Low-voltage three-phase four-wire system zero line breaking fault identification method and device and readable medium

Abstract

The invention relates to the technical field of power distribution networks, in particular to a low-voltage three-phase four-wire system zero-line fault identification method and device and a readable medium, and the method comprises the steps: firstly, calculating a three-phase phase voltage phasor and a zero-sequence voltage phasor according to the effective value of a three-phase phase voltage and the geometrical relationship of the three-phase phase voltage phasor in a rectangular plane coordinate system; solving a phase angle of the three-phase current according to the three-phase phase voltage phasor, and obtaining a three-phase current phasor and a zero-sequence current phasor according to the effective value of the three-phase current and the phase angle; and calculating a zero-sequence impedance phasor according to the zero-sequence voltage phasor and the zero-sequence current phasor, and judging whether the low-voltage three-phase four-wire system has a zero-line breaking fault or not according to the zero-sequence impedance phasor. According to the invention, the zero-sequence impedance phasor is calculated by directly utilizing the effective value data of the three-phase phase voltage and the three-phase current, so that the problem that the existing acquisition terminal or system does not support phasor data acquisition and does not have the measurement and calculation conditions of the zero-sequence impedance is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power distribution network, in particular to a low-voltage three-phase four-wire system zero-break fault identification method, device and readable medium. BACKGROUND

[0002] Zero sequence voltage and zero sequence current are both quantities for measuring the degree of imbalance of three-phase voltage and current of a power system, and they play a very important role in the safe, efficient and stable operation of low-voltage distribution network lines, equipment and loads, the improvement of power supply quality and the improvement of the efficiency of terminal users' use of electric energy. According to the research on zero sequence impedance, for a three-phase four-wire system, if the zero sequence voltage and the zero sequence current of the system can be measured, the total zero sequence impedance data of the distribution transformer and its lead, the unbranched three-phase four-wire line can be calculated and obtained, so as to realize the identification and judgment of the neutral line circuit impedance deterioration defect or poor contact fault of the distribution transformer and its lead, and provide optimization and rectification basis for improving the qualified rate of low-voltage system power supply voltage.

[0003] At present, the domestic low-voltage power supply system mainly adopts the power supply mode of three-phase four-wire system neutral point direct grounding. The collection method or device of relevant voltage and current data generally only involves three-phase voltage (phase voltage or line voltage) and current effective value data, and generally does not have the function of collecting zero sequence voltage and zero sequence current data. Although zero sequence voltage and zero sequence current data can be calculated and synthesized by using the phasor sum of three-phase voltage and current, for a three-phase four-wire line, the approximate value of zero sequence current can also be directly obtained by installing a current transformer in the neutral line (i.e. zero line), however, a large number of distribution transformer monitoring terminals, intelligent circuit breakers, intelligent electric meters and other device terminals currently running in low-voltage distribution network only support three-phase voltage and current effective value collection, and do not all support phasor data collection, so they do not all have the conditions for direct collection or indirect synthesis calculation of zero sequence voltage and zero sequence current, and do not have the conditions for measurement and calculation of zero sequence impedance.

[0004] Therefore, the present application proposes a low-voltage three-phase four-wire system zero-break fault identification method, device and readable medium, which directly uses the three-phase phase voltage and three-phase current effective value data provided by the existing terminal or system to calculate the zero sequence impedance without changing the existing collection terminal or system, and plays an important role in the zero-break fault judgment of the low-voltage three-phase four-wire system which does not have the phasor data collection capability and does not have the conditions for measurement and calculation of zero sequence impedance. SUMMARY

[0005] The purpose of the present application is to propose a low-voltage three-phase four-wire system zero-break fault identification method, device and readable medium for the above-mentioned technical problems.

[0006] In a first aspect, the present application provides a low-voltage three-phase four-wire system zero-break fault identification method, comprising the following steps: S1, obtain the effective values ​​of the three-phase phase voltage and three-phase current of the low-voltage three-phase four-wire system simultaneously; S2. Establish a Cartesian coordinate system. Based on the effective values ​​of the three-phase voltages, construct the three-phase voltage phasors in the Cartesian coordinate system. The starting point of each three-phase voltage phasor is set at the origin of the Cartesian coordinate system. Calculate the coordinates of the endpoints of the three-phase voltage phasors in the Cartesian coordinate system based on the geometric relationship of the three-phase voltage phasors in the Cartesian coordinate system and the effective values ​​of the three-phase voltages. Generate the three-phase voltage phasors. Calculate the zero-sequence voltage phasor based on the three-phase voltage phasors. S3, calculate the phase angle of the three-phase current based on the three-phase voltage phasor, generate the three-phase current phasor based on the effective value of the three-phase current and the phase angle of the three-phase current, and calculate the zero-sequence current phasor based on the three-phase current phasor; S4, calculate the zero-sequence impedance based on the zero-sequence voltage phasor and the zero-sequence current phasor; S5, set a judgment threshold, compare the zero-sequence impedance with the judgment threshold, obtain the comparison result, and determine whether there is a zero-disconnection fault in the system based on the comparison result. If so, issue an early warning and return to step S1; otherwise, return to step S1.

[0007] Preferably, step S2 specifically includes: The three-phase voltage includes phase A voltage, phase B voltage, and phase C voltage. The effective values ​​of phase A voltage, phase B voltage, and phase C voltage are respectively represented by U. a =a、U b =b and U c =c, where a, b, and c are all positive real numbers; In a Cartesian coordinate system, three directed line segments with lengths a, b, and c originating from the origin correspond to the A-phase, B-phase, and C-phase voltage phasors, respectively. The initial phase of the A-phase voltage phasor is set to 0°, and its endpoint coordinates are denoted as (a, 0). The endpoint coordinates of the B-phase voltage phasor are denoted as (x, 0). b ,y b The endpoint coordinates of the C-phase voltage phasor are represented as (x c ,y c Based on the geometric relationships of the three-phase voltage phasors, the following set of equations is established: ; Solve the system of equations to obtain x. b y b x c and y c The value of is shown in the following formula: ; in: ; According to x b y b x c and y c The value of can be used to obtain the coordinates of the endpoint of the three-phase voltage phasor in the plane coordinate system, and generate the three-phase voltage phasor. The expression of the three-phase voltage phasor is as follows: ; in, , , These represent the voltage phasors of phase A, phase B, and phase C, respectively. The zero-sequence voltage phasor is calculated based on the three-phase phase voltage phasors, as shown in the following formula: ; in, This represents the zero-sequence voltage phasor, and the effective value of the zero-sequence voltage is expressed as: .

[0008] Preferably, step S3 specifically includes: Calculate the phase angles of the three-phase currents based on the three-phase voltage phasors. Generate the three-phase current phasors based on the effective values ​​and phase angles of the three-phase currents. Calculate the zero-sequence current phasor based on the three-phase current phasors. The three-phase current includes phase A current, phase B current, and phase C current. The effective values ​​of phase A current, phase B current, and phase C current are expressed as follows: , and ; Based on the expression for the three-phase voltage phasors, the three-phase voltage phasors can be written in the form of effective value - phase angle, as shown in the following equation: ; in, , and These represent the phase angles of the three-phase voltages; The three-phase power factors are obtained and expressed as cosθ. a cosθ b cosθ c ; When the three-phase power factor is not 1, the phase angles of the three-phase currents are respectively , and , , and The expressions for the power factor angle and the three-phase current phasors are shown in the following equations: ; in, , and These represent the current phasors of phase A, phase B, and phase C, respectively. When the three-phase power factor is 1, the three-phase voltage and the three-phase current are in phase. The expression for the three-phase current phasor is as follows: ; The zero-sequence current phasor is calculated based on the three-phase current phasors, as shown in the following formula: ; in, This represents the zero-sequence current phasor, and the effective value of the zero-sequence current is expressed as: .

