Broadband harmonic protection optimization method, system and equipment based on dynamic threshold and medium

Abstract

The invention discloses a broadband harmonic protection optimization method, system and device based on a dynamic threshold and a medium, and relates to the technical field of power system voltage protection. The method comprises the following steps: when an air-drop transformer executes an opening operation, recording a current amplitude and an opening angle at an opening moment; the magnitude of residual magnetism is determined according to the current amplitude and the opening angle at the opening moment, a dynamic protection action threshold value is determined according to other input values generating residual magnetic field scenes and the magnitude of loads, and the currently adopted protection action threshold value is a single-pole action threshold value; before an air-drop transformer executes closing operation, a current protection action threshold value of the protection system is set as a transition action threshold value, and whether the attenuation condition of the inrush current of the converter transformer is completed or not is monitored in combination with an auxiliary criterion; and if the attenuation condition of the inrush current of the converter transformer is completed, changing the current protection action threshold value from the transition action threshold value to a bipolar action threshold value. The accuracy of the protection action can be improved by using a dynamic protection action threshold method, and the efficient and safe operation of the direct-current power transmission system is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of power system voltage protection, and in particular to a method, system, device and medium for optimizing broadband harmonic protection based on a dynamic threshold. Background Art

[0002] When the converter station is closed due to no-load of the positive converter transformer, the converter transformers in parallel operation will generate excitation inrush current and parallel harmonic inrush current, causing a sudden drop in the AC bus voltage. Due to the small amplitude of the harmonic inrush current and the amplitude of each harmonic, the inrush current cannot be accurately identified and the broadband harmonic protection cannot be locked in time, causing the protection to malfunction. It can be seen that the converter transformer inrush current has a negative impact on the voltage harmonic protection. Therefore, based on the complexity of the DC transmission system and the particularity of the converter transformer, the existing converter transformer inrush current identification strategy is difficult to accurately and quickly identify the converter transformer inrush current every time. Summary of the invention

[0003] The purpose of the present invention is to provide a wideband harmonic protection optimization method, system, device and medium based on dynamic threshold, which can improve the accuracy of protection action by using the method of dynamic protection action threshold and ensure the efficient and safe operation of DC transmission system.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] A broadband harmonic protection optimization method based on dynamic threshold, comprising:

[0006] When the air-drop transformer performs the opening operation, the current amplitude and the opening angle at the opening moment are recorded;

[0007] The residual magnetism is determined according to the current amplitude and the opening angle at the time of opening, and the dynamic protection action threshold is determined according to the input value and load size of other residual magnetism generating scenarios. The protection action threshold currently used is the single-pole action threshold.

[0008] Before the air-drop transformer is closed, the current protection action threshold of the protection system is set to the transition action threshold, and the auxiliary criterion is combined to monitor whether the attenuation of the commutation transformer inrush current is completed;

[0009] If the attenuation of the commutation transformer surge current has been completed, the current protection action threshold is changed from the transition action threshold to the bipolar action threshold.

[0010] Optionally, the opening angle is determined by the opening moment.

[0011] Optionally, the calculation process of the dynamic protection action threshold is:

[0012] Calculating the residual magnetism according to the current amplitude at the opening moment and the opening angle;

[0013] Obtaining artificial input values ​​of residual magnetism based on other residual magnetism-generating scenarios, and monitoring load size in real time;

[0014] The residual magnetism of the commutation transformer core is determined according to the manual input value and the residual magnetism size, and the dynamic protection action threshold is calculated according to the residual magnetism of the commutation transformer core and the load size, and the single-pole action threshold is determined as the current protection action threshold.

[0015] Optionally, the auxiliary criterion is a second harmonic criterion.

[0016] Optionally, the calculation formula of the transition action threshold is:

[0017] K set =1.2×(6.03308-0.00379P+1.24772×10 -5 P 2

[0018] -1.532×10 -8 P 3 -1.17068×10 -10 P 4

[0019] +2.6435×10 -13 P 5 -4.48865B r +34.51635B r 2

[0020] -16.62417B r 3 -19.5764B r 4 +15.32452B r 5 )

[0021] Among them, P represents the load size, B r Indicates the residual magnetism of the commutation transformer core.

