Three-phase four-wire system low-voltage distribution network analysis method and device based on phase voltage difference

Abstract

The invention relates to the technical field of power distribution networks, in particular to a three-phase four-wire system low-voltage power distribution network analysis method and device based on phase voltage difference, and the method comprises the steps: S1, collecting the effective values of the three-phase phase voltage of a three-phase four-wire system low-voltage power distribution network at m moments in a statistical period, and calculating the maximum phase voltage difference at each moment; s2, correcting the maximum phase voltage difference at each moment according to the correction coefficient to obtain zero-sequence voltage estimated values, and taking the maximum value of the zero-sequence voltage estimated values in the statistical period as a zero-sequence voltage reference value of the statistical period; s3, comparing the zero-sequence voltage reference value in the statistical period with a zero-sequence voltage threshold value, and judging whether the distribution transformer of the three-phase four-wire system low-voltage power distribution network and the zero line loop of the low-voltage line have poor contact faults and defects or not, or identifying the winding wiring group of the distribution transformer; the problems that in the prior art, the neutral point displacement voltage cannot be directly measured, and optimization analysis on the low-voltage distribution network is inconvenient due to zero-sequence voltage data are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power distribution network, in particular to a three-phase four-wire low-voltage power distribution network analysis method and device based on phase voltage difference. BACKGROUND

[0002] In public low-voltage power distribution networks, three-phase load imbalance is almost inevitable, especially when the distributed photovoltaic power generation system (PV) is connected to the low-voltage power distribution network, the local power grid faces challenges in power quality. One of the key problems is the influence of the neutral point displacement voltage in the low-voltage power distribution network. The three-phase four-wire low-voltage power distribution network adopts star connection, and its voltage stability and symmetry are crucial. The neutral point displacement voltage refers to the potential difference between the neutral point of the power supply and the neutral point of the load, which is directly related to the operation state of the power grid. When the neutral point contact is poor or the impedance of the zero line increases, it will cause the increase of the neutral point displacement voltage, and then cause the three-phase voltage imbalance fluctuation, resulting in the increase of the voltage of one phase of the three-phase voltage and the decrease of the voltage of the other phase, and in severe cases, the bidirectional over-limit of the power supply voltage, which makes the three-phase voltage have both high voltage and low voltage. This imbalance fluctuation not only makes it difficult to maintain the specified standard of the user end phase voltage effective value, reduces the voltage qualification rate, but also seriously affects the power quality of the user and the stability of the power grid. In addition, three-phase voltage imbalance will also cause the output of three-phase power equipment to decrease, which will have an adverse effect on production efficiency and energy consumption.

[0003] However, in the three-phase four-wire low-voltage power distribution network in operation, it is difficult to directly measure the neutral point displacement voltage. Zero sequence voltage refers to the voltage between any one phase of the three-phase voltage of the power grid system and the neutral point, which is an important basis for evaluating system imbalance, determining fault type and optimizing power system performance. The zero sequence voltage has a strong correlation with the neutral point displacement voltage, zero sequence current and zero sequence impedance, and the neutral point displacement voltage and zero sequence impedance of the power grid can also be indirectly understood through the zero sequence voltage. At present, a large number of installed and operated measurement, protection and metering terminals generally do not provide zero sequence voltage data, but only provide three-phase voltage effective value data. In theory, the zero sequence voltage can be synthesized by three-phase voltage phasor, but if there is no phase information of the three-phase voltage, the zero sequence voltage cannot be calculated.

[0004] Therefore, it is of great significance to calculate the zero sequence voltage according to the three-phase phase voltage effective value data and the phase voltage difference, so as to evaluate the system imbalance, analyze the fault and optimize the performance of the power system of the low-voltage power distribution network. SUMMARY

[0005] The purpose of the present application is to propose a three-phase four-wire low-voltage power distribution network analysis method and device based on phase voltage difference for the above-mentioned technical problems.

[0006] In a first aspect, the present invention provides an analysis method for a three-phase four-wire low-voltage distribution network based on phase voltage difference, comprising the following steps:

[0007] S1. Collect the effective values ​​of the three-phase phase voltage of the three-phase four-wire low-voltage distribution network at m times within a statistical period, and calculate the difference between the maximum and minimum values ​​of the effective values ​​of the three-phase phase voltage at each time to obtain the maximum phase voltage difference at each time.

[0008] S2, set the correction coefficient, correct the maximum phase voltage difference at each moment according to the correction coefficient, obtain the zero-sequence voltage estimate at each moment, and take the maximum value of the zero-sequence voltage estimate at m moments in the statistical period as the zero-sequence voltage reference value of the statistical period.

[0009] S3, set the zero-sequence voltage threshold, compare the zero-sequence voltage reference value within the statistical period with the zero-sequence voltage threshold to obtain the first comparison result, and determine whether there is a poor contact fault or defect in the distribution transformer and its low-voltage line neutral circuit of the three-phase four-wire low-voltage distribution network based on the first comparison result, and / or determine the winding connection group of the distribution transformer based on the first comparison result.

[0010] Preferably, the correction factor is set in the following ways:

[0011] S21, Construct a zero-sequence voltage offset model. The parameters of the zero-sequence voltage offset model include: the effective value range of the zero-sequence voltage is... The offset step size of the effective value of the zero-sequence voltage is The unit is V. The phase angle of the zero-sequence voltage ranges from 0 to 180°, and the offset step size of the phase angle of the zero-sequence voltage is... The unit is °. An initial phasor of the zero-sequence voltage is set. A set of zero-sequence voltage offset data is constructed by offsetting the initial phasor of the zero-sequence voltage based on the offset step size of the effective value of the zero-sequence voltage and / or the offset step size of the phase angle. The zero-sequence voltage offset data includes several zero-sequence voltage offset phasors. ;

[0012] S22, construct a simplified equivalent circuit model of the distribution transformer and low-voltage lines of a three-phase four-wire low-voltage distribution network. The equivalent voltage sources A, B, and C on the low-voltage side of the distribution transformer are respectively... , and Under three-phase voltage symmetry, , and They are 220∠0°, 220∠-120°, and 220∠120° respectively, based on the three-phase equivalent voltage source and each zero-sequence voltage offset phasor. Calculate the three-phase voltage corresponding to each zero-sequence voltage offset phasor using the following formula:

[0013] ;

[0014] wherein, 、 and respectively represent the A, B, C three-phase voltage phasors corresponding to each zero-sequence voltage offset phasor;

[0015] S23, calculate the difference between the maximum and minimum of the effective values of the three-phase voltage phasors corresponding to each zero-sequence voltage offset phasor, to obtain the maximum phase voltage difference corresponding to each zero-sequence voltage offset phasor;

[0016] S24, calculate the ratio of the effective value of each zero-sequence voltage offset phasor to the maximum phase voltage difference corresponding thereto, to obtain the to-be-determined correction coefficient corresponding to each zero-sequence voltage offset phasor;

[0017] S25, calculate the average of the to-be-determined correction coefficients corresponding to all zero-sequence voltage offset phasors, to obtain the correction coefficient.

[0018] As a preferred, the maximum phase voltage difference at each moment is corrected according to the correction coefficient, to obtain the zero-sequence voltage estimation value at each moment, and the calculation formula is as follows:

[0019] ;

[0020] wherein, 、 and respectively represent the effective values of the A, B, C three-phase voltages of the three-phase four-wire low-voltage distribution network at a certain moment collected in step S1, represents the maximum value of the effective values of the three-phase voltages, represents the minimum value of the effective values of the three-phase voltages, and VRT represents the correction coefficient. represents the zero-sequence voltage estimation value at a certain moment.

[0021] As a preferred, after step S2, it further comprises:

[0022] S4, obtaining the effective values of the zero-sequence currents of the three-phase four-wire low-voltage distribution network at m moments within a statistical period;

[0023] S5, calculating the ratio of the zero-sequence voltage estimation value at each moment to the effective value of the zero-sequence current, to obtain m zero-sequence impedance estimation values, and calculating the average of the m zero-sequence impedance estimation values, to obtain a zero-sequence impedance reference value;

[0024] S6, set the zero-sequence impedance threshold, compare the zero-sequence impedance reference value with the zero-sequence impedance threshold to obtain a second comparison result, and determine whether there is a poor contact fault or defect in the distribution transformer and its low-voltage line neutral circuit of the three-phase four-wire low-voltage distribution network based on the second comparison result, and / or determine the winding connection group of the distribution transformer based on the second comparison result.

[0025] Preferably, if the first comparison result is that the zero-sequence voltage reference value is greater than the zero-sequence voltage threshold, or the second comparison result is that the zero-sequence impedance reference value is greater than the zero-sequence impedance threshold, then the winding connection group of the transformer in the three-phase four-wire low-voltage distribution network is Yyn0, or there is a contact failure or defect in the neutral circuit of the transformer and its low-voltage line in the three-phase four-wire low-voltage distribution network; otherwise, the winding connection group of the transformer in the three-phase four-wire low-voltage distribution network is Dyn11, and the neutral circuit of the transformer and its low-voltage line is normal.