[0009] Preferably, the zero-sequence impedance is calculated based on the zero-sequence voltage phasor and the zero-sequence current phasor, as shown in the following equation: ; in, This represents the zero-sequence impedance phasor, and the effective value of the zero-sequence impedance is shown in the following formula: .

[0010] Preferably, step S1 is followed by: S6, check the effectiveness of the three-phase voltages by comparing the sum of the effective values ​​of any two phase voltages with the effective value of the third phase voltage. If the condition is met: U a +U b >U c U b +U c >U a And U c +U a >U b If the condition is met, proceed to step S2; otherwise, return to step S1.

[0011] Preferably, step S5 specifically includes: The judgment thresholds include the degradation threshold and the fault threshold, wherein the degradation threshold is less than the fault threshold; The effective value of the zero-sequence impedance is compared with the set degradation threshold and fault threshold. When the effective value of the zero-sequence impedance is less than the degradation threshold, the zero-sequence impedance of the distribution transformer and its leads in the low-voltage three-phase four-wire system is normal, and the process returns to step S1. When the effective value of the zero-sequence impedance is greater than the degradation threshold and less than the fault threshold, the zero-sequence impedance of the distribution transformer and its leads in the low-voltage three-phase four-wire system exceeds the normal range. There is impedance degradation phenomenon of broken strands or poor contact in the distribution transformer or the lead neutral circuit. A degradation warning is issued and the system returns to step S1. When the effective value of the zero-sequence impedance is greater than the fault threshold, the zero-sequence impedance of the distribution transformer and its leads in the low-voltage three-phase four-wire system exceeds the normal range. A serious contact failure or zero-break fault occurs inside the distribution transformer or in the lead neutral circuit. A fault warning is issued and the system returns to step S1.

[0012] Secondly, the present invention provides a device for identifying zero-off faults in a low-voltage three-phase four-wire system, comprising: The data acquisition module is configured to acquire the effective values ​​of the three-phase phase voltage and three-phase current of the low-voltage three-phase four-wire system at the same time. The zero-sequence voltage calculation module is configured to establish a Cartesian coordinate system, construct three-phase voltage phasors in the Cartesian coordinate system based on the effective values ​​of the three-phase voltages, with the starting point of each three-phase voltage phasor set at the origin of the Cartesian coordinate system. The coordinates of the endpoints of the three-phase voltage phasors in the Cartesian coordinate system are calculated based on the geometric relationship of the three-phase voltage phasors in the Cartesian coordinate system and the effective values ​​of the three-phase voltages, and the three-phase voltage phasors are generated. The zero-sequence voltage phasor is then calculated based on the three-phase voltage phasors. The zero-sequence current calculation module is configured to calculate the phase angle of the three-phase current based on the three-phase phase voltage phasors, generate the three-phase current phasors based on the effective value of the three-phase current and the phase angle of the three-phase current, and calculate the zero-sequence current phasor based on the three-phase current phasors. The zero-sequence impedance calculation module is configured to calculate the zero-sequence impedance based on the zero-sequence voltage phasor and the zero-sequence current phasor. The fault identification module is configured to set a judgment threshold, compare the zero-sequence impedance with the judgment threshold, obtain the comparison result, and determine whether there is a zero-disconnection fault in the system based on the comparison result. If so, an early warning is issued and the system returns to step S1; otherwise, the system returns to step S1.

[0013] Thirdly, the present invention provides an electronic device including one or more processors; and a memory for storing one or more programs, which, when executed by one or more processors, cause the one or more processors to implement the method as described in any implementation of the first aspect.

[0014] Fourthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method as described in any of the implementations of the first aspect.

[0015] Fifthly, the present invention provides a computer program product, including a computer program that, when executed by a processor, implements the method as described in any of the implementations in the first aspect.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention can use the effective value data of three-phase phase voltage and three-phase current provided by existing voltage, current, power and energy measurement devices to calculate zero-sequence voltage, zero-sequence current and zero-sequence impedance, thereby realizing the identification of zero-off fault in low-voltage three-phase four-wire system, overcoming the problems that the existing technology does not support phasor data acquisition and does not have the conditions for measuring and calculating zero-sequence impedance.

[0017] (2) The change of zero-sequence impedance calculated by the method proposed in this invention can reflect the change of the real zero-sequence impedance. Therefore, the zero-sequence impedance calculated in this application has accuracy and practicality in zero-sequence fault judgment. It can detect defects or faults in the neutral line circuit in a timely manner, which helps to improve the power supply reliability and voltage qualification rate of the low-voltage distribution network. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating a method for identifying zero-off faults in a low-voltage three-phase four-wire system according to an embodiment of this application. Figure 2 A simplified circuit model of a low-voltage three-phase four-wire system according to an embodiment of this application; Figure 3 The circuit model of the low-voltage three-phase four-wire system after internal impedance reduction is shown in the embodiment of this application. Figure 4 This is a voltage phasor diagram for a three-phase voltage symmetrical embodiment of this application. Figure 5 This is a voltage phasor diagram for a three-phase voltage imbalance according to an embodiment of this application. Figure 6 This is a Simulink simulation model diagram of an embodiment of this application; Figure 7 The graphs show the simulated values ​​of the three-phase phase voltage and zero-sequence voltage of an embodiment of this application. Figure 8 The graphs show the simulated values ​​of three-phase current and zero-sequence current in embodiments of this application. Figure 9A comparison graph of simulated and calculated zero-sequence voltage values ​​from embodiments of this application; Figure 10 A comparison graph of simulated and calculated zero-sequence current values ​​from embodiments of this application; Figure 11 A comparison graph of simulated and calculated zero-sequence impedance values ​​from embodiments of this application; Figure 12 For the different embodiments of this application r n Value and Comparison of graphics; Figure 13 The three-phase voltage curve of Kang*cun No.1 transformer is shown in the embodiment of this application. Figure 14 The three-phase current curves of Kang*cun No.1 transformer are shown in the embodiments of this application. Figure 15 This is a graph comparing the error between measured and calculated zero-sequence current data from embodiments of this application. Figure 16 A graph showing the calculated values ​​of zero-sequence voltage, zero-sequence current, and zero-sequence impedance for embodiments of this application; Figure 17 The overvoltage curve for an embodiment of this application, dated 2024-02-13; Figure 18 The overvoltage curve for an embodiment of this application, dated 2024-02-13; Figure 19 The zero-sequence voltage, zero-sequence current, and zero-sequence impedance curves during a neutral wire fault in an embodiment of this application are shown. Figure 20 This is a schematic diagram of a low-voltage three-phase four-wire system zero-off fault identification device according to an embodiment of this application; Figure 21 This is a schematic diagram of the hardware structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] Figure 1 This application illustrates an embodiment of a method for identifying zero-off faults in a low-voltage three-phase four-wire system, comprising the following steps: S1, obtain the effective values ​​of the three-phase phase voltage and three-phase current of the low-voltage three-phase four-wire system simultaneously.

[0022] In a specific embodiment, step S1 is followed by step S6.