[0022] The present invention also provides a broadband harmonic protection optimization system based on dynamic threshold, comprising:

[0023] A data acquisition unit is used to record the current amplitude and the opening angle at the time of the opening when the air-drop transformer performs the opening operation;

[0024] A trip state threshold determination unit, used to determine the residual magnetism according to the current amplitude at the trip moment and the trip angle, and to determine the dynamic protection action threshold according to the input value and load size of other residual magnetism generating scenarios. The currently adopted protection action threshold is a single-pole action threshold;

[0025] The transition state threshold determination unit is used to set the current protection action threshold of the protection system to the transition action threshold before the air-dropped transformer performs the closing operation, and monitor whether the attenuation of the commutation transformer inrush current is completed in combination with the auxiliary judgment criteria;

[0026] The closing state threshold determination unit is used to change the current protection action threshold from the transition action threshold to the bipolar action threshold if the attenuation of the commutation transformer inrush current has been completed.

[0027] The present invention also provides an electronic device, including a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to execute the above-mentioned wide-band harmonic protection optimization method based on dynamic threshold.

[0028] The present invention also provides a computer-readable storage medium storing a computer program, wherein the computer program, when executed by a processor, implements the above-mentioned wide-band harmonic protection optimization method based on dynamic threshold.

[0029] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0030] The present invention discloses a method, system, device and medium for optimizing broadband harmonic protection based on dynamic thresholds, wherein the method includes recording the current amplitude and the opening angle at the time of opening when the air-drop transformer performs the opening operation; determining the residual magnetism size according to the current amplitude and the opening angle at the time of opening, and determining the current protection action threshold as the dynamic protection action threshold according to the input value and load size of other residual magnetism generating scenes; before the air-drop transformer performs the closing operation, setting the current protection action threshold of the protection system as the transition state dynamic protection action threshold, and combining the auxiliary criterion to monitor whether the attenuation of the commutation transformer surge current is completed; if the attenuation of the commutation transformer surge current is completed, changing the current protection action threshold from the transition action threshold to the bipolar action threshold. The present invention can improve the accuracy of the protection action by using the method of the dynamic protection action threshold, and ensure the efficient and safe operation of the DC transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Figure 1 It is a flow chart of a broadband harmonic protection optimization method based on dynamic threshold of the present invention;

[0033] Figure 2 Schematic diagram of the effect of the closing angle on the transformer core magnetic flux in this embodiment;

[0034] Figure 3 The relationship between the dynamic protection threshold and the system operation status in this embodiment;

[0035] Figure 4 This is a flow chart of dynamic protection threshold calculation in this embodiment;

[0036] Figure 5 A logic diagram for using the dynamic protection threshold in this embodiment;

[0037] Figure 6 This is a schematic diagram of comprehensively considering the influence of load and residual magnetism in this embodiment;

[0038] Figure 7 It is a schematic diagram of the dynamic protection threshold fitting effect in this embodiment. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The purpose of the present invention is to provide a wideband harmonic protection optimization method, system, device and medium based on dynamic threshold, which can improve the accuracy of protection action by using the method of dynamic protection action threshold and ensure the efficient and safe operation of DC transmission system.

[0041] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] like Figure 1 As shown, the present invention provides a broadband harmonic protection optimization method based on dynamic threshold, comprising:

[0043] Step 100: When the air-drop transformer performs a tripping operation, the current amplitude and the tripping angle at the time of the tripping are recorded.

[0044] Step 200: Determine the residual magnetism size according to the current amplitude at the opening moment and the opening angle, and determine the dynamic protection action threshold according to the input values ​​and load size of other residual magnetism generating scenarios. The currently used protection action threshold is the single-pole action threshold.

[0045] Step 300: Before the air-drop transformer performs the closing operation, the current protection action threshold of the protection system is set to the transition action threshold, and the attenuation of the commutation transformer inrush current is monitored in combination with the auxiliary criterion to see whether it is completed.

