Low-voltage line fault adaptive protection method and system based on multi-frequency point leakage current

Abstract

The invention provides a low-voltage line fault self-adaptive protection method and system based on multi-frequency-point leakage current. The method comprises the following steps of 1, collecting leakage current and calculating judgment current in a specified protection area; step 2, pre-processing the leakage current; step 3, fault starting and preliminary mode judgment based on break variable detection; 4, calculating and judging the proportion Ep0 of the current power frequency signal in the total signal; 5, judging a multi-frequency-point protection mode; the network topology change is monitored in real time, if the topology change occurs, the relation matrix and the threshold value are dynamically updated, and the calculation parameters in the step 3 are synchronously updated; and 7, adaptively setting the threshold: dynamically calculating the threshold based on real-time operation parameters of the system instead of a fixed constant. According to the technical scheme, through multi-frequency-point analysis and a self-adaptive mechanism, the defects can be effectively overcome, and the protection sensitivity and reliability are improved.

Description

Technical Field

[0001] This invention relates to the field of electrical engineering power system relay technology, and in particular to an adaptive protection method and system for low-voltage line faults based on multi-frequency leakage current. Background Technology

[0002] In the field of relay protection for low-voltage distribution networks, leakage current protection based on power frequency (50Hz) is a well-known and widely used technology. This technology is widely applied due to its stable power frequency signal, high protection reliability, and simple design and setting. Its core principle is to detect changes in the amplitude of the power frequency leakage current, preset a fixed threshold, and when the current exceeds the threshold, a ground fault is detected, triggering the protection action. However, this technology relies on the assumption that the fault current is predominantly power frequency. In practical applications, it is difficult to effectively capture fault characteristics when facing complex operating conditions containing harmonics or high-frequency components, exhibiting significant limitations.

[0003] The closest existing technology to this invention is a distributed leakage current protection system based on power frequency. The implementation process of this system is as follows: First, fixed protection zones are defined in the power distribution network. The power frequency signal of the leakage current is collected in real time through the protection terminal unit at the external connection point. Then, the phasor or effective value of the power frequency leakage current is calculated and compared with preset fixed action thresholds and restraint thresholds. If the current value exceeds the threshold, tripping or alarm actions are triggered. The core of this system relies on a single power frequency component, the protection range is fixed, and the threshold settings are based on historical power frequency data, requiring no dynamic adjustment.

[0004] However, the aforementioned existing technologies have the following technical drawbacks:

[0005] The frequency analysis is limited: it relies solely on power frequency quantities for judgment, and cannot effectively detect non-power frequency components. Under complex operating conditions, it does not fully capture leakage current characteristics, resulting in low protection accuracy.

[0006] Poor adaptability: The fixed protection area division and unchanging threshold preset make it difficult to cope with dynamic changes in network topology such as load switching and line reconfiguration, which can easily lead to protection range deviation or failure.

[0007] Weak anti-interference capability: Power frequency quantities are easily polluted by harmonics. During intermittent grounding faults, the fault current waveform is unstable and the signal fluctuates greatly, making it difficult to guarantee protection sensitivity and often resulting in false tripping or failure to trip.

[0008] Insufficient intelligence: It relies on manual parameter setting, lacks a self-learning and dynamic adjustment mechanism based on multi-frequency data, and cannot optimize protection strategies according to the real-time operating status of the system.

[0009] The aforementioned shortcomings lead to a decline in the protection performance of existing protection methods under complex operating conditions, topology changes, and intermittent fault scenarios, making it difficult to meet the higher requirements of low-voltage distribution networks for relay protection sensitivity, reliability, and adaptability. Therefore, there is an urgent need for a new protection method that can solve the above problems. Summary of the Invention

[0010] In view of this, the purpose of the present invention is to provide a low-voltage line fault adaptive protection method and system based on multi-frequency leakage current. Through multi-frequency analysis and adaptive mechanism, the above-mentioned shortcomings can be effectively solved and the sensitivity and reliability of protection can be improved.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: a low-voltage line fault adaptive protection method based on multi-frequency leakage current, comprising the following steps:

