A power distribution network grounding and broken line fault detection method based on phase parameter measurement

Abstract

The application discloses a kind of distribution network grounding and broken wire fault detection methods based on phase parameter measurement, actively regulate and control zero sequence voltage, construct asymmetric line three-phase ground distribution capacitance-conductance calculation matrix equation, provide basic data support for in-depth cognition distribution network and fault detection.The fault detection method presented in the application only needs to compare and analyze the change characteristics of phase parameters before and after fault, and can realize grounding fault and broken wire fault detection, fault type judgment and fault information acquisition without complex operation processing on system electrical parameters;Based on the change rule of phase parameters caused by different fault types, the unified detection of distribution network grounding fault and broken wire fault is realized, which overcomes the line selection limitation of traditional fault detection method depending on fault characteristic signal, effectively reduces the fault detection cost and maintenance difficulty.

Description

Technical Field

[0001] This invention relates to the field of power distribution network fault detection technology, specifically a method for detecting grounding and open circuit faults in power distribution networks based on phase parameter measurement. Background Technology

[0002] In my country, low- and medium-voltage distribution networks generally operate using low-current grounding. When a single-phase ground fault occurs, the line voltage remains symmetrical, and the fault current is weak, allowing the system to operate energized for 1-2 hours. However, if the fault is not handled promptly, it may damage the weak insulation layer of the line, leading to multiple ground faults. Arcing grounding can also cause overvoltage in the entire system, damaging equipment. Besides single-phase ground faults, open-circuit faults caused by lightning strikes and other factors are also common fault types in distribution networks. These open-circuit faults are diverse in type and manifestation, easily triggering fires and causing large-scale power outages and other serious accidents. Therefore, it is necessary to conduct in-depth research on detection methods for ground faults and open-circuit faults in distribution lines to achieve reliable line and phase selection.

[0003] The phase parameters of a power distribution line are the smallest basic units constituting a zero-sequence circuit, directly reflecting the state change characteristics of the zero-sequence circuit. Power distribution networks have numerous types of faults, and corresponding fault detection methods are also diverse, but these are often only effective for specific fault types and difficult to apply broadly to all types. Faults such as grounding and open circuits alter the operating state of the zero-sequence circuit, most directly manifested in changes in the natural parameters of the faulty phase distribution: in grounding faults, only the conductance to ground of the faulty phase changes, while in open circuit faults, both the capacitance to ground and the conductance to ground change. Therefore, line phase parameters are the most direct and fundamental fault characteristics that can be used to identify and detect various types of faults.

[0004] A search of existing technical fields revealed Chinese patent application number 202111492670.6, authorization announcement number CN 114113914 A, entitled "A Method for Detecting Single-Phase Ground Faults in Distribution Networks Based on Zero-Sequence Impedance Comparison." This patent measures the zero-sequence admittance of the line based on the changes in zero-sequence voltage and current before and after the fault. However, this patent cannot achieve a high-precision measurement level of single-phase parameters of the line. Another Chinese patent application number is 202110872750.8, authorization announcement number CN 113484692 B, entitled "A Method for Detecting Ground Faults in Distribution Networks Based on Zero-Sequence Current Analysis." This patent achieves fault line selection by performing wavelet decomposition on the three-phase zero-sequence currents after the fault. However, this patent requires complex computational processing of the fault characteristic signal of the three-phase zero-sequence current, making it difficult to quickly and accurately identify the faulty line directly based on the fundamental nature of the fault. Summary of the Invention

[0005] Technical Problem: The technical problem to be solved by this invention is to provide a method for detecting grounding and open circuit faults in distribution networks based on phase parameter measurement. By constructing a matrix equation to calculate the phase parameters of the faulty line, the method solves for the faulty phase parameters and the grounding fault resistance. By comparing the dynamic changes of each phase parameter laterally, the method can simultaneously identify the fault type, select the faulty line and phase, and other detection processes, which significantly reduces the fault detection time and improves the detection efficiency.

