A method, device and readable storage medium for locating single-phase grounding fault in distribution network based on zero-sequence current continuous regulation

Abstract

The present invention discloses a method, device and readable storage medium for locating single-phase grounding faults in a distribution network based on zero-sequence current continuous regulation. When the positioning method is applied to the fault feeder positioning, the neutral point voltage is regulated successively, and the zero-sequence current on each feeder after each regulation is collected; the change in the zero-sequence current amplitude of each feeder is calculated, and the feeder with the largest change is the fault feeder; when it is applied to the fault section positioning, the neutral point voltage is regulated successively, and the fault section is identified by using the cumulative amplitude of each section or by using the cumulative amplitude of each section and the change trend to identify the fault section. The present invention solves the problem of fault positioning with a brand-new technical idea, and greatly improves the accuracy of line selection and positioning.

Description

Technical Field

[0001] The present invention belongs to the technical field of distribution network, and in particular relates to a method, a device and a readable storage medium for locating a single-phase grounding fault in a distribution network based on zero-sequence current continuous modulation. Background Art

[0002] my country's distribution network generally adopts the operation mode of non-effective grounding of the neutral point. Its advantage is that it can continue to operate with the fault for up to 2 hours after a single-phase grounding fault occurs, which is effective in improving the reliability of distribution network power supply. Its disadvantage is that the accuracy of grounding line selection and fault section location needs to be further improved. In particular, for the resonant grounding system, due to the compensation effect of the arc suppression coil, the power frequency current in the fault section has no obvious fault characteristics compared with the non-fault section. In particular, when a high-resistance single-phase grounding fault occurs, the fault location is quite difficult due to factors such as weak fault current and unstable grounding arc. In the key work tasks issued by the State Grid Corporation of China in 2020, it is further proposed to fully ensure the safe and stable operation of the power grid and promote the high-quality development of the power grid. As the focus of construction and transformation in recent years, the distribution network needs to quickly and accurately locate and remove the fault when a fault occurs in order to ensure its power supply reliability and safety. Therefore, it is of great significance to study the fault line selection and location technology of the distribution network.

[0003] At present, the positioning methods are mainly divided into two categories according to the type of signal used for fault location: using the characteristics of the fault quantity itself to locate the fault and completing the fault location through external signals. The first method is affected by factors such as the neutral point grounding method, transition resistance and device sensitivity, and the results are mixed in practical applications. In the second method, in addition to the commonly used "S" injection method, the method of using neutral point online injection signals to identify single-phase grounding faults has also been widely used. How to effectively improve positioning accuracy and precision has been a hot topic of research in this field. Summary of the invention

[0004] The purpose of the present invention is to provide a new method, device and readable storage medium for locating single-phase grounding faults in distribution networks based on zero-sequence current continuous regulation, wherein the locating method solves the problem of fault locating with a new technical idea, and by continuously regulating and amplifying the zero-sequence current multiple times, it is convenient for the device to detect and extract the steady-state characteristic quantity of the fault, and realize the accurate positioning of the fault feeder and the fault section. In particular, under high-resistance grounding faults, the method of the present invention can avoid the failure of injecting a single characteristic signal in high-resistance grounding faults, and greatly improve the line selection and positioning accuracy. And the method can be applied to various types of single-phase grounding faults occurring in neutral ungrounded distribution networks.

[0005] On the one hand, the present invention provides a method for locating a single-phase grounding fault in a distribution network based on zero-sequence current continuous modulation, which, when applied to locating a faulty feeder, comprises the following steps:

[0006] The neutral point voltage is adjusted by injecting current signals one by one, and the zero-sequence current on each feeder after each adjustment is collected;

[0007] Calculate the change in the zero-sequence current amplitude of each feeder;

[0008] Among them, the feeder with the largest change is the faulty feeder.

[0009] The present invention has found that by changing the control system λ to control the neutral point voltage, the change in the zero-sequence current amplitude of the fault feeder will be significantly greater than the change in the zero-sequence current amplitude of the non-fault feeder, and thus the fault feeder and the sound feeder can be effectively identified. Among them, when the neutral point voltage is controlled successively, it is preferred to suppress the fault phase voltage to zero first, and then adjust the injection current size in sequence to amplify the fault phase voltage.

[0010] Optionally, it is also used to locate the fault section of the faulty feeder, and it is a non-high-resistance grounding fault, and the transition resistance R f ≤(E R / 10), where E R is the power supply voltage of the fault phase R in the distribution network, R is one phase among A, B, and C, and the method further comprises the following steps:

[0011] The injected current regulates the neutral point voltage successively, and the zero-sequence current at both ends of each section on the fault feeder is collected after each regulation;

[0012] Calculate the magnitude of the zero-sequence current difference at both ends of each section;

[0013] Then, based on the amplitude of the zero-sequence current difference obtained in each section at each regulation, the cumulative amplitude of each section is calculated, and the fault section is identified by using the cumulative amplitude of each section; or based on the amplitude of the zero-sequence current difference obtained in each section at each regulation, the amplitude change trend of each section is identified, and then the fault section is identified by using the amplitude change trend of each section;

[0014] Among them, if the cumulative amplitude is less than the set threshold, the corresponding section is a healthy section; if the cumulative amplitude is greater than the set threshold, the corresponding section is a faulty section. The set threshold corresponding to section MN is as follows:

[0015] |I set |=n(I 0M0 -I 0N0 )+σ

[0016] In the formula, |I set | is the set threshold, σ is the margin, n is the number of adjustments, are the zero-sequence current of section MN when the fault arc is extinguished, and the detection points at both ends of section MN are M and N, Y MNis the scalar sum of the earth admittance of the line between the detection point N and the detection point M;

[0017] When the amplitude change trend of the section increases with the increase of the fault phase voltage, the corresponding section is a fault section; when the amplitude change trend of the section decreases with the increase of the fault phase voltage, the corresponding section is a sound section.

