Control method for preventing protection malfunction based on monitoring of branch impedance of capacitor bank

Abstract

The present invention relates to a control method for preventing protection maloperation based on the monitoring of the branch impedance of a capacitor bank. This method realizes the safety protection of the power system by monitoring the residual power rate and equivalent impedance of the branch capacitors in real time. The specific steps include: initializing the technical parameters of the branch capacitors, calculating the residual power rate, and performing clustering analysis on it to determine the state of the branch capacitors. By monitoring the equivalent impedance and its change rate, if it is found that the change rate exceeds the preset threshold, an initial protection preparation is issued and the preparation state is entered. Subsequently, by checking the clustering number, the charge and discharge stability is judged to determine whether to initiate the protection action. This control method can effectively reduce the risk of protection maloperation caused by capacitor failures and improve the reliability and safety of the power system.

Description

Technical Field

[0001] The present invention relates to the field of circuit devices or systems for power supply or distribution, and particularly to a control method for preventing protection misoperation based on monitoring the impedance of capacitor bank branches. Background Art

[0002] In a power system, capacitor banks are widely used to improve power quality, improve power factor, and stabilize the power grid. However, during operation, capacitor banks may be affected by various factors, such as overvoltage, overcurrent, harmonics, and equipment aging. These factors may cause capacitor failures or performance degradation, thereby affecting the normal operation of the system. In addition, when a protection device detects an abnormal situation, it will automatically operate to prevent equipment damage, but sometimes misoperations occur, resulting in unnecessary power outages or ineffective equipment protection.

[0003] Current capacitor bank protection methods mainly rely on the monitoring of current and voltage, but these methods generally do not fully consider the impedance changes of capacitor bank branches. When transient or persistent abnormalities occur in the system, impedance changes will cause the protection device to misjudge, thereby triggering misoperations. Therefore, it is particularly important to develop a control method based on monitoring the impedance of capacitor bank branches.

[0004] In the prior art, the main technical routes for preventing protection misoperation based on monitoring the impedance of capacitor bank branches are as follows, and there are corresponding technical drawbacks:

[0005] 1. Traditional protection schemes based on current and voltage monitoring: Rely on real-time monitoring of the current and voltage of the capacitor bank, calculate the impedance using these parameters, and set fixed thresholds for anomaly determination. This method is simple but vulnerable to instantaneous fluctuations, resulting in a high misoperation rate;

[0006] Disadvantages: High misoperation rate: Relying on fixed thresholds, it is difficult to adapt to dynamically changing operating conditions and is prone to misoperations; Unable to respond in real time: Slow to react to instantaneous fluctuations and may miss real fault situations.

[0007] 2. Intelligent impedance monitoring systems: Introduce intelligent sensors and data processing technologies to real-time monitor the branch impedance and establish a dynamic model based on historical data analysis. Adjust the monitoring threshold through an adaptive algorithm to improve the ability to identify abnormal situations;

[0008] Disadvantages: Increased complexity: Introducing an adaptive algorithm and a dynamic model makes the system complex and increases the difficulty of debugging and maintenance; Strong environmental dependence: In extreme environments (such as temperature and humidity changes), the performance of sensors may be unstable, affecting the monitoring accuracy.

[0009] 3. Pattern Recognition and Machine Learning Techniques: Use machine learning algorithms to perform pattern recognition on impedance data and establish a fault feature library. By analyzing the impedance change trend, determine whether an abnormality occurs and reduce the probability of misjudgment;

[0010] Disadvantages: High data demand: A large amount of high-quality data is required to train an effective model, and the data acquisition and processing costs are high; Algorithm black box effect: The decision-making process of the machine learning model is not transparent, which may lead to a decrease in the trust in fault judgment.

[0011] 4. Dynamic Model and Simulation Techniques: Based on the dynamic characteristics of the power system, construct a dynamic model of the capacitor bank branch for real-time simulation and prediction. Determine whether the current state is within the safe range through the simulation results;

[0012] Disadvantages: Dependence on model accuracy: The accuracy of the model depends on the parameter selection and system simplification, which may lead to inaccurate prediction results. Lack of real-time performance: The simulation calculation time is relatively long, and real-time response cannot be guaranteed.