[0023] S6, check the effectiveness of the three-phase voltages by comparing the sum of the effective values ​​of any two phase voltages with the effective value of the third phase voltage. If the condition is met: U a +U b >U c U b +U c >U a AndU c +U a >U b If the condition is met, proceed to step S2; otherwise, return to step S1.

[0024] S2. Establish a Cartesian coordinate system. Based on the effective values ​​of the three-phase voltages, construct the three-phase voltage phasors in the Cartesian coordinate system. The starting point of each three-phase voltage phasor is set at the origin of the Cartesian coordinate system. Calculate the coordinates of the endpoints of the three-phase voltage phasors in the Cartesian coordinate system based on the geometric relationship of the three-phase voltage phasors in the Cartesian coordinate system and the effective values ​​of the three-phase voltages. Generate the three-phase voltage phasors. Calculate the zero-sequence voltage phasor based on the three-phase voltage phasors.

[0025] In a specific embodiment, step S2 specifically includes: The three-phase voltage includes phase A voltage, phase B voltage, and phase C voltage. The effective values ​​of phase A voltage, phase B voltage, and phase C voltage are respectively represented by U. a =a、U b =b and U c =c, where a, b, and c are all positive real numbers; In a Cartesian coordinate system, three directed line segments with lengths a, b, and c originating from the origin correspond to the A-phase, B-phase, and C-phase voltage phasors, respectively. The initial phase of the A-phase voltage phasor is set to 0°, and its endpoint coordinates are denoted as (a, 0). The endpoint coordinates of the B-phase voltage phasor are denoted as (x, 0). b ,y b The endpoint coordinates of the C-phase voltage phasor are represented as (x c ,y c Based on the geometric relationships of the three-phase voltage phasors, the following set of equations is established: ; Solve the system of equations to obtain x. b y b x c and y c The value of is shown in the following formula: ; in: ; According to x b y b x c and y c The value of can be used to obtain the coordinates of the endpoint of the three-phase voltage phasor in the plane coordinate system, and generate the three-phase voltage phasor. The expression of the three-phase voltage phasor is as follows: ; in, , , These represent the voltage phasors of phase A, phase B, and phase C, respectively. The zero-sequence voltage phasor is calculated based on the three-phase phase voltage phasors, as shown in the following formula: ; in, This represents the zero-sequence voltage phasor, and the effective value of the zero-sequence voltage is expressed as: .

[0026] Specifically, the low-voltage side of the distribution transformer is a three-phase four-wire system. At the main meter position of the power metering gate on the low-voltage side of the distribution transformer or below the low-voltage lead end, the effective values ​​of the three-phase phase voltage, the effective values ​​of the three-phase current, and the three-phase power factor at the same time are obtained using a three-phase four-wire phase voltage and phase current measuring or metering device.

[0027] To achieve zero-sequence voltage calculation using three-phase phase voltages on the low-voltage side of a three-phase four-wire system, it is necessary to first solve for the phasor values ​​of the three-phase phase voltages using the implicit known conditions of the distribution transformer, and then obtain the zero-sequence voltage through the synthesis of the three-phase phase voltage phasors.

[0028] Figure 2 A simplified circuit model of a low-voltage three-phase four-wire system is shown, E a E b E c Z is the equivalent voltage source on the low-voltage side of the distribution transformer. ta Z tb Z tc For the equivalent internal impedance of the transformer, r a r b r c r is the equivalent internal impedance of the phase conductor. n Z is the equivalent internal impedance of the neutral conductor. a Z b Z c This represents the impedance of a three-phase load.

[0029] For a distribution transformer with a connection group of Dyn11 and a voltage of 10 / 0.4kV and its lead-out conductors, its internal impedance is usually much smaller than the load impedance, and the three-phase internal impedance values ​​are basically the same, i.e., Z ta ≈Z tb ≈Z tc r a ≈r b ≈r c Ideally, if the three-phase line voltages on the 10kV power supply side of the distribution transformer are symmetrical, then the three-phase voltage source phase voltages output on the low-voltage side after being stepped down by the transformer windings will also necessarily be symmetrical, i.e., E a =E b =E c Therefore, the line voltages of the three-phase voltage sources are also symmetrical, i.e., E ab =E bc =E ca Since the low-voltage side is a three-phase four-wire system, when the three-phase load impedance is unbalanced, i.e., Z... a ≠Z b ≠Z c In this system, the three-phase circuits A, B, and C will generate zero-sequence voltage and zero-sequence current. The neutral loop will also generate neutral point displacement voltage and neutral line current. Neglecting residual current, the neutral line current can be approximated as the sum of the phasors of the three-phase zero-sequence currents, and the sum of the phasors of the neutral point displacement voltage and the three-phase zero-sequence voltage is approximated as the total zero-sequence voltage. To simplify the analysis, assume that the three-phase internal impedances of the distribution transformer and low-voltage lines are completely identical, and that the voltage drop caused by the internal impedance is negligible. Therefore, the three-phase internal impedances of the distribution transformer and low-voltage lines can be attributed to the neutral line. Figure 3 The circuit model of a low-voltage three-phase four-wire system after internal impedance reduction is shown in the figure. trn This is the neutral line equivalent impedance after the three-phase internal impedance is reduced.

[0030] Based on the above analysis, the electrical model problem can be established as follows: Given that the three-phase line voltages of the power supply are symmetrical, i.e., E ab =E bc =E ca However, the magnitude of the three-phase line voltage is unknown; the endpoint D of the measurement point is known. a D b D c The effective value of the three-phase phase voltage between n and n is U a U b U c However, the phase angle is unknown. Find the three-phase voltage phasors and the zero-sequence voltage phasor. .

[0031] The above electrical model problem is transformed into a plane geometry model problem for solution.

[0032] Plane geometry model problem: Let the effective value of the three-phase phase voltage be U. aU b U c Let a, b, and c correspond to the lengths of three line segments in a Cartesian coordinate system, respectively. Therefore, a, b, and c are all positive real numbers and satisfy the following conditions: .

[0033] In a Cartesian coordinate system, three line segments of lengths a, b, and c have one end at the origin O and the other end at coordinate points E, F, and G, respectively. Find the coordinate positions of points E, F, and G when the distances between points E, F, and G are equal.

[0034] Figure 4 The voltage phasor diagram for symmetrical three-phase voltages is shown, with directed line segments OE, OF, and OG placed in a Cartesian coordinate system. Directed line segments OE, OF, and OG correspond to the three-phase voltage phasors of phases A, B, and C, respectively. , , Let the phase voltage phasor corresponding to OE be the initial phase with a phase angle of 0°, and let one end of a, b, and c be at the origin O. Let the coordinates of E, F, and G be E(a,0), F(x,0), and G(x,0) respectively. b ,y b ), G(x c ,y c ).like Figure 3 As shown, when a=b, b=c, and c=a, the three-phase voltages are symmetrical, and the triangle ΔEFG formed by points EFG is an equilateral triangle. Therefore, the included angles ∠EOF, ∠FOG, and ∠GOE between the three-phase voltages are all 120°. According to the zero-sequence voltage phasor calculation formula... The effective value of the zero-sequence voltage can obviously be calculated. . Figure 5 The diagram shows the voltage phasor diagram when the three-phase voltages are unbalanced. When a≠b, b≠c, or c≠a, the three-phase voltages are unbalanced, and the phase difference between the three-phase voltage phasors is not equal to 120°. Therefore, the effective value of the zero-sequence voltage is... .because The corresponding point E has coordinates (a, 0). The phase sequence of the three-phase voltages is A, B, and C, with a phase angle difference of approximately 120°. The corresponding point F(x) b ,y b In the third and fourth quadrants of the Cartesian coordinate system, The corresponding point G(x) c ,y c In the first and second quadrants of a Cartesian coordinate system, then x a >x b And x a >x c y b <y cTo ensure that the distances between points E, F, and G are equal, according to the distance formula between two points in a plane, points F and G can be moved within their respective quadrants along circles of radius b and c, respectively, until both |EF|=|FG| and |EG|=|FG| are satisfied. This yields the system of equations in step S2, and allows for the calculation of the coordinates of points E, F, and G, ultimately resulting in the three-phase voltage phasors.