[0018] The present invention has found that for healthy sections, the difference in zero-sequence current amplitude is only related to the ground parameters of the section; for faulty sections, the zero-sequence current amplitude is not only related to the ground parameters, but also related to the transition resistance value. Therefore, after multiple adjustments and amplifications, the zero-sequence current amplitudes of each section are superimposed, and the difference between the healthy section and the faulty section becomes more obvious, and the judgment rules for the above thresholds are further summarized. At the same time, based on the amplitude study of its changing law, the above judgment rules based on the amplitude change trend are also summarized. Both rules are satisfied for non-high-resistance grounding faults, so any one of the judgment rules can be selected for judgment.

[0019] Among them, the present invention takes margin into consideration when setting the threshold. The margin is set according to the accuracy of the engineering site and the detection equipment, which can minimize the impact of reduced positioning accuracy caused by these factors. Compared with the "small current grounding fault line selection and positioning method by injecting half-wave DC" in the prior art, a DC current signal is injected into the fault system through the neutral point, and the signal is tracked to find the fault point, but the size of the injected current needs to rely on the detection accuracy. Retaining the margin can solve the problem to a certain extent and improve the positioning accuracy.

[0020] Optionally, it is also used to locate the fault section of the faulty feeder and is suitable for high-resistance grounding faults. The transition resistance R f ≥(E R / 10), where E R is the power supply voltage of the fault phase R in the distribution network, R is one phase among A, B, and C, and the method further comprises the following steps:

[0021] The injected current regulates the neutral point voltage one by one, collects the zero-sequence current at both ends of each section on the fault feeder after each regulation, and calculates the amplitude of the zero-sequence current difference at both ends of each section;

[0022] Based on the amplitude of the zero-sequence current difference obtained in each section during each regulation, the cumulative amplitude of each section is calculated and the amplitude change trend of each section is identified;

[0023] Then use the accumulated amplitude and change trend of each section to identify the faulty section;

[0024] Among them, when the cumulative amplitude is greater than the set threshold, the corresponding section is the fault section; or when the amplitude changes with the increase of the fault phase voltage and shows a trend of first decreasing and then increasing, the corresponding section is the fault section;

[0025] When the cumulative amplitude of the section is less than the set threshold and the amplitude changes in a decreasing trend with the increase of the fault phase voltage, the corresponding section is a sound section;

[0026] The set thresholds corresponding to the segment MN are as follows:

[0027] |I set |=n(I 0M0 -I 0N0 )+σ

[0028] In the formula, |I set | is the set threshold, σ is the margin, n is the number of adjustments, are the zero-sequence current of section MN when the fault arc is extinguished, and the detection points at both ends of section MN are M and N, Y MN is the scalar sum of the ground admittance of the line between the detection point N and the detection point M, R f is the transition resistance, E R is the power supply voltage of the fault phase R in the distribution network, where R is one phase among A, B, and C.

[0029] The present invention can effectively identify the fault section under high-resistance grounding fault by using the above-mentioned means. Since in the aforementioned threshold judgment rule, for high-resistance grounding fault, when the cumulative amplitude is less than the threshold, it is not necessarily a healthy section. Therefore, the present invention introduces the change trend of the amplitude to further identify whether it is a healthy section or a fault section. Compared with the prior art "active distribution network single-phase grounding fault line selection method based on injection signal", the above-mentioned technology proposes a fault processing method of injecting a single characteristic signal into the distribution network by adjusting the inverter strategy, but when high-resistance grounding, the characteristic signal flows through the transition resistor, and the shunt effect of the capacitor causes the characteristic signal energy to decrease, and the judgment accuracy is reduced. The present invention controls and amplifies the zero-sequence current multiple times, comprehensively considers the cumulative amplitude and the amplitude change trend, avoids the detection failure of injecting a single characteristic signal under high-resistance grounding fault, and greatly improves the positioning accuracy. And for high-resistance grounding faults with extremely weak fault characteristics, by accurately controlling the injection signal, the change trend of the zero-sequence current amplitude characteristics of each section during the control process is used to identify the fault section. The effect is considerable.

[0030] Optionally, when the neutral point voltage is regulated successively, it is regulated within a set regulation range, and the regulation range is determined according to the transition resistance of the current distribution network, and the rules are as follows:

[0031] When R f ≤(E R / 10), the range of the control coefficient λ is: [0,10R f / E R ],(10R f / ER )∈[0,1];

[0032] When R f ≥(E R / 10), the range of the control coefficient λ is: [0,1];

[0033] Among them, R f is the transition resistance, E R is the power supply voltage of the fault phase R in the distribution network, R is one of the phases A, B, and C, and the control coefficient λ represents the voltage of the fault phase caused by the injected current signal. Regulated to be λ times the fault phase power supply voltage E R .

[0034] The present invention further considers that the residual current at the fault point of 6-66 kV distribution network specified in GB / T 50064-2014 should not exceed 10 A, and then concludes that the coefficient λ for regulating the magnitude of the fault phase voltage after arc extinguishing delay satisfies: λ≤(10R f / E C It should be understood that the present invention is not limited to this, and a smaller range can be selected within the range, which also belongs to the protection content of the present invention.

[0035] Optionally, when adjusting the control coefficient within the control range, the control is performed at equal intervals, and the difference between any two adjacent control coefficients is the same.

[0036] Optionally, when the neutral point voltage is regulated successively, it is regulated within a set regulation range, and the regulation range is determined according to the transition resistance of the current distribution network, and the rules are as follows:

[0037] When the transition resistance R f ≤(E R / 10), the range of the control coefficient λ is: [0,10R f / E C ];

[0038] When the transition resistance R f ≥(E R / 10), the range of the control coefficient λ is: [λ0,1], λ0 is the control coefficient corresponding to the dividing point where the segment amplitude change trend first decreases and then increases, and the control coefficient λ indicates that the injected current signal will increase the fault phase voltage Regulated to be λ times the fault phase power supply voltage E R , wherein, when [λ0,1] is regulated in sequence, when the amplitude change trend of the section increases with the increasing regulation coefficient, the corresponding section is the fault section. In a second aspect, the present invention also provides a single-phase grounding fault location method for a distribution network based on zero-sequence current continuous regulation,

[0039] Applied to fault section location of faulty feeder, and it is not a high-resistance grounding fault, the transition resistance R f ≤(E R / 10), where E R is the power supply voltage of the fault phase R in the distribution network, R is one phase among A, B, and C, and the method further comprises the following steps:

[0040] The injected current regulates the neutral point voltage successively, and the zero-sequence current at both ends of each section on the fault feeder is collected after each regulation;

[0041] Calculate the magnitude of the zero-sequence current difference at both ends of each section;

[0042] Then, the cumulative amplitude of each section is calculated based on the amplitude of the zero-sequence current difference obtained in each regulation, and the faulty section is identified by using the cumulative amplitude of each section; or the amplitude change trend of each section is identified based on the amplitude of the zero-sequence current difference obtained in each regulation, and the faulty section is identified by using the amplitude change trend of each section.