[0006] Technical Solution: To solve the above technical problems, this invention proposes a method for detecting grounding and open-circuit faults in distribution networks based on phase parameter measurement. This method includes the following steps:

[0007] Step a: When the distribution network is operating normally, let n be the total number of transmission lines in the distribution network. i For the line under test ( i =1,2,3…n), actively regulate the zero-sequence voltage of the system (adjust the neutral point impedance to ground or to ground), and denote the zero-sequence voltages before and after regulation as follows: The zero-sequence currents of the line before and after regulation are respectively ; calculate the circuit using Equations 1 and 2 respectively. i Earth parameters Line asymmetry vector and :

[0008] Formula 1

[0009] Formula 2

[0010] In the formula, The lines are respectively i Three-phase ground parameters; and The first i The three-phase equivalent capacitance to ground of the line, and The first i The three-phase-to-ground equivalent conductance of the line; A and B are the line parameters respectively. The imaginary and real parts; For phase transformation operators, C and D are the line asymmetry vectors and... The imaginary and real parts;

[0011] Step b: According to Equations 1 and 2, the equations for the sum of the phase capacitances and the sum of the insulation conductances of the line can be obtained:

[0012] Formula 3

[0013] Formula 4

[0014] Step c: The linear relationship between the phase-to-ground insulation conductance and the distributed capacitance to ground of each phase of the distribution network line is as follows:

[0015] Formula 5

[0016] In the formula, For the line i The leakage current constant;

[0017] Step d: Based on equations 3 and 5, the specific value of the line leakage current constant can be calculated:

[0018] Formula 6

[0019] Step e: Considering that the three-phase ground capacitance and insulation conductance of the distribution network line always satisfy equations 1, 2, and 5, a calculation matrix equation for the three-phase ground capacitance and insulation conductance of the line can be constructed. Solving the equation will allow you to calculate the line capacitance and insulation conductance. i Phase parameters under normal conditions:

[0020] Formula 7

[0021] Step f: Monitor the system zero-sequence voltage in real time. If the zero-sequence voltage increment exceeds 3.5% of the nominal phase voltage, a system fault is determined; otherwise, return to step a. Regardless of whether the system experiences a single-phase ground fault or a single-phase open-circuit fault, the three-phase-to-ground capacitance after the line fault can be assumed to be... The three-phase ground conductivity is , For the ground fault conductance, Equation 8 shows the relationship between the phase-to-ground capacitance and phase-to-ground conductance of each phase of the faulted line. By adjusting the zero-sequence voltage of the fault, the parameters of the faulted line and the asymmetric vector sum can be calculated using Equations 9 and 10:

[0022] Formula 8

[0023] Formula 9

[0024] Formula 10

[0025] Step g: Based on the data obtained in step f, construct the phase parameter calculation matrix equation for the faulty line:

[0026] Formula 11

[0027] Step h: Based on the line phase parameters under normal conditions in step e, and the fault line phase parameters and ground conductance obtained in step g, the phase-to-ground capacitance and conductance values ​​of each phase are compared laterally to achieve distribution network fault detection and fault type judgment;

[0028] Furthermore, the distribution network fault detection and fault type determination in step h are as follows:

[0029] Step h-1: If the capacitance is equal and the conductance is not equal in each phase before and after the fault, then the phase in which the conductance changes is the faulty phase, and the line in which it is located is determined to be the faulty line, and the specific fault type is single-phase ground fault.

[0030] If the capacitance and conductance are not equal before and after the fault, then a single-phase open circuit fault has occurred in the line. The phase in which the phase parameters change is the faulty phase. Step h-2 is executed to locate the open circuit fault, and step h-3 is executed to determine the specific type of open circuit fault.

[0031] Step h-2: Locate the open circuit fault by comparing the capacitance ratio of the faulty component to ground before and after the system fault.

[0032] Formula 12

[0033] In the formula, The fault coefficient characterizes the location where the fault occurs.

[0034] Step h-3: Based on the grounding conductance value obtained in step e, further determine the specific type of open circuit fault:

[0035] like This further confirms that a line breakage or ungrounded fault has occurred.

[0036] like If so, it can be further determined that a single-phase open circuit has occurred and the power supply side has a ground fault.