[0046] Step 400: If the attenuation of the commutation transformer inrush current has been completed, the current protection action threshold is changed from the transition action threshold to a bipolar action threshold.

[0047] Based on the above steps, the detailed processing procedures are provided as follows.

[0048] When the system is operating normally, three factors have the most obvious impact on the protection action coefficient: closing angle, residual magnetism, and load. The closing angle is mainly determined by the closing moment. If the phase selection closing operation cannot be performed, the closing angle is a random variable. The residual magnetism generation scenarios are relatively diverse. If the system is operating normally, it is mainly caused by the opening operation. There are also many measurement methods for other residual magnetism generation scenarios. The load is determined by the operation plan and is difficult to predict in advance.

[0049] The dynamically changing action threshold of broadband harmonic protection must fully consider three influencing factors and adopt different processing methods for different factors: the randomly determined closing angle is determined according to the worst impact on the inrush current; the residual magnetism is calculated based on the last opening angle or self-input; the load size is considered through real-time monitoring of the system.

[0050] Figure 2 The influence of the closing angle of the air-drop transformer on the core magnetic flux is shown. The magnetic flux amplitudes corresponding to different closing angles are also different. The relationship between magnetic flux and current is nonlinear. The two are positively correlated but not proportional. The harmonic components contained in the generated inrush current will produce a voltage drop on the power supply impedance, causing a temporary drop in the bus voltage and an increase in the protection action. In the subsequent analysis, the analysis and explanation of the influence of the residual magnetism and load conditions on the protection action coefficient should be carried out according to the closing angle of 0°, so as to propose a dynamically changing protection action threshold.

[0051] The introduction of the broadband harmonic protection dynamic protection action threshold is mainly to deal with the bus voltage distortion caused by the surge current of the converter transformer. The operating conditions that may cause the surge current should be considered, and various influencing factors should be considered comprehensively. When the system is operating normally without the risk of converter transformer surge current, the action threshold needs to be reduced to an appropriate value.

[0052] like Figure 3As shown in the figure, the bipolar DC transmission system has two operating modes: unipolar operation and bipolar operation. Switching between the two modes requires opening and closing operations. The dynamic protection action threshold should have different action thresholds for different operating modes, which can be divided into three types: the dynamic threshold of normal bipolar operation, the action threshold of unipolar operation after one pole is opened, and the action threshold of the bipolar operation process from closing operation to the system restoring stability.

[0053] like Figure 4 As shown in the figure, the commutation transformer inrush current occurs in the transition state from unipolar operation to bipolar operation. In this process, the protection threshold should consider two factors: load and residual magnetism. The load condition needs to be detected in real time, and the residual magnetism caused by the opening of the gate can be calculated based on the opening angle and the current amplitude at the time of opening. The residual magnetism generated by other conditions can be manually input. The expression of the appropriate dynamic protection threshold is obtained in advance through simulation and analysis of the system parameters. When used, the dynamic protection threshold that should be taken before closing the gate is directly calculated based on the obtained load and residual magnetism.

[0054] like Figure 5 As shown in the figure, before the closing operation, the protection system is instructed to increase the protection action threshold to the calculated transition process protection action threshold. At the same time, the attenuation of the commutation transformer inrush current is identified and monitored in combination with other auxiliary criteria. After it is determined that the commutation transformer inrush current has been attenuated, that is, the DC transmission system has entered a bipolar stable operation state, the action threshold is changed to the protection action threshold under stable operation.

[0055] As a specific implementation method, the following example is provided.

[0056] Taking the parameters of the converter transformer of a converter station in Zhangbei DC transmission as an example, the total resistance of the power supply and the line before the transformer is selected as 100Ω, the traditional protection setting value is selected as 5% as the action threshold, the size of the second harmonic auxiliary judgment criterion is selected as a fixed value of 43A, and the transition state is set to the positive pole converter transformer no-load closing, and the negative pole converter transformer normal operation before closing. The simulation model is built using PSCAD software to illustrate the calculation method of the dynamic protection action threshold. The converter transformer parameters are shown in Table 1.