[0043] For specific identification rules, please refer to the detailed descriptions above and below.

[0044] In a third aspect, the present invention also provides a method for locating a single-phase grounding fault in a distribution network based on zero-sequence current continuous modulation.

[0045] It is used to locate the fault section of the fault feeder and is suitable for high-resistance grounding faults. The transition resistance R f ≥(E R / 10), where E R is the power supply voltage of the fault phase R in the distribution network, R is one phase among A, B, and C, and the method further comprises the following steps:

[0046] The injected current regulates the neutral point voltage one by one, collects the zero-sequence current at both ends of each section on the fault feeder after each regulation, and calculates the amplitude of the zero-sequence current difference at both ends of each section;

[0047] Based on the amplitude of the zero-sequence current difference obtained in each section during each regulation, the cumulative amplitude of each section is calculated and the amplitude change trend of each section is identified;

[0048] The accumulated amplitude and change trend of each section are then used to identify the faulty section.

[0049] For specific identification rules, please refer to the detailed descriptions above and below.

[0050] The present invention is aimed at high-resistance grounding faults with extremely weak fault characteristics, and can effectively identify the fault section under the high-resistance grounding fault. In particular, compared with the prior art "active distribution network single-phase grounding fault line selection method based on injection signal", it has higher accuracy and reliability.

[0051] In a fourth aspect, the present invention further provides a device based on the above method, comprising: a PWM active inverter device, a zero-sequence current detection element and a processor, wherein the PWM active inverter device and the zero-sequence current detection element are both connected to the processor;

[0052] Wherein, the PWM active inverter device is connected to the distribution network to provide injection current to regulate the neutral point voltage;

[0053] The zero-sequence current detection element is connected to the distribution network to collect the zero-sequence current of the feeder and / or the zero-sequence current at both ends of each section of the feeder;

[0054] The processor is connected to the zero-sequence current detection element, and is used to obtain the collected zero-sequence current, and locate the faulty feeder and / or the faulty section according to a single-phase grounding fault location method for a distribution network based on zero-sequence current continuous regulation, wherein the processor is also used to control the magnitude of the injected current through the PWM active inverter device.

[0055] In a fifth aspect, the present invention further provides a readable storage medium storing a computer program, wherein the computer program is called by a processor to execute the steps of the method for locating a single-phase grounding fault in a distribution network based on zero-sequence current regulation.

[0056] Beneficial Effects

[0057] 1. The present invention provides a method for locating single-phase grounding faults in distribution networks based on continuous regulation of zero-sequence current, which realizes fault location with a completely new technical idea and technical means. The method can be applied to locating fault feeders and locating fault sections through the technical idea of ​​continuously regulating and amplifying zero-sequence current for multiple times.

[0058] 2. The present invention provides a single-phase grounding fault location method for a distribution network based on continuous regulation of zero-sequence current. Based on the idea of ​​continuously regulating the zero-sequence current for multiple times, the method can be applied to both ordinary grounding faults and high-resistance grounding faults. Especially when applied to high-resistance grounding faults, the method can significantly amplify the fault characteristics and realize accurate positioning of the fault section.

[0059] 3. The present invention provides a method for locating single-phase grounding faults in distribution networks based on zero-sequence current modulation, which can be applied to situations where different types of single-phase grounding faults occur in distribution networks with ungrounded neutral points. Compared with the prior art "Research on small current grounding fault line selection technology based on injection principle" which is only applicable to systems with ungrounded neutral points, the method described in the present invention has a wider range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1This is the schematic diagram of the neutral point injection signal structure;

[0061] Figure 2 It is a schematic diagram of the experimental principle of the present invention in a specific application example;

[0062] Figure 3 is a schematic diagram of a flow chart of an embodiment of the present invention;

[0063] Figure 4 It is a trend diagram of the amplitude variation of the zero-sequence current difference in the high-resistance fault section of the present invention;

[0064] Figure 5 It is the amplitude of the detection points at both ends of the 1kΩ transition resistance fault section (PQ). DETAILED DESCRIPTION

[0065] The present invention provides a single-phase grounding fault location method for a distribution network based on zero-sequence current modulation, which is used to locate the faulty feeder and / or the faulty section. The principle thereof will be explained as follows. In the following content, phase C is selected as the faulty phase as an example. It should be understood that the present invention is not limited to this.

[0066] Figure 1 This is the schematic diagram of the neutral point injection signal structure. The neutral point is grounded through an arc suppression coil. Assume that a single-phase grounding fault occurs on phase C: are the three-phase power supply voltage of the distribution network, G A , G B , G C , C A , C B , C C are the three-phase conductance and capacitance to ground of the system. is the zero-sequence current injected by the PWM active inverter, is the neutral point voltage, L is the arc suppression coil inductance, R f is the transition resistor.

[0067] Take phase C as the reference phase, Figure 1 The distribution network shown in the figure has a single-phase grounding fault on phase C. Estimate the transition resistance R f as follows:

[0068]

[0069] Where: U f is the fault point voltage, G ∑ , C ∑ are the system-to-ground conductance and capacitance respectively, ω is the power frequency electrical angular velocity, for the distribution automation master station, the fault point voltage U f The inductance value L of the arc suppression coil is easy to obtain. Currently, there are many methods to measure the system ground parameters, which will not be described in detail.

