A method for locating high-resistance grounding fault in distribution network based on voltage and current phase variation

Abstract

A method for locating high-resistance grounding faults in a distribution network based on voltage and current phasor variations belongs to the technical field of relay protection for power systems. It is characterized in that it includes the following steps: collecting three-phase voltage and three-phase current of the distribution network; extracting the power frequency phasors of the three-phase voltage and the residual current; obtaining the normalized phasors of the residual current before and after the fault; calculating the phase angle difference between the three-phase voltage phasor and the normalized phasor variation of the residual current; and judging whether the line is a sound line or a faulty line. In the method for locating high-resistance grounding faults in a distribution network based on voltage and current phasor variations, the normalized phasors of the residual current before and after the fault are constructed with reference to the three-phase voltage power frequency phasors, and the residual current phasor variation obtained with the residual current normalized phasor is the residual current phasor generated by the real fault, which eliminates the influence of unbalanced current, greatly improves the purity and accuracy of the fault electrical quantity used, and lays the foundation for the detection of small resistance and high resistance grounding faults.

Description

Technical Field

[0001] The invention relates to a method for locating high-resistance grounding faults in a distribution network based on voltage and current phase quantity changes, and belongs to the technical field of relay protection of power systems. Background Art

[0002] The problem of fault location in low-resistance grounding systems has long plagued power supply operation departments. Low-resistance grounding systems have small zero-sequence impedance. When a high-resistance grounding fault occurs, the transient process is not obvious, the zero-sequence voltage and current amplitudes are low, and traditional protection methods have poor resistance to transition resistance. In the prior art, the commonly used detection methods for single-phase grounding faults in low-resistance grounding systems mainly use zero-sequence current over-limit, which has limited resistance to transition resistance; the inverse time zero-sequence current protection method and other protection methods using zero-sequence current and voltage all have the problem of poor resistance to transition resistance, making it difficult to ensure the reliability of the action. In addition, the detection method relying on zero-sequence voltage and zero-sequence current is not suitable for some distribution network automation equipment that does not have the conditions for collecting zero-sequence voltage and zero-sequence current.

[0003] The current generated by a high-resistance grounding fault is very weak. When the system parameters are unbalanced, the residual current (unbalanced current) existing during normal operation will affect the reliability of fault detection. The existing methods do not consider the impact of unbalanced current. The Chinese invention patent with application number 201811469547.0 and application date November 28, 2018, and the patent name "A single-phase high-resistance grounding fault detection method, system and storage medium for distribution network" discloses a technical solution, in which the phase relationship between the fault phase voltage and the zero-sequence current is used to determine whether a fault has occurred. When there is a residual current during normal operation, the "zero-sequence current" is essentially the superposition of the unbalanced current and the fault-generated current. The high-resistance grounding fault current itself is very weak, and it is difficult to reliably determine the fault by superimposing the fault-generated current on the unbalanced current. In the prior art, the method of eliminating unbalanced current only processes the current through signal processing means, which is easily affected by system frequency changes and device crystal oscillator errors, and the effect is poor. Summary of the invention

[0004] The technical problem to be solved by the present invention is: to overcome the shortcomings of the prior art, and to provide a method for locating high-resistance grounding faults in distribution networks based on the changes in voltage and current phasors, which takes the three-phase voltage power frequency phasors as a reference, constructs the residual current normalized phasors before and after the fault, and obtains the residual current phasor change amount using the residual current normalized phasors, which is the residual current phasor generated by the actual fault, eliminates the influence of unbalanced current, greatly improves the purity and accuracy of the fault electrical quantities used, and lays the foundation for the detection of small-resistance high-resistance grounding faults.