[0026] Secondly, the present invention provides a three-phase four-wire low-voltage distribution network analysis device based on phase voltage difference, comprising:

[0027] The first data acquisition module is configured to collect the effective values ​​of the three-phase phase voltage of the three-phase four-wire low-voltage distribution network at m times within a statistical period, and calculate the difference between the maximum and minimum values ​​of the effective values ​​of the three-phase phase voltage at each time to obtain the maximum phase voltage difference at each time.

[0028] The zero-sequence voltage correction module is configured to set a correction coefficient, correct the maximum phase voltage difference at each moment according to the correction coefficient, obtain the zero-sequence voltage estimate at each moment, and take the maximum value of the zero-sequence voltage estimate at m moments within the statistical period as the zero-sequence voltage reference value of the statistical period.

[0029] The first analysis module is configured to set a zero-sequence voltage threshold, compare the zero-sequence voltage reference value within the statistical period with the zero-sequence voltage threshold, obtain a first comparison result, and determine whether there are poor contact faults or defects in the distribution transformer and its low-voltage line neutral circuit of the three-phase four-wire low-voltage distribution network based on the first comparison result, and / or determine the winding connection group of the distribution transformer based on the first comparison result.

[0030] Preferably, the zero-sequence voltage correction module is followed by:

[0031] The second data acquisition module is configured to acquire the effective value of the zero-sequence current of a three-phase four-wire low-voltage distribution network at m times within a statistical period.

[0032] The zero-sequence impedance calculation module is configured to calculate the ratio of the estimated zero-sequence voltage to the effective value of the zero-sequence current at each moment, obtain m estimated zero-sequence impedance values, and calculate the average value of the m estimated zero-sequence impedance values ​​to obtain the zero-sequence impedance reference value.

[0033] The second analysis module is configured to set a zero-sequence impedance threshold, compare the zero-sequence impedance reference value with the zero-sequence impedance threshold to obtain a second comparison result, and determine whether there are poor contact faults or defects in the distribution transformer and its low-voltage line neutral circuit of the three-phase four-wire low-voltage distribution network based on the second comparison result, and / or determine the winding connection group of the distribution transformer based on the second comparison result.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The three-phase four-wire low-voltage distribution network analysis method proposed in this application can quickly calculate the zero-sequence voltage of the low-voltage distribution network system based on the relationship between the zero-sequence voltage and the neutral point displacement voltage and the effective value data of the three-phase voltage. Furthermore, the zero-sequence impedance can be calculated based on the effective value data of the zero-sequence current. The calculated zero-sequence voltage and zero-sequence impedance can be used to evaluate the imbalance of the low-voltage distribution network system, analyze the faults, and optimize the power system performance. This solves the problem in the prior art that it is inconvenient to evaluate the system imbalance, analyze the faults, and optimize the power system performance of the low-voltage distribution network because the neutral point displacement voltage and zero-sequence voltage data cannot be directly measured.

[0039] (2) The three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference proposed in this application calculates the zero-sequence impedance reference value by performing multiple measurements to calculate the zero-sequence impedance estimate value, so as to overcome the inherent error of the correction coefficient VRT, thereby correcting the theoretical calculation error and reducing the random measurement error, so as to ensure the effectiveness and accuracy of the method proposed in this application in practical applications.

[0040] (3) The three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference provided in the application analyzes the data distribution of a plurality of to-be-determined correction coefficients calculated from a group of zero-sequence voltage offset data in the process of setting the correction coefficient, and determines a reasonable correction coefficient by using a statistical method, so as to ensure the accuracy of the zero-sequence voltage estimated value calculated according to the correction coefficient. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0042] Figure 1 The low-voltage outlet phase voltage and phase current daily curve of a certain power supply enterprise distribution transformer 1;

[0043] Figure 2 The low-voltage outlet phase voltage and phase current daily curve of a certain power supply enterprise distribution transformer 2;

[0044] Figure 3 The flowchart of the three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference of the embodiment one of the present application;

[0045] Figure 4 The schematic diagram of the three-phase four-wire low-voltage distribution network analysis device based on phase voltage difference of the embodiment one of the present application;

[0046] Figure 5 The flowchart of the three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference of the embodiment two of the present application;

[0047] Figure 6 The schematic diagram of the three-phase four-wire low-voltage distribution network analysis device based on phase voltage difference of the embodiment two of the present application;

[0048] Figure 7 The distribution transformer and low-voltage line simplified equivalent circuit model of the three-phase four-wire low-voltage distribution network of the embodiment of the present application;

[0049] Figure 8 The total zero-sequence impedance measurement and calculation equivalent circuit model of the three-phase four-wire low-voltage distribution network of the embodiment of the present application;

[0050] Figure 9 The three-phase voltage and zero-sequence voltage phasor relationship analysis diagram of the embodiment of the present application;

[0051] Figure 103D distribution diagram of maximum phase voltage difference, zero sequence voltage and to-be-determined correction coefficient of embodiments of the present application;

[0052] Figure 11 3D distribution diagram of maximum phase voltage difference, zero sequence voltage and to-be-determined correction coefficient of embodiments of the present application; Figure 10 Distribution top view of

[0053] Figure 12 Simulink simulation model diagram of embodiments of the present application;

[0054] Figure 13 Three-phase phase voltage and zero sequence voltage simulation value diagram of embodiments of the present application;

[0055] Figure 14 Three-phase current and zero sequence current simulation value diagram of embodiments of the present application;

[0056] Figure 15 Comparison diagram of zero sequence voltage measured value and zero sequence voltage estimated value of distribution transformer one of embodiments of the present application;

[0057] Figure 16 Comparison diagram of zero sequence impedance measured value and zero sequence voltage estimated value of distribution transformer one of embodiments of the present application;

[0058] Figure 17 Comparison diagram of zero sequence voltage measured value and zero sequence voltage estimated value of distribution transformer two of embodiments of the present application;

[0059] Figure 18 Comparison diagram of zero sequence impedance measured value and zero sequence voltage estimated value of distribution transformer two of embodiments of the present application;

[0060] Figure 19 Hardware structure schematic diagram of an electronic device provided by an embodiment of the present application. DETAILED DESCRIPTION

[0061] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0062] According to the provisions of the national standard "Power Quality, Supply Voltage Deviation" D-class voltage qualified rate, the qualified range of 220V low-voltage single-phase power supply voltage is 198-235.4V. When implementing the standard, the power supply enterprise generally considers the voltage value greater than the upper limit value as high voltage, and less than the upper limit value as low voltage. If high voltage and low voltage occur simultaneously in a statistical cycle, it is called bidirectional over-limit of supply voltage. Figure 1 andFigure 2 are respectively the daily voltage and current curves of two public distribution transformers (referred to as distribution transformer 1 and distribution transformer 2) of a certain power supply enterprise, and the voltage and current are measured every 15 minutes. The data is from the power production management information system. The low-voltage users of the two distribution transformers include multiple photovoltaic grid-connected power generation users. From Figure 1 It can be seen that during the period of 8-18, the three-phase voltage of distribution transformer 1 has a large difference, the voltage qualification rate is low, and the voltage bidirectional limit phenomenon occurs multiple times. The three-phase current appears negative value and the three-phase voltage rises before and after noon, which is obviously due to the influence of photovoltaic grid-connected power generation. Distribution transformer 1 appears the phenomenon of reverse power transmission from the 0.4kV side to the 10kV side, which leads to the situation that the low-voltage B-phase voltage rises sharply and exceeds the upper limit. By comparing Figure 1 and Figure 2 , the effective values of the three-phase voltage of distribution transformer 2 at each time point are basically consistent. Although it is also affected by photovoltaic grid-connected power generation, during the period of 8-16, the three-phase current appears negative value and the three-phase voltage rises, but the three-phase voltage can still be maintained within the qualified range. The low-voltage side lines of distribution transformer 1 and distribution transformer 2 both include distributed photovoltaic power generation systems (PV), and the three-phase load characteristics of the two are not much different, but the power quality and voltage curves of the two are obviously different. This is due to the strong correlation of the neutral point displacement voltage, zero sequence voltage and zero sequence impedance of the same system.

[0063] Therefore, the three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference provided by the present application is for three-phase four-wire low-voltage distribution network, which provides a method that can quickly calculate the corresponding zero sequence voltage and zero sequence impedance using only the three-phase phase voltage and zero line current effective value data without the support of voltage phase information. The zero sequence voltage and zero sequence impedance data calculated by the method provided by the present application can be used for low-voltage distribution network system imbalance evaluation, fault analysis and power system performance optimization.