[0013] 5. Event-driven Intelligent Protection Mechanism: Adopt an event-driven model. When an abnormal impedance change is detected, quickly trigger the intelligent decision-making mechanism and automatically execute protection measures. This method reduces manual intervention and improves the response speed;

[0014] Disadvantages: Risk of misjudgment: In the event recognition stage, false triggering of protection actions may occur due to noise or other interference factors; Lack of flexibility: The preset decision-making logic may not be able to adapt to complex operating environments, resulting in unnecessary protection actions. Summary of the Invention

[0015] In view of the above problems, the object of the present invention is to propose a control method for preventing misoperation of protection based on impedance monitoring of capacitor bank branches, including the following steps:

[0016] S1. Initialization: Number the branch capacitors in the capacitor bank, check the technical parameters of all branch capacitors, and determine the allowable interval of the technical parameters of the capacitor bank;

[0017] S2. Determine the residual power rate of the branch capacitor: Charge and discharge the branch capacitor connected to the grid, and calculate the residual power rate based on the residual power in the charge and discharge cycles of the branch capacitor during the evaluation period , satisfying:

[0018] ,

[0019] where the superscript represents the serial number of the branch capacitor; represents the serial number of the branch capacitor, and The residual charge rate of the last charge-discharge cycle completed before the moment; Indicates the serial number is The nominal electrical degree of the branch capacitance; and Respectively indicate the serial number The branch capacitance is The charge and discharge capacity of the last charge and discharge cycle completed before the time;

[0020] S3. Performing cluster analysis on the residual power rates of all branch capacitors: performing cluster analysis on the residual power rates of the branch capacitors, and determining the cluster group to which each branch capacitor belongs and its cluster number;

[0021] S4, monitor the equivalent impedance and equivalent impedance change rate of the branch capacitor; monitor the branch voltage and branch current of the branch capacitor, and calculate the equivalent impedance and equivalent impedance change rate based on the branch voltage and branch capacitance, satisfying:

[0022] ,

[0023] ,

[0024] in, Respectively indicate the serial number The branch capacitance is The partial voltage, partial current and equivalent impedance at each moment; Indicates the serial number is The branch capacitance is The equivalent impedance change rate at time , To monitor the sampling period, Indicates the serial number is The branch capacitance is The equivalent impedance at the moment;

[0025] S5, initial protection preparation: for the branch capacitor whose equivalent impedance change rate exceeds the preset threshold, the initial protection preparation is issued, and the protection action is started and the protection state is entered;

[0026] S6. Review and start or release of protection action: For the branch capacitors prepared for initial protection, check their cluster numbers and return the verification results, and execute the start of the protection action or release the prepared state based on the verification results.

[0027] Furthermore, in step S1, numbering the branch capacitors in the capacitor bank specifically refers to: numbering all the branch capacitors in the capacitor bank as a branch capacitor set ,satisfy:

[0028]

[0029] Among them, represents the th branch capacitor, and

[0030] is the total number of branch capacitors.

[0031] Furthermore, in step S1, the technical parameters of the capacitor bank at least include the nominal charge, rated voltage, rated current, and equivalent impedance of the capacitor.

[0032] Furthermore, in step S3, k-means clustering analysis method is adopted for clustering analysis.

[0033] S31. Adopt the k-means clustering analysis method to perform clustering analysis on the residual power rate of all branch capacitors to obtain clustering groups and number them to obtain a set of clustering numbers , satisfying:

[0034] ,

[0035] Among them, represents the clustering numbers of the first to the last clustering groups obtained after performing clustering analysis on the residual power rate of all branch capacitors at time ;

[0036] S32. Check the branch capacitors in each clustering group, record the clustering numbers to the corresponding branch capacitors, and obtain a set of capacitor clustering information , satisfying:

[0037] ,

[0038] Among them, ,…, , represents that the clustering number obtained after performing clustering analysis on the residual power rate of the branch capacitor with the serial number at time is .

[0039] Furthermore, in step S5, the branch capacitor with the equivalent impedance change rate exceeding the preset threshold refers to that for any branch capacitor , the situation of occurs; among them, represents the preset threshold of the equivalent impedance change rate.

[0040] Furthermore, in step S6, checking its clustering number and returning the check result specifically means: for the branch capacitor whose equivalent impedance change rate exceeds the preset threshold at time , extract its clustering number in the charge-discharge cycle before the moment and the clustering number in the charge-discharge cycle after the moment and the moment Check whether the following conditions are met: ,

[0041] ,

[0042] If the above formula is satisfied, return that the charge-discharge check result is stable; if not, return that the charge-discharge check result is abnormal.

