A method and system for locating single-phase grounding faults in distribution networks based on the impedance method of zero-sequence components.

Abstract

A method and system for locating single-phase grounding faults in distribution networks based on zero-sequence component impedance is disclosed. This method utilizes the zero-sequence parameters of the upstream section of the main line connected to the beginning of the main line segment and the zero-sequence parameters of the downstream section of the main line connected to the end of the main line segment to obtain the zero-sequence voltage equation at the fault point of the main line. The true root of the zero-sequence voltage equation at the fault point of the main line is determined using the length of the main line segment, i.e., the fault distance of the main line. When the fault distance of the main line is equal to 0 or the length of the main line segment, the zero-sequence voltage equation at the fault point of the branch line is obtained using the zero-sequence parameters of the branch line segment connected to the beginning or end of the main line segment and the zero-sequence parameters of the main line segment. The true root of the zero-sequence voltage equation at the fault point of the branch line is determined using the length of the branch line segment, i.e., the fault distance of the branch line. This invention maintains high accuracy under various distribution network structures such as mixed lines and multi-branch lines, and the ranging accuracy is not affected by grounding resistance and fault phase angle.

Description

Technical Field

[0001] This invention belongs to the field of power system technology, and more specifically, relates to a method and system for locating single-phase grounding faults in distribution networks based on the impedance method using zero-sequence components. Background Technology

[0002] In my country, the vast majority of medium-voltage distribution networks use either ungrounded neutral points or grounded via arc suppression coils. Statistics show that single-phase grounding faults account for over 80% of all faults. Therefore, accurate fault location is crucial for improving the reliability of distribution network power supply. When a single-phase grounding fault occurs in a distribution network, the resulting fault current is small and the fault characteristics are weak, making fault location extremely difficult. While fault location technology for transmission networks is relatively mature, and many fault location methods have been proposed for distribution networks, due to the complex structure of distribution networks and the high cost of line construction, current practical engineering applications of distribution network fault location still largely focus on fault line selection and fault section location.

[0003] In existing technologies, fault location techniques for distribution networks can be broadly categorized into two types based on their principles: the traveling wave method and the impedance method. The traveling wave method calculates the fault distance by recording the time difference between the arrival of the traveling wave generated by the fault and the busbar. However, the traveling wave method is significantly affected by the phase angle at the time of the fault; when the phase angle is small, the traveling wave signal is weak, increasing the distance measurement error. Furthermore, distribution networks typically have short lines, numerous branches, and complex topologies, making the installation of high-sampling-rate traveling wave ranging devices costly. Therefore, the traveling wave method has not been widely adopted in distribution networks. The impedance method calculates the impedance of the fault circuit based on the measured voltage and current during a fault. Line impedance is proportional to line length, thus determining the distance from the ranging device to the fault point. Depending on the location of the required electrical quantity measurement, the impedance method is further divided into single-ended and double-ended methods. The single-ended impedance method requires only information from one side, has low hardware requirements, and is easy to implement. However, it is difficult to avoid the influence of grounding resistance and the power supply at the measuring end, inevitably introducing errors and resulting in low ranging accuracy. The methods and systems for single-phase grounding fault location based on distribution automation systems (CN105334430B), the method and system for small-current grounding fault location in ungrounded distribution network systems (CN113484680A), and the existing technology CN113507116B all propose to locate faults based on the zero-sequence voltage and zero-sequence current at both ends of the distribution line. However, they have not conducted in-depth research on the solution results of the zero-sequence voltage equation. Especially when the distribution network adopts a radial topology, it is easy to mislocate faults on branch lines to the main line, which will affect the safe and stable operation of the distribution network.

[0004] In summary, there is an urgent need to propose an impedance-based fault location technology for distribution networks that is applicable to various distribution network structures, has high ranging accuracy, and is unaffected by grounding resistance and fault phase angle. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method and system for locating single-phase grounding faults in distribution networks based on the impedance method using zero-sequence components. The method acquires steady-state zero-sequence signals after a single-phase grounding fault occurs by using PMU devices at the busbar and the end of the line. It proposes an impedance-based location technology based on zero-sequence components, which is applicable to radial distribution networks with ungrounded neutral points or grounded via arc suppression coils.

[0006] The present invention adopts the following technical solution.

[0007] This invention proposes a single-phase grounding fault location method for distribution networks based on zero-sequence component impedance. The distribution line is divided into multiple main line sections and branch line sections. For any main line section, the zero-sequence voltage equation at the fault point is obtained using the zero-sequence parameters of the upstream section of the main line connected to the beginning of the main line section and the downstream section of the main line connected to the end of the main line section. The true root of the zero-sequence voltage equation at the fault point of the main line is determined using the length of the main line section, i.e., the fault distance of the main line. When the fault distance of the main line is equal to 0 or the length of the main line section, the zero-sequence voltage equation at the fault point of the branch line is obtained using the zero-sequence parameters of the branch line sections connected to the beginning or end of the main line section and the zero-sequence parameters of the main line section. The true root of the zero-sequence voltage equation at the fault point of the branch line is determined using the length of the branch line section, i.e., the fault distance of the branch line.

[0008] The impedance-based method for locating single-phase ground faults in distribution networks, based on zero-sequence components, includes the following steps:

[0009] Step 1: Divide the power distribution line into multiple main line sections and multiple branch line sections; obtain the line length of each section of the power distribution line, the power distribution network topology, and the installation location of the PMU (Phasor Measurement Unit);

[0010] Step 2: After a single-phase ground fault is determined to have occurred, the zero-sequence parameters of the line are identified using PMU measurement data. The time-domain signals of the collected zero-sequence voltage and zero-sequence current are subjected to fast Fourier transform to obtain the power frequency components of the zero-sequence voltage and zero-sequence current of each section of the line.