[0064] Embodiment one

[0065] Figure 3 A three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference provided by embodiment one of the present application is shown, which includes the following steps:

[0066] S1, collect the effective values of the three-phase phase voltage of the three-phase four-wire low-voltage distribution network at m time points in a statistical period, and calculate the difference between the maximum value and the minimum value of the effective value of the three-phase phase voltage at each time point to obtain the maximum phase voltage difference at each time point.

[0067] S2, set a correction coefficient, correct the maximum phase voltage difference at each time point according to the correction coefficient to obtain the zero sequence voltage estimation value at each time point, and take the maximum value of the zero sequence voltage estimation value at m time points in the statistical period as the zero sequence voltage reference value of the statistical period.

[0068] In specific embodiments, setting the correction coefficient specifically includes:

[0069] S21, constructing a zero sequence voltage offset model, parameters of the zero sequence voltage offset model including: a value range of an effective value of the zero sequence voltage is , an offset step of the effective value of the zero sequence voltage is , unit: V, a value range of a phase angle of the zero sequence voltage is 0~180°, an offset step of the phase angle of the zero sequence voltage is , unit: °, setting an initial phasor of the zero sequence voltage, offsetting the initial phasor of the zero sequence voltage according to the offset step of the effective value of the zero sequence voltage and / or the offset step of the phase angle to construct a set of zero sequence voltage offset data, the zero sequence voltage offset data including a plurality of zero sequence voltage offset phasors ;

[0070] S22, constructing a simplified equivalent circuit model of a distribution transformer and a low-voltage line of a three-phase four-wire low-voltage distribution network, the A, B, C three-phase equivalent voltage sources on the low-voltage side of the distribution transformer being 、 and , under the condition of three-phase symmetry, 、 and being 220∠0°, 220∠-120° and 220∠120° respectively, calculating three-phase phase voltages corresponding to each zero sequence voltage offset phasor according to the three-phase equivalent voltage sources and each zero sequence voltage offset phasor , the calculation formula being as follows:

[0071] ;

[0072] wherein, 、 and represent A, B, C three-phase phase voltage phasors corresponding to each zero sequence voltage offset phasor respectively;

[0073] S23, calculating a difference between a maximum value and a minimum value in effective values of the three-phase phase voltage phasors corresponding to each zero sequence voltage offset phasor to obtain a maximum phase voltage difference corresponding to each zero sequence voltage offset phasor;

[0074] S24, calculating a ratio between the effective value of each zero sequence voltage offset phasor and the maximum phase voltage difference corresponding thereto to obtain a to-be-determined correction coefficient corresponding to each zero sequence voltage offset phasor;

[0075] S25, calculating an average value of the to-be-determined correction coefficients corresponding to all zero sequence voltage offset phasors to obtain the correction coefficient.

[0076] In specific embodiments, the maximum phase voltage difference at each time is corrected according to the correction coefficient to obtain the zero sequence voltage estimation value at each time, and the calculation formula is as follows:

[0077] ;

[0078] wherein, 、 and respectively represent the effective values of the A, B, and C three-phase voltages of the three-phase four-wire low-voltage distribution network at a certain time collected in step S1, represents the maximum value among the effective values of the three-phase voltages, represents the minimum value among the effective values of the three-phase voltages, and VRT represents the correction coefficient, represents the zero sequence voltage estimation value at a certain time.

[0079] S3, set the zero sequence voltage threshold value, compare the zero sequence voltage reference value in the statistical period with the zero sequence voltage threshold value to obtain a first comparison result, determine whether the distribution transformer and its low-voltage line zero line loop of the three-phase four-wire low-voltage distribution network have a poor contact fault, defect based on the first comparison result, and / or determine the winding connection group of the distribution transformer based on the first comparison result.

[0080] In specific embodiments, for the three-phase four-wire low-voltage distribution network with the winding connection group of the distribution transformer being Dyn11, when the first comparison result is that the zero sequence voltage reference value is greater than the zero sequence voltage threshold value, the distribution transformer and its low-voltage line zero line loop of the three-phase four-wire low-voltage distribution network have a poor contact fault, defect, otherwise, the distribution transformer and its low-voltage line zero line loop of the three-phase four-wire low-voltage distribution network are normal;

[0081] For the three-phase four-wire low-voltage distribution network with the winding connection group of the distribution transformer being unknown, when the first comparison result is that the zero sequence voltage reference value is greater than the zero sequence voltage threshold value, the winding connection group of the distribution transformer of the three-phase four-wire low-voltage distribution network is Yyn0, or the distribution transformer and its low-voltage line zero line loop of the three-phase four-wire low-voltage distribution network have a poor contact fault, defect, otherwise, the winding connection group of the distribution transformer of the three-phase four-wire low-voltage distribution network is Dyn11, and the distribution transformer and its low-voltage line zero line loop are normal.

[0082] Specifically, the contact failure fault and defects of the distribution transformer and its low-voltage line zero line circuit of the three-phase four-wire low-voltage distribution network include: the zero line circuit fault of the distribution transformer body; and defects such as broken strands and poor contact of the zero line conductor or connecting device between the distribution transformer and the measurement point. In actual application, the recommended value of the zero sequence voltage threshold can be 3-10V, which can be set according to the distance of the measurement point from the distribution transformer, and the closer the measurement point is to the distribution transformer, the smaller the zero sequence voltage threshold. The recommended value of the zero sequence impedance threshold can be 0.01-0.1Ω, which can be set according to the capacity model of the distribution transformer and the distance of the measurement point from the distribution transformer, and the closer the measurement point is to the distribution transformer, the smaller the zero sequence impedance threshold. The above steps S1-S3 do not necessarily represent the order between the steps, but the step symbols, and the order between the steps can be adjusted.

[0083] Further, with reference to Figure 4 , the embodiment one of the present application also provides an embodiment of a three-phase four-wire low-voltage distribution network analysis device based on phase voltage difference, which corresponds to the method embodiment shown in Figure 3 , and the device can be applied to various electronic devices.

[0084] The embodiment one of the present application provides a three-phase four-wire low-voltage distribution network analysis device based on phase voltage difference, which comprises:

[0085] A first data acquisition module 1 is configured to collect the effective values of the three-phase phase voltages of the three-phase four-wire low-voltage distribution network at m time points in a statistical period, and calculate the difference between the maximum value and the minimum value of the effective values of the three-phase phase voltages at each time point to obtain the maximum phase voltage difference at each time point.

[0086] A zero sequence voltage correction module 2 is configured to set a correction coefficient, correct the maximum phase voltage difference at each time point according to the correction coefficient to obtain the zero sequence voltage estimation value at each time point, and take the maximum value of the zero sequence voltage estimation values at the m time points in the statistical period as the zero sequence voltage reference value of the statistical period.

[0087] A first analysis module 3 is configured to set a zero sequence voltage threshold, compare the zero sequence voltage reference value in the statistical period with the zero sequence voltage threshold to obtain a first comparison result, determine whether the distribution transformer and its low-voltage line zero line circuit of the three-phase four-wire low-voltage distribution network have contact failure faults and defects based on the first comparison result, and / or determine the winding connection group of the distribution transformer based on the first comparison result.

[0088] Embodiment two

[0089] The difference between the embodiment two and the embodiment one of the present application is that after step S2, the embodiment two further comprises:

[0090] S4, obtaining the effective values of the zero sequence currents of the three-phase four-wire low-voltage distribution network at the m time points in the statistical period.

[0091] S5, calculate the ratio of the zero sequence voltage estimation value and the effective value of the zero sequence current at each time, obtain m zero sequence impedance estimation values, and calculate the average of the m zero sequence impedance estimation values to obtain a zero sequence impedance reference value.

[0092] Specifically, the ratio of the zero sequence voltage estimation value and the effective value of the zero sequence current at each time is calculated to obtain m zero sequence impedance estimation values, and the calculation formula is as follows:

[0093] ;

[0094] wherein, represents the zero sequence impedance estimation value, represents the effective value of the zero sequence current;

[0095] The average of the m zero sequence impedance estimation values is calculated to obtain a zero sequence impedance reference value, and the calculation formula is as follows:

[0096] ;

[0097] wherein, represents the zero sequence impedance reference value.

[0098] S6, set a zero sequence impedance threshold value, compare the zero sequence impedance reference value with the zero sequence impedance threshold value to obtain a second comparison result, determine whether the distribution transformer and its low-voltage line zero line loop of the three-phase four-wire low-voltage distribution network exist a poor contact fault, defect based on the second comparison result, and / or determine the winding connection group of the distribution transformer based on the second comparison result.

[0099] Figure 5 An analysis method for a three-phase four-wire low-voltage distribution network based on phase voltage difference is shown. The above steps S1-S6 do not necessarily represent the order between the steps, but the step symbols represent that the order between the steps can be adjusted.