[0070] Neutral point voltage With injection current The relationship is:

[0071]

[0072] Where: is the asymmetric vector sum of the system, α=e j120° , Y A , Y B , Y C are the three-phase distributed admittance of the system respectively, α is a complex operator, j is the imaginary unit, and e is the base of the natural logarithm.

[0073] After a fault occurs, the neutral point voltage is first adjusted Make the fault phase voltage To achieve fault arc extinguishing, zero-sequence current is injected at this time The value should be:

[0074]

[0075] The present invention installs zero-sequence current detection elements along the feeder of the distribution network, and divides the detection sections according to the zero-sequence current detection elements, wherein a section is formed between every two zero-sequence current detection elements. In the present invention, the zero-sequence current detection element can be selected as FTU or fault indicator or other elements with detection function. The specific detection process is: using FTU or fault indicator to collect the zero-sequence current signal at the end of the corresponding section and upload it to the main station, and the zero-sequence current collected at both ends of each section during arc extinguishing is subtracted and the amplitude is extracted as follows:

[0076]

[0077] In the formula, are the zero-sequence currents flowing through adjacent detection points MN (where N=M+1), and the corresponding sections are section MN, Y MN is the scalar sum of the ground admittance of the line between the detection point N and the detection point M, G MN , C MN are the conductance and capacitance to ground between the adjacent detection point N and detection point M respectively.

[0078] The technical idea of ​​the present invention is to change the injected current after a certain period of time after the fault arc is extinguished, such as changing the injected current signal after a delay of 5 seconds to adjust the neutral point voltage, thereby adjusting the fault phase voltage. The fault phase power supply voltage is λ times: at this time Considering that the fault phase voltage and neutral point voltage do not exceed The phase voltage is doubled, and the domain of the control coefficient λ is λ∈[0,1]. According to formula (2), the corresponding injection current for:

[0079]

[0080] The duration of zero-sequence current regulation is 50ms. After the compensation arc extinguishing is put into operation for 2s, the regulation coefficient λ is changed to continue regulation. The present invention takes into account the standard GB / T 50064-2014 that stipulates that the residual current at the fault point of 6-66kV distribution network should not exceed 10A. Therefore, the coefficient λ of regulating the fault phase voltage after the arc extinguishing delay satisfies:

[0081] λ≤(10R f / E C ) (6)

[0082] According to formula (6), the initial control range is determined: when R f ≤(E C / 10), the control coefficient λ range is [0,10R f / E C ], where (10R f / E C )∈[0,1]; when R f ≥(E C / 10), the control coefficient can take values ​​in the entire definition domain [0,1]. f ≤(E C / 10) indicates a non-high-resistance ground fault, R f ≥(E C / 10) indicates a high-resistance ground fault.

[0083] First, analyze non-high-resistance ground faults:

[0084] For the healthy detection section, the difference in zero-sequence current amplitude is only related to the ground parameters of the section, as shown in the following formula (7); for the fault detection section, in addition to the ground parameters, it is also related to the transition resistance value, as shown in the following formula (8). Therefore, the amplitude of the zero-sequence current difference of each detection section is:

[0085]

[0086]

[0087] Where: represents the zero-sequence current corresponding to the x-th segment MN (3≤x≤6, the total number of adjustments is n, for example, n=4 is taken as an example, but the present invention is not limited to this), and the fault phase voltage is regulated to λ xThe zero-sequence current of the adjacent M and N detection points when the power supply voltage is times the power supply voltage. Assume that the interval value of each control coefficient is α>0, that is, λ x+1 =λ x +α, A represents the healthy detection section, and B represents the fault detection section. After adding the amplitudes of each detection section after multiple adjustments and amplifications, we get:

[0088]

[0089]

[0090]

[0091]

[0092] Where: n represents the nth control system, and λ1 represents the first control coefficient. The above formulas (9) and (10) are general formulas for nth control, and formulas (11) and (12) are formulas obtained by taking n=4 in this embodiment and the control coefficient interval as an example. It should be understood that this expression is for ease of understanding, and the present invention is not limited to the method described in this embodiment. In this embodiment, when n=4, when the transition resistance is small, R f ≤(E C / 10), assuming that the interval between two consecutive control coefficients is α = 10R f / 4E C , select the first control coefficient λ1=α. When the transition resistance is large, the control range is [0,1] interval, α=0.25.

[0093] The amplitude characteristics of the healthy section in formula (9) show a decreasing trend. Considering that the maximum amplitude characteristic of the healthy section is less than the threshold, substitute formula (4) into (9) to set the threshold |I set |=n(I 0M0 -I 0N0 )+σ, retaining a certain margin σ, which is set according to the accuracy of the project site and the detection equipment. The present invention summarizes the following judgment rules based on the zero-sequence current amplitude distribution characteristics of the fault feeder:

[0094] The detection section whose amplitude superposition is greater than the set threshold is determined to be the fault section, that is:

[0095]

[0096]

[0097] It should be understood that the above formula (13) and formula (14) can effectively identify the fault section on the fault feeder for non-high-resistance grounding faults. In order to be applicable to high-resistance grounding faults, in addition to considering the amplitude superposition, it is also necessary to consider the amplitude change trend, as follows:

[0098] 2) In order to further improve the applicability of the positioning method in high-resistance grounding faults, the amplitude variation trend of the zero-sequence current difference in each section is analyzed.

[0099] When the control coefficient λ is gradually increased within the control range, the fault phase voltage gradually increases from 0 in the arc extinguishing state, and the system zero-sequence voltage decreases. The amplitude of the zero-sequence current difference in the sound detection section in formula (7) is only related to the ground parameter, and its change trend is decreasing. That is, for a section, the amplitude difference of two adjacent controls is calculated as a whole, and then the trend parameter H is accumulated and calculated. A It should be noted that the technical characteristics of the present invention have a monotonic trend, so the amplitude trend can be expressed by the following formula:

[0100]

[0101] Therefore, for a healthy section under a high-resistance grounding fault, the cumulative amplitude is less than the set threshold and the amplitude change trend is a decreasing trend. At the same time, it should be understood that the amplitude change trend has nothing to do with the size of the transition resistance. Therefore, under a non-high-resistance grounding fault, when the amplitude change trend is a decreasing trend, the corresponding section can be determined to be a healthy section.