[0011] Step 3: Determine the zero-sequence network after the fault based on the distribution network topology; for any main line section, obtain the zero-sequence voltage equation of the fault point of the main line using the zero-sequence parameters of the upstream section of the main line connected to the beginning of the main line section and the zero-sequence parameters of the downstream section of the main line connected to the end of the main line section; determine the true root of the zero-sequence voltage equation of the fault point of the main line using the length of the main line section, i.e., the fault distance of the main line.

[0012] When the fault distance of the main line is equal to 0 or the length of the main line section, the zero-sequence voltage equation of the branch line fault point is obtained by using the zero-sequence parameters of the branch line section connected to the beginning or end of the main line section and the zero-sequence parameters of the main line section. The true root of the zero-sequence voltage equation of the branch line fault point is determined by using the length of the branch line section, that is, the fault distance of the branch line.

[0013] Preferably, in step 1, the trunk line section includes: the section from the beginning of the trunk line to the beginning of the branch line, the section from the beginning of the branch line to the fault point, and the section from the end of the trunk line to the beginning of the branch line; the branch line section includes: the section from the beginning of the branch line to the end of the branch line.

[0014] Preferably, the PMU installation locations include: the beginning of the main line, the end of the main line, and the end of the branch line.

[0015] Preferably, during normal operation, the PMU monitors the three-phase voltage and current at the beginning and end of the main line and the end of each branch line;

[0016] After determining that a single-phase ground fault has occurred, the PMU acquires the zero-sequence voltage and zero-sequence current at the beginning of the main line, the zero-sequence voltage at the end of the main line, and the zero-sequence voltage at the end of the branch line.

[0017] Preferably, step 2 includes:

[0018] Step 2.1, set the zero-sequence voltage start-up value;

[0019] Step 2.2: Measure the three-phase phase voltages using a PMU and calculate the composite line voltage and zero-sequence voltage;

[0020] Step 2.3: When the line phase voltage changes, if the amplitude and phase difference of the three line voltages remain unchanged and the zero-sequence voltage value exceeds the zero-sequence voltage starting value, then a single-phase ground fault is determined to have occurred.

[0021] Step 2.4: Initiate single-phase ground fault location. Use the PMU to sample the steady-state zero-sequence voltage and steady-state zero-sequence current at the beginning of the main line, and the steady-state zero-sequence voltage at the end of the main line and the beginning of the branch line. The sampling frequency is 5kHz.

[0022] Step 2.5: Apply Fast Fourier Transform to the time-domain signals of steady-state zero-sequence voltage and steady-state zero-sequence current within 4 sampling periods after a 0.5s delay from the time of the fault occurrence to filter out higher harmonic components and obtain the power frequency components of steady-state zero-sequence voltage and zero-sequence current.

[0023] Preferably, in step 3, each segment in the post-fault zero-sequence network is a lumped-parameter π-type equivalent circuit.

[0024] Preferably, in step 3, determining the fault distance of the main line includes:

[0025] Step 3.1.1: For any main line section, using the power frequency components of the zero-sequence voltage and zero-sequence current of the upstream section of the main line connected to the beginning of the main line section, based on the zero-sequence network after each section fault, the first zero-sequence voltage function of the main line fault point is obtained.

[0026] Step 3.1.2: Utilize the zero-sequence voltage of the downstream section of the main line connected to the end of the main line section and calculate the power frequency component of the zero-sequence current. Based on the zero-sequence network after each section fault, obtain the second zero-sequence voltage function of the fault point of the main line.

[0027] Step 3.1.3: Based on the fact that the first zero-sequence voltage function and the second zero-sequence voltage function of the fault point on the main line are equal, the zero-sequence voltage equation of the fault point on the main line is obtained.

[0028] Step 3.1.4: Solve the zero-sequence voltage equation at the fault point of the main line, and use the length of the main line section to eliminate the false roots of the equation, so that the true root that meets the discrimination threshold is taken as the fault distance of the main line.

[0029] Preferably, in step 3.1.4, when the real and imaginary parts of the true root of the zero-sequence voltage equation at the fault point of the main line satisfy the discrimination thresholds shown in the following relationship, the true root is the fault distance of the main line:

[0030]

[0031] In the formula,

[0032] L is the length of the main trunk line section.

[0033] ε represents the maximum permissible relative error of the ranging result, with a value not less than 5%.

[0034] l is the fault distance of the main line, which is the distance from the fault point to the beginning of the main line section.

[0035] Preferably, in step 3, determining the fault distance of the branch line includes:

[0036] Step 3.2.1: When the fault distance of the main line is equal to 0, the power frequency components of the zero-sequence voltage and zero-sequence current of the branch line section connected to the beginning of the main line section, as well as the power frequency components of the zero-sequence voltage and zero-sequence current of the main line section, are used to obtain the zero-sequence voltage equation of the branch line fault point based on the zero-sequence network after each section fault.

[0037] Step 3.2.2: When the fault distance of the main line is equal to the length of the main line section, the power frequency components of the zero-sequence voltage and zero-sequence current of the branch line section connected to the end of the main line section, as well as the power frequency components of the zero-sequence voltage and zero-sequence current of the main line section, are used to obtain the zero-sequence voltage equation of the branch line fault point based on the zero-sequence network after the fault in each section.

[0038] Step 3.2.3: Solve the zero-sequence voltage equation at the fault point of the branch line, and use the length of the branch line section to eliminate the false roots of the equation, so that the true root that meets the discrimination threshold is taken as the fault distance of the branch line.