[0100] In a specific embodiment, for the three-phase four-wire low-voltage distribution network with the winding connection group of the distribution transformer being Dyn11, when the second comparison result is that the zero sequence impedance reference value is greater than the zero sequence impedance threshold value, the distribution transformer and its low-voltage line zero line loop of the three-phase four-wire low-voltage distribution network exist a poor contact fault, defect, otherwise, the distribution transformer and its low-voltage line zero line loop of the three-phase four-wire low-voltage distribution network are normal;

[0101] For the three-phase four-wire low-voltage distribution network with unknown winding connection group of the distribution transformer, when the second comparison result is that the zero sequence impedance reference value is greater than the zero sequence impedance threshold value, the winding connection group of the distribution transformer of the three-phase four-wire low-voltage distribution network is Yyn0, or there is a poor contact fault or defect in the zero line loop of the distribution transformer and the low-voltage line of the three-phase four-wire low-voltage distribution network, otherwise, the winding connection group of the distribution transformer of the three-phase four-wire low-voltage distribution network is Dyn11, and the zero line loop of the distribution transformer and the low-voltage line is normal.

[0102] Further, referring to Figure 6 , the embodiment two of the present application also provides an embodiment of a three-phase four-wire low-voltage distribution network analysis device based on phase voltage difference, which corresponds to the method embodiment shown in Figure 5 , and the device can be applied to various electronic devices.

[0103] The three-phase four-wire low-voltage distribution network analysis device based on phase voltage difference provided by the embodiment two of the present application is different from the three-phase four-wire low-voltage distribution network analysis device based on phase voltage difference of the embodiment one in that:

[0104] The zero sequence voltage correction module 2 further comprises:

[0105] The second data acquisition module 4 is configured to acquire the effective value of the zero sequence current of the three-phase four-wire low-voltage distribution network at m time instants within a statistical period;

[0106] The zero sequence impedance calculation module 5 is configured to calculate the ratio of the zero sequence voltage estimation value to the effective value of the zero sequence current at each time instant, obtain m zero sequence impedance estimation values, and calculate the average value of the m zero sequence impedance estimation values to obtain a zero sequence impedance reference value;

[0107] The second analysis module 6 is configured to set a zero sequence impedance threshold value, compare the zero sequence impedance reference value with the zero sequence impedance threshold value to obtain a second comparison result, determine whether there is a poor contact fault or defect in the zero line loop of the distribution transformer and the low-voltage line of the three-phase four-wire low-voltage distribution network based on the second comparison result, and / or determine the winding connection group of the distribution transformer based on the second comparison result.

[0108] The relationship between the phase voltage, the zero sequence voltage and the neutral point displacement voltage of the three-phase four-wire low-voltage distribution network is analyzed below to further illustrate the present application.

[0109] Referring to Figure 7 , a simplified equivalent circuit model of the distribution transformer and the low-voltage line of the three-phase four-wire low-voltage distribution network is constructed to facilitate the analysis of the variation law of the neutral point displacement voltage in the three-phase four-wire low-voltage distribution network and the influencing factors. According to Figure 7 , the low-voltage connection columns a, b and c points to the load neutral point The relationship between the voltage at a point and the voltage source can be expressed as follows:

[0110] ;

[0111] in, , , They represent points a and a respectively. Voltage at point b, point b pair Voltage at point C, point C pair Voltage at a point; , , This indicates the equivalent voltage sources of phases A, B, and C on the low-voltage side of the distribution transformer. , , The three-phase voltages are symmetrical. This represents the neutral point displacement voltage.

[0112] Points a, b, and c The relationship between the voltage at point a and the voltage source can be used to deduce the voltage relationship between points a, b, and c. Zero-sequence voltage of the neutral line As shown in the following formula:

[0113] .

[0114] Based on the above analysis of the relationship between phase voltage, zero-sequence voltage, and neutral point displacement voltage, it can be concluded that points a, b, and c are related to... Zero-sequence voltage of the neutral line With neutral point displacement voltage The relationship between them is that they are equal in magnitude and have a phase difference of 180°.

[0115] Furthermore, the relationship between zero-sequence voltage and zero-sequence impedance in a three-phase four-wire low-voltage distribution network system is analyzed. The zero-sequence voltage is 1 / 3 of the sum of the phasors of the three-phase phase voltages.

[0116] exist At point 1, the relationship between the total zero-sequence voltage and the three-phase voltage on the load side is as follows:

[0117] ;

[0118] in, , , This indicates the neutral point of the three-phase low-voltage line of the distribution transformer relative to the load. voltage, express , , arrive The total zero-sequence voltage on the load side of the point.

[0119] The relationship between the single-phase impedance of the distribution transformer winding, phase line and the zero sequence impedance of the three-phase four-wire low-voltage distribution network is analyzed as follows. , the zero sequence impedance of the distribution transformer is , wherein the reference Figure 7 , , , represents the three-phase equivalent internal impedance of the distribution transformer, represents the primary and secondary winding impedance of the distribution transformer.

[0120] When , the three-phase phase line zero sequence impedance is , wherein the reference Figure 7 , , , represents the three-phase equivalent impedance of the phase line, represents the phase line impedance, represents the zero line impedance. The total zero sequence impedance composed of the distribution transformer, phase line and zero line is . Therefore, the equivalent circuit for measuring and calculating the total zero sequence impedance can be drawn as shown in Figure 8 .

[0121] For the distribution transformer with winding connection group Dyn11, under normal conditions, the impedance values of the primary and secondary winding impedance , the phase line impedance and the zero line impedance are extremely small (much smaller than 0.05Ω), and the change caused by temperature change is also extremely small, so they can be regarded as a constant value with extremely small impedance value. For the distribution transformer with winding connection group Yyn0, under normal conditions, although the impedance of the distribution transformer winding and the line is extremely small, due to the connection group, the internal single-phase impedance Z t of the distribution transformer can be approximately equal to the sum of the distribution transformer excitation impedance Z m , the secondary winding impedance Z t2 , and Z m >>Z t2 At this time, the impedance of the distribution transformer and its line is dominated by Z m , and the value of Z t is much larger than the winding impedance (Z t may be greater than 0.05Ω). Through the analysis of the value of the total zero sequence impedance Z0, the type of the winding connection group of the distribution transformer can be qualitatively identified, or whether the phase line and zero line impedance is abnormal can be analyzed.

[0122] Referring to Figure 8 , , according to Ohm's law, the zero sequence impedance is as follows:

[0123] ;

[0124] The equation is simplified by moving the term to obtain the following equation:

[0125] ;

[0126] And the modulo operation is performed to obtain the following equation:

[0127] .

[0128] Total zero sequence voltage on the load side The magnitude of the value can be approximated by the zero sequence voltage of the distribution transformer , the phase line zero sequence voltage , and the zero line zero sequence voltage , i.e. the neutral line displacement voltage . Therefore, in this application, the equation can be used to calculate and analyze the changes of internal zero sequence impedance, phase line equivalent zero sequence impedance, and zero line impedance.

[0129] The above analysis process is based on the analysis between voltage phasor data, and the existing three-phase four-wire low-voltage distribution network can only obtain the effective value of three-phase voltage. Therefore, in the embodiments of the present application, according to the circuit model of Figure 7 , the possible positions of the zero sequence voltage phasor on the two-dimensional plane and the changes of the three-phase voltage phasor when the three-phase load changes under different sizes of zero sequence impedance are analyzed, and the three-phase voltage and zero sequence voltage phasor relationship analysis diagram is drawn. Figure 9

[0130] As can be seen from Figure 9 , when the three-phase power supply is symmetrical, , , The phasor endpoints can form an equilateral triangle ΔEFG with E, F, and G as vertices, and the center point p of ΔEFG corresponds to the neutral point of the power supply. Assuming that the phase angle of is 0°, then the phase angles of , are -120° and 120°, respectively. , are the effective values of the zero sequence voltage under different zero sequence impedances, and points , are the positions when the phase angles of the zero sequence voltage , are 90° and -90°, respectively, and . Figure 9 In , , , the three-phase voltage phasor corresponding to , ,​ , For corresponding The three-phase voltage phasors. When With the size remaining constant (i.e., the length remaining constant), when the phase angle rotates counterclockwise, it will form a circle with p as the center and radius as... The circle, at this moment, , , The length and phase will also change with It changes with the phase angle, and , , The three are not all equal in size. Similarly, , , The length and phase will also change with The phase angle changes, and the three factors are not all equal in magnitude. Through comparison... , It can be seen that, under the same phase angle, when , , , The difference between the maximum and minimum values ​​of the three Less than , , The difference between the maximum and minimum values ,Right now Therefore, it can be concluded that... and , and The two are correlated in size.