[0035] This application transforms the electrical problem of solving three-phase voltage phasors into a plane geometry problem based on the effective value of three-phase voltages. Therefore, it proposes a calculation method for three-phase voltage phasors based on the effective value of three-phase voltages, thereby realizing the calculation of three-phase voltage phasors with strong practicality.

[0036] S3 calculates the phase angle of the three-phase current based on the three-phase voltage phasors, generates the three-phase current phasors based on the effective value of the three-phase current and the phase angle of the three-phase current, and calculates the zero-sequence current phasor based on the three-phase current phasors.

[0037] In a specific embodiment, step S3 specifically includes: Calculate the phase angles of the three-phase currents based on the three-phase voltage phasors. Generate the three-phase current phasors based on the effective values ​​and phase angles of the three-phase currents. Calculate the zero-sequence current phasor based on the three-phase current phasors. The three-phase current includes phase A current, phase B current, and phase C current. The effective values ​​of phase A current, phase B current, and phase C current are expressed as follows: , and ; Based on the expression for the three-phase voltage phasors, the three-phase voltage phasors can be written in the form of effective value - phase angle, as shown in the following equation: ; in, , and These represent the phase angles of the three-phase voltages; The three-phase power factors are obtained and expressed as cosθ. a cosθ b cosθ c ; When the three-phase power factor is not 1, the phase angles of the three-phase currents are respectively , and , , and The expressions for the power factor angle and the three-phase current phasors are shown in the following equations: ; in, , and These represent the current phasors of phase A, phase B, and phase C, respectively. When the three-phase power factor is 1, the three-phase voltage and the three-phase current are in phase. The expression for the three-phase current phasor is as follows: ; The zero-sequence current phasor is calculated based on the three-phase current phasors, as shown in the following formula: ; in, This represents the zero-sequence current phasor, and the effective value of the zero-sequence current is expressed as: .

[0038] Specifically, existing voltage, current, power, and energy measuring devices not only provide RMS voltage and current data, but some devices also provide power factor data. The phase difference between voltage and current can be obtained through the power factor. Therefore, in the embodiments of this application, the three-phase voltage phase angle is calculated based on the three-phase voltage phasors obtained in step S2. The RMS value of the three-phase current and the three-phase power factor are obtained through a phase current measuring or metering device. Then, the three-phase current phase angle is directly calculated based on the three-phase voltage phase angle and the three-phase power factor. Finally, the three-phase current phasors are obtained based on the RMS value of the three-phase current and the phase angle.

[0039] For public distribution transformers, in actual operation, automatic reactive power compensation devices are usually installed on the low-voltage side. In most cases, the three-phase load power factor of the distribution transformer is close to 1. Therefore, if the measuring device does not provide the power factor, as an approximation, the three-phase voltage and three-phase current can be considered to be in phase.

[0040] In the embodiments of this application, zero-sequence voltage and zero-sequence current can also be used for other purposes. For example, zero-sequence voltage can be used to assess the symmetry of three-phase voltage, reflecting the quality of the power supply voltage; zero-sequence current includes neutral current and residual current, which can be used to intuitively assess the magnitude of neutral current or residual current, reflecting the balance of three-phase load, detecting and assessing whether the neutral wire is overloaded, or indirectly reflecting the insulation of phase wires to ground in a low-voltage three-phase four-wire system. For example, when the measuring device provides neutral current, the zero-sequence current calculated by the method of this application and the direct measurement data of neutral current can be used to calculate residual current (leakage current) data, thereby detecting the grounding fault of the phase wire.

[0041] S4, calculate the zero-sequence impedance based on the zero-sequence voltage phasor and the zero-sequence current phasor.

[0042] In a specific embodiment, the zero-sequence impedance is calculated based on the zero-sequence voltage phasor and the zero-sequence current phasor, as shown in the following formula: ; in, This represents the zero-sequence impedance phasor, and the effective value of the zero-sequence impedance is shown in the following formula: .

[0043] S5, set a judgment threshold, compare the zero-sequence impedance with the judgment threshold, obtain the comparison result, and determine whether there is a zero-disconnection fault in the system based on the comparison result. If so, issue an early warning and return to step S1; otherwise, return to step S1.

[0044] In a specific embodiment, step S5 specifically includes: The judgment thresholds include the degradation threshold and the fault threshold, wherein the degradation threshold is less than the fault threshold; The effective value of the zero-sequence impedance is compared with the set degradation threshold and fault threshold. When the effective value of the zero-sequence impedance is less than the degradation threshold, the zero-sequence impedance of the distribution transformer and its leads in the low-voltage three-phase four-wire system is normal, and the process returns to step S1. When the effective value of the zero-sequence impedance is greater than the degradation threshold and less than the fault threshold, the zero-sequence impedance of the distribution transformer and its leads in the low-voltage three-phase four-wire system exceeds the normal range. There is impedance degradation phenomenon of broken strands or poor contact in the distribution transformer or the lead neutral circuit. A degradation warning is issued and the system returns to step S1. When the effective value of the zero-sequence impedance is greater than the fault threshold, the zero-sequence impedance of the distribution transformer and its leads in the low-voltage three-phase four-wire system exceeds the normal range. A serious contact failure or zero-break fault occurs inside the distribution transformer or in the lead neutral circuit. A fault warning is issued and the system returns to step S1.

[0045] Specifically, the degradation threshold Z th1 This is the threshold for judging the deterioration of the neutral line impedance. Its value range is determined by factors such as the type of transformer (e.g., connection group, insulation medium type, energy efficiency rating), capacity, and the type of lead wire (e.g., copper, aluminum), wire diameter, and length. Fault threshold Z th2 This is the threshold for determining a serious contact failure or neutral wire breakage fault inside the distribution transformer or in the lead-in neutral wire circuit; its value ranges from 5 to 10 times Z. th1 For example, for distribution transformers with connection group Dyn11, energy efficiency rating S9 or higher, and capacity of 100~400kVA, when the lead length is within 5 meters, Z th1 The value can be set between 0.05 and 0.1Ω, Z th2 The value can be set to 0.5Ω. Of course, Z... th1 Z th2 It can also be set based on the initial measurement values ​​after the distribution transformer is installed and passes inspection.

[0046] The technical effects of the embodiments of this application will be illustrated below using Simulink simulation experiments.

[0047] refer to Figure 6 The simulation model includes a 10kV power supply, a 10kV distribution line, a distribution transformer, a 0.4kV distribution line, a simulated load, and voltage and current measuring devices. The distribution transformer parameters are: voltage 10 / 0.4kV, capacity 500kVA, connection group Dyn11, and winding impedance... Magnetizing impedance The voltage and current measuring device M1 is a voltage and current measuring device.