[0039] Preferably, in step 3.2.3, when the real and imaginary parts of the true root of the zero-sequence voltage equation at the branch line fault point satisfy the discrimination thresholds shown in the following relationship, the true root is the branch line fault distance:

[0040]

[0041] In the formula,

[0042] L' is the length of the branch line section.

[0043] ε represents the maximum permissible relative error of the ranging result, with a value not exceeding 5%.

[0044] l' represents the distance from the fault point to the beginning of the branch line section.

[0045] A single-phase grounding fault location system for distribution networks based on zero-sequence component impedance method includes: a signal acquisition module, a signal processing module, and a fault location module;

[0046] The signal acquisition module is used to divide the power distribution line into multiple main line sections and multiple branch line sections; and to obtain the line length of each section of the power distribution line, the power distribution network topology, and the PMU installation location.

[0047] The signal processing module is used to identify the zero-sequence parameters of the line using PMU measurement data after a single-phase ground fault is detected. It performs fast Fourier transform on the time-domain signals of the acquired zero-sequence voltage and zero-sequence current to obtain the power frequency components of the zero-sequence voltage and zero-sequence current of each section of the line.

[0048] The fault location module is used to determine the zero-sequence network after a fault based on the distribution network topology. For any main line segment, the zero-sequence voltage equation at the fault point of the main line is obtained using the zero-sequence parameters of the upstream segment of the main line connected to the beginning of the main line segment and the zero-sequence parameters of the downstream segment of the main line connected to the end of the main line segment. The true root of the zero-sequence voltage equation at the fault point of the main line is determined using the length of the main line segment, i.e., the fault distance of the main line. When the fault distance of the main line is equal to 0 or the length of the main line segment, the zero-sequence voltage equation at the fault point of the branch line is obtained using the zero-sequence parameters of the branch line segment connected to the beginning or end of the main line segment and the zero-sequence parameters of the main line segment. The true root of the zero-sequence voltage equation at the fault point of the branch line is determined using the length of the branch line segment, i.e., the fault distance of the branch line.

[0049] The system is applicable to distribution networks where the neutral point is ungrounded or grounded via an arc suppression coil; the distribution network topology is radial.

[0050] The beneficial effects of this invention are that, compared with the prior art, this invention can maintain high accuracy under various power distribution network structures such as mixed lines and multi-branch lines, and the ranging accuracy is not affected by grounding resistance and fault phase angle. It is suitable for engineering practice, has high positioning accuracy, and has good academic value and practicality. Attached Figure Description

[0051] Figure 1 The present invention provides a flowchart of a single-phase grounding fault location method for distribution networks based on the impedance method of zero-sequence components;

[0052] Figure 2 This is a schematic diagram of a single-phase ground fault occurring at section AD of the second main line in the distribution network according to Embodiment 2 of the present invention.

[0053] Figure 3 In Embodiment 2 of the present invention Figure 2 The corresponding zero-order network diagram after the fault. Detailed Implementation

[0054] 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.

[0055] Example 1.

[0056] This invention proposes a single-phase grounding fault location method for distribution networks based on zero-sequence component impedance. The distribution line is divided into multiple main line sections and branch line sections. For any main line section, the zero-sequence voltage equation at the fault point is obtained using the zero-sequence parameters of the upstream section of the main line connected to the beginning of the main line section and the downstream section of the main line connected to the end of the main line section. The true root of the zero-sequence voltage equation at the fault point of the main line is determined using the length of the main line section, i.e., the fault distance of the main line. When the fault distance of the main line is equal to 0 or the length of the main line section, the zero-sequence voltage equation at the fault point of the branch line is obtained using the zero-sequence parameters of the branch line sections connected to the beginning or end of the main line section and the zero-sequence parameters of the main line section. The true root of the zero-sequence voltage equation at the fault point of the branch line is determined using the length of the branch line section, i.e., the fault distance of the branch line.

[0057] A method for locating single-phase grounding faults in distribution networks based on the impedance method of zero-sequence components, such as... Figure 1 As shown, it includes the following steps:

[0058] Step 1: Divide the power distribution line into multiple main line sections and multiple branch line sections; obtain the line length of each section of the power distribution line, the power distribution network topology, and the PMU installation location.

[0059] It is worth noting that the power line parameters obtained in this application when locating single-phase grounding faults in the distribution network include, but are not limited to: the length of each section of the line, the topology of the distribution network, the zero-sequence parameters of each section of the line, and the installation location and corresponding node of the PMU.

[0060] Specifically, in step 1, the main line section includes: the section from the beginning of the main line to the beginning of the branch line, the section from the beginning of the branch line to the fault point, and the section from the end of the main line to the beginning of the branch line; the branch line section includes: the section from the beginning of the branch line to the end of the branch line.

[0061] Specifically, the PMU installation locations include: the beginning of the trunk line, the end of the trunk line, and the end of the branch line.

[0062] Specifically, during normal operation, the PMU monitors the three-phase voltage and current at the beginning and end of the main line and the end of each branch line;

[0063] After determining that a single-phase ground fault has occurred, the PMU acquires the zero-sequence voltage and zero-sequence current at the beginning of the main line, the zero-sequence voltage at the end of the main line, and the zero-sequence voltage at the end of the branch line.

[0064] Step 2: After a single-phase ground fault is determined to have occurred, the zero-sequence parameters of the line are identified using PMU measurement data. The time-domain signals of the collected zero-sequence voltage and zero-sequence current are subjected to fast Fourier transform to obtain the power frequency components of the zero-sequence voltage and zero-sequence current of each section of the line.

[0065] In Example 1, the three-phase voltage, current and zero-sequence voltage and current are monitored by the PMU at the beginning of the main line and the miniature PMU at the end of the line installed on the bus side. Based on the characteristic that the line voltage remains unchanged when a single-phase ground fault occurs in the system and the change of the zero-sequence voltage, it is determined whether a single-phase ground fault has occurred.