[0012] Step 1: Leakage current acquisition and current calculation for designated protection areas;

[0013] Step 2: Leakage current preprocessing: Preprocessing the judgment current... Perform Fourier analysis to obtain the amplitude at each frequency. Where x is the harmonic order, x = 1, 2, ...;

[0014] Step 3: Fault initiation and preliminary mode determination based on mutation detection;

[0015] Step 4: Calculate and determine the proportion E of the current power frequency signal in the total signal. p0 ;

[0016] Step 5: Multi-frequency protection mode judgment: The sum of the currents at the three frequency points with the largest amplitude is... Calculate its proportion relative to the power frequency signal. ,like ≥ , To set a threshold, a ground fault is detected in the protected area, and multi-frequency protection mode is activated; if < No ground fault was determined.

[0017] Step 6: Topology Adaptive Adjustment: Monitor network topology changes in real time; if a topology change occurs, dynamically update the relationship matrix. and threshold I set0 , I setΣ The calculation parameters in step 3 are updated synchronously.

[0018] Step 7: Threshold Adaptive Tuning: Threshold I set0 , IsetΣ It is calculated dynamically based on real-time system operating parameters, rather than as a fixed constant.

[0019] In a preferred embodiment, in step 1, each protection terminal in the system synchronously acquires the instantaneous value signal of the leakage current. When the number of terminals is N, the time series of the acquired instantaneous leakage current values ​​is recorded as follows: ;in, It is the instantaneous value of the local leakage current collected by each terminal; the current supplied to the relay judgment unit within the selected protection area of ​​the system. and The following relationship exists: ;in, It is a matrix showing the relationship between a designated protected area and its external communication terminal nodes.

[0020] In a preferred embodiment, step 3 involves calculating the power frequency phasor abrupt change in the determination current within the protected area. and harmonic abrupt changes at multiple frequency points The mutation detection matrix is ​​obtained. as follows:

[0021]

[0022] Detection matrix in judgment The maximum value in; if Maximum and exceeding the set threshold I set0 If so, proceed to step 4 for precise mode selection; if If it is not the maximum, then the sum of the current surges at the three frequency points with the largest amplitudes, and the sum of these current surges, must exceed a set threshold. I setΣ Proceed to step 5 to activate the multi-frequency protection mode.

[0023] In a preferred embodiment, in step 4, E th0 It is a fixed value, set to 0.2.

[0024] In a preferred embodiment, in step 5, ; It is a fixed value, set to 0.1.

[0025] In a preferred embodiment, the tuning process in step 7 follows the following formula and logic: ;

[0026] Where K is the reliability coefficient, which ranges from 1.1 to 1.3; It is the power frequency component of the estimated maximum normal unbalanced leakage current under the current protection area; It is the sum of the harmonic components of the estimated maximum normal unbalanced leakage current in the current protected area; E rr It is a margin introduced to account for measurement error and calculation error factors.

[0027] The present invention also provides a low-voltage line fault adaptive protection system based on multi-frequency leakage current, including a processor, a memory and a bus, wherein the memory stores machine-readable instructions executed by the processor;

[0028] When the system is running, the processor and the memory communicate via a bus, and the machine-readable instructions are executed by the processor as described in the low-voltage line fault adaptive protection method based on multi-frequency leakage current.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) This application obtains the full spectrum through Fourier analysis and innovatively introduces criteria such as “proportion of major harmonics”, which can effectively identify harmonic-dominated faults, such as the core problem of insufficient detection sensitivity of complex faults such as arc grounding.

[0031] (2) The threshold of this application is dynamically calculated based on the real-time parameters of the system. For example, it is adaptively adjusted according to the estimated maximum unbalanced current of the protection area so that the protection setting is always matched with the current system state, avoiding false operation or failure to operate.