[0131] Based on the preceding analysis, Point corresponding For example, Figure 9 The phasors satisfy the following equation relationship:

[0132] ;

[0133] And it satisfies:

[0134] .

[0135] set up Any point within the circumcircle of ΔEFG also satisfies the above relationship.

[0136] According to steps S21 to S25, set the minimum value of the effective value of the zero-sequence voltage. The maximum value is The value range is 0~220V, and the offset step size of the effective value of the zero-sequence voltage is... The unit is V. The phase angle of the zero-sequence voltage ranges from 0 to 180°, and the offset step size of the phase angle of the zero-sequence voltage is... The unit is °. The initial phasor of the zero-sequence voltage is set to 0∠0°. The initial phasor of the zero-sequence voltage is offset according to the offset step size of the effective value of the zero-sequence voltage and / or the offset step size of the phase angle to construct a set of zero-sequence voltage offset data. The zero-sequence voltage offset data includes: 0∠0°, 3.67∠0°, 7.34∠0°, 3.67∠3°, ..., 216.53∠177°, 220∠177°, 220∠180°. It should be noted that when... The voltage is taken as 0V, which in this model refers to a value close to 0 but not equal to 0. Then, the three-phase voltages after neutral point shift are calculated according to the formulas in steps S22 to S24. , , The maximum phase voltage difference and the undetermined correction coefficient VR are calculated using the following formula:

[0137] .

[0138] In the embodiments of this application, using phase angle Plot a 3D distribution chart of the correction coefficients, with the X-axis as the x-axis, the effective values ​​as the y-axis, and the undetermined correction coefficient VR as the z-axis. Figure 10 As shown, for ease of analysis The maximum phase voltage difference of the three phases when the value ranges from close to 0V to close to the standard effective value of the phase voltage (220V) and the phase angle is arbitrary. With zero sequence voltage The distribution of the ratio VR between the two. Table 1 provides a simplified table of undetermined correction coefficients VR values ​​for the ratio of maximum phase voltage difference to zero-sequence voltage. Figure 10 As can be seen from Table 1, in Within the range approaching 0 or reaching the rated phase voltage value, VR will exhibit a minimum or maximum value at a specific amplitude and phase angle. The value range of VR is between 1 and 1.732. Therefore, in a three-phase four-wire system, when neutral point voltage shift occurs due to system load asymmetry, if the effective values ​​of the three-phase phase voltages are used as the data source to estimate the magnitude of the zero-sequence voltage, and the difference between the maximum and minimum voltage phases is subtracted, the maximum possible error if the difference is used as the zero-sequence voltage reference value is 1.732 times the actual value of the zero-sequence voltage.

[0139] Table 1. Simplified table of undetermined correction coefficients (VR values) for the ratio of maximum phase voltage difference to zero-sequence voltage.

[0140]

[0141] Considering that in low-voltage power supply systems, under normal circumstances The effective value is much smaller than the system's rated phase voltage. In the embodiments of this application, it can be obtained by statistically analyzing a large number of existing, normally operating distribution transformers of various capacity types. The effective value ranges from 0 to 37V; therefore, in the following analysis, the minimum effective value of the zero-sequence voltage is set. The maximum value is ,Depend on Figure 10 As shown in Table 1, in a system with a rated phase voltage of 220V, when At that time, VR's maximum value was 1.732 and its minimum value was 1.432, therefore... VR data in the voltage range of 0-37V and phase range of 0-180° is defined as follows: The voltage value most frequently occurs within the data range VRC, and the data distribution within VRC is as follows: Figure 11 As shown. Figure 11 The arithmetic mean of the values ​​at all points in the VRC region is obtained. and The typical voltage ratio is 1.675, i.e., the correction factor VRT = 1.675. Because, when hour, Therefore, in a specific embodiment, when When VRT=1.675 is used as the correction factor for calculating the zero-sequence voltage reference value within the VRC region, the same statistical method is applied. If multiple measurements are performed... The maximum value is relatively small, for example, The maximum value is 12V, then The effective value ranges from 0 to 7.34V. The three-phase voltages after neutral point offset are calculated according to the formulas in steps S22 to S24. , , The maximum phase voltage difference and the undetermined correction factor, therefore, VR data in the voltage range of 0-7.34V and phase range of 0-180° is defined as follows: The data range VRC in which the voltage value most frequently appears is used. At this time, the average value of the data range VRC is 1.65. In order to further improve the calculation accuracy of the zero-sequence voltage estimate in the subsequent calculation, VRT is set to 1.65.

[0142] When the correction factor VRT is set to 1.675, if the calculation is performed for each measurement... All satisfied This allows us to determine the theoretical error between the estimated zero-sequence voltage value and the actual value in each measurement. The numerical range is [-14.5%, 3.4%]. According to probability principles, if multiple measurements are calculated... The arithmetic mean operation is performed, and the obtained The average value will be reduced and tend to 0. In specific embodiments, if a more accurate zero sequence voltage value is to be obtained, the zero sequence voltage estimates calculated by multiple measurements can also be averaged. Since the three-phase load of the utility distribution transformer is constantly fluctuating, the average error between the zero sequence voltage estimate obtained after the average calculation and the average of the measured zero sequence voltage values measured by the special device will be reduced, and the error value will tend to 0 as the number of measurements increases. Therefore, the method proposed in the present application for calculating the zero sequence voltage estimate is accurate.

[0143] Thus, the zero sequence voltage estimate and the zero sequence voltage reference value can be calculated according to steps S1 and S2, and the zero sequence impedance estimate and the zero sequence impedance reference value can be calculated according to steps S4 and S5. The three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference proposed in the present application can quickly calculate the corresponding zero sequence voltage and zero sequence impedance using only the three-phase phase voltage and zero line current effective value data without the support of voltage phase information.

[0144] In the embodiments of the present application, the correction coefficient VRT=1.675 is set, and the reciprocal of the correction coefficient can be calculated as follows:

[0145]

[0146] The calculation formulas of the zero sequence voltage estimate and the zero sequence impedance estimate are simplified as follows:

[0147]

[0148]

[0149] Under ideal conditions, the total zero sequence impedance Z0 of the distribution transformer and its low-voltage line should be a constant value, but due to the inherent error of the correction coefficient VRT, the same error will occur in each calculation To reduce the error of single measurement calculation , multiple measurements can be performed , and the arithmetic mean of multiple measurements is obtained to achieve the purpose of correcting the theoretical calculation error and reducing the measurement random error.

[0150] ​​​In summary, for a three-phase four-wire low-voltage power distribution system, when the neutral point voltage deviates due to asymmetric load, the effective values of three-phase phase voltage and zero-sequence current can be obtained, and the corresponding zero-sequence voltage estimation value and zero-sequence impedance estimation value can be quickly estimated according to the set correction coefficient, the simplified zero-sequence voltage estimation value and the calculation formula of the zero-sequence impedance estimation value, so as to facilitate subsequent imbalance evaluation, fault analysis and power system performance optimization of the low-voltage power distribution system.

[0151] The technical effects of the technical solutions of the embodiments of the application are described below by using Simulink simulation experiments.

[0152] Reference Figure 12 The Simulink simulation model includes a 10kV power supply, a 10kV distribution line, a distribution transformer, a 0.4kV distribution line, a simulation load and a voltage and current measurement device. Among them, the distribution transformer parameters are: voltage 10 / 0.4kV, capacity 500kVA, winding connection group Dyn11, winding impedance , ; , , , is the distribution transformer line impedance; , , is the low-voltage three-phase load impedance; the voltage and current measurement device M1 is a voltage and current measurement device.

[0153] The simulation distribution transformer zero line serious contact failure is set as , and the phase line , , value is set to 0 to simplify the model. , , is a random variable three-phase load impedance, a pseudo-random number uniformly distributed in the interval [0, 1] is generated by the function rank(), and a random variable impedance is formed, and its expression is: z+z*rand()*k, where z=2.4Ω, k=5. The simulation time is 0.4 seconds, and the random number is re-generated every 0.04 seconds , , to realize the simulation of low-voltage three-phase load current in the interval 16.7-100A, and 10 groups of voltage and current data can be obtained in one simulation experiment, and table 2 data and Figure 13 and Figure 14 are drawn, table 2 is the simulation value data table of phase voltage, phase current, zero-sequence voltage and zero-sequence current; Figure 13 is the three-phase voltage and zero-sequence voltage simulation value graph, Figure 14The graphs show the simulated values ​​of three-phase current and zero-sequence current.

[0154] Table 2 Simulation values ​​of phase voltage, phase current, and zero-sequence voltage and zero-sequence current.