[0048] Based on the transformer winding impedance The data allows for the calculation of the total zero-sequence impedance of the transformer body. for Experiment 1 simulates a fault with severe poor contact in the neutral wire lead of a distribution transformer. The parameter r is set as follows: n =1Ω, to simplify the model, the phase lead r a r b r c All values ​​are set to 0. Z a Z b Z c To generate a randomly variable three-phase load impedance, a uniformly distributed pseudo-random number within the interval [0, 1] is generated using the function rank(), forming the random variable impedance. Its expression is: z + z * rand() * k, where z = 2.4Ω and k = 5. Each simulation lasts 0.4 seconds, and Z is randomly generated again every 0.04 seconds. a Z b Z c Numerical simulations were performed to achieve low-voltage three-phase load current in the range of 16.7–100A. One simulation experiment yields 10 sets of voltage and current data. Table 1 shows the simulated values ​​of phase voltage, phase current, zero-sequence voltage, and zero-sequence current. In Table 1, U... 0S I represents the simulated value of the zero-sequence voltage. 0S This represents the simulated value of the zero-sequence current, and the zero-sequence voltage U in each row. 0S The effective value of the sum of the three-phase phase voltage phasors in the simulation model, and the zero-sequence current I. 0S The effective value of the sum of the three-phase current phasors in the simulation model is given, and plotted as follows: Figure 7 The simulated values ​​of the three-phase phase voltage and zero-sequence voltage shown are graphical representations. Figure 8 The graphs show the simulated values ​​of the three-phase current and zero-sequence current.

[0049] Table 1 Simulated values ​​of phase voltage, phase current, and zero-sequence voltage and zero-sequence current Using steps S1 to S4 of the low-voltage three-phase four-wire system zero-off fault identification method proposed in this application, based on the effective values ​​of the three-phase phase voltage and three-phase current in Table 1, the fault value when r is zero can be calculated. n The calculated values ​​of zero-sequence voltage, zero-sequence current, and zero-sequence impedance when the impedance is 1Ω are expressed as U. 0C I 0C Z 0C Z 0S This represents the simulated value of zero-sequence impedance, and U... 0C I 0C Z 0C with U 0S I 0S Z 0S A comparison is made, as shown in Table 2. , , The relative errors between the simulated and calculated values ​​of zero-sequence voltage, zero-sequence current, and zero-sequence impedance are represented, and plotted as follows: Figure 9 , 10 Figure 11 shows a comparison graph of the simulated and calculated values ​​of zero-sequence voltage, zero-sequence current, and zero-sequence impedance.

[0050] Table 2 U when rn = 1Ω 0C I 0C Z 0C with U 0S I 0S Z 0S contrast The true value of the zero-sequence impedance Z is calculated based on simulation parameters. 0R As shown in the following formula: ; For the simulated value Z of zero-sequence impedance 0S Based on the formula relating zero-sequence voltage and zero-sequence current, the simulated zero-sequence impedance for any experiment numbered 1 to 10 is calculated to be 1.0011Ω, i.e. ; in, This represents the simulated value of the zero-sequence impedance of the i-th group. This represents the simulated value of the zero-sequence voltage in the i-th group. This represents the simulated value of the zero-sequence current in the i-th group, where i represents the sequence number. .

[0051] Clearly, the simulated zero-sequence impedance values ​​from each experiment are consistent with the actual values, i.e. .

[0052] By comparing the data in the graphs and tables, it can be clearly seen that the errors between the simulated and calculated values ​​of zero-sequence voltage and zero-sequence current are very small under different load conditions. In 10 random experiments, the average errors of the calculated values ​​of zero-sequence voltage and zero-sequence current were 0.64% and -1.61%, respectively, thus verifying the accuracy of the zero-sequence impedance calculation method proposed in this invention, so as to facilitate the subsequent judgment of zero-sequence faults based on the calculated zero-sequence impedance.

[0053] Furthermore, the corresponding zero-sequence impedance value can be calculated using the zero-sequence voltage and zero-sequence current values ​​of each group, as shown in the following formula: ; in, This represents the calculated value of the zero-sequence impedance of the i-th group. This represents the calculated value of the zero-sequence voltage in the i-th group. This represents the calculated value of the zero-sequence current in the i-th group.

[0054] Calculated value of zero-sequence impedance Z 0C Simulated value of zero-sequence impedance Z 0S In comparison, its maximum error is 7.14%, its minimum error is -0.15%, and its average error is 2.34%. Therefore, Z is calculated to be... 0C The values ​​are sufficient to meet the application requirements for the measurement and statistics of zero-sequence impedance of distribution transformers and their leads.

[0055] Experiment 2 differs from Experiment 1 in that: the r in the simulation model is... n The values ​​are set sequentially to 0, 0.001, 0.005, 0.01, 0.1, and 1.0Ω, with other parameters remaining unchanged. In each r... n Ten randomized simulation experiments were conducted under the parameter conditions of different r values ​​to obtain different results. n Simulated average value of zero-sequence impedance at a value Calculate the average value The error and its value are shown in Table 3. Based on the data in Table 3, the following can be plotted: Figure 12 The different r shown n Value and Comparison chart.

[0056] Table 3 Different r n Simulated average value of zero-sequence impedance at a value Calculate the average value and error δ Z0 Through Table 3 and Figure 12 Analysis shows that, although when r n The value is close to the total zero-sequence impedance Z of the transformer body.0T Time (Z) 0T =0.0044Ω), the Z0 error percentage reaches its maximum of 17.6%, but it still significantly reflects the effect of r n The change in total zero-sequence impedance caused by the change still satisfies the application requirements for the measurement and statistics of the total zero-sequence impedance of the transformer and its leads; when r n Increased to a value much greater than the total zero-sequence impedance Z of the transformer body 0T When, i.e., impedance degradation occurs in the neutral wire (e.g., r...), n =0.1Ω) or poor contact fault (such as r n When =1Ω), the error δ Z0 The rates decreased rapidly, to 4.18% and 2.33% respectively, which can more accurately reflect r. n The changes in the zero-sequence impedance further prove the accuracy of the zero-sequence impedance calculated by the method proposed in this invention. Therefore, the method proposed in this application can calculate the zero-sequence impedance based solely on the effective values ​​of the three-phase phase voltages and the three-phase currents, and can detect faults such as neutral wire breakage and poor neutral wire contact in a three-phase four-wire system based on the changes in the zero-sequence impedance. It is highly practical in judging neutral wire breakage faults.

[0057] To further verify the accuracy of the method proposed in this invention, the historical operating data of a rural public distribution transformer containing zero-sequence current was retrieved from the power consumption information collection system of a power supply company for calculation and verification. The data information is as follows: (1) Transformer name: Kang* Village No.1 transformer; (2) Type parameters: connection group Dyn11, model SBH15-M-400 / 10 amorphous alloy transformer, low voltage lead length less than 5 meters, CT ratio 120 times; (3) Data acquisition device: distribution transformer monitoring terminal, providing three-phase voltage, three-phase current, and effective value of zero-sequence current; (4) Data time: 1:00 to 12:00 on January 9, 2023, with a data interval of 60 minutes.