[0043] Furthermore, in step S6, determining the activation or cancellation of the protection action according to the check result specifically means: if the returned check result is that the charge-discharge is stable, cancel the preparatory state of the protection action; if the returned check result is that the charge-discharge is abnormal, activate the protection action.

[0044] Furthermore, in step S6, the activation of the protection action specifically means cutting out the branch capacitor involved from the circuit.

[0045] The beneficial effects of the present invention are as follows:

[0046] 1. Improve the reliability of the protection system: By real-time monitoring of the impedance of the capacitor bank branches, this control method can effectively identify and prevent misoperations caused by capacitor aging or faults, ensuring the safe and stable operation of the power system.

[0047] 2. Real-time status monitoring: This method realizes dynamic monitoring of the charge-discharge process of the branch capacitors, can timely obtain the residual power rate and equivalent impedance change of each branch capacitor, and enhances the understanding of the health status of the capacitor bank.

[0048] Reduce the risk of misoperation: Through the clustering analysis of the branch capacitors and the monitoring of the equivalent impedance change rate, a warning can be issued before potential protection misoperations occur, reducing power system accidents caused by improper protection actions.

[0049] 4. Optimize the maintenance strategy: Based on the analysis of the monitoring data, the state of the capacitor can be evaluated, so as to formulate more accurate maintenance and replacement strategies, reducing the operation and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a schematic flow chart of the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0051] To deepen the understanding of the present invention, the following will further elaborate on the present invention in combination with embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation to the protection scope of the present invention.

[0052] Embodiment 1:

[0053] According to Figure 1 As shown, this embodiment provides a control method for preventing misoperation of protection based on monitoring the impedance of capacitor bank branches, including the following steps:

[0054] S1. Initialization: Number the branch capacitors in the capacitor bank, check the technical parameters of all branch capacitors, and determine the allowable range of the technical parameters of the capacitor bank;

[0055] S2. Determine the residual energy rate of the branch capacitor: Charge and discharge the incoming branch capacitor, and calculate the residual energy rate based on the residual energy in the charge and discharge cycles of the branch capacitor during the evaluation period , satisfying:

[0056] ,

[0057] where the superscript represents the serial number of the branch capacitor; represents the residual energy rate of the last charge and discharge cycle completed by the branch capacitor with serial number before the moment; represents the nominal energy of the branch capacitor with serial number ; and respectively represent the charge energy and discharge energy of the last charge and discharge cycle completed by the branch capacitor with serial number before the moment;

[0058] S3. Perform cluster analysis on the residual energy rates of all branch capacitors: Perform cluster analysis on the residual energy rates of the branch capacitors, and determine the cluster groups to which each branch capacitor belongs and its cluster number;

[0059] S4. Monitor the equivalent impedance and equivalent impedance change rate of the branch capacitor; Monitor the partial voltage and partial current of the branch capacitor, and calculate the equivalent impedance and equivalent impedance change rate based on the partial voltage and partial capacitance of the branch, satisfying:

[0060] ,

[0061] ,

[0062] where respectively represent the partial voltage, partial current and equivalent impedance of the branch capacitor with serial number at the moment; represents the partial voltage of the branch capacitor with serial number at the Equivalent impedance change rate at a moment is the monitoring sampling period denotes the equivalent impedance of the branch capacitor with serial number at the moment ;

[0063] S5. Initial protection preparation: For the branch capacitors with equivalent impedance change rate exceeding the preset threshold, issue initial protection preparation and start the protection action to transfer to the preparation state;

[0064] S6. Protection action review and start or release: For the branch capacitors with initial protection preparation, check their clustering numbers and return the check results, and execute the start or release of the protection action according to the check results.

[0065] Furthermore, in step S1, specifically numbering the branch capacitors in the capacitor bank means: numbering all the branch capacitors in the capacitor bank as the branch capacitor set , satisfying:

[0066] ,

[0067] wherein represents the th branch capacitor is the total number of branch capacitors.

[0068] In step S1, the technical parameters of the capacitor bank include at least the nominal charge, rated voltage, rated current, and equivalent impedance of the capacitor.

[0069] Step S3 specifically includes:

[0070] S31. Use the k-means clustering analysis method to perform clustering analysis on the residual power rate of all branch capacitors, obtain the clustering groups and number them to obtain the clustering number set , satisfying:

[0071] ,

[0072] wherein represents the clustering numbers of the first to the last clustering groups obtained after performing clustering analysis on the residual power rate of all branch capacitors at the moment ;

[0073] S32. Check the branch capacitors in each clustering group, record the clustering number to the corresponding branch capacitor, and obtain the capacitor clustering information set , satisfying:

[0074] ,

[0075] wherein ,…, , indicates that the residual charge rate of the branch capacitor with the serial number at the moment after performing clustering analysis, the obtained clustering number is .