[0155]

[0156] In the embodiments of this application, the correction coefficient VRT = 1.675 is set, and the three-phase phase voltage data in Table 2, from serial number 1 to 10, are substituted row by row into the calculation formula for the zero-sequence voltage estimation value in step S2 to calculate the maximum phase voltage difference and the zero-sequence voltage estimation value. The data in Table 3 is obtained, among which, The error value is calculated for the zero-sequence voltage. Calculate the percentage error for zero-sequence voltage. and The calculation formula is as follows:

[0157] ;

[0158] .

[0159] Table 3 Comparison of Simulated and Estimated Zero-Sequence Voltage Values

[0160]

[0161] Calculated from the data of 10 random simulation experiments in Table 3 The values ​​show that the simulation results in this group are... The maximum error is -4.08%, and the average error is 0.19%. Therefore, based on the above... The error in the zero-sequence voltage estimate calculated by the formula is acceptable. To verify whether the correction factor VRT value of 1.675 for each simulation data is consistent with the theoretical analysis, the simulation data were substituted into the calculation formula for the undetermined correction factor VR. Calculations were performed. The results showed that, according to the VR calculation formula, the maximum value was 1.743, the minimum value was 1.618, and the average value was 1.672. This data is very close to the set correction coefficient VRT=1.675, thus verifying the rationality of the VRT value setting.

[0162] According to step S3 of the method proposed in this application, the zero-sequence voltage threshold Ust is set to 10V, and the zero-sequence voltage estimate obtained from Table 3 is used. The maximum value in As a zero-sequence voltage reference value, since , and the winding connection group of the transformer is Dyn11, so it is determined that there is a serious contact failure between the zero line from the low-voltage side of the transformer to the measuring point M1. The calculation result and the determination conclusion are consistent with the preset conditions of the simulation model.

[0163] Further, in the embodiment of the present application, the effective value of the zero sequence current is obtained according to steps S4 and S5, and the zero sequence impedance estimation value is calculated. The three-phase phase voltages and the zero sequence currents in Table 2 are substituted into the calculation method of the zero sequence impedance estimation value in step S5 to obtain the zero sequence impedance estimation values in Table 4. According to the data comparison between the simulation values and the calculation values in Table 4, it can be obtained that the maximum deviation value is -0.041Ω, and the maximum error percentage can be calculated as -4.1%. According to the calculation method of the zero sequence impedance reference value in step S5, the average value of all zero sequence impedance reference values in Table 4 is calculated to obtain the zero sequence impedance reference value 0.999Ω, and the average value error percentage is 0.2%. Obviously, the zero sequence impedance reference value is very close to the simulation values in Table 4, thereby verifying the effectiveness of the method proposed in the present application.

[0164] According to step S6 of the method proposed in the present application, the zero sequence impedance threshold value is set as the upper limit value 0.1Ω, and is compared with . If , it indicates that the zero sequence impedance of the point upstream of the measuring point is too large. According to Table 4, the zero sequence impedance reference value is 0.999Ω, , so it can be determined that there is a serious contact failure between the zero line from the low-voltage side of the transformer to the measuring point M1. The zero sequence impedance reference value is very close to the zero line impedance simulation parameter , and the accuracy of the method proposed in the present application is also verified.

[0165] Table 4: Data table of zero sequence impedance simulation values and zero sequence impedance estimation values

[0166]

[0167] In order to further verify the accuracy of the method proposed in the present application, Table 5 shows 12 hours of actual measurement data of the phase voltage and current of a public transformer (referred to as transformer one) of a certain power supply enterprise. The data in the table correspond to Figure 1The data shown is the voltage and current data of distribution transformer 1 from 1:00 to 12:00 on a certain day in November 2024. Verification revealed that the transformer is model S9-100, with a capacity of 100kVA, winding connection group Yyn0, and commissioning date of 2007. The measuring device is a new model distribution transformer monitoring terminal, located inside the integrated distribution box on the low-voltage side of the transformer. The low-voltage terminals of the transformer are connected to the integrated distribution box via wires. This terminal can simultaneously measure the effective values ​​and phases of three-phase voltage and current. The measurement accuracy of the effective values ​​of voltage and current is one and two decimal places, respectively, and the measurement accuracy of the voltage and current phase angle is one decimal place. In Table 5, the effective values ​​of the three-phase phase voltage and three-phase current are measured data. Due to measurement limitations, the zero-sequence voltage U0 and zero-sequence current I0 were not directly measured. In Table 5, U0 and I0 are data calculated and synthesized from the three-phase phase voltage and current phasors.

[0168] Table 5 Measured Data of Three-Phase Phase Voltage and Three-Phase Current of Distribution Transformer 1

[0169]

[0170] According to steps S1 to S3 of the method proposed in this application, a preset correction coefficient VRT=1.675 is used to calculate the zero-sequence voltage estimate. Zero-sequence voltage calculation error value The undetermined correction factor VR was used to obtain the measured and estimated zero-sequence voltage data of distribution transformer 1, as shown in Table 6, and a plot was drawn. Figure 15 .according to Figure 15 The zero-sequence voltage estimate can be obtained. Measured value of zero sequence voltage Basically the same, in the table The maximum error was -16.91%, and the average error was -5.55%. The maximum, minimum, and average VR values ​​were 1.768, 1.392, and 1.582, respectively. Combining the three-phase current data in Table 5, it can be seen that the three-phase current showed negative values ​​during the 8-12 hour period. This indicates that due to photovoltaic grid-connected power generation, distribution transformer 1 experienced reverse power transmission from the low-voltage side to the high-voltage side. Table 6 shows that during this period... The numerical value did not change significantly, thus proving that the zero-sequence voltage calculation method described in this invention is also correct in this case.

[0171] Table 6. Measured and Estimated Zero-Sequence Voltage Values ​​for Distribution Transformer 1

[0172]

[0173] For transformer 1, the correction factor VRT is set to 1.675. According to the embodiments of this application, steps S2 and S3 of the three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference determine the maximum value of the zero-sequence voltage estimate. as a zero sequence voltage reference value, and compared with a zero sequence voltage threshold value . Since , it can be qualitatively determined that there is a possible poor contact fault of the zero line between the low-voltage side of the transformer substation and the measurement point, or the winding connection group is Yyn0.

[0174] Further, according to steps S4 to S6 of the three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference according to the embodiments of the present application, the zero sequence voltage estimated value is calculated, the zero sequence voltage measured value, the zero sequence voltage estimated value, the zero sequence impedance measured value and the zero sequence impedance estimated value data table of the transformer substation one are shown in Table 7, and the zero sequence impedance measured value and the zero sequence voltage estimated value comparison chart of the transformer substation one is drawn as shown in FIG. 6. Figure 16

[0175] Table 7 Zero sequence voltage measured value, zero sequence voltage estimated value, zero sequence impedance measured value and zero sequence impedance estimated value data table of transformer substation one

[0176]

[0177] According to step S5 of the three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference according to the embodiments of the present application, the zero sequence impedance reference value is calculated by substituting each time data into the calculation formula of the zero sequence impedance reference value, and the zero sequence impedance reference value is 0.5092Ω, and the average error percentage is -5.55%. Obviously, , the zero sequence impedance measured value is very close, thereby verifying the effectiveness of the three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference according to the embodiments of the present application.

[0178] According to step S6 of the three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference according to the embodiments of the present application, the zero sequence impedance reference value is compared with the zero sequence impedance threshold value , if , it indicates that the zero sequence impedance of the point upstream of the measurement point is too large. In the embodiments of the present application, the zero sequence impedance threshold value is set to 0.5Ω, and from the data in Table 7, the zero sequence impedance reference value is 0.5092Ω, , it can be determined that there is a serious poor contact fault of the zero line between the low-voltage side of the transformer substation and the measurement point.

[0179] Referring to Table 3, Table 4, Table 6 and Table 7, compared with the , calculated by the simulation test, the zero sequence voltage calculation error percentage and the zero sequence impedance calculation error percentage are all-5.55%, which is obviously higher than the corresponding calculation error percentage of the simulation experiment, the main reason is that the calculated 、 is small, and the highest precision of the data source is two decimal places. At this time, due to the systematic error and random error of the voltage and current measuring device, the overall error becomes large, but this does not affect the application of the present application.

[0180] Table 8 shows 12-hour measured data of phase voltage and current of another public distribution transformer (referred to as distribution transformer two) of a certain power supply enterprise. The data in the table correspond to the voltage and current data of distribution transformer two at 1-12 o'clock on November 2024. After checking, the model of the distribution transformer is S13-M-400 / 10, the capacity is 400 kVA, the winding connection group is Dyn11, and the operation time is 2024. The voltage and current data measurement method is the same as that of distribution transformer one. Figure 2

[0181] Table 8 Measured data table of three-phase phase voltage and three-phase current of distribution transformer two

[0182]

[0183] According to the steps S1, S2, S3, S4, S5 and S6 of the three-phase four-wire low-voltage distribution network analysis method based on phase voltage difference according to the embodiments of the present application, the measured value of zero sequence voltage, the estimated value of zero sequence voltage, the measured value of zero sequence impedance, and the estimated value of zero sequence impedance data table of distribution transformer two shown in Table 9 are calculated, and the comparison chart of the measured value of zero sequence voltage and the estimated value of zero sequence voltage shown in Figure 17 and the comparison chart of the measured value of zero sequence impedance and the estimated value of zero sequence impedance shown in Figure 18 are drawn.