[0066] Specifically, step 2 includes:

[0067] Step 2.1, set the zero-sequence voltage start-up value;

[0068] Step 2.2: Measure the three-phase phase voltages using a PMU and calculate the composite line voltage and zero-sequence voltage;

[0069] Step 2.3: When the line phase voltage changes, if the amplitude and phase difference of the three line voltages remain unchanged and the zero-sequence voltage value exceeds the zero-sequence voltage starting value, then a single-phase ground fault is determined to have occurred.

[0070] Step 2.4: Initiate single-phase ground fault location. Use the PMU to sample the steady-state zero-sequence voltage and steady-state zero-sequence current at the beginning of the main line, and the steady-state zero-sequence voltage at the end of the main line and the beginning of the branch line. The sampling frequency is 5kHz.

[0071] Step 2.5: Apply Fast Fourier Transform to the time-domain signals of steady-state zero-sequence voltage and steady-state zero-sequence current within 4 sampling periods after a 0.5s delay from the time of the fault occurrence to filter out higher harmonic components and obtain the power frequency components of steady-state zero-sequence voltage and zero-sequence current.

[0072] Step 3: Determine the zero-sequence network after the fault based on the distribution network topology; for any main line section, obtain the zero-sequence voltage equation of the fault point of the main line using the zero-sequence parameters of the upstream section of the main line connected to the beginning of the main line section and the zero-sequence parameters of the downstream section of the main line connected to the end of the main line section; determine the true root of the zero-sequence voltage equation of the fault point of the main line using the length of the main line section, i.e., the fault distance of the main line.

[0073] When the fault distance of the main line is equal to 0 or the length of the main line section, the zero-sequence voltage equation of the branch line fault point is obtained by using the zero-sequence parameters of the branch line section connected to the beginning or end of the main line section and the zero-sequence parameters of the main line section. The true root of the zero-sequence voltage equation of the branch line fault point is determined by using the length of the branch line section, that is, the fault distance of the branch line.

[0074] Specifically, in step 3, each segment in the post-fault zero-sequence network is a lumped-parameter π-type equivalent circuit.

[0075] In Example 1, by traversing each segment of the system and solving the fault location equation for each segment, segment location and fault location can be achieved simultaneously. Fault location formulas for each segment are established based on the post-fault zero-sequence network. The power frequency components of the steady-state zero-sequence voltage and zero-sequence current are substituted into the fault location formula corresponding to the first segment of the line. False roots are eliminated and true roots are determined based on the segment length limitation. If no true root is found, the segment is excluded, and the fault location formula for the next segment is applied to determine the distance until the true root is found.

[0076] Specifically, in step 3, determining the fault distance of the main line includes:

[0077] Step 3.1.1: For any main line section, using the power frequency components of the zero-sequence voltage and zero-sequence current of the upstream section of the main line connected to the beginning of the main line section, based on the zero-sequence network after each section fault, the first zero-sequence voltage function of the main line fault point is obtained.

[0078] Step 3.1.2: Utilize the zero-sequence voltage of the downstream section of the main line connected to the end of the main line section and calculate the power frequency component of the zero-sequence current. Based on the zero-sequence network after each section fault, obtain the second zero-sequence voltage function of the fault point of the main line.

[0079] Step 3.1.3: Based on the fact that the first zero-sequence voltage function and the second zero-sequence voltage function of the fault point on the main line are equal, the zero-sequence voltage equation of the fault point on the main line is obtained.

[0080] Step 3.1.4: Solve the zero-sequence voltage equation at the fault point of the main line, and use the length of the main line section to eliminate the false roots of the equation, so that the true root that meets the discrimination threshold is taken as the fault distance of the main line.

[0081] Specifically, in step 3.1.4, when the real and imaginary parts of the true root of the zero-sequence voltage equation at the fault point of the main line satisfy the discrimination thresholds shown in the following relationship, the true root is the fault distance of the main line:

[0082]

[0083] In the formula,

[0084] L is the length of the main trunk line section.

[0085] ε represents the maximum permissible relative error of the ranging result, with a value not less than 5%.

[0086] l is the fault distance of the main line, which is the distance from the fault point to the beginning of the main line section.

[0087] In Example 1, when a single-phase ground fault occurs in a certain branch line section, theoretically, there must exist a real solution where the fault point is located at the end of the upstream section of the main line connected to the beginning of the branch line; theoretically, there must also exist a real solution where the fault point is located at the beginning of the downstream section of the main line adjacent to the beginning of the branch line; when the ranging result of a certain section of the main line is located at the beginning or end of the section, the ranging formula of the branch line section connected to the main line section needs to be applied for accurate positioning.

[0088] Specifically, in step 3, determining the fault distance of the branch line includes:

[0089] Step 3.2.1: When the fault distance of the main line is equal to 0, the power frequency components of the zero-sequence voltage and zero-sequence current of the branch line section connected to the beginning of the main line section, as well as the power frequency components of the zero-sequence voltage and zero-sequence current of the main line section, are used to obtain the zero-sequence voltage equation of the branch line fault point based on the zero-sequence network after each section fault.

[0090] Step 3.2.2: When the fault distance of the main line is equal to the length of the main line section, the power frequency components of the zero-sequence voltage and zero-sequence current of the branch line section connected to the end of the main line section, as well as the power frequency components of the zero-sequence voltage and zero-sequence current of the main line section, are used to obtain the zero-sequence voltage equation of the branch line fault point based on the zero-sequence network after the fault in each section.

[0091] Step 3.2.3: Solve the zero-sequence voltage equation at the fault point of the branch line, and use the length of the branch line section to eliminate the false roots of the equation, so that the true root that meets the discrimination threshold is taken as the fault distance of the branch line.