[0005] The technical solution adopted by the present invention to solve the technical problem is: the method for locating high-resistance grounding faults in a distribution network based on voltage and current phase quantity changes is characterized by comprising the following steps:

[0006] Step a, collecting the three-phase voltage and three-phase current on the outgoing line side in real time through the collection device in the substation and the collection devices in each section of the line;

[0007] Step b, the acquisition device synthesizes the acquired three-phase voltage and three-phase current into a zero-sequence voltage and a zero-sequence current, and determines whether the amplitudes of the synthesized zero-sequence voltage and the synthesized zero-sequence current meet a preset threshold value, if so, executing step c, otherwise executing step a;

[0008] Step c, taking the fault start time as a reference, intercepting the data of the three-phase voltage and residual current before and after the fault at each detection point, and obtaining the three-phase voltage and residual current before the fault, and the three-phase voltage and residual current after the fault;

[0009] Step d, respectively obtaining the power frequency components of the three-phase voltage and the residual current before the fault, and the power frequency components of the three-phase voltage and the residual current after the fault;

[0010] Step e, calculating the normalized phasor of residual current before the fault, the normalized phasor of residual current after the fault, and the change of the normalized phasor of residual current before and after the fault;

[0011] Step f, obtaining the phase angle of the three-phase voltage phasor after the fault and the phase angle of the residual current normalized phasor change;

[0012] Step g, calculating the phase angle difference between the three-phase voltage phasor and the residual current normalized phasor variation;

[0013] Step i, judging whether the line meets the sound criterion or the fault criterion. If the sound criterion is met, it indicates that the line is a sound line. If the fault criterion is met, it is determined that a high-resistance grounding fault occurs in the line.

[0014] Preferably, when performing step e,

[0015] The residual current power frequency phase V before the fault i01 , and the three-phase voltage power frequency phasor V before the fault uphaseA1 、V uphaseB1 and V uphaseC1 Calculate the phase difference respectively and get the normalized phase of residual current before fault: V i01-uphaseA1 、V i01-uphaseB1 and V i01-uphaseC1 ;

[0016] The residual current power frequency phase V after the fault i02 , and the three-phase voltage power frequency phasor V after the fault uphaseA2 、VuphaseB2 and V uphaseC2 Calculate the phase difference respectively and get the normalized phase of residual current after fault: V i02-uphaseA2 、V i02-uphaseB2 and V i02-uphaseC2 .

[0017] Preferably, when executing step g, according to the phase of the power frequency component of the three-phase voltage obtained in step f: The phases of the residual current phase change Subtract them to get their respective phase angle difference: as well as

[0018] Preferably, in step i, the robust criterion is: the robust criterion is the phase angle difference of phase A satisfy At the same time, the phase angle difference of phase B satisfy At the same time, the phase angle difference of phase C satisfy

[0019] Preferably, in step i, the fault criterion is: the phase angle difference of phase A Phase angle difference of phase B Phase angle difference of phase C Any one that satisfies

[0020] Preferably, after executing step i and determining that a high-resistance grounding fault occurs in the line, the fault section and the fault phase are determined.

[0021] Preferably, firstly, a data collection device in the substation determines whether a healthy line or a faulty line is present. After the faulty line is determined, the data collection device in the faulty line sequentially performs steps a to i, and the section between the device that meets the fault criterion and the adjacent device that meets the healthy criterion is the faulty section.

[0022] The phase line whose phase angle difference between the three-phase voltage phasor and the residual current phasor change quantity in the acquisition device upstream of the fault section in the fault line meets the fault judgment criterion is the fault phase.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. In this method for locating high-resistance grounding faults in distribution networks based on the change in voltage and current phasors, the normalized phasors of residual currents before and after the fault are constructed with reference to the three-phase voltage power frequency phasors. The normalized phasors of residual currents before the fault are the residual current phasors of the normal operation of the system constructed with reference to the three-phase voltage power frequency phasors, and the normalized phasors of residual currents after the fault are the current phasors of the residual currents of the normal operation of the system constructed with reference to the three-phase voltage power frequency phasors and the superposition of the fault current. Innovatively, the three-phase voltage is used as a reference, and the voltage phasors and residual current phasors are considered in the same scenario, eliminating the influence of factors such as the current system frequency change and the crystal oscillator error of the device. The constructed residual current phasors are the most realistic relative to the current scenario. The residual current phasor change obtained with the residual current normalized phasor is the residual current phasor generated by the real fault, which eliminates the influence of unbalanced current, greatly improves the purity and accuracy of the fault electrical quantities used, and lays the foundation for the detection of small resistance and high-resistance grounding faults.

[0025] 2. In this method for locating high-resistance grounding faults in distribution networks based on voltage and current phasor changes, the phase angle difference between the three-phase voltage power frequency phasor and the residual current power frequency phasor change is used to realize high-resistance grounding fault detection, which reduces the influence of zero-sequence voltage on the reliability of protection action and improves the ability to withstand transition resistance.