[0037] Beneficial Effects: This invention proposes a method for detecting grounding and open-circuit faults in distribution networks based on phase parameter measurement. First, during normal operation of the distribution network, the system zero-sequence voltage and the zero-sequence current of each line are recorded. The system zero-sequence voltage is actively adjusted to calculate the three-phase-to-ground distribution parameters of each line. Then, if a fault occurs in the system, the system fault zero-sequence voltage is adjusted to calculate the three-phase-to-ground distribution parameters of each line after the fault. Subsequently, the phase-to-ground capacitance and conductance of each phase are compared laterally to achieve fault line and phase selection and fault type determination. This method has the following advantages:

[0038] 1. By constructing the capacitance-conductance calculation matrix equation for each phase of the line, independent measurement of parameters of any phase of any line is realized, overcoming the technical bottleneck that the accuracy of existing distribution network parameter measurement is limited to the overall level.

[0039] 2. Based on the phase parameter change characteristics caused by different fault types, a fault detection criterion is constructed. Compared with traditional fault detection methods, there is no need to perform complex calculations on the system fault characteristic signals. The faulty line and faulty phase can be accurately and quickly identified directly based on the fundamental nature of the fault.

[0040] 3. It can comprehensively and uniformly detect grounding faults and open-circuit faults in the distribution network, and simultaneously realize the detection process such as fault type judgment, fault line and phase selection, and grounding fault resistance, effectively reducing detection costs and maintenance difficulty. Attached Figure Description

[0041] Figure 1 Equivalent operational circuit diagram of zero-sequence loop fault in distribution network

[0042] Figure 2 Flowchart of distribution network fault detection based on phase parameter measurement

[0043] Figure 3 Simulation system topology diagram

[0044] Figure 4 Zero-sequence current fault waveforms under different grounding resistances Specific implementation methods

[0045] To make the technical means, creative features, technical solutions, advantages and effects of the present invention clearer, detailed implementation methods and specific operation processes are given below with reference to the accompanying drawings in the embodiments of the present invention. Figure 1 This is the equivalent circuit diagram for a zero-sequence loop fault in a distribution network. The network contains n feeders, connected via switches. and Grounding fault types in the switching control system; the implementation of this invention can directly obtain the zero-sequence voltage signal of the power grid bus and obtain the actual zero-sequence current signal of the feeder from the zero-sequence current transformer of each feeder. The following is based on… Figure 2 The detailed implementation steps are as follows.

[0046] Step 1: When the distribution network is operating normally, let n be the total number of transmission lines in the distribution network. i ( i Zero-sequence currents of (e.g., 1, 2, 3…n) and asymmetric vectors The expression is:

[0047] Formula 1

[0048] Formula 2

[0049] In the formula, These are the electromotive forces of the three-phase power supply in the power distribution network; This is the zero-sequence voltage during normal system operation. , , The lines are respectively i Three-phase ground parameters; and These are the three-phase-to-ground equivalent capacitances of the i-th line. and The first i The three-phase ground equivalent conductance of the line; For phase transformation operators, ;

[0050] Step 2: Actively regulate the system zero-sequence voltage (adjust the neutral point's impedance to ground or the power supply to ground), and record the regulated zero-sequence voltage as... The zero-sequence current of the line after regulation is The circuit is calculated using Equations 3 and 4 respectively. i Earth parameters Line asymmetry vector and :

[0051] Formula 3

[0052] Formula 4

[0053] In the formula, A and B are the line-to-ground parameters, respectively. The imaginary and real parts; C and D are the line asymmetry vectors and respectively. The imaginary and real parts;

[0054] Step 3: Based on equations 2, 3, and 4, the equations for the sum of the phase capacitances and the sum of the insulation conductances of the line can be obtained:

[0055] Formula 5

[0056] Formula 6

[0057] Step 4: The formula for calculating capacitor leakage current is:

[0058] Formula 7

[0059] In the formula, This is the capacitor leakage current; K Leakage current constant ; C This is the nominal capacitance of the capacitor; The DC voltage across the capacitor;

[0060] Step 5: The ratio of the DC voltage applied to the capacitor to the resulting leakage current is called the insulation resistance of the capacitor. Therefore, the definition of insulation resistance is as follows:

[0061] Formula 8

[0062] In the formula, Insulation resistance;

[0063] Step 6: The insulation conductivity can be obtained according to Equations 7 and 8. G With capacitor C Relationship:

[0064] Formula 9

[0065] Step 7: The capacitor always maintains the inherent insulation characteristics shown in Equation 9, and its insulation characteristics remain unchanged regardless of the type of voltage applied (DC or AC); therefore, the linear relationship between the phase-to-ground insulation conductance and the phase-to-ground distributed capacitance in the power distribution line is as follows:

[0066] Formula 10

[0067] In the formula, For the line i The leakage current constant;

[0068] Step 8: Based on Equations 5 and 10, the specific value of the line leakage current constant can be calculated:

[0069] Formula 11

[0070] Step 9: Considering that the three-phase-to-ground capacitance and insulation conductance of the distribution network line always satisfy equations 5, 6, and 10, a calculation matrix equation for the three-phase-to-ground capacitance and insulation conductance of the line can be constructed. Solving the equation will allow you to calculate the line's capacitance and insulation conductance. i Phase parameters under normal conditions:

[0071] Formula 12

[0072] Step 10: When a ground fault or open circuit fault occurs in the distribution network, the essence is only the corresponding change in the insulation parameters of the faulty phase in the faulty line, but the specific parameter changes are different:

[0073] If a single-phase ground fault occurs in the system, only the faulty phase... grounding conductivity The change occurs, and its magnitude is equal to the sum of the conductance and transition resistance of the faulty phase, while the insulation parameters of the non-faulty phase remain unchanged:

[0074] Formula 13

[0075] In the formula: For ground fault conductance;

[0076] Single-phase open-circuit faults include single-phase open-circuit without grounding faults and single-phase open-circuit power supply side grounding faults. The parameters of the faulty phase will change with the location of the fault; therefore, a fault coefficient needs to be set. To characterize the location of the fault; if a single-phase open-circuit ungrounded fault occurs in the line, the fault relative to the ground distributed capacitance is... Insulation conductivity to ground The linear relationship remains unchanged and is always equal to the leakage current constant. The parameters of the fault phase change as follows:

[0077] Formula 14

[0078] If a single-phase open-circuit ground fault occurs on the power supply side of the line, the distributed capacitance relative to the ground of the fault is... Insulation conductivity to ground The parameters change as follows:

[0079] Formula 15

[0080] In the formula: For power supply side ground fault conductance;

[0081] Step 11: Based on the parameter change patterns of the fault phases after grounding and open-circuit faults in Step 10, it can be assumed that the three-phase-to-ground capacitance after a line fault is... The three-phase ground conductivity is , The conductance of the ground fault is given; if the faulty phase is phase C, the relationship between the phase-to-ground capacitance and the conductance to ground of each phase of the faulty line is shown in Equation 16:

[0082] Formula 16

[0083] Step 12: Monitor the system zero-sequence voltage in real time. If the zero-sequence voltage increment exceeds 3.5% of the nominal phase voltage, a system fault is determined. Adjust the fault zero-sequence voltage. The ground parameters and asymmetry vector sum of the faulty line can be calculated using equations 17 and 18.

[0084] Formula 17

[0085] Formula 18

[0086] Step 13: Based on the data obtained in Steps 11 and 12, construct the line phase parameter calculation matrix equation after the system fault:

[0087] Formula 19

[0088] Step 14: Based on the line phase parameters under normal conditions obtained in Step 9, and the line phase parameters and ground conductance obtained in Step 13 after the fault, compare the phase-to-ground capacitance and conductance of each line in the distribution network laterally to achieve distribution network fault detection and fault type determination.

[0089] If the capacitance is equal but the conductance is not equal in each phase before and after the fault, then the phase in which the conductance changes is the faulty phase, and the line in which it is located is determined to be a faulty line, and the specific fault type is a single-phase ground fault.

[0090] If the capacitance and conductance are not equal before and after the fault, then a single-phase open circuit fault has occurred in the line. The phase in which the phase parameters change is the faulty phase. Step 15 is executed to locate the open circuit fault, and step 16 is executed to determine the specific type of open circuit fault.

[0091] Step 15: Locate the open circuit fault by comparing the capacitance ratio of the faulty phase to ground before and after the system fault.

[0092] Formula 20

[0093] In the formula, The fault coefficient represents the location where the fault occurs.