[0092] Specifically, in step 3.2.3, when the real and imaginary parts of the true root of the zero-sequence voltage equation at the branch line fault point satisfy the discrimination thresholds shown in the following relationship, the true root is the branch line fault distance:

[0093]

[0094] In the formula,

[0095] L' is the length of the branch line section.

[0096] ε represents the maximum permissible relative error of the ranging result, with a value not exceeding 5%.

[0097] l' represents the distance from the fault point to the beginning of the branch line section.

[0098] Example 2.

[0099] For single-phase grounding faults in radial distribution networks Figure 2 and Figure 3The diagrams show the fault diagrams and the corresponding zero-sequence network after the fault when a single-phase ground fault occurs at the second main line section AD in the distribution network in Embodiment 2 of the present invention.

[0100] Figure 2 The main trunk line sections include: the first main trunk line section MA, the second main trunk line section AD, the third main trunk line section DN, the first branch line section AB, and the second branch line section DE. The arrows in the diagram indicate the direction of current.

[0101] Let the lengths of the first main trunk line segment MA, the second main trunk line segment AD, the third main trunk line segment DN, the first branch line segment AB, and the second branch line segment DE be L respectively. MA L AD L DN L AB L DE The distance from the fault point to point A is l. The fault point experiences a phase A ground fault.

[0102] The zero-sequence voltage at point A, the starting point of the first branch line section AB, is calculated from point M, the starting point of the first main line section MA, using the following formula.

[0103]

[0104] In the formula,

[0105] R0, L0, and C0 represent the zero-sequence resistance, inductance, and capacitance to ground per unit length of the line, respectively.

[0106] Z CM The zero-sequence conductance of the MA section of the first main line.

[0107] Z0 is the zero-sequence impedance of the first main trunk line section MA.

[0108] The zero-sequence voltage is the voltage at point M, the starting point of the first main trunk line section MA.

[0109] The zero-sequence current of the MA in the first main line section;

[0110] Then, the zero-sequence voltage at the fault point is calculated from point A using the following formula.

[0111]

[0112] In the formula,

[0113] Y AB The zero-sequence admittance of the first branch line segment AB.

[0114] This refers to the zero-sequence current of AD in the second main line section.

[0115] The zero-sequence voltage at point A, the starting point of the second main line section AD;

[0116] Similarly, from point N at the end of the third main line section DN, the zero-sequence voltage at point D at the beginning of the second branch line section DE is calculated using the following formula.

[0117]

[0118] In the formula,

[0119] Z cN The zero-sequence conductance of DN in the third main line section.

[0120] The zero-sequence voltage at point N, the end of section DN of the third main trunk line.

[0121] Then, the zero-sequence voltage at the fault point is calculated from point D using the following formula.

[0122]

[0123] Let the zero-sequence voltage at the fault point calculated from both points M and N be... If they are equal, we can obtain the following equation:

[0124]

[0125] Expanding equation (5) according to equations (1) to (4) yields a quadratic complex equation for l. Solving the equation gives the two roots of l.

[0126] Solving a system of quadratic complex equations in one variable can result in multiple roots. The true root, i.e., the fault distance l, must be between 0 and L. AD For real numbers within the range, considering that there will inevitably be some error in the amplitude and phase angle during signal measurement and Fourier transform, the formula for determining the true root is as follows:

[0127]

[0128] In the formula,

[0129] L is the length of the main line section;

[0130] ε is the maximum allowable relative error of the ranging result. The value range is not less than 5% according to the accuracy requirements of the actual fault ranging. It can also be adjusted according to the specific ranging conditions of the line.

[0131] l is the fault distance of the main line, which is the distance from the fault point to the beginning of the main line section.

[0132] Solving the equation yields the roots of l. Similarly, we can use equation (6) to eliminate false roots and determine the true roots. When both roots obtained by equation (5) are outside the range and belong to false roots, it can be determined that the fault point is not located within the second main line section AD.

[0133] according to Figure 2 and Figure 3 The diagram of the ground fault and the zero-sequence network after the fault are shown. When a ground fault occurs in the second main line section AD, the process of calculating the zero-sequence voltage at the fault point from both sides of points M and N and establishing a quadratic complex equation about l can be simplified as follows:

[0134] ① Calculated from point M:

[0135]

[0136]

[0137] ② Calculated from point N:

[0138]

[0139]

[0140] The same method can be used to establish fault location equations for the first main line segment MA and the third main line segment DN, and the fault distance can be solved. Similarly, to achieve fault location for the first branch line segment AB, it is only necessary to add the measurement of the zero-sequence voltage at point B at the end of the first branch line segment AB. It should be noted that when a fault occurs in the first branch line segment AB, the fault location formula for the first main line segment MA theoretically necessarily implies l = L. MA The distance measurement formula for the second main line section AD must have a real solution with l = 0. That is, when both the distance measurement formulas for the first main line section MA and the second main line section AD have true solutions, and the fault point is located near point A, it means that the fault point may be located on the first branch line section AB, and the distance measurement formula for the first branch line section AB needs to be applied for precise location.

[0141] To verify the correctness of the proposed single-phase grounding fault location strategy, a simulation model was built using EMTP / ATP simulation software. The distribution network line MN is 10km long, and the zero-sequence parameter per unit length is: R0 = 1.23 × 10⁻⁶. -3 Ω / m, L0=9.167×10 -7 H / m, C0 = 2.58333 × 10 -10F / m. There are first branch line segment AB and second branch line segment DE at distances of 3km and 6km from point M, respectively. The length of first branch line segment AB is 6km, and the length of second branch line segment DE is 5km. The zero-sequence parameter per unit length of the line is: R1 = 2.1 × 10⁻⁶. -4 Ω / m, L1=7×10 -6 H / m, C1 = 4.66 × 10 -12 The grounding resistance is 200Ω and the fault point is set at 1km from point A in the first branch line section AB. The time for a single-phase ground fault is set to 0.1s.