[0026] 3. In this method for locating high-resistance grounding faults in distribution networks based on voltage and current phasor changes, the phase angle difference between the three-phase voltage power frequency phasor and the residual current power frequency phasor change is used to realize high-resistance grounding fault detection, which can realize the fault line selection, location and phase selection functions at the same time, reducing the fault search time, reducing the fault power outage time, and improving the power supply reliability.

[0027] 4. It uses three-phase voltage and three-phase current signals, without the need to add additional primary equipment or cooperate with other primary equipment, and has high practical application value.

[0028] 5. Use signal processing methods such as discrete Fourier transform to extract the power frequency phasor of voltage and current, and compare the phase angle difference of the power frequency phasor. No other processing methods are required, the calculation amount is low, and the operation speed of the distribution automation device is improved.

[0029] 6. Utilize the power frequency components of the three-phase voltage and three-phase current during a high-resistance grounding fault. The power frequency components account for a high proportion and are stable, and the requirements for the A / D sampling frequency of the distribution automation device are low, making it easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The flowchart of the method for locating high-resistance grounding fault in distribution network based on the change of voltage and current phase quantities is shown in the figure. DETAILED DESCRIPTION

[0031] Figure 1 The best embodiment of the present invention is shown below in conjunction with the attached Figure 1 The present invention is further described.

[0032] like Figure 1 As shown, the method for locating high-resistance grounding faults in a distribution network based on voltage and current phase quantity changes includes the following steps:

[0033] Step 1001, collecting three-phase voltage and three-phase current of the distribution network;

[0034] The three-phase voltage and three-phase current on the outgoing line side are collected in real time through the centralized high-resistance fault line selection device or line protection device in the substation, and the distribution automation device or fault indicator in each section of the line collects the three-phase voltage and three-phase current on the outgoing line side in real time. The centralized high-resistance fault line selection device or line protection device that collects signals (three-phase voltage and three-phase current) in the substation, and the distribution automation device or fault indicator that collects signals in the line, are collectively referred to as the collection device below.

[0035] Step 1002, determining whether the signal exceeds a preset threshold;

[0036] The signal is the three-phase voltage and three-phase current detected by each acquisition device in step 1001. After the acquisition device synthesizes the zero-sequence voltage and zero-sequence current, it is determined whether the amplitudes of the synthesized zero-sequence voltage and the synthesized zero-sequence current meet the preset threshold. If the preset threshold is met, it is preliminarily determined that a fault has occurred in the distribution network, and step 1003 is executed. If the amplitudes of the synthesized zero-sequence voltage and the synthesized zero-sequence current do not meet the preset threshold, return to step 1001.

[0037] Step 1003, intercepting data of three-phase voltage and three-phase current;

[0038] Taking the fault starting time as the benchmark, the three-phase voltage and residual current before and after the fault of each detection point are intercepted. The data interception length is selected as 3 cycles before the starting time and 3 cycles after the starting time. The intercepted three-phase voltage and residual current before the fault are: u phaseA1_cut (t),u phaseB1_cut (t),u phaseC1_cut (t) and i 01_cut (t), the three-phase voltage and residual current after the fault are intercepted are: u phaseA2_cut (t),u phaseB2_cut (t),u phaseC2_cut (t) and i 02_cut (t).

[0039] Step 1004, extracting the power frequency phasors of the three-phase voltage and the residual current;

[0040] The acquisition device processes the three-phase voltage and residual current intercepted in step 1003 to obtain the power frequency components of the three-phase voltage and residual current before the fault, and the power frequency components of the three-phase voltage and residual current after the fault.

[0041] To obtain the residual current i after the fault 02_cut (t) as an example:

[0042]

[0043] Where k = 0, 1, ..., N-1 is the N DFT coefficients, i A_Δ F (k)=|i A_Δ F (k)|exp[jθ(k)] is the kth DFT coefficient, |i 02_cut F (k)| and θ(k) are the amplitude spectrum and phase spectrum respectively. 02_cut F (k)| and θ(k) can obtain the power frequency phasor V i02 .