[0076] In step S5, the "branch capacitor with the equivalent impedance change rate exceeding the preset threshold" means that for any branch capacitor , the situation of occurs; where represents the threshold of the preset equivalent impedance change rate.

[0077] In step S6, "check its clustering number and return the check result" specifically means: for the branch capacitor whose equivalent impedance change rate exceeds the preset threshold at the moment , extract its clustering number in the previous charge-discharge cycle before the moment and the clustering number in the next charge-discharge cycle after the moment , and check whether it satisfies:

[0078] ,

[0079] If the above formula is satisfied, return the check result as stable charge-discharge; if the above formula is not satisfied, return the check result as abnormal charge-discharge.

[0080] In step S6, determining the start or cancellation of the protection action according to the check result specifically means: if the returned check result is stable charge-discharge, execute the cancellation of the preparatory state of the protection action; if the returned check result is abnormal charge-discharge, execute the start of the protection action.

[0081] In step S6, the start of the protection action specifically means cutting out the involved branch capacitor from the circuit.

[0082] Embodiment 2:

[0083] This embodiment is directed to a control method for preventing misoperation of protection based on monitoring the branch impedance of a capacitor bank, and is specifically applied to the capacitor bank of a certain power substation to improve the stability and safety of the power system.

[0084] Step 1: Initialization:

[0085] In the capacitor bank, number all branch capacitors. Assume that the capacitor bank has a total of 10 branch capacitors, marked as and . First, check the technical parameters of each capacitor, including nominal capacitance, rated voltage, rated current, and equivalent impedance. Confirm that these parameters are within the allowable range through experiments and equipment manuals. For example, the nominal capacitance is 20 μF and the rated voltage is 400 V to ensure the basic safety of the system.

[0086] Step 2: Determine the residual capacitance rate:

[0087] Charge and discharge the branch capacitor C1, and record its charging capacitance and discharging capacitance during a certain period. According to the actual situation after the last charge and discharge, assume is 15 μF and is 5 μF, and calculate the residual capacitance rate through the following formula :

[0088] ,

[0089] In this way, the specific value of can be obtained for subsequent analysis.

[0090] Step 3: Cluster analysis:

[0091] Use the k-means clustering method to analyze the residual capacitance rates of all branch capacitors. Through calculation and data processing, obtain the clustering number set , for example, and are classified into the same clustering group , and this step can identify capacitors with similar states to provide a basis for protection decisions.

[0092] Step 4: Monitor the impedance

[0093] Real-time monitor the partial voltage and partial current of the branch capacitor . For example, assume that at time t, is 200 V and is 0.5 A, then calculate its equivalent impedance :

[0094] ,

[0095] In addition, monitor the change rate of the equivalent impedance through the formula:

[0096] ,

[0097] to evaluate the state change of C1.

[0098] Step 5: Initial protection preparation:

[0099] If found Exceeding the set threshold (For example, If the risk factor is set to 80%, the system will issue an initial protection preparation and automatically enter the protection preparation state for further risk assessment and control.

[0100] Step 6: Review of protection actions:

[0101] For branch capacitors that enter the protection preparation state , check its cluster number. Extract time Cluster numbers before and after and , and compare. If the condition is met , it returns to charge and discharge stability 8, and the protection preparation state is released; if it is not satisfied, it returns to charge and discharge abnormality, and the system will automatically start the protection action. Cut out the circuit to avoid further risk.

[0102] Through the above implementation steps, the method effectively realizes the real-time monitoring and dynamic protection of the capacitor bank, significantly reduces the risk of false protection operation, improves the operation safety and stability of the power system, and provides an effective technical means for the management and maintenance of power companies.