[0142] First, the fault location formula for the MA section of the first main trunk line is applied. Assume the fault point is located on the MA section of the first main trunk line, at a distance l from the starting point M. The zero-sequence voltage at points M and N, and the zero-sequence current at point M are sampled synchronously and subjected to Fourier transform. The fundamental zero-sequence voltage and current phasor values ​​are obtained as follows:

[0143] Zero-sequence voltage at point M:

[0144] N-point zero-sequence voltage:

[0145] Zero-sequence current at point M:

[0146] according to The zero-sequence voltage at point D and the zero-sequence current at point D, the end of the second main line section AD, can be obtained as follows:

[0147] Zero-sequence voltage at point D

[0148] Zero-sequence current at point D:

[0149] Similarly, according to and The zero-sequence voltage at point A and the zero-sequence current at point A, the end of the first main line section MA, can be obtained as follows:

[0150] Zero-sequence voltage at point A:

[0151] Zero-sequence current at point A:

[0152] according to The distance measurement equation for the first main trunk line section MA can be established as follows:

[0153]

[0154] By solving the distance measurement equation for MA in the first main trunk line section, we can obtain the two roots of l as follows:

[0155] l1 = -3.356 × 10 +6 -1.438×10 +7 j, l2 = 2998.446 - 0.0298j

[0156] According to equation (6), l1 can be determined to be a pseudo-root, and the fault point determined by l2 is located near point A. It is necessary to continue applying the distance measurement formula for the second main line section AD. Let the fault point be located within the second main line section AD, and the distance from the beginning of the section, point A, be l:

[0157] according to and The zero-sequence voltage and current across AD in the second main line section can be obtained as follows:

[0158]

[0159]

[0160] Substituting into equation (5) and solving, we can obtain the two roots of l:

[0161] l1=-1.554-0.030j, l2=4.120×10 +6 +1.759×10 +7 j

[0162] According to equation (6), l2 can be determined to be a pseudo-root, and the fault point determined by l1 is located near point A. Therefore, the fault location formula for the first branch line section AB needs to be applied. and The zero-sequence voltage and current at point A, the starting end of the first branch line segment AB, can be obtained as follows:

[0163] At this moment, the zero-sequence voltage measured at point B is:

[0164] according to and The distance measurement equation for the first branch line section AB can be established as follows:

[0165]

[0166] By solving the distance measurement equation for the first branch line segment AB, we can obtain the two roots of l:

[0167] l1=1000.146+0.111j、l2=-6.286×10 +8 -5.998×10 +7 j

[0168] According to equation (6), l1 is the true root and l2 is the false root. The fault point is 1000.146m away from point A.

[0169] When the fault phase angle α is 45°, the ranging results for a multi-branch mixed line in a distribution network with a neutral point grounded via an arc suppression coil are shown in the table below:

[0170]

[0171] For both neutral point ungrounded and arc suppression coil operation modes, by setting the fault point at different sections and setting the grounding resistance to 10Ω, 200Ω, 1000Ω, and 5000Ω respectively, and taking the fault phase angle α to be 90°, 45°, and 0° respectively, the method proposed in this invention can maintain high accuracy.

[0172] This invention maintains high accuracy in various power distribution network structures, such as mixed lines and multi-branch lines, and the ranging accuracy is not affected by grounding resistance and fault phase angle.

[0173] In another aspect, the present invention proposes a single-phase grounding fault location system for distribution networks based on the impedance method of zero-sequence component, comprising: a signal collection module, a signal processing module, and a fault location module;

[0174] The signal acquisition module is used to divide the power distribution line into multiple main line sections and multiple branch line sections; and to obtain the line length of each section of the power distribution line, the power distribution network topology, and the PMU installation location.

[0175] The signal processing module is used to identify the zero-sequence parameters of the line using PMU measurement data after a single-phase ground fault is detected. It performs fast Fourier transform on the time-domain signals of the acquired zero-sequence voltage and zero-sequence current to obtain the power frequency components of the zero-sequence voltage and zero-sequence current of each section of the line.

[0176] The fault location module is used to determine the zero-sequence network after a fault based on the distribution network topology. For any main line segment, the zero-sequence voltage equation at the fault point of the main line is obtained using the zero-sequence parameters of the upstream segment of the main line connected to the beginning of the main line segment and the zero-sequence parameters of the downstream segment of the main line connected to the end of the main line segment. The true root of the zero-sequence voltage equation at the fault point of the main line is determined using the length of the main line segment, i.e., the fault distance of the main line. When the fault distance of the main line is equal to 0 or the length of the main line segment, the zero-sequence voltage equation at the fault point of the branch line is obtained using the zero-sequence parameters of the branch line segment connected to the beginning or end of the main line segment and the zero-sequence parameters of the main line segment. The true root of the zero-sequence voltage equation at the fault point of the branch line is determined using the length of the branch line segment, i.e., the fault distance of the branch line.

[0177] The system is applicable to distribution networks where the neutral point is ungrounded or grounded via an arc suppression coil; the distribution network topology is radial.

[0178] The beneficial effects of this invention are that, compared with the prior art, this invention can maintain high accuracy under various power distribution network structures such as mixed lines and multi-branch lines, and the ranging accuracy is not affected by grounding resistance and fault phase angle. It is suitable for engineering practice, has high positioning accuracy, and has good academic value and practicality.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] Various aspects of this disclosure are described herein with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer-readable program instructions.