[0058] The measured data of three-phase voltage, three-phase current, and zero-sequence current at the integer point are shown in Table 4, and the curves are plotted as follows: Figure 13 and 14 As shown. Steps S1 to S4 of the method proposed in this invention can calculate the zero-sequence voltage, zero-sequence current, and zero-sequence impedance at each time point, respectively expressed as U. 0C I 0C Z 0C The error ΔI0% between the measured and calculated zero-sequence current data is calculated, as shown in Table 5. Based on Table 5, a graph comparing the error between the measured and calculated zero-sequence current data is plotted. Figure 15 As shown.

[0059] Table 4 Measured data of three-phase voltage, three-phase current, and zero-sequence current of Kang* Village No. 1 transformer Table 5. Error data between measured and calculated values ​​of zero-sequence voltage, zero-sequence current, zero-sequence impedance, and zero-sequence current at Kang*cun No. 1 transformer. Combination Figure 15 As shown in Table 5, the measured and calculated values ​​of the zero-sequence current are similar, and their fluctuation patterns are completely consistent. The maximum, minimum, and average errors ΔI0 are -61.99%, 1.08%, and -19.11%, respectively. Compared with the calculation error value of the simulation model, the error between the measured and calculated values ​​of the zero-sequence current is larger. Possible influencing factors include: the symmetry of the three-phase voltage on the high-voltage side of the distribution transformer, the accuracy of the measuring device, and the influence of the power factor. Nevertheless, for the zero-sequence impedance of the distribution transformer and its leads, the difference between the value under normal conditions and the value under conditions of neutral line impedance deterioration or poor contact is extremely large. Under the condition of neutral line fault, the zero-sequence impedance can increase to tens or even hundreds of times the normal value. In comparison, the errors of the zero-sequence voltage and zero-sequence current calculated using the method described in this invention are basically negligible. Therefore, we can still use the calculated zero-sequence voltage and zero-sequence current to further calculate the zero-sequence impedance.

[0060] The zero-sequence impedance at each time point is calculated using the formula for calculating the effective value of zero-sequence impedance in step S4. Based on the calculation results, the following graph can be plotted: Figure 16 The graph shows the calculated values ​​of zero-sequence voltage, zero-sequence current, and zero-sequence impedance. The maximum value of the zero-sequence impedance is 0.0596Ω, the minimum value is 0.0069Ω, and the average value is 0.0232Ω. Considering that the impedance of the three-phase windings and the phase lead impedance on the low-voltage side of the distribution transformer cannot be completely consistent, fluctuations in the three-phase load will cause fluctuations in the zero-sequence impedance. This conclusion has been disclosed in existing technology and will not be further derived or elaborated here. When the zero-sequence current value is small, the calculated zero-sequence impedance value is too large. The maximum value of the zero-sequence impedance in the statistical data can be regarded as an outlier. If the maximum value of the zero-sequence impedance is removed before averaging, the average value of the zero-sequence impedance is 0.02Ω. Finally, it can be considered that the statistically calculated average value of the zero-sequence impedance is closest to the actual total zero-sequence impedance of the distribution transformer and its leads.

[0061] In the embodiments of this application, the accuracy of the method proposed in this application is verified by comparing the measured data of zero-sequence current with the zero-sequence current calculated based on the three-phase phase voltage and three-phase current using historical operating data of rural public distribution transformers.

[0062] Below, historical data of a rural public distribution transformer that had previously experienced a neutral wire contact failure were retrieved from the power consumption information collection system of a power supply company. The method proposed in this application was used to identify the neutral wire disconnection fault. The data information is as follows: (1) Transformer name: Transformer; (2) Type parameters: Connection group Dyn11, Model S11-M-400 / 10.5, Low voltage lead length less than 5 meters, CT ratio 120 times; (3) Data acquisition time: 16:00 to 24:00 on February 13, 2024, with a data acquisition interval of 15 minutes; (4) Data acquisition device: Transformer monitoring terminal, providing three-phase voltage and three-phase current effective values; (5) Fault occurrence and handling process: On the evening of February 13, 2024, the low voltage user of the transformer reported abnormal voltage. After on-site inspection, the maintenance personnel found that the low voltage neutral line terminal of the transformer was loose and had poor contact. At 20:11, they reported to the dispatching console to apply for an emergency power outage and put the transformer into hot standby mode. After handling, they reported to the dispatching console at 20:50 to restore power.

[0063] The three-phase voltage and three-phase current curves obtained by the electricity information acquisition system are as follows: Figure 17 , 18 As shown in Table 6, the actual measured data are as follows.

[0064] Table 6 Measured data of three-phase voltage and current on the low-voltage side of the transformer on February 13, 2024 According to steps S1 to S4 of the method proposed in this application, the zero-sequence voltage U0, zero-sequence current I0, and zero-sequence impedance Z0 during the period from 16:00 to 23:45 are calculated and shown in Table 7. Curves of zero-sequence voltage, zero-sequence current, and zero-sequence impedance are also plotted. Figure 19 As shown.

[0065] Table 7 shows the zero-sequence voltage, zero-sequence current, and zero-sequence impedance of the transformer during the period from 16:00 to 23:45. according to Figure 19 The curve shown divides the fault period of the over-zero line into three stages: before the fault occurs, during the fault, and after the fault is repaired. According to step S5 of the method proposed in this application, a pre-set degradation threshold Z is established. th1 =0.1Ω, fault threshold Z th2 =0.5Ω, and the zero-sequence impedance Z0 calculated at each time point is successively compared with the degradation threshold Z. th1 Fault threshold Z th2 By comparing the results, we can distinguish between three situations: normal neutral impedance, deteriorated neutral impedance, and faulty neutral impedance.

[0066] The first stage, from 16:00 to 18:15, is the pre-fault stage, based on the zero-sequence impedance Z0 and the degradation threshold Z.th1 、Comparison result of the fault threshold Z th2 At the three time points of 16:30, 16:45, and 15:00, the zero-sequence impedances Z0 are 0.2160 Ω, 0.1318 Ω, and 0.1219 Ω respectively. Their values satisfy the judgment condition of Zth1 ≤ Z0 < Zth2. Therefore, it can be determined that the neutral line impedance deterioration phenomenon occurs at this time; The second stage is the four time points during the period from 18:30 to 19:15. The zero-sequence impedance Z0 suddenly increases. The Z0 values are 45.9508 Ω, 6.8198 Ω, 6.9821 Ω, and 7.1385 Ω respectively. Their values satisfy the Z0 ≥ Z th2 judgment condition. Therefore, it can be determined that the neutral line impedance poor contact fault phenomenon occurs at this time; From 19:30 to 20:00, the maintenance personnel disconnected the low-voltage circuit breaker on the load side, the three-phase current dropped to zero, and the three-phase voltage recovered to normal. From 20:15 to 20:30, the maintenance personnel carried out power outage on the distribution transformer to handle the neutral line fault, and the distribution transformer monitoring terminal lost voltage and stopped operating. Therefore, the three-phase voltage and three-phase current data cannot be collected; The third stage is the power supply restoration operation stage after the fault is processed from 20:45 to 23:45. All time points in this period satisfy Z0 ≤ Z th1 judgment condition, and it can be determined that the zero-sequence impedance of the distribution transformer and its leads is normal at this time. According to the Z0 data of this period, the maximum value and minimum value of Z0 can be statistically obtained as 0.0403 Ω and 0.0088 Ω respectively. After removing the maximum value, the sample average value and standard deviation can be calculated as 0.0161 Ω and 0.0072 Ω respectively. Further calculation shows that the coefficient of variation of Z0 in this period is 0.4457. The average value and coefficient of variation of Z0 measured and calculated after the neutral line fault repair show that: the value of Z0 is small and the volatility is also small. The test data of the neutral line poor contact fault of the distribution transformer shows good performance after repair, but there is a slight asymmetry in the three-phase internal impedance of the distribution transformer and its leads.