[0044] Similarly, obtain the power frequency phasor V of the three-phase voltage before the fault uphaseA1 、V uphaseB1 、V uphaseB1 , the power frequency phasor V of the three-phase voltage after the fault uphaseA2 、V uphaseB2 、V uphaseB2 , and the residual current before the fault i 01_cut (t) of the power frequency phasor V i01 .

[0045] Further obtain the power frequency phase of the residual current before / after the fault: V i01 / V i02 .

[0046] Step 1005, calculating and obtaining the normalized phase quantity and variation of the residual current before and after the fault;

[0047] Taking the three-phase voltage phasors before and after the fault as reference, the normalized phasor of the residual current is obtained, and the change of the residual current phasor before and after the fault is calculated;

[0048] When obtaining the normalized phase of residual current before fault:

[0049] The residual current power frequency phase V before the fault i01 , and the three-phase voltage power frequency phasor V before the fault uphaseA1 、V uphaseB1 and V uphaseC1 Calculate the phase difference respectively and get the normalized phase of residual current before fault: Vi01-uphaseA1 、V i01-uphaseB1 and V i01-uphaseC1 .

[0050] When obtaining the normalized phase of residual current after a fault:

[0051] The residual current power frequency phase V after the fault i02 , and the three-phase voltage power frequency phasor V after the fault uphaseA2 、V uphaseB2 and V uphaseC2 Calculate the phase difference respectively and get the normalized phase of residual current after fault: V i02-uphaseA2 、V i02-uphaseB2 and V i02-uphaseC2 .

[0052] The phase difference between the normalized phase of residual current before the fault and the normalized phase of residual current after the fault is calculated to obtain the change of residual current phase: V i0A_△ 、V i0B_△ and V i0C_△ .

[0053] Step 1006, respectively obtaining the phase angle of the three-phase voltage phasor and the phase angle of the residual current normalized phasor change after the fault;

[0054] The phase of the extracted three-phase voltage phasor is recorded as

[0055] The phase angle of the residual current phasor variation obtained in step 1005 is extracted and recorded as:

[0056] Step 1007, calculating the phase angle difference between the three-phase voltage phasor and the residual current normalized phasor variation;

[0057] According to the phase of the power frequency component of the three-phase voltage obtained in step 1006: The phases of the residual current phase change Subtract them to get their respective phase angle difference:

[0058]

[0059] Step 1008, determining whether the line meets the soundness criterion;

[0060] The acquisition device determines whether the sound criterion is met based on the phase angle difference between the three-phase voltage phasor and the residual current phasor change obtained in step 1007. The sound criterion is that the phase angle difference of phase A is satisfy At the same time, the phase angle difference of phase B satisfy At the same time, the phase angle difference of phase C satisfy Execute step 1010;

[0061] When the phase angle difference of at least one phase meets the fault criterion, step 1009 is executed. The fault criterion is that the phase angle difference of phase A Phase angle difference of phase B Phase angle difference of phase C Any one that satisfies in Indicates the fault line judgment margin, the sound judgment criterion and the fault judgment criterion as well as They represent the healthy judgment margin and fault judgment respectively, and are related to the transformer measurement error.

[0062] Step 1009: the current line is a faulty line, and step 1011 is executed;

[0063] Step 1010, the current line is a sound line, and step 1012 is executed;

[0064] Step 1011, determining the fault section and the fault phase;

[0065] When executing the above steps 1001 to 1010, the data collection device in the substation first determines whether a healthy line or a faulty line is present. After the faulty line is determined, the data collection device in the faulty line sequentially executes the above steps 1001 to 1010. The section between the device that meets the fault criterion and the adjacent device that meets the healthy criterion is the fault section.

[0066] The phase line whose phase angle difference between the three-phase voltage phasor and the residual current phasor change quantity in the acquisition device upstream of the fault section in the fault line meets the fault judgment criterion is the fault phase.

[0067] Step 1012, end.