[0032] (3) This application monitors network topology changes in real time and dynamically updates the relationship matrix of the protected area and all relevant set thresholds to ensure that the protection scope and capabilities can be automatically adjusted according to the operation mode and maintain the accuracy of protection. Attached Figure Description

[0033] Figure 1 This is a flowchart of a preferred embodiment of the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0036] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0037] An adaptive protection method for low-voltage line faults based on multi-frequency leakage current, referenced Figure 1 Through multi-frequency point analysis and adaptive mechanisms, the above-mentioned shortcomings can be effectively solved, and the sensitivity and reliability of protection can be improved. Specifically: (1) Multi-frequency point analysis comprehensively captures fault characteristics by monitoring the power frequency and other frequency components, avoiding the problem of insufficient sensitivity caused by the low proportion of power frequency; (2) Adaptive mechanism dynamically adjusts the closed surface and protection criteria according to real-time topology changes, improving the adaptability to network structure changes; (3) Intelligent decision-making automatically selects the protection mode through the proportion of power frequency, identifies and blocks abnormal equipment, and further reduces false operation. Specifically, it includes the following steps:

[0038] Step 1: Leakage Current Acquisition and Designated Protection Area Judgment Current Calculation. Each protection terminal in the system synchronously acquires the instantaneous value signal of the leakage current. When the number of terminals is N, the time series of the acquired instantaneous leakage current values ​​is recorded as follows: .in, This is the instantaneous value of the local leakage current collected by each terminal. Within the selected protection zone of the system, the current supplied to the relay judgment unit... and The following relationship exists:

[0039]

[0040] in, It is a matrix showing the relationship between a designated protected area and its external communication terminal nodes.

[0041] Step 2: Leakage Current Preprocessing. Based on the real-time judgment current within the protected area, perform Fourier analysis to obtain the spectrum of the corresponding leakage current, and record the amplitude at each frequency as... Where x represents the xth harmonic, which is usually an integer, x=1, 2, ...; the larger x is, the higher the harmonic order.

[0042] Step 3: Fault Initiation and Preliminary Mode Judgment Based on Abrupt Change Detection. Calculate the power frequency phasor abrupt change in the judgment current within the protected area. and harmonic abrupt changes at multiple frequency points The mutation detection matrix can be obtained. as follows:

[0043]

[0044] Detection matrix in judgment The maximum value in. If Maximum and exceeding the set threshold I set0 Then proceed to step 4 for precise mode selection. If If it is not the maximum, then the sum of the current surges at the three frequency points with the largest amplitudes, and the sum of these current surges, must exceed a set threshold. I setΣ Proceed to step 5 to activate the multi-frequency protection mode.

[0045] Step 4: Calculate and determine the proportion E of the current power frequency signal in the total signal. p0 If E p0 ≥E th0 The power frequency protection mode is activated, and a ground fault is determined to exist within the protection area; if E p0 <E th0 Therefore, it was determined that there was no ground fault within the protected area.

[0046]

[0047] E th0 It is usually a fixed value, set to 0.2.

[0048] Step 5: The sum of the currents at the three frequencies with the largest amplitudes is denoted as... Calculate its magnitude relative to the power frequency signal and record it as . .like ≥ Initiate multi-frequency protection mode and determine that a ground fault exists within the protection area; if < Therefore, it was determined that there was no ground fault within the protected area.

[0049]

[0050] It is usually a fixed value, set to 0.1.

[0051] Step 6: Monitor network topology changes in real time, such as load switching and line handover. If the topology changes, dynamically update the relationship matrix. and the corresponding set threshold I set0 , I setΣ This allows the protection range and protection settings to be adaptively adjusted as the network structure changes, and updates the calculation parameters in step 3 to prevent protection failure.

[0052] Step 7: As described in Step 3 I set0 and I setΣ The adaptive tuning approach involves replacing constants with variables calculated based on real-time system operating parameters. The tuning process follows these formulas and logic:

[0053]

[0054] Where K is the reliability coefficient, which is usually taken as 1.1 to 1.3, to ensure the reliability of the protection under critical conditions and avoid false tripping; It is the power frequency component of the estimated maximum normal unbalanced leakage current under the current protection area; It is the sum of the harmonic components of the estimated maximum normal unbalanced leakage current in the current protected area. E rr It is a margin introduced to take into account factors such as measurement error and calculation error.