[0184] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to produce a machine such that, when executed by the processor of the computer or other programmable data processing apparatus, they create means for implementing the functions / actions specified in one or more blocks of the flowchart and / or block diagram. These computer-readable program instructions can also be stored in a computer-readable storage medium that causes a computer, programmable data processing apparatus, and / or other device to operate in a particular manner; thus, the computer-readable medium storing the instructions comprises an article of manufacture that includes instructions for implementing aspects of the functions / actions specified in one or more blocks of the flowchart and / or block diagram.

[0185] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby causing the instructions executed on the computer, other programmable data processing apparatus, or other device to perform the functions / actions specified in one or more boxes of a flowchart and / or block diagram.

[0186] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of an instruction containing one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions marked in the blocks may occur in a different order than those shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0187] 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 method for locating single-phase grounding faults in distribution networks based on zero-sequence component impedance, characterized in that: The power distribution line is divided into multiple main line sections and branch line sections. For any main line section, the zero-sequence voltage equation of the fault point of the main line is obtained by using the zero-sequence parameters of the upstream section of the main line connected to the beginning of the main line section and the zero-sequence parameters of the downstream section of the main line connected to the end of the main line section. The true root of the zero-sequence voltage equation of the fault point of the main line is determined by the length of the main line section, that is, the fault distance of the main line. When the fault distance of the main line is equal to 0, the zero-sequence voltage equation of the fault point of the branch line is obtained by using the zero-sequence parameters of the branch line section connected to the beginning of the main line section and the zero-sequence parameters of the main line section. When the fault distance of the main line is equal to the length of the main line section, the zero-sequence voltage equation of the branch line fault point is obtained by using the zero-sequence parameters of the branch line section connected to the end of the main line section and the zero-sequence parameters of the main line section. The true root of the zero-sequence voltage equation of the branch line fault point, i.e., the fault distance of the branch line, is determined by using the length of the branch line section.

2. The impedance method based on zero sequence component for single-phase-to-ground fault location of distribution network according to claim 1, characterized in that, Includes the following steps: Step 1: Divide the power distribution lines into multiple main line sections and multiple branch line sections; Obtain the line length of each section of the power distribution line, the topology of the power distribution network, and the installation location of the PMU; Step 2: After a single-phase ground fault is determined to have occurred, the zero-sequence parameters of the line are identified using PMU measurement data. The time-domain signals of the collected zero-sequence voltage and zero-sequence current are subjected to fast Fourier transform to obtain the power frequency components of the zero-sequence voltage and zero-sequence current of each section of the line. Step 3: Determine the zero-sequence network after the fault based on the distribution network topology; for any main line section, obtain the zero-sequence voltage equation of the fault point of the main line using the zero-sequence parameters of the upstream section of the main line connected to the beginning of the main line section and the zero-sequence parameters of the downstream section of the main line connected to the end of the main line section; determine the true root of the zero-sequence voltage equation of the fault point of the main line using the length of the main line section, i.e., the fault distance of the main line. When the fault distance of the main line is equal to 0, the zero-sequence voltage equation of the branch line fault point is obtained by using the power frequency components of the zero-sequence voltage and zero-sequence current of the branch line section connected to the beginning of the main line section, as well as the power frequency components of the zero-sequence voltage and zero-sequence current of the main line section. When the fault distance of the main line is equal to the length of the main line section, the zero-sequence voltage equation of the branch line fault point is obtained by using the power frequency components of the zero-sequence voltage and zero-sequence current of the branch line section connected to the end of the main line section, as well as the power frequency components of the zero-sequence voltage and zero-sequence current of the main line section. The true root of the zero-sequence voltage equation of the branch line fault point, i.e., the fault distance of the branch line, is determined by using the length of the branch line section.

3. The method for locating single-phase grounding faults in distribution networks based on zero-sequence component impedance according to claim 2, characterized in that: In step 1, the main line section includes: the section from the beginning of the main line to the beginning of the branch line, the section from the beginning of the branch line to the fault point, and the section from the end of the main line to the beginning of the branch line; the branch line section includes: the section from the beginning of the branch line to the end of the branch line.

4. The method for locating single-phase grounding faults in distribution networks based on zero-sequence component impedance according to claim 3, characterized in that: PMU installation locations include: the beginning of the main line, the end of the main line, and the end of the branch line.

5. The method for locating single-phase grounding faults in distribution networks based on zero-sequence component impedance according to claim 4, characterized in that: During normal operation, the PMU monitors the three-phase voltage and current at the beginning and end of the main line and the end of each branch line; After determining that a single-phase ground fault has occurred, the PMU acquires the zero-sequence voltage and zero-sequence current at the beginning of the main line, the zero-sequence voltage at the end of the main line, and the zero-sequence voltage at the end of the branch line.

6. The method for locating single-phase grounding faults in distribution networks based on zero-sequence component impedance according to claim 5, characterized in that: Step 2 includes: Step 2.1, set the zero-sequence voltage start-up value; Step 2.2: Measure the three-phase phase voltages using a PMU and calculate the composite line voltage and zero-sequence voltage; Step 2.3: When the line phase voltage changes, if the amplitude and phase difference of the three line voltages remain unchanged and the zero-sequence voltage value exceeds the zero-sequence voltage starting value, then a single-phase ground fault is determined to have occurred. Step 2.4: Initiate single-phase ground fault location. Use the PMU to sample the steady-state zero-sequence voltage and steady-state zero-sequence current at the beginning of the main line, and the steady-state zero-sequence voltage at the end of the main line and the beginning of the branch line. The sampling frequency is 5kHz. Step 2.5: Apply Fast Fourier Transform to the time-domain signals of steady-state zero-sequence voltage and steady-state zero-sequence current within 4 sampling periods after a 0.5s delay from the time of the fault occurrence to filter out higher harmonic components and obtain the power frequency components of steady-state zero-sequence voltage and zero-sequence current.