[0102] The amplitude characteristics of the fault section are affected by the transition resistance and the ground distribution parameters, and change nonlinearly during the regulation process. When it is a non-high-resistance ground fault, the transition resistance R f ≤(E C / 10), the fault grounding current is dominant in the zero-sequence current. As the fault phase voltage increases, the amplitude of the zero-sequence current difference increases nonlinearly. In [0,10R f / E C ] within the control range to meet H B <0, therefore, under non-high-resistance grounding fault conditions, the corresponding section can be directly determined as the fault section based on the increasing trend of the amplitude change.

[0103] When it is a high-resistance ground fault, that is, the transition resistance R f ≥(E C / 10), in the initial stage of regulation, the fault grounding current is small. As the zero-sequence voltage decreases, the amplitude characteristics of the zero-sequence current difference decrease. When the regulation coefficient λ increases, the fault characteristics are further amplified. At this time, the grounding current rise increases, and the amplitude characteristic change trend increases. Therefore, the overall trend is first decreasing and then increasing. At this time: Calculate the amplitude trend H of the fault sectionB =E C (D1-D n ), for the convenience of calculation, the following calculation is based on n = 4 as an example:

[0104] H B =E C (D1-D4) (16)

[0105] Expand to get:

[0106]

[0107] Where: b = Y MN R f ; c=G MN R f The denominator is greater than zero, and λ1 is used as the independent variable. Let equation (15) equal to 0, and the unique zero point is obtained:

[0108]

[0109] Where: 0<λ0<1. Take the molecular formula constructor h(λ1) in equation (15) and take its derivative:

[0110] h′(λ1)=-2(α+αb 2 +2αc) (19)

[0111] From formula (17), we can get: h′(λ1)<0, and h(1)<0. Therefore, H is satisfied in the control range [λ0,1]. B <0, that is, the amplitude change trend of the zero-sequence current difference in the fault section is increasing within the control range [λ0,1]. Select the first control coefficient λ1=λ0+α, the control coefficient interval value α=(1-λ0) / 4, and substitute it into formula (16). Since G MN ≈R f ,get:

[0112]

[0113] In summary, when facing a high-resistance grounding fault, that is, the transition resistance R f ≥(E R / 10), if the cumulative amplitude of the section is less than the set threshold and the amplitude changes in a decreasing trend with the increase of the fault phase voltage, the corresponding section is a healthy section; if the section amplitude changes in a decreasing and then increasing trend with the increase of the fault phase voltage, the corresponding section is a faulty section.

[0114] It should also be noted that for high-resistance grounding faults, if the cumulative amplitude is greater than the threshold, the corresponding section is a faulty section; and precisely because the cumulative amplitude is less than the threshold, there is a possibility that it may be a sound section or a faulty section, therefore, it is also necessary to introduce the above-mentioned amplitude change trend for judgment.

[0115] Furthermore, if the transition resistance R f ≤(E R / 10), the range of the control coefficient λ is: [0,10R f / E C ], within this range, the amplitude characteristics of the zero-sequence current difference in the fault section will simultaneously satisfy: and H B <0 (you can choose any one of them as the judgment standard); if the transition resistance R f ≥(E C / 10), the precise control range is [λ0,1], within which the amplitude characteristics of the zero-sequence current difference in the fault section will satisfy: H B <0. For healthy sections, no matter what control range is set, the following conditions are met: and H A >0, when it is not a high-resistance grounding fault, any one of them can be selected as the judgment standard; if it is a high-resistance grounding fault, in order to eliminate the misjudgment of the fault section, the judgment standards of the two inequalities need to be met at the same time.

[0116] The above is to determine the fault section based on the known fault feeder. The following will introduce the idea of ​​zero-sequence current continuous regulation to realize the location of the fault feeder.

[0117] 3) In the process of changing λ to regulate the neutral point voltage successively, for the fault feeder, the change of zero-sequence current after two adjustments It can be expressed as:

[0118]

[0119] Where: Z 0f is the zero-sequence impedance of the fault feeder.

[0120] For the non-fault feeder, the change in zero-sequence current after two adjustments is for:

[0121]

[0122] Where: Z 0k is the zero-sequence impedance of the non-fault feeder k (k∈{1,...,N}), and N is the total number of feeders. Since the zero-sequence impedance of the distribution network line is generally much larger than the resistance of the fault point to ground, we have:

[0123]

[0124] Therefore, by comparing formula (19) with formula (21), we can see that: That is, by changing λ to regulate the system zero-sequence voltage, the zero-sequence current changes of each feeder in the system can be measured and compared simultaneously through the acquisition device. The zero-sequence current amplitude change of the faulty feeder will be significantly greater than that of the non-faulty feeder.

[0125] Based on the above theoretical statements, the present invention will be further described below in conjunction with embodiments based on the theoretical content.

[0126] Embodiment 1:

[0127] This embodiment provides a method for locating a single-phase grounding fault in a distribution network based on zero-sequence current continuous modulation, based on the theoretical description of the third part above, and when applied to locating a faulty feeder, includes the following steps:

[0128] The neutral point voltage is adjusted by injecting current signals one by one, and the zero-sequence current on each feeder after each adjustment is collected;

[0129] Calculate the change in the zero-sequence current amplitude of each feeder;

[0130] Among them, the feeder with the largest change is the faulty feeder.

[0131] It should be noted that when the neutral point voltage is adjusted successively, it is preferably adjusted according to the control range determined according to the transition resistance mentioned above. Furthermore, the present invention can realize the identification of the faulty feeder and the faulty section under the control without the need to control the faulty feeder and the faulty section separately.

[0132] At this time, it is preferred to follow Figure 3 The process shown is to identify the faulty feeder and the faulty section as follows:

[0133] Step 1: Monitor whether a ground fault occurs. If so, proceed to step 2.

