault characteristics containing nonlinear arc resistance based on zero-sequence current harmonic extraction and distortion analysis; The step 1 specifically includes: Step 1.1: Construct a discretized computer simulation model of the arc model from the perspective of energy balance; The general mathematical equation for the arc model is: （1）； Where g is the arc conductance per unit length, e is the arc voltage per unit length; p loss is the power dissipated per unit arc length; τ is the time coefficient of the arc; V arc is a voltage variable related to the arc dissipation power; i is the current flowing through the arc; Compensate dt using simulation Representative, dg use - Representative, then at the simulation time The arc real-time conductance is calculated using the arc time coefficient at the previous step t. , current flowing through the arc and arc conductance It is concluded that the mathematical expression of the discretized computer simulation model of the arc model is as follows: （2）； Where, is the simulation step, based on which the arc parameters at time t are obtained Arc conductance at time ; Step 1.2: Build a discretized computer simulation model of the arc model in the power system electromagnetic transient simulation software, convert the discretized simulation mechanism model of the nonlinear arc shown in formula (2) into the integration link and absolute value link in the power system electromagnetic transient simulation software, and realize the power system electromagnetic transient simulation through the TACS subroutine.

2. The method for characterizing a single-phase grounding fault in a distribution network taking into account nonlinear arc resistance according to claim 1, wherein: The step 2 specifically includes: Step 2.1: Test the ground resistance of the distribution conductor in four conditions: single-phase grounding through concrete, asphalt pad, gravel patch, and grass; Based on the ground resistance test results in step 2.1, determine the fault arc model parameters under four conditions.

3. The method for characterizing a single-phase grounding fault in a distribution network taking into account nonlinear arc resistance according to claim 2, wherein: The arc fault model parameters include dissipated power voltage V arc , arc time constant Variable A and variable B in.

4. The method for characterizing a single-phase grounding fault in a distribution network taking into account nonlinear arc resistance according to claim 1, wherein: The step 3 specifically includes: first, building a discrete computer simulation model of the distribution network's overhead lines, cable lines, transformers, loads, etc., and connecting these discrete computer simulation models to form a normal operating model of the distribution network; then, seamlessly embedding the discrete computer simulation model of the arc model established in step 1 into the normal operating model of the distribution network, and inputting the fault arc model parameters determined in step 2 into the discrete computer simulation model of the arc model to realize simulation analysis of single-phase grounding faults in the distribution network.

5. The method for characterizing a single-phase grounding fault in a distribution network taking into account nonlinear arc resistance according to claim 4, wherein: The simulation analysis of single-phase grounding fault in the distribution network specifically includes: Step 3.1: Characterize the single-phase grounding fault characteristics when the neutral point of the distribution network is ungrounded: Simulate and analyze the characteristics of single-phase grounding faults through trees and single-phase grounding faults through gravel / grass / concrete. Then, analyze and extract the harmonics of the zero-sequence current and analyze the distortion rate to extract the characteristics of the single-phase grounding fault in the distribution network. Step 3.2: Conduct single-phase grounding arc fault characteristic analysis when the neutral point of the distribution network is grounded through an arc suppression coil: simulate and analyze to obtain the single-phase grounding fault characteristics through trees and single-phase grounding fault characteristics through gravel / grass / concrete respectively; analyze and extract each harmonic of the zero-sequence current and analyze the distortion rate to extract and form the characteristic representation of the single-phase grounding fault of the distribution network.

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