7. The method for locating single-phase grounding faults in distribution networks based on zero-sequence component impedance according to claim 2, characterized in that: In step 3, each segment in the post-fault zero-sequence network is an equivalent circuit using lumped parameters π-type.

8. The method for locating single-phase grounding faults in distribution networks based on zero-sequence component impedance according to claim 7, characterized in that: In step 3, determining the fault distance of the main line includes: Step 3.1.1: For any main line section, using the power frequency components of the zero-sequence voltage and zero-sequence current of the upstream section of the main line connected to the beginning of the main line section, based on the zero-sequence network after each section fault, the first zero-sequence voltage function of the main line fault point is obtained. Step 3.1.2: Utilize the zero-sequence voltage of the downstream section of the main line connected to the end of the main line section and calculate the power frequency component of the zero-sequence current. Based on the zero-sequence network after each section fault, obtain the second zero-sequence voltage function of the fault point of the main line. Step 3.1.3: Based on the fact that the first zero-sequence voltage function and the second zero-sequence voltage function of the fault point on the main line are equal, the zero-sequence voltage equation of the fault point on the main line is obtained. Step 3.1.4: Solve the zero-sequence voltage equation at the fault point of the main line, and use the length of the main line section to eliminate the false roots of the equation, so that the true root that meets the discrimination threshold is taken as the fault distance of the main line.

9. The method for locating single-phase grounding faults in distribution networks based on zero-sequence component impedance according to claim 8, characterized in that: In step 3.1.4, when the real and imaginary parts of the true root of the zero-sequence voltage equation at the fault point of the main line satisfy the discrimination thresholds shown in the following relationship, the true root is the fault distance of the main line: In the formula, The length of the main line section, The maximum allowable relative error for the ranging result is within a range of not less than 5%. The fault distance on the main line is the distance from the fault point to the beginning of the main line section.

10. The method for locating single-phase grounding faults in distribution networks based on zero-sequence component impedance according to claim 8, characterized in that: In step 3, determining the fault distance of the branch line includes: Step 3.2.1: When the fault distance of the main line is equal to 0, the power frequency components of the zero-sequence voltage and zero-sequence current of the branch line section connected to the beginning of the main line section, as well as the power frequency components of the zero-sequence voltage and zero-sequence current of the main line section, are used to obtain the zero-sequence voltage equation of the branch line fault point based on the zero-sequence network after each section fault. Step 3.2.2: When the fault distance of the main line is equal to the length of the main line section, the power frequency components of the zero-sequence voltage and zero-sequence current of the branch line section connected to the end of the main line section, as well as the power frequency components of the zero-sequence voltage and zero-sequence current of the main line section, are used to obtain the zero-sequence voltage equation of the branch line fault point based on the zero-sequence network after each section fault. Step 3.2.3: Solve the zero-sequence voltage equation at the fault point of the branch line, and use the length of the branch line section to eliminate the false roots of the equation, so that the true root that meets the discrimination threshold is taken as the fault distance of the branch line.

11. The method for locating single-phase grounding faults in distribution networks based on zero-sequence component impedance according to claim 10, characterized in that: In step 3.2.3, when the real and imaginary parts of the true root of the zero-sequence voltage equation at the branch line fault point satisfy the discrimination thresholds shown in the following relationship, the true root is the fault distance of the branch line: In the formula, The length of the branch line section, The maximum allowable relative error for the ranging result is within a range of no more than 5%. This is the distance from the fault point to the beginning of the branch line section.

12. A single-phase ground fault location system for a distribution network based on zero-sequence component impedance method for implementing the method of any one of claims 1 to 11, comprising: The signal acquisition module, signal processing module, and fault location module are characterized by: The signal acquisition module is used to divide the power distribution line into multiple main line sections and multiple branch line sections; and to obtain the line length of each section of the power distribution line, the power distribution network topology, and the PMU installation location. The signal processing module is used to identify the zero-sequence parameters of the line using PMU measurement data after a single-phase ground fault is detected. It performs fast Fourier transform on the time-domain signals of the acquired zero-sequence voltage and zero-sequence current to obtain the power frequency components of the zero-sequence voltage and zero-sequence current of each section of the line. The fault location module is used to determine the zero-sequence network after a fault based on the distribution network topology. For any main line segment, the zero-sequence voltage equation at the fault point of the main line is obtained using the zero-sequence parameters of the upstream segment of the main line connected to the beginning of the main line segment and the zero-sequence parameters of the downstream segment of the main line connected to the end of the main line segment. The true root of the zero-sequence voltage equation at the fault point of the main line is determined using the length of the main line segment, i.e., the fault distance of the main line. When the fault distance of the main line is equal to 0, the zero-sequence voltage equation at the fault point of the branch line is obtained using the zero-sequence parameters of the branch line segment connected to the beginning of the main line segment and the zero-sequence parameters of the main line segment. When the fault distance of the main line is equal to the length of the main line segment, the zero-sequence voltage equation at the fault point of the branch line is obtained using the zero-sequence parameters of the branch line segment connected to the end of the main line segment and the zero-sequence parameters of the main line segment. The true root of the zero-sequence voltage equation at the fault point of the branch line is determined using the length of the branch line segment, i.e., the fault distance of the branch line.

13. The single-phase grounding fault location system for distribution networks based on zero-sequence component impedance method according to claim 12, characterized in that: The system is applicable to distribution networks where the neutral point is ungrounded or grounded via an arc suppression coil; the distribution network topology is radial.

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