[0134] Step 2: Calculate the transition resistance, determine the control range based on the transition resistance, and then adjust the neutral point voltage step by step.

[0135] Step 3: Collect the zero-sequence current on each feeder after each regulation, and calculate the change in the zero-sequence current amplitude of each feeder, where the feeder with the largest change is the fault feeder.

[0136] Step 4: Extract the amplitude of the zero-sequence current difference at both ends of each section, and identify the faulty section according to the identification method of non-high-resistance grounding fault or the identification method of high-resistance grounding fault.

[0137] Among them, if the fault section is identified according to the identification method of non-high-resistance grounding fault, the cumulative amplitude of each section is used to identify the fault section: if the cumulative amplitude is less than the set threshold, the corresponding section is a healthy section; if the cumulative amplitude is greater than the set threshold, the corresponding section is a faulty section. Or based on the amplitude of the zero-sequence current difference obtained by each regulation of each section, the amplitude change trend of each section is identified, and then the amplitude change trend of each section is used to identify the fault section: when the amplitude change trend of the section increases with the increase of the fault phase voltage, the corresponding section is a faulty section; when the amplitude change of the section decreases with the increase of the fault phase voltage, the corresponding section is a healthy section.

[0138] If the fault section is identified according to the high-resistance grounding fault identification method, the cumulative amplitude is greater than the set threshold, and the corresponding section is a fault section; or when the amplitude change trend is first decreasing and then increasing with the increase of the fault phase voltage, the corresponding section is a fault section; when the cumulative amplitude of the section is less than the set threshold and the amplitude change is decreasing with the increase of the fault phase voltage, the corresponding section is a sound section. Or when the control coefficient λ range is: [λ0,1]; when [λ0,1] is controlled in sequence, as the control coefficient increases in sequence, the amplitude change trend of the section is increasing, the corresponding section is a fault section.

[0139] Based on the above criteria, Figure 1 As shown, first determine whether the cumulative amplitude of the section is greater than the set threshold. If it is, directly determine that the corresponding section is a faulty section; otherwise, determine based on the amplitude change trend. Among them, in the case of a high-resistance grounding fault and when [λ0,1] is adjusted in sequence, as the control coefficient increases in sequence, the amplitude change trend of the section increases, and the corresponding section is a faulty section; as the control coefficient increases in sequence, the amplitude change of the section decreases, and the corresponding section is a healthy section. In the case of non-high-resistance grounding fault, in [0,10R f / E C ]When the control coefficients are adjusted successively, when the amplitude change trend of the section shows an increasing trend as the control coefficients increase successively, the corresponding section is a faulty section; when the amplitude change of the section shows a decreasing trend as the control coefficients increase successively, the corresponding section is a sound section.

[0140] Embodiment 2:

[0141] The present invention provides a method for locating a single-phase grounding fault in a distribution network based on zero-sequence current continuous modulation, wherein a fault feeder is known (the fault feeder can be determined in the manner of embodiment 1 or in other ways), and a fault section is identified on the known fault feeder, and the method is applied to locate the fault section of the fault feeder, and when the fault is not a high-resistance grounding fault, the method further includes the following steps:

[0142] The injected current regulates the neutral point voltage one by one, collects the zero-sequence current at both ends of each section on the fault feeder after each regulation, and calculates the amplitude of the zero-sequence current difference at both ends of each section;

[0143] Then, the cumulative amplitude of each section is calculated based on the amplitude of the zero-sequence current difference obtained in each regulation, and the faulty section is identified by using the cumulative amplitude of each section; or the amplitude change trend of each section is identified based on the amplitude of the zero-sequence current difference obtained in each regulation, and the faulty section is identified by using the amplitude change trend of each section.

[0144] Among them, when the cumulative amplitude is less than the set threshold, the corresponding section is a healthy section; when the cumulative amplitude is greater than the set threshold, the corresponding section is a faulty section. Or when the amplitude change trend of the section increases with the increase of the fault phase voltage, the corresponding section is a faulty section; when the amplitude change of the section decreases with the increase of the fault phase voltage, the corresponding section is a healthy section.

[0145] Embodiment 3:

[0146] The present invention provides a method for locating a single-phase grounding fault in a distribution network based on zero-sequence current continuous modulation. The method has a known fault feeder and identifies a fault section on the known fault feeder. The method is applied to locate the fault section of the fault feeder and is applicable to non-high-resistance grounding faults and high-resistance grounding faults. The method also includes the following steps:

[0147] The injected current regulates the neutral point voltage one by one, collects the zero-sequence current at both ends of each section on the fault feeder after each regulation, and calculates the amplitude of the zero-sequence current difference at both ends of each section;

[0148] Based on the amplitude of the zero-sequence current difference obtained in each section during each regulation, the cumulative amplitude of each section is calculated and the amplitude change trend of each section is identified;

[0149] The accumulated amplitude and change trend of each section are then used to identify the faulty section.

[0150] Among them, when the cumulative amplitude is greater than the set threshold, the corresponding section is a fault section; or when the amplitude changes with the increase of the fault phase voltage and shows a trend of first decreasing and then increasing, the corresponding section is a fault section; when the cumulative amplitude of the section is less than the set threshold and the amplitude changes with the increase of the fault phase voltage and shows a decreasing trend, the corresponding section is a sound section;

[0151] Or when the transition resistance R f ≥(E R / 10), the range of the control coefficient λ is: [λ0,1]; when [λ0,1] is controlled in sequence, when the cumulative amplitude of the section is greater than the set threshold and the amplitude change trend increases with the sequential increase of the control coefficient, the corresponding section is a fault section.

[0152] The present invention provides a device based on the above method, comprising: a PWM active inverter device, a zero-sequence current detection element and a processor, wherein the PWM active inverter device and the zero-sequence current detection element are both connected to the processor.

[0153] The PWM active inverter device is connected to the power distribution network to provide injection current to regulate the neutral point voltage.