[0068] From the above, it can be seen that in the distribution network high-resistance grounding fault location method based on the voltage and current phasor change, the three-phase voltage power frequency phasor is used as a reference to construct the residual current normalized phasor before and after the fault. Among them, the residual current normalized phasor before the fault is the residual current phasor of the system in normal operation constructed with the three-phase voltage power frequency phasor as a reference, and the residual current normalized phasor after the fault is the current phasor of the residual current and the fault current superimposed on the system in normal operation constructed with the three-phase voltage power frequency phasor as a reference. Innovatively, the three-phase voltage is used as a reference, and the voltage phasor and the residual current phasor are considered in the same scenario, eliminating the influence of factors such as the current system frequency change and the crystal oscillator error of the device. The constructed residual current phasor is the most real relative to the current scenario. The residual current phasor change obtained by the residual current normalized phasor is the residual current phasor generated by the real fault, which eliminates the influence of unbalanced current, greatly improves the purity and accuracy of the fault electrical quantity used, and lays the foundation for the detection of small resistance high-resistance grounding faults.

[0069] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A method for locating high-resistance grounding faults in a distribution network based on voltage and current phase variation, characterized in that: The steps include: Step a, collecting the three-phase voltage and three-phase current on the outgoing line side in real time through the collection device in the substation and the collection devices in each section of the line; Step b, the acquisition device synthesizes the acquired three-phase voltage and three-phase current into a zero-sequence voltage and a zero-sequence current, and determines whether the amplitudes of the synthesized zero-sequence voltage and the synthesized zero-sequence current meet a preset threshold value, if so, executing step c, otherwise executing step a; Step c, taking the fault start time as a reference, intercepting the data of the three-phase voltage and residual current before and after the fault at each detection point, and obtaining the three-phase voltage and residual current before the fault, and the three-phase voltage and residual current after the fault; Step d, respectively obtaining the power frequency components of the three-phase voltage and the residual current before the fault, and the power frequency components of the three-phase voltage and the residual current after the fault; Step e, calculating the normalized phasor of residual current before the fault, the normalized phasor of residual current after the fault, and the change of the normalized phasor of residual current before and after the fault; Step f, obtaining the phase angle of the power frequency component of the three-phase voltage after the fault and the phase angle of the normalized phase change of the residual current; Step g, calculating the phase angle difference between the power frequency component of the three-phase voltage and the normalized phase change of the residual current after the fault; Step i, judging whether the line meets the sound criterion or the fault criterion, if the sound criterion is met, it means that the line is a sound line, and if the fault criterion is met, it is determined that a high-resistance grounding fault occurs in the line; When executing step e, The residual current power frequency phase V before the fault i01 , and the three-phase voltage power frequency phasor V before the fault uphaseA1 、V uphaseB1 and V uphaseC1 Calculate the phase difference respectively and get the normalized phase of residual current before fault: V i01-uphaseA1 、V i01-uphaseB1 and V i01-uphaseC1 ; The residual current power frequency phase V after the fault i02 , and the three-phase voltage power frequency phasor V after the fault uphaseA2 、V uphaseB2 and V uphaseC2 Calculate the phase difference respectively and get the normalized phase of residual current after fault: V i02-uphaseA2 、V i02-uphaseB2 and V i02-uphaseC2 ; When executing step g, according to the phase of the power frequency component of the three-phase voltage obtained in step f: The phases of the residual current phase change Subtract them to get their respective phase angle difference: as well as In step i, the robust criterion is: The robust criterion is the phase angle difference of phase A satisfy At the same time, the phase angle difference of phase B satisfy At the same time, the phase angle difference of phase C satisfy represents the soundness judgment margin; In step i, the fault criterion is: the phase angle difference of phase A Phase angle difference of phase B Phase angle difference of phase C Any one that satisfies Indicates the fault line judgment margin.

2. The method for locating high-resistance grounding faults in a distribution network based on voltage and current phase quantity changes according to claim 1 is characterized in that: After executing step i and determining that a high-resistance grounding fault occurs in the line, the fault section and the fault phase are determined.

3. The method for locating high-resistance grounding faults in a distribution network based on voltage and current phase quantity changes according to claim 2 is characterized in that: First, the data collection device in the substation determines whether a healthy line or a faulty line is present. After the faulty line is determined, the data collection device in the faulty line sequentially performs steps a to i. The section between the device that meets the fault criterion and the adjacent device that meets the healthy criterion is the faulty section. The phase line whose phase angle difference between the three-phase voltage phasor and the residual current phasor change quantity in the acquisition device upstream of the fault section in the fault line meets the fault judgment criterion is the fault phase.

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