[0094] Step 16: Based on the ground fault conductance value obtained in Step 13, further determine the specific type of open circuit fault:

[0095] like If so, it can be further determined that the line has a broken wire and is not grounded;

[0096] like If so, it can be further determined that a single-phase open circuit has occurred and the power supply side has a ground fault.

[0097] The above steps were verified using MATLAB / Simulink simulation to validate the distribution network grounding and open-circuit fault detection method based on phase parameter tracking measurement. Figure 3 To simulate the system topology, the simulation system is a 10kV distribution network with three feeders. The specific phase parameter settings are shown in Table 1.

[0098] Table 1. Phase parameter settings for simulated power distribution lines

[0099]

[0100] To verify the application of this invention to the phase parameters of various lines in the distribution network To ensure the accuracy of the measurement, during normal system operation, the zero-sequence voltage of the system is actively regulated by injecting fundamental current into the neutral point of the system. The zero-sequence voltage of the system and the zero-sequence current of the line before and after the zero-sequence voltage regulation are measured and recorded. The three-phase-to-ground distributed parameters of each line of the distribution network are calculated by substituting into Equation 12. The phase parameter measurement results are shown in Table 2. Error analysis is performed on the calculation results and the actual simulation values.

[0101] Table 2 Simulation results of phase parameters for power distribution lines

[0102]

[0103] As shown in Table 2, the maximum measurement error of each phase-to-ground parameter of the distribution line is only 0.001. Therefore, the present invention can accurately and independently measure the distributed capacitance to ground and the insulation conductance to ground of any phase in any line of the distribution network, realizing the measurement of the smallest component unit of the zero-sequence circuit of the distribution network.

[0104] To verify the accuracy of this invention in detecting single-phase ground faults in a system, single-phase ground faults under different fault conditions were randomly set up. The zero-sequence voltage of the system after the fault was adjusted, and the zero-sequence voltage and line zero-sequence current of the system before and after adjustment were collected. Substituting these data into Equation 19, the three-phase-to-ground distributed parameters and ground fault resistance of each line after the system fault were calculated. Since the ground fault does not change the phase-to-ground distributed capacitance of each line in the system, it is only necessary to compare the phase-to-ground insulation conductance of each line before and after the system fault. The lines and phases with unequal conductances to ground are the faulty lines and phases. The ground fault detection results based on phase parameter measurements under different fault resistances are shown in Table 3. The zero-sequence current fault waveforms of each line are shown in Table 3. Figure 4 As shown.

[0105] Table 3. Single-phase ground fault detection results based on phase parameter measurements.

[0106]

[0107] As shown in Table 3, regardless of the change in fault resistance, the insulation resistance of the faulty phase is significantly different from that under normal conditions. This significant change in insulation resistance not only provides a reliable basis for quickly and accurately identifying faulty lines and phases, but also greatly improves the sensitivity of high-resistance grounding fault detection.

[0108] To verify the accuracy of this invention in detecting system open-circuit grounding faults, single-phase open-circuit faults at different fault locations were randomly set in the system. The zero-sequence voltage of the system after the fault was adjusted, and the zero-sequence voltage and line zero-sequence current of the system before and after adjustment were collected. The three-phase-to-ground distributed parameters and grounding fault resistance of each line after the system fault were calculated by substituting them into Equation 19. Since the open-circuit fault does not change the inherent proportional relationship between the phase-to-ground distributed capacitance and the insulation conductance to ground of each line in the system, that is, their changing trends are interrelated, when locating the fault, it is only necessary to compare the phase-to-ground distributed capacitance or insulation conductance to ground of each line before and after the system fault. The line and phase where the phase residual number is not equal are the faulty line and faulty phase. The open-circuit fault detection results based on phase parameter tracking measurement under different fault coefficients are shown in Tables 4 and 5.

[0109] Table 4. Detection of single-phase open-circuit and ungrounded faults based on phase parameter measurements.

[0110]

[0111] Table 5. Ground fault detection on the power supply side of a single-phase open circuit based on phase parameter measurement.

[0112]

[0113] As shown in Tables 4 and 5, regardless of whether the system experiences a single-phase open-circuit fault or a single-phase open-circuit power-side ground fault, and regardless of how the fault point changes, the phase parameters of the faulty phase are significantly different from those under normal conditions. This enables rapid and accurate identification of the faulty line and phase. Therefore, this invention only needs to compare whether the phase parameters have changed before and after the fault to achieve efficient integration of the detection processes for grounding faults and open-circuit faults in the distribution network, fault type judgment, and grounding resistance calculation. This significantly reduces fault detection time and improves detection efficiency.