[0154] The zero-sequence current detection element is connected to the distribution network and is used to collect the zero-sequence current of the feeder and / or the zero-sequence current at both ends of each section of the feeder. The processor is connected to the zero-sequence current detection element and is used to obtain the collected zero-sequence current and locate the faulty feeder and / or the faulty section according to the method steps described in any one of claims 1 to 8, wherein the processor is also used to control the injection current size of the PWM active inverter.

[0155] For the specific implementation process, please refer to the content of the aforementioned method, which will not be repeated here.

[0156] The present invention provides a readable storage medium storing a computer program, which is called by a processor to execute the steps of the distribution network single-phase grounding fault locating method based on zero-sequence current continuous regulation.

[0157] The present invention provides a device, comprising a processor and a memory, wherein the memory stores a computer program, and the processor calls the computer program to execute the steps of the distribution network single-phase grounding fault locating method based on zero-sequence current continuous regulation.

[0158] For the specific implementation process of each step, please refer to the content of the aforementioned method.

[0159] It should be understood that in the embodiments of the present invention, the processor may be a central processing unit (CPU), and the processor may also be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc. The memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A portion of the memory may also include a non-volatile random access memory. For example, the memory may also store information about the type of device.

[0160] The readable storage medium is a computer-readable storage medium, which may be an internal storage unit of the controller described in any of the foregoing embodiments, such as a hard disk or memory of the controller. The readable storage medium may also be an external storage device of the controller, such as a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), etc. equipped on the controller. Furthermore, the readable storage medium may also include both an internal storage unit of the controller and an external storage device. The readable storage medium is used to store the computer program and other programs and data required by the controller. The readable storage medium may also be used to temporarily store data that has been output or is to be output.

[0161] Specific application examples:

[0162] like Figure 2 As shown in the figure, in a specific application example, the 10kV distribution network considers the asymmetry of line impedance and three-phase distribution parameters, and sets the system damping rate to 1.8% and the asymmetry to 3.81%. The feeder is an overhead line, and the system three-phase parameters to ground are: C A =2.93μF, C B =2.58μF, C C =2.86μF, R A =210.26kΩ, R B =227.79kΩ, R C =205.34kΩ. Feeder parameters are: l1=20km, l2=15km, l3=18km, l4=15km. Divide each section according to the detection device, and calculate the arc extinguishing coil as 10% overcompensation, then the L value is 1.1H.

[0163] It is assumed that the neutral point is grounded through the arc suppression coil. At 0.05s, a single-phase grounding fault occurs in line l4. The compensation device is put into operation to extinguish the arc at 0.1s. The neutral point voltage is adjusted in succession at 0.2s. Simulations are performed for different fault locations and different grounding resistances. Table 1 shows the superposition value and positioning result of the amplitude of the zero-sequence current difference in each detection section after multiple adjustments. In the example, the threshold value |ΔI is set set |=4.

[0164] Table 1 Amplitude of zero-sequence current difference and positioning results in each detection section

[0165]

[0166]

[0167] It can be seen from Table 1 that when the grounding resistance is small, the amplitude of the zero-sequence current difference in the fault section is greater than the set threshold, and the amplitude in the healthy section is less than the threshold, so the fault section can be accurately identified. f >(E C / 10)=578Ω, the amplitude characteristic of the fault section may be greater than the threshold, and its amplitude characteristic change trend needs to be further analyzed. When the transition resistance is equal to 1kΩ, 5kΩ and 10kΩ, the calculated λ0 is 0, 0.024, and 0.34 respectively, and the corresponding control coefficient interval value α is 0.25, 0.244, and 0.15 respectively. The change trend H of the amplitude characteristics of each detection section during the control process is obtained, and the results are shown in Table 2. The change trend of the amplitude characteristics of the non-fault section is relatively stable and shows a decreasing trend. H is greater than zero, while the trend change value of the high-resistance fault section is less than zero, and the positioning result is correct.

[0168] Table 2 Amplitude characteristic change values ​​and positioning results

[0169]

[0170] It should be emphasized that the examples described in the present invention are illustrative rather than restrictive, and therefore the present invention is not limited to the examples described in the specific embodiments. Any other embodiments derived by those skilled in the art based on the technical solution of the present invention that do not depart from the purpose and scope of the present invention, whether modified or replaced, also fall within the scope of protection of the present invention.

Claims

1. A method for locating single-phase grounding faults in a distribution network based on zero-sequence current continuous modulation, characterized in that: When applied to fault feeder location, the following steps are included: The neutral point voltage is adjusted by injecting current signals one by one, and the zero-sequence current on each feeder after each adjustment is collected; Calculate the change in the zero-sequence current amplitude of each feeder; the feeder with the largest change is the fault feeder; It is also used to locate the fault section of the fault feeder, and it is a non-high-resistance grounding fault, and the transition resistance R f ≤(E R / 10), where E R is the power supply voltage of the fault phase R in the distribution network, R is one phase among A, B, and C, and the method further comprises the following steps: The injected current regulates the neutral point voltage successively, and the zero-sequence current at both ends of each section on the fault feeder is collected after each regulation; Calculate the magnitude of the zero-sequence current difference at both ends of each section; Based on the amplitude of the zero-sequence current difference obtained in each section at each regulation; Then, based on the amplitude of the zero-sequence current difference obtained in each section at each regulation, the cumulative amplitude of each section is calculated, and the fault section is identified by using the cumulative amplitude of each section; or based on the amplitude of the zero-sequence current difference obtained in each section at each regulation, the amplitude change trend of each section is identified, and then the fault section is identified by using the amplitude change trend of each section; Among them, if the cumulative amplitude is less than the set threshold, the corresponding section is a healthy section; if the cumulative amplitude is greater than the set threshold, the corresponding section is a faulty section. The set threshold corresponding to section MN is as follows: |I set |=n(I 0M0 -I 0N0 )+σ In the formula, |I set | is the set threshold, σ is the margin, n is the number of adjustments, are the zero-sequence current of section MN when the fault arc is extinguished, and the detection points at both ends of section MN are M and N, Y MN is the scalar sum of the earth admittance of the line between the detection point N and the detection point M; When the amplitude change trend of the section increases with the increase of the fault phase voltage, the corresponding section is a fault section; when the amplitude change trend of the section decreases with the increase of the fault phase voltage, the corresponding section is a sound section.