[0184] Table 9 Measured value of zero sequence voltage, estimated value of zero sequence voltage, measured value of zero sequence impedance, and estimated value of zero sequence impedance data table of distribution transformer two

[0185]

[0186] For distribution transformer two, according to steps S1 to S3, the zero sequence voltage threshold is set to be 0.1 V, and the maximum value of is calculated , and the first comparison result is , so it can be determined that the impedance value of the zero line between the low-voltage side of the distribution transformer and the measuring point M1 is extremely low, and the winding connection group of the distribution transformer is Dyn11.

[0187] According to steps S4 to S6, the zero sequence impedance threshold is set to be the lower limit value 0.01Ω, and the average value of is calculated ​is 0.5092Ω, and the zero sequence impedance reference value of the power transformer two is 0.0031Ω, that is, even if the value is set to the lower limit value 0.01Ω, , it can be determined that the zero sequence impedance value between the low-voltage side of the power transformer and the measurement point M1 is extremely low, and the winding connection group of the power transformer is Dyn11. ,

[0188] According to Tables 7 and 9, compared with the data corresponding to the power transformer one, the calculation error percentage is obviously increased, the calculation error percentage of the zero sequence voltage corresponding to the power transformer two is 91.64%, which is obviously higher than the calculation error percentage of the zero sequence voltage corresponding to the power transformer one , , and the calculation error percentage of the zero sequence impedance , , the main reason is that: first, due to the fact that the three-phase input voltage of the high-voltage side of the power transformer is not perfect three-phase symmetry, that is, the amplitudes of the A, B and C three-phase voltages cannot be completely equal, the phase difference of the three-phase voltage cannot be exactly equal to 120°, and the three-phase winding structure characteristics and manufacturing process errors of the power transformer and other factors, the maximum phase voltage difference is large; second, the calculated , value is small, and the highest accuracy of the data source is two decimal places. At this time, since the systematic error of the voltage and current measurement device has become the dominant factor, the influence of random error can be basically ignored, so when the measured and calculated zero sequence voltage and zero sequence impedance are small, the overall error will be significantly positively biased, but this does not affect the application of the present application.

[0189] The embodiment of the present application provides the zero sequence voltage reference value and the zero sequence impedance reference value of two public power transformers (power transformer one and power transformer two) of a certain power supply enterprise, which are calculated by using the three-phase four-wire low-voltage power distribution network analysis method based on the phase voltage difference. Specifically, the zero sequence impedance reference value of the power transformer one from the low-voltage lead to the measurement point is 0.5092Ω, and the zero sequence impedance reference value of the power transformer two is 0.0031Ω. In terms of numerical value, the power transformer one is much larger than the power transformer two, which means that under the same unbalanced current, the neutral point displacement voltage of the power transformer one will be much larger than that of the power transformer two, so that the power transformer one generates a large three-phase voltage imbalance, which leads to the situation that the three-phase voltage exceeds the upper limit or the lower limit, and the voltage qualification rate is seriously reduced. This theoretically and numerically explains the reason why the voltage fluctuation range and the voltage qualification rate of the power transformer one and the power transformer two are very different.

[0190] ​​Comparing the two sets of distribution transformers, the winding connection group of distribution transformer one is Yyn0, the model is S9, the capacity is 100 kVA, and the operation time is 2007; the winding connection group of distribution transformer two is Dyn11, the model is S13, the capacity is 400 kVA, and the operation time is 2024. If the low-voltage side output voltage qualified rate of distribution transformer one is to be improved, the total zero sequence impedance thereof needs to be reduced. The most effective measures are: 1, replacing the transformer with Dyn11; 2, checking whether the connecting wires from the distribution transformer to the comprehensive distribution box are aged, whether the wire diameter and type are qualified, and whether there is a poor contact phenomenon at the connection position, tightening the screws at the connection position, or replacing the connecting wires; 3, increasing the capacity of the transformer.

[0191] In summary, based on the relationship among phase voltage, zero sequence voltage, neutral point displacement voltage and zero sequence impedance, through theoretical derivation, the present application proposes a method for a three-phase four-wire low-voltage distribution network system containing a distribution transformer, which directly calculates the corresponding zero sequence voltage and zero sequence impedance using three-phase voltage effective values without supporting three-phase phase voltage phasor data. The method comprises: using three-phase phase voltage effective value data, using the difference between the maximum and minimum values of the simultaneously measured three-phase phase voltage, and dividing by a correction coefficient to obtain a zero sequence voltage estimation value; dividing the calculated zero sequence voltage estimation value by the zero sequence current effective value or the zero line current effective value to obtain the zero sequence impedance. Further, comparing the maximum value of the zero sequence voltage estimation values calculated by multiple measurements with a zero sequence voltage threshold value, or comparing the reference value of the zero sequence impedance calculated by multiple measurements with a zero sequence impedance threshold value, the comparison results can be used to judge the poor contact fault or defect of the distribution transformer and its low-voltage line zero line loop, or to identify the winding connection group of the distribution transformer. Through simulation experiments and calculation and analysis of the actual measured data of distribution transformer one and distribution transformer two, it is verified that the calculation of the zero sequence voltage and the zero sequence impedance in the three-phase four-wire low-voltage distribution network analysis method based on the phase voltage difference proposed by the present application is correct, and the accuracy can meet the requirements of practical application.

[0192] The calculation results and the judgment comparison results obtained by the three-phase four-wire low-voltage distribution network analysis method based on the phase voltage difference proposed by the present application can be used to give early warning, analysis and rectification of faults and defects of the distribution transformer body and the low-voltage outgoing line or the three-phase four-wire line, which is beneficial to improve the voltage qualified rate of the distribution transformer area and the three-phase voltage balance degree, and reduce the power loss of the distribution transformer, the line and the terminal electrical equipment caused by the zero line loop fault or defect.

[0193] Figure 19 The hardware structure schematic diagram of the electronic equipment provided for the embodiment of the present application is shown in FIG. 1. Figure 19As shown, the electronic device of the embodiment includes a processor 1901 and a memory 1902; the memory 1902 is configured to store computer execution instructions; the processor 1901 is configured to execute the computer execution instructions stored in the memory to implement each step performed by the electronic device in the above embodiment. For details, refer to the related description in the foregoing method embodiment.

[0194] Optionally, the memory 1902 can be independent or integrated with the processor 1901.

[0195] When the memory 1902 is independently arranged, the electronic device further includes a bus 1903 for connecting the memory 1902 and the processor 1901.

[0196] The embodiment of the application further provides a computer storage medium, and the computer storage medium stores computer execution instructions; when the processor 1901 executes the computer execution instructions, the method described above is implemented.

[0197] The embodiment of the application further provides a computer program product, and the computer program product includes a computer program; when the computer program is executed by the processor 1901, the method described above is implemented.

[0198] In the embodiments of the application, it should be understood that the disclosed devices and methods can be implemented in other manners. For example, the above-described device embodiments are merely illustrative; for example, the division of the modules is merely logical function division; actual implementation can be in another manner, for example, a plurality of modules can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed coupling or direct coupling or communication connection between the modules can be indirect coupling or communication connection through some interfaces, devices or modules, and can be electrical, mechanical or in other forms.

[0199] The modules illustrated as separate components can or can not be physically separate, and the components illustrated as modules can or can not be physical units, i.e., can be located in one place, or can be distributed on a plurality of network units. Some or all of the modules can be selected according to actual needs to implement the embodiment of the application.

[0200] In addition, each functional module in each embodiment of the application can be integrated in one processing unit, or each module can be physically present alone, or two or more modules can be integrated in one unit. The unit formed by the above modules can be realized in the form of hardware, or in the form of hardware plus software function unit.

[0201] The integrated modules implemented in the form of software function modules can be stored in a computer readable storage medium. The software function modules are stored in a storage medium and include a number of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) or the processor 1901 to perform some steps of the methods of various embodiments of the present application.

[0202] It should be understood that the processor 1901 can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), or the like. The general-purpose processor can be a microprocessor or the processor 1901 can also be any conventional processor 1901, and the like. The steps of the methods disclosed in the present application can be directly embodied as the execution of the processor 1901 in hardware, or be executed by a combination of hardware and software modules in the processor 1901.

[0203] The memory 1902 can include a high-speed RAM memory, and can also include a non-volatile storage NVM, for example, at least one disk memory, and can also be a U disk, a mobile hard disk, a read-only memory, a magnetic disk or an optical disk, and the like.