[0103] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A control method for preventing protection malfunction based on capacitor bank branch impedance monitoring, characterized in that: The following steps are involved: S1. Initialization of capacitors: number the branch capacitors in the capacitor bank, check the technical parameters of all branch capacitors, and determine the allowable range of the technical parameters of the capacitor bank; S2. Determine the residual power rate of the branch capacitor: Charge and discharge the branch capacitor connected to the grid, and calculate the residual power rate based on the residual power of the branch capacitor in the charge and discharge cycle during the evaluation period; the residual power rate satisfy: ； Among them, the superscript Indicates the serial number of the branch capacitor; Indicates the serial number is The branch capacitance is The residual charge rate of the last charge-discharge cycle completed before the moment; Indicates the serial number is The nominal electrical degree of the branch capacitance; and Respectively indicate the serial number The branch capacitance is The charge and discharge capacity of the last charge and discharge cycle completed before the time; S3. Performing cluster analysis on the residual power rates of all branch capacitors: performing cluster analysis on the residual power rates of the branch capacitors, and determining the cluster group to which each branch capacitor belongs and its cluster number; S4, monitoring the equivalent impedance and equivalent impedance change rate of the branch capacitor; monitoring the branch voltage and branch current of the branch capacitor, and calculating the equivalent impedance and equivalent impedance change rate based on the branch voltage and branch capacitance; S5, initial protection preparation: for the branch capacitor whose equivalent impedance change rate exceeds the preset threshold, the initial protection preparation is issued, and the protection action is started and the protection state is entered; S6. Review and start or release of protection action: For the branch capacitors prepared for initial protection, check their cluster numbers and return the verification results, and execute the start of the protection action or release the prepared state based on the verification results.

2. A control method for preventing protection malfunction based on capacitor bank branch impedance monitoring according to claim 1, characterized in that: In step S1, numbering the branch capacitors in the capacitor bank specifically refers to: numbering all the branch capacitors in the capacitor bank as a branch capacitor set ,satisfy: ， in, Indicates The branch capacitance, is the total number of branch capacitances; The technical parameters of the capacitor bank include at least the nominal capacity, rated voltage, rated current and equivalent impedance of the capacitor.

3. A control method for preventing protection malfunction based on capacitor bank branch impedance monitoring according to claim 2, characterized in that: In step S4, the equivalent impedance and the equivalent impedance change rate are calculated based on the branch voltage and the branch capacitance, satisfying: ； in, Respectively indicate the serial number The branch capacitance is The partial voltage, partial current and equivalent impedance at each moment; Indicates the serial number is The branch capacitance is The equivalent impedance change rate at time , To monitor the sampling period, Indicates the serial number is The branch capacitance is The equivalent impedance at time.

4. A control method for preventing protection malfunction based on capacitor bank branch impedance monitoring according to claim 3, characterized in that: In step S3, the cluster analysis adopts the k-means cluster analysis method.

5. A control method for preventing protection malfunction based on capacitor bank branch impedance monitoring according to claim 4, characterized in that: Step S3 specifically includes: S31. Use k-means cluster analysis method to analyze the residual charge rate of all branch capacitors. Perform cluster analysis, get cluster groups and number them, get cluster number set ,satisfy: ； in, Indicates the residual charge rate of all branch capacitors at time After cluster analysis, the cluster numbers from the first to the last cluster group are obtained; S32, check the branch capacitance in each cluster group, record the cluster number to the corresponding branch capacitance, and obtain the capacitance cluster information set ,satisfy: ； in, ,…, , Indicates the serial number is The residual charge rate of the branch capacitor is at time After cluster analysis, the cluster numbers obtained are .

6. A control method for preventing protection malfunction based on capacitor bank branch impedance monitoring according to claim 5, characterized in that: In step S5, the branch capacitor whose equivalent impedance change rate exceeds the preset threshold value means that for any branch capacitor ,Appear of the situation; among which, Indicates the preset threshold value of the equivalent impedance change rate.

7. A control method for preventing protection malfunction based on capacitor bank branch impedance monitoring according to claim 6, characterized in that: In step S6, checking the cluster number and returning the checking result specifically refers to: The branch capacitance whose equivalent impedance change rate exceeds the preset threshold , extract its The cluster number of the previous charge and discharge cycle and time The cluster number of the next charge and discharge cycle , check whether it meets: ； If the above formula is satisfied, the verification result returned is stable charging and discharging. If the above formula is not satisfied, the verification result returned is abnormal charging and discharging.

8. A control method for preventing protection malfunction based on capacitor bank branch impedance monitoring according to claim 7, characterized in that: In step S6, determining whether to start or release the protection action according to the verification result specifically means: if the verification result returned is that the charging and discharging are stable, the preparatory state of the protection action is released; if the verification result returned is that the charging and discharging are abnormal, the protection action is started.

9. A control method for preventing protection malfunction based on capacitor bank branch impedance monitoring according to claim 8, characterized in that: In step S6, the initiation of the protection action specifically refers to cutting the branch capacitor involved out of the circuit.

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