Claims

1. A method for detecting grounding and open-circuit faults in distribution networks based on phase parameter measurement, characterized in that, The steps include the following: Step a: When the distribution network is operating normally, let n be the total number of transmission lines in the distribution network. i For the circuit under test, i =1,2,3…n, the zero-sequence voltage of the actively controlled system is denoted as , and the zero-sequence voltages before and after control are respectively . The zero-sequence currents of the line before and after regulation are respectively ; Calculate the circuit using Equations 1 and 2 respectively. i Earth parameters Line asymmetry vector and : Formula 1 Formula 2 In the formula, The lines are respectively i Three-phase ground parameters; The first i The three-phase equivalent capacitance to ground of the line, and are respectively the first i The three-phase-to-ground equivalent conductance of the line; A and B are the line parameters respectively. The imaginary and real parts; For phase transformation operators, C and D are the line asymmetry vectors and... The imaginary and real parts; Step b: According to Equations 1 and 2, the equations for the sum of the phase capacitances and the sum of the insulation conductances of the line can be obtained: Formula 3 Formula 4 Step c: The linear relationship between the phase-to-ground insulation conductance and the distributed capacitance to ground of each phase of the distribution network line is as follows: Formula 5 In the formula, For the line i The leakage current constant; Step d: Based on equations 3 and 5, the specific value of the line leakage current constant can be calculated: Formula 6 Step e: Considering that the three-phase ground capacitance and insulation conductance of the distribution network line always satisfy equations 1, 2, and 5, a calculation matrix equation for the three-phase ground capacitance and insulation conductance of the line can be constructed. Solving the equation will allow you to calculate the line capacitance and insulation conductance. i Phase parameters under normal conditions: Formula 7 Step f: Monitor the system zero-sequence voltage in real time. If the zero-sequence voltage increment exceeds 3.5% of the nominal phase voltage, a system fault is determined; otherwise, return to step a. Regardless of whether the system experiences a single-phase ground fault or a single-phase open-circuit fault, the three-phase-to-ground capacitance after the line fault can be assumed to be... The three-phase ground conductivity is , For the ground fault conductance, Equation 8 shows the relationship between the phase-to-ground capacitance and phase-to-ground conductance of each phase of the faulted line. By adjusting the zero-sequence voltage of the fault, the parameters of the faulted line and the asymmetric vector sum can be calculated using Equations 9 and 10: Formula 8 Formula 9 Formula 10 Step g: Based on the data obtained in step f, construct the phase parameter calculation matrix equation for the faulty line: Formula 11 Step h: Based on the line phase parameters under normal conditions in step e, and the fault line phase parameters and ground conductance obtained in step g, the phase-to-ground capacitance and ground conductance values ​​of each phase are compared laterally to realize the fault detection and fault type judgment of the distribution network.

2. The method for detecting grounding and open-circuit faults in a distribution network based on phase parameter measurement according to claim 1, characterized in that, The specific steps for distribution network fault detection and fault type determination in step h are as follows: Step h-1: If the capacitance is equal and the conductance is not equal in each phase before and after the fault, then the phase in which the conductance changes is the faulty phase, and the line in which it is located is determined to be the faulty line, and the specific fault type is single-phase ground fault. If the capacitance and conductance are not equal before and after the fault, then a single-phase open circuit fault has occurred in the line. The phase in which the phase parameters change is the faulty phase. Step h-2 is executed to locate the open circuit fault, and step h-3 is executed to determine the specific type of open circuit fault. Step h-2: Locate the open circuit fault by comparing the capacitance ratio of the faulty component to ground before and after the system fault. Formula 12 In the formula, The fault coefficient characterizes the location where the fault occurs. Step h-3: Based on the grounding conductance value obtained in step e, further determine the specific type of open circuit fault: like This further confirms that a line breakage or ungrounded fault has occurred. like If so, it can be further determined that a single-phase open circuit has occurred and the power supply side has a ground fault.

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