Claims

1. A low-voltage line fault adaptive protection method based on multi-frequency leakage current, characterized in that, Includes the following steps: Step 1: Leakage current acquisition and current calculation for designated protection areas; Step 2: Leakage current preprocessing: Preprocessing the judgment current... Perform Fourier analysis to obtain the amplitude at each frequency. Where x is the harmonic order, x = 1, 2, ...; Step 3: Fault initiation and preliminary mode determination based on mutation detection; Step 4: Calculate and determine the proportion E of the current power frequency signal in the total signal. p0 ; Step 5: Multi-frequency protection mode judgment: The sum of the currents at the three frequency points with the largest amplitude is... Calculate its proportion relative to the power frequency signal. ,like ≥ , To set a threshold, a ground fault is detected in the protected area, and multi-frequency protection mode is activated; if < No ground fault was determined. Step 6: Topology Adaptive Adjustment: Monitor network topology changes in real time; if a topology change occurs, dynamically update the relationship matrix. and threshold I set0 , I setΣ The calculation parameters in step 3 are updated synchronously. Step 7: Threshold Adaptive Tuning: Threshold I set0 , I setΣ It is calculated dynamically based on real-time system operating parameters, rather than as a fixed constant.

2. The adaptive protection method for low-voltage line faults based on multi-frequency leakage current according to claim 1, characterized in that, In step 1, each protection terminal in the system synchronously acquires the instantaneous value signal of the leakage current. When the number of terminals is N, the time series of the acquired instantaneous leakage current values ​​is recorded as follows: ;in, It is the instantaneous value of the local leakage current collected by each terminal; the current supplied to the relay judgment unit within the selected protection area of ​​the system. and The following relationship exists: ;in, It is a matrix showing the relationship between a designated protected area and its external communication terminal nodes.

3. The adaptive protection method for low-voltage line faults based on multi-frequency leakage current according to claim 1, characterized in that, Step 3 calculates the power frequency phasor abrupt change of the judgment current within the protection area. and harmonic abrupt changes at multiple frequency points The mutation detection matrix is ​​obtained. as follows: Detection matrix in judgment The maximum value in; if Maximum and exceeding the set threshold I set0 If so, proceed to step 4 for precise mode selection; if If it is not the maximum, then the sum of the current surges at the three frequency points with the largest amplitudes, and the sum of these current surges, must exceed a set threshold. I setΣ Proceed to step 5 to activate the multi-frequency protection mode.

4. The adaptive protection method for low-voltage line faults based on multi-frequency leakage current according to claim 1, characterized in that, In step 4, E th0 It is a fixed value, set to 0.

2.

5. The adaptive protection method for low-voltage line faults based on multi-frequency leakage current according to claim 1, characterized in that, In step 5, ; It is a fixed value, set to 0.

1.

6. The adaptive protection method for low-voltage line faults based on multi-frequency leakage current according to claim 1, characterized in that, The tuning process in step 7 follows the formulas and logic below: ; Where K is the reliability coefficient, which ranges from 1.1 to 1.3; It is the power frequency component of the estimated maximum normal unbalanced leakage current under the current protection area; It is the sum of the harmonic components of the estimated maximum normal unbalanced leakage current in the current protected area; E rr It is a margin introduced to account for measurement error and calculation error factors.

7. A low-voltage line fault adaptive protection system based on multi-frequency leakage current, comprising a processor, a memory, and a bus, wherein the memory stores machine-readable instructions executed by the processor; characterized in that, When the system is running, the processor and the memory communicate via a bus, and the machine-readable instructions are executed by the processor as described in any one of claims 1 to 6. This is a low-voltage line fault adaptive protection method based on multi-frequency leakage current.

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