2. The method according to claim 1, characterized in that: It is also used to locate the fault section of the fault feeder and is suitable for high-resistance grounding faults. The transition resistance R f ≥(E R / 10), where E R is the power supply voltage of the fault phase R in the distribution network, R is one phase among A, B, and C, and the method further comprises the following steps: The injected current regulates the neutral point voltage successively, and the zero-sequence current at both ends of each section on the fault feeder after each regulation is collected, and the amplitude of the zero-sequence current difference at both ends of each section is calculated; Based on the amplitude of the zero-sequence current difference obtained in each section during each regulation, the cumulative amplitude of each section is calculated and the amplitude change trend of each section is identified; Then use the accumulated amplitude and change trend of each section to identify the faulty section; Among them, when the cumulative amplitude is greater than the set threshold, the corresponding section is the fault section; or when the amplitude changes with the increase of the fault phase voltage and shows a trend of first decreasing and then increasing, the corresponding section is the fault section; When the cumulative amplitude of the section is less than the set threshold and the amplitude changes in a decreasing trend with the increase of the fault phase voltage, the corresponding section is a sound section; The set thresholds corresponding to the segment MN are as follows: |I set |=n(I 0M0 -I 0N0 )+σ In the formula, |I set | is the set threshold, σ is the margin, n is the number of adjustments, are the zero-sequence current of section MN when the fault arc is extinguished, and the detection points at both ends of section MN are M and N, Y MN is the scalar sum of the ground admittance of the line between the detection point N and the detection point M, R f is the transition resistance, E R is the power supply voltage of the fault phase R in the distribution network, where R is one phase among A, B, and C.

3. The method according to claim 1 or 2, characterized in that: When the neutral point voltage is adjusted successively, it is adjusted within the set control range. The control range is determined according to the transition resistance of the current distribution network. The rules are as follows: When R f ≤(E R / 10), the range of the control coefficient λ is: [0,10R f / E R ],(10R f / E R )∈[0,1]; When R f ≥(E R / 10), the range of the control coefficient λ is: [0,1]; Among them, R f is the transition resistance, E R is the power supply voltage of the fault phase R in the distribution network, R is one of the phases A, B, and C, and the control coefficient λ represents the voltage of the fault phase caused by the injected current signal. Regulated to be λ times the fault phase power supply voltage E R .

4. The method according to claim 3, characterized in that: When adjusting the control coefficient within the control range, the control is performed at equal intervals, and the difference between any two adjacent control coefficients is the same.

5. The method according to claim 2, characterized in that: When the neutral point voltage is adjusted successively, it is adjusted within the set control range. The control range is determined according to the transition resistance of the current distribution network. The rules are as follows: When the transition resistance R f ≤(E R / 10), the range of the control coefficient λ is: [0,10R f / E C ]; When the transition resistance R f ≥(E R / 10), the range of the control coefficient λ is: [λ0,1], λ0 is the control coefficient corresponding to the dividing point where the segment amplitude change trend first decreases and then increases, and the control coefficient λ indicates that the injected current signal will increase the fault phase voltage Regulated to be λ times the fault phase power supply voltage E R , where [λ0,1] is regulated in sequence, and when the amplitude change trend of the segment increases with the increasing regulation coefficient, the corresponding segment is a fault segment.

6. A method for locating single-phase grounding faults in a distribution network based on zero-sequence current continuous modulation, characterized in that: Applied to fault section location of faulty feeder, and it is not a high-resistance grounding fault, the transition resistance R f ≤(E R / 10), where E R is the power supply voltage of the fault phase R in the distribution network, R is one phase among A, B, and C, and the method further comprises the following steps: The injected current regulates the neutral point voltage successively, and the zero-sequence current at both ends of each section on the fault feeder is collected after each regulation; Calculate the magnitude of the zero-sequence current difference at both ends of each section; Then, the cumulative amplitude of each section is calculated based on the amplitude of the zero-sequence current difference obtained in each regulation, and the faulty section is identified by using the cumulative amplitude of each section; or the amplitude change trend of each section is identified based on the amplitude of the zero-sequence current difference obtained in each regulation, and the faulty section is identified by using the amplitude change trend of each section.

7. A method for locating single-phase grounding faults in a distribution network based on zero-sequence current continuous modulation, characterized in that: It is used to locate the fault section of the fault feeder and is suitable for high-resistance grounding faults. The transition resistance R f ≥(E R / 10), where E R is the power supply voltage of the fault phase R in the distribution network, R is one phase among A, B, and C, and the method further comprises the following steps: The injected current regulates the neutral point voltage successively, and the zero-sequence current at both ends of each section on the fault feeder after each regulation is collected, and the amplitude of the zero-sequence current difference at both ends of each section is calculated; Based on the amplitude of the zero-sequence current difference obtained in each section during each regulation, the cumulative amplitude of each section is calculated and the amplitude change trend of each section is identified; The accumulated amplitude and change trend of each section are then used to identify the faulty section.

8. A device based on the method according to any one of claims 1 to 7, characterized in that: include: The PWM active inverter device, the zero-sequence current detection element and the processor are connected to the processor via the PWM active inverter device and the zero-sequence current detection element; Wherein, the PWM active inverter device is connected to the distribution network to provide injection current to regulate the neutral point voltage; The zero-sequence current detection element is connected to the distribution network to collect the zero-sequence current of the feeder and / or the zero-sequence current at both ends of each section of the feeder; The processor is connected to the zero-sequence current detection element, and is used to obtain the collected zero-sequence current, and locate the fault feeder and / or the fault section according to the method steps described in any one of claims 1-7, wherein the processor is also used to control the injection current size through the PWM active inverter device.

9. A readable storage medium, characterized in that: A computer program is stored, and the computer program is called by a processor to execute the steps of the method according to any one of claims 1 to 7.

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