[0067] In low-voltage three-phase four-wire systems, zero-sequence voltage and zero-sequence current data have significant practical value, especially in monitoring neutral impedance degradation and poor contact faults. However, many existing low-voltage monitoring and protection terminals or systems do not provide zero-sequence voltage and current measurement functions or have the conditions for zero-sequence impedance measurement and calculation. This invention utilizes the effective values ​​of three-phase phase voltage and current provided by existing voltage, current, power, and energy measuring devices, combined with the geometric relationship of the three-phase voltage vector, to calculate zero-sequence voltage, zero-sequence current, and zero-sequence impedance. The calculated zero-sequence impedance can be used for monitoring neutral impedance degradation and poor neutral contact faults in distribution transformers and their leads. It provides data basis for optimizing and rectifying the neutral point displacement voltage of low-voltage distribution networks, and can also promptly detect defects or faults in the neutral circuit, significantly promoting the power supply reliability and voltage qualification rate of low-voltage distribution networks. Furthermore, this application demonstrates, through simulation experiments and analysis of measured data from on-site equipment operation, that the zero-sequence voltage and zero-sequence current can be calculated directly using the effective values ​​of three-phase voltage and three-phase current provided by existing terminals or systems without altering the existing acquisition terminals or systems. The zero-sequence impedance can then be calculated for use in monitoring the neutral impedance degradation and poor neutral contact faults of distribution transformers and their leads, thus verifying the effectiveness and accuracy of the method proposed in this application.

[0068] The steps S1-S6 above do not necessarily represent the order of the steps, but are represented by step symbols. The order of the steps can be adjusted.

[0069] Further reference Figure 20 As an implementation of the methods shown in the above figures, this application provides an embodiment of a low-voltage three-phase four-wire system zero-break fault identification device, which is similar to... Figure 1 Corresponding to the method embodiments shown, this device can be specifically applied to various electronic devices.

[0070] This application provides a device for identifying zero-off faults in a low-voltage three-phase four-wire system, including: Data acquisition module 1 is configured to acquire the effective values ​​of the three-phase phase voltage and three-phase current of the low-voltage three-phase four-wire system at the same time; Zero-sequence voltage calculation module 2 is configured to establish a Cartesian coordinate system, construct three-phase voltage phasors in the Cartesian coordinate system based on the effective values ​​of the three-phase voltages, with the starting point of each three-phase voltage phasor set at the origin of the Cartesian coordinate system. The coordinates of the endpoints of the three-phase voltage phasors in the Cartesian coordinate system are calculated based on the geometric relationship of the three-phase voltage phasors in the Cartesian coordinate system and the effective values ​​of the three-phase voltages, and the three-phase voltage phasors are generated. The zero-sequence voltage phasor is then calculated based on the three-phase voltage phasors. The zero-sequence current calculation module 3 is configured to calculate the phase angle of the three-phase current based on the three-phase phase voltage phasors, generate the three-phase current phasors based on the effective value of the three-phase current and the phase angle of the three-phase current, and calculate the zero-sequence current phasor based on the three-phase current phasors. Zero-sequence impedance calculation module 4 is configured to calculate zero-sequence impedance based on zero-sequence voltage phasor and zero-sequence current phasor; The fault identification module 5 is configured to set a judgment threshold, compare the zero-sequence impedance with the judgment threshold, obtain the comparison result, and determine whether there is a zero-disconnection fault in the system based on the comparison result. If so, an early warning is issued and the system returns to step S1; otherwise, the system returns to step S1.

[0071] Figure 21 This is a schematic diagram of the hardware structure of an electronic device provided in an embodiment of the present invention. For example... Figure 21 As shown, the electronic device in this embodiment includes a processor 2101 and a memory 2102; wherein the memory 2102 is used to store computer execution instructions; and the processor 2101 is used to execute the computer execution instructions stored in the memory to implement the various steps performed by the electronic device in the above embodiment. For details, please refer to the relevant descriptions in the foregoing method embodiments.

[0072] Alternatively, the memory 2102 can be either standalone or integrated with the processor 2101.

[0073] When the memory 2102 is set up independently, the electronic device also includes a bus 2103 for connecting the memory 2102 and the processor 2101.

[0074] This invention also provides a computer storage medium storing computer execution instructions, which, when executed by the processor 2101, implement the above method.

[0075] This invention also provides a computer program product, including a computer program that, when executed by processor 2101, implements the above-described method.

[0076] In the embodiments provided by this invention, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be indirect coupling or communication connection through some interfaces, devices, or modules, and may be electrical, mechanical, or other forms.

[0077] The modules described as separate components may or may not be physically separate. The components shown as modules may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to implement the solution of this embodiment according to actual needs.

[0078] Furthermore, the functional modules in the various embodiments of the present invention can be integrated into one processing unit, or each module can exist physically separately, or two or more modules can be integrated into one unit. The unit composed of the above modules can be implemented in hardware or in the form of hardware plus software functional units.

[0079] The integrated modules described above, implemented as software functional modules, can be stored in a computer-readable storage medium. These software functional modules, stored in a storage medium, include several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor 2101 to execute certain steps of the methods of the various embodiments of this application.

[0080] It should be understood that the processor 2101 described above can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), etc. The general-purpose processor can be a microprocessor, or the processor 2101 can be any conventional processor 2101. The steps of the method disclosed in this invention can be directly manifested as execution by the hardware processor 2101, or execution by a combination of hardware and software modules within the processor 2101.

[0081] The memory 2102 may include high-speed RAM memory, and may also include non-volatile memory NVM, such as at least one disk storage, and may also be a USB flash drive, portable hard drive, read-only memory, disk or optical disc, etc.

[0082] Bus 2103 can be an Industry Standard Architecture (ISA), a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. Bus 2103 can be divided into address bus, data bus, control bus, etc. For ease of illustration, the bus 2103 in the accompanying drawings of this application is not limited to only one bus 2103 or one type of bus 2103.

[0083] The aforementioned storage medium can be implemented from any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk. The storage medium can be any available medium accessible to general-purpose or special-purpose computers.

[0084] An exemplary storage medium is coupled to a processor 2101, enabling the processor 2101 to read information from and write information to the storage medium. Alternatively, the storage medium can be an integral part of the processor 2101. The processor 2101 and the storage medium can reside in an application-specific integrated circuit (ASIC). Alternatively, the processor 2101 and the storage medium can exist as discrete components in an electronic device or a host device.