[0204] The bus 1903 can be an industry standard architecture (ISA), a peripheral component interconnect (PCI) bus, or an extended industry standard architecture (EISA) bus, or the like. The bus 1903 can be divided into an address bus, a data bus, a control bus, and the like. For the sake of convenience, the bus 1903 in the drawings of the present application does not limit only one bus 1903 or one type of bus 1903.

[0205] The storage medium can be realized by 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 that can be accessed by a general-purpose or special-purpose computer.

[0206] An example storage medium is coupled to the processor 1901 such that the processor 1901 can read information from, and can write information to, the storage medium. Of course, the storage medium can be a part of the processor 1901. Consistent with the teachings provided herein, the processor 1901 can be implemented using a digital processor, a digital computer, a microprocessor, and / or any other hardware recited in the above description.

[0207] Those skilled in the art can understand that all or part of the steps of the above-mentioned method embodiments can be completed by program instruction related hardware. The foregoing program can be stored in a computer readable storage medium. When the program is executed, the steps of the above-mentioned method embodiments are executed; and the foregoing storage medium includes: ROM, RAM, magnetic disk or optical disk and various media that can store program codes.

[0208] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the above embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for analyzing a three-phase four-wire low-voltage distribution network based on phase voltage difference, characterized in that, Includes the following steps: S1. Collect the effective values ​​of the three-phase phase voltage of the three-phase four-wire low-voltage distribution network at m times within a statistical period, and calculate the difference between the maximum and minimum values ​​of the effective values ​​of the three-phase phase voltage at each time to obtain the maximum phase voltage difference at each time. S2, set a correction coefficient, correct the maximum phase voltage difference at each moment according to the correction coefficient, obtain the zero-sequence voltage estimate at each moment, and take the maximum value of the zero-sequence voltage estimate at m moments in the statistical period as the zero-sequence voltage reference value of the statistical period. S3, set a zero-sequence voltage threshold, compare the zero-sequence voltage reference value within the statistical period with the zero-sequence voltage threshold to obtain a first comparison result, and determine whether there is a poor contact fault or defect in the distribution transformer and its low-voltage line neutral circuit of the three-phase four-wire low-voltage distribution network based on the first comparison result, and / or determine the winding connection group of the distribution transformer based on the first comparison result.

2. The method for analyzing a three-phase four-wire low-voltage distribution network based on phase voltage difference according to claim 1, characterized in that, The specified correction coefficient includes: S21, Construct a zero-sequence voltage offset model, wherein the parameters of the zero-sequence voltage offset model include: the effective value range of the zero-sequence voltage is... The offset step size of the effective value of the zero-sequence voltage is The unit is V. The phase angle of the zero-sequence voltage ranges from 0 to 180°, and the offset step size of the phase angle of the zero-sequence voltage is... The unit is °. An initial phasor of the zero-sequence voltage is set. A set of zero-sequence voltage offset data is constructed by offsetting the initial phasor of the zero-sequence voltage based on the offset step size of the effective value of the zero-sequence voltage and / or the offset step size of the phase angle. The zero-sequence voltage offset data includes several zero-sequence voltage offset phasors. ; S22, construct a simplified equivalent circuit model of the distribution transformer and low-voltage lines of a three-phase four-wire low-voltage distribution network. The equivalent voltage sources A, B, and C on the low-voltage side of the distribution transformer are respectively... , and Under three-phase voltage symmetry, , and They are 220∠0°, 220∠-120°, and 220∠120° respectively, based on the three-phase equivalent voltage source and each of the zero-sequence voltage offset phasors. The three-phase voltage corresponding to each of the zero-sequence voltage offset phasors is calculated using the following formula: ； in, , and These represent the A, B, and C phase voltage phasors corresponding to each zero-sequence voltage offset phasor; S23, calculate the difference between the maximum and minimum effective values ​​of the three-phase phase voltage phasors corresponding to each zero-sequence voltage offset phasor, and obtain the maximum phase voltage difference corresponding to each zero-sequence voltage offset phasor; S24, calculate the ratio of the effective value of each zero-sequence voltage offset phasor to its corresponding maximum phase voltage difference, and obtain the undetermined correction coefficient corresponding to each zero-sequence voltage offset phasor; S25, calculate the average value of the undetermined correction coefficients corresponding to all zero-sequence voltage offset phasors, and obtain the correction coefficients.

3. The method for analyzing a three-phase four-wire low-voltage distribution network based on phase voltage difference according to claim 1, characterized in that, The maximum phase voltage difference at each moment is corrected according to the correction coefficient to obtain the zero-sequence voltage estimate at each moment. The calculation formula is as follows: ； in, , and These represent the effective values ​​of the three-phase voltages (A, B, and C) of a three-phase four-wire low-voltage distribution network at a certain moment, collected in step S1. This represents the maximum effective value of the three-phase phase voltage. VRT represents the minimum effective value of the three-phase phase voltage, and VRT represents the correction factor. This represents the estimated zero-sequence voltage at a certain moment.

4. The method for analyzing a three-phase four-wire low-voltage distribution network based on phase voltage difference according to claim 1, characterized in that, Step S2 is followed by: S4, obtain the effective value of the zero-sequence current of the three-phase four-wire low-voltage distribution network at m times within the statistical period; S5, calculate the ratio of the zero-sequence voltage estimate to the effective value of the zero-sequence current at each moment to obtain m zero-sequence impedance estimates, and calculate the average value of the m zero-sequence impedance estimates to obtain the zero-sequence impedance reference value. S6, set a zero-sequence impedance threshold, compare the zero-sequence impedance reference value with the zero-sequence impedance threshold to obtain a second comparison result, and determine whether there is a poor contact fault or defect in the distribution transformer and its low-voltage line neutral circuit of the three-phase four-wire low-voltage distribution network based on the second comparison result, and / or determine the winding connection group of the distribution transformer based on the second comparison result.

5. The method for analyzing a three-phase four-wire low-voltage distribution network based on phase voltage difference according to claim 4, characterized in that, If the first comparison result is that the zero-sequence voltage reference value is greater than the zero-sequence voltage threshold, or the second comparison result is that the zero-sequence impedance reference value is greater than the zero-sequence impedance threshold, then the winding connection group of the transformer in the three-phase four-wire low-voltage distribution network is Yyn0, or there is a contact failure or defect in the neutral circuit of the transformer and its low-voltage line in the three-phase four-wire low-voltage distribution network; otherwise, the winding connection group of the transformer in the three-phase four-wire low-voltage distribution network is Dyn11, and the neutral circuit of the transformer and its low-voltage line is normal.

6. A three-phase four-wire low-voltage distribution network analysis device based on phase voltage difference, characterized in that, include: The first data acquisition module is configured to collect the effective values ​​of the three-phase phase voltage of the three-phase four-wire low-voltage distribution network at m times within a statistical period, and calculate the difference between the maximum and minimum values ​​of the effective values ​​of the three-phase phase voltage at each time to obtain the maximum phase voltage difference at each time. The zero-sequence voltage correction module is configured to set a correction coefficient, correct the maximum phase voltage difference at each moment according to the correction coefficient, obtain the zero-sequence voltage estimate at each moment, and take the maximum value of the zero-sequence voltage estimate at m moments within the statistical period as the zero-sequence voltage reference value of the statistical period. The first analysis module is configured to set a zero-sequence voltage threshold, compare the zero-sequence voltage reference value within the statistical period with the zero-sequence voltage threshold, obtain a first comparison result, and determine whether there is a poor contact fault or defect in the distribution transformer and its low-voltage line neutral circuit of the three-phase four-wire low-voltage distribution network based on the first comparison result, and / or determine the winding connection group of the distribution transformer based on the first comparison result.

7. The three-phase four-wire low-voltage distribution network analysis device based on phase voltage difference according to claim 6, characterized in that, The zero-sequence voltage correction module is followed by: The second data acquisition module is configured to acquire the effective value of the zero-sequence current of the three-phase four-wire low-voltage distribution network at m times within the statistical period; The zero-sequence impedance calculation module is configured to calculate the ratio of the estimated zero-sequence voltage to the effective value of the zero-sequence current at each moment, obtain m zero-sequence impedance estimates, and calculate the average value of the m zero-sequence impedance estimates to obtain a zero-sequence impedance reference value. The second analysis module is configured to set a zero-sequence impedance threshold, compare the zero-sequence impedance reference value with the zero-sequence impedance threshold to obtain a second comparison result, and determine whether there is a poor contact fault or defect in the distribution transformer and its low-voltage line neutral circuit of the three-phase four-wire low-voltage distribution network based on the second comparison result, and / or determine the winding connection group of the distribution transformer based on the second comparison result.

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 1-5.

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 1-5.

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 1-5.

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