[0085] Those skilled in the art will understand that all or part of the steps of the above-described method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0086] 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 them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for identifying zero-off faults in a low-voltage three-phase four-wire system, characterized in that, Includes the following steps: S1, obtain the effective values ​​of the three-phase phase voltage and three-phase current of the low-voltage three-phase four-wire system simultaneously; S2, Establish a Cartesian coordinate system. Based on the effective values ​​of the three-phase voltages, construct three-phase voltage phasors in the Cartesian coordinate system. The starting point of each of the three-phase voltage phasors is set at the origin of the Cartesian coordinate system. Calculate the coordinates of the endpoints of the three-phase voltage phasors in the Cartesian coordinate system based on the geometric relationship of the three-phase voltage phasors in the Cartesian coordinate system and the effective values ​​of the three-phase voltages, and generate the three-phase voltage phasors. Calculate the zero-sequence voltage phasor based on the three-phase voltage phasors. S3, calculate the phase angle of the three-phase current based on the three-phase voltage phasors, generate the three-phase current phasors based on the effective value of the three-phase current and the phase angle of the three-phase current, and calculate the zero-sequence current phasor based on the three-phase current phasors; S4, calculate the zero-sequence impedance based on the zero-sequence voltage phasor and the zero-sequence current phasor; S5, set a judgment threshold, compare the zero-sequence impedance with the judgment threshold, obtain the comparison result, and determine whether there is a zero-disconnection fault in the system based on the comparison result. If so, issue an early warning and return to step S1. Otherwise, return to step S1.

2. The method for identifying zero-off faults in a low-voltage three-phase four-wire system according to claim 1, characterized in that, Step S2 specifically includes: The three-phase voltages include phase A, phase B, and phase C, and the effective values ​​of phase A, phase B, and phase C are respectively represented by U. a =a、U b =b and U c =c, where a, b, and c are all positive real numbers; In a Cartesian coordinate system, three directed line segments with lengths a, b, and c, originating from the origin, correspond to the A-phase, B-phase, and C-phase voltage phasors, respectively. The initial phase of the A-phase voltage phasor is set to 0°, and the endpoint coordinates of the A-phase voltage phasor are denoted as (a, 0). The endpoint coordinates of the B-phase voltage phasor are denoted as (x, 0). b ,y b The endpoint coordinates of the C-phase voltage phasor are represented as (x c ,y c Based on the geometric relationship of the three-phase voltage phasors, the following set of equations is derived: ； Solve the system of equations to obtain x. b y b x c and y c The value of is shown in the following formula: ； in: ； According to the x b y b x c and y c The value of can be used to obtain the coordinates of the endpoint of the three-phase voltage phasor in the plane coordinate system, and generate the three-phase voltage phasor. The expression of the three-phase voltage phasor is as follows: ； in, , , These represent the voltage phasors of phase A, phase B, and phase C, respectively. The zero-sequence voltage phasor is calculated based on the three-phase phase voltage phasors, as shown in the following formula: ； in, This represents the zero-sequence voltage phasor, and the effective value of the zero-sequence voltage is expressed as: .

3. The method for identifying zero-off faults in a low-voltage three-phase four-wire system according to claim 2, characterized in that, Step S3 specifically includes: The phase angles of the three-phase currents are calculated based on the three-phase voltage phasors. Three-phase current phasors are generated based on the effective values ​​of the three-phase currents and their phase angles. The zero-sequence current phasor is then calculated based on the three-phase current phasors. The three-phase current includes phase A current, phase B current, and phase C current, and the effective values ​​of phase A current, phase B current, and phase C current are respectively expressed as: , and ; Based on the expression for the three-phase voltage phasors, the three-phase voltage phasors can be written in the form of effective value-phase angle, as shown in the following equation: ； in, , and These represent the phase angles of the three-phase voltages; The three-phase power factors are obtained and expressed as cosθ. a cosθ b cosθ c ; When the three-phase power factor is not 1, the phase angles of the three-phase currents are respectively , and , , and The expressions for the power factor angle and the three-phase current phasors are shown in the following equations: ； in, , and These represent the current phasors of phase A, phase B, and phase C, respectively. When the three-phase power factor is 1, the three-phase voltage and the three-phase current are in phase, and the expression for the three-phase current phasor is as follows: ； The zero-sequence current phasor is calculated based on the three-phase current phasors, as shown in the following formula: ； in, This represents the zero-sequence current phasor, and the effective value of the zero-sequence current is expressed as: .

4. The method for identifying zero-off faults in a low-voltage three-phase four-wire system according to claim 3, characterized in that, The zero-sequence impedance is calculated based on the zero-sequence voltage phasor and the zero-sequence current phasor, as shown in the following formula: ； in, This represents the zero-sequence impedance phasor, and the effective value of the zero-sequence impedance is shown in the following formula: 。 5. The method for identifying zero-off faults in a low-voltage three-phase four-wire system according to claim 2, characterized in that, The process following step S1 also includes: S6, check the effectiveness of the three-phase voltages by comparing the sum of the effective values ​​of any two phase voltages with the effective value of the third phase voltage. If the condition is met: U a +U b >U c U b +U c >U a AndU c +U a >U b If the condition is met, proceed to step S2; otherwise, return to step S1.

6. The method for identifying zero-off faults in a low-voltage three-phase four-wire system according to claim 1, characterized in that, Step S5 specifically includes: The judgment threshold includes a degradation threshold and a fault threshold, wherein the degradation threshold is less than the fault threshold; The effective value of the zero-sequence impedance is compared with the set degradation threshold and fault threshold. When the effective value of the zero-sequence impedance is less than the degradation threshold, the zero-sequence impedance of the distribution transformer and its leads in the low-voltage three-phase four-wire system is normal, and the process returns to step S1. When the effective value of the zero-sequence impedance is greater than the degradation threshold and less than the fault threshold, the zero-sequence impedance of the distribution transformer and its leads in the low-voltage three-phase four-wire system exceeds the normal range. There is impedance degradation phenomenon of broken strands or poor contact in the distribution transformer or the lead neutral circuit. A degradation warning is issued and the system returns to step S1. When the effective value of the zero-sequence impedance is greater than the fault threshold, the zero-sequence impedance of the distribution transformer and its leads in the low-voltage three-phase four-wire system exceeds the normal range. A serious contact failure or zero-break fault occurs inside the distribution transformer or in the lead neutral circuit. A fault warning is issued and the system returns to step S1.

7. A device for identifying zero-off faults in a low-voltage three-phase four-wire system, characterized in that, include: The data acquisition module is configured to acquire the effective values ​​of the three-phase phase voltage and three-phase current of the low-voltage three-phase four-wire system at the same time. The zero-sequence voltage calculation module is configured to establish a Cartesian coordinate system, construct three-phase voltage phasors in the Cartesian coordinate system based on the effective values ​​of the three-phase voltages, with the starting point of each three-phase voltage phasor set at the origin of the Cartesian coordinate system. The coordinates of the endpoints of the three-phase voltage phasors in the Cartesian coordinate system are calculated based on the geometric relationship of the three-phase voltage phasors in the Cartesian coordinate system and the effective values ​​of the three-phase voltages, and the three-phase voltage phasors are generated. The zero-sequence voltage phasor is then calculated based on the three-phase voltage phasors. The zero-sequence current calculation module is configured to calculate the phase angle of the three-phase current based on the three-phase phase voltage phasors, generate three-phase current phasors based on the effective value of the three-phase current and the phase angle of the three-phase current, and calculate the zero-sequence current phasor based on the three-phase current phasors. The zero-sequence impedance calculation module is configured to calculate the zero-sequence impedance based on the zero-sequence voltage phasor and the zero-sequence current phasor. The fault identification module is configured to set a judgment threshold, compare the zero-sequence impedance with the judgment threshold, obtain the comparison result, determine whether there is a zero-disconnection fault in the system based on the comparison result, and if so, issue an early warning and return to step S1. Otherwise, return to step S1.

8. An electronic device, characterized in that, include: One or more processors; Memory, used to store one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in any one of claims 1-6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1-6.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-6.

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