[0057] Table 1 Parameters of a converter

[0058]

[0059] When the converter station is in normal bipolar operation, the voltage, current and protection action coefficient are shown in Table 2, where the voltage is not distorted, the total voltage effective value and the fundamental voltage effective value are basically equal, and the protection action coefficient is close to 0. The normal operation of the converter station in unipolar mode is similar to that in bipolar mode, and the change in the protection action coefficients of the two operating states is not much different when common faults occur. Taking the half-load condition as an example, the amplitudes of the protection action coefficients of unipolar and bipolar operation in the face of faults are shown respectively.

[0060] Table 2 Comparison of K values ​​when unipolar and bipolar operation fails

[0061]

[0062]

[0063] The difference between the protected action coefficients of bipolar and unipolar operation under common fault types is not large, so there is no need to set different action thresholds for the stable state of the two operating modes. According to the provisions of Chinese standards, the voltage distortion rate should be less than 2%, and the conventional action threshold setting is generally set to 5%. This setting is still used for the stable state of unipolar and bipolar.

[0064] The key to setting the dynamic protection action threshold lies in the selection of the threshold for the transition process from unipolar to bipolar operation of the DC transmission system. In this process, it is necessary to pay attention to the influence of the two parameters of load and residual magnetism on the protection action coefficient.

[0065] In normal operation, the magnetic flux inside the transformer core is generally 0.6-0.8 times the saturation flux, and the residual magnetism that may be generated is generally no more than 0.7 times the saturation flux. Here, 0-0.8 times the saturation flux are taken for illustration. It is generally difficult for a DC transmission system to maintain full load operation. The impact of the load can be analyzed at intervals of 10% and the transmission system load can be analyzed from 10% to 120% of the rated capacity.

[0066] Considering the effect of load on the action coefficient alone, the residual magnetism can be regarded as a constant value, here taking 0.4 times of the saturation flux, and changing the load condition to find the relationship between the protection coefficient and the load. It can be seen that the relationship between the load and the protection action coefficient is a nearly linear negative correlation. Under the same residual magnetism, the greater the load, the smaller the protection action coefficient.

[0067] To analyze the effect of residual magnetism on the protection factor, the load value can be specified as constant, and the load can be selected as half of the rated load. The relationship between residual magnetism and the protection action coefficient is obviously nonlinear, and can be divided into two sections, which is similar to the conventional two-section linear simplification result of the hysteresis loop. Moreover, with the change of residual magnetism, the range of the protection action coefficient also has a large span. The boundary between the worst case of commutation transformer inrush current and the fault condition gradually blurs. In order to protect more accurate action and prevent the protection from not acting in the event of a fault during normal operation, a dynamically changing threshold should be used for the transition state, and the influence of residual magnetism and load should be fully considered.

[0068] Comprehensively consider the influence of residual magnetism and load size on the protection action coefficient during the transition state (such as Figure 6 ), and at the same time, take values ​​according to the changes in load and residual magnetism to obtain the possible protection action coefficient.

[0069] like Figure 7 As shown, the 132 data obtained are fitted by two-dimensional ploynomial nonlinear surface fitting, and the residual magnetization size B can be obtained. r The formula with load size P as the independent variable and protection action coefficient K as the dependent variable is obtained. Considering the possible errors in the fitting process and the fact that the protection action threshold should have a certain margin with the possible protection coefficient, the dynamic protection threshold that should be used in the transition process can be obtained by multiplying the formula by a coefficient of 1.2.

[0070] K set =1.2×(6.03308-0.00379P+1.24772×10 -5 P 2

[0071] -1.532×10 -8 P 3 -1.17068×10 -10 P 4

[0072] +2.6435×10 -13 P 5 -4.48865B r +34.51635B r 2

[0073] -16.62417B r 3 -19.5764B r 4 +15.32452B r 5 )

[0074] Among them, P represents the load size, B r Indicates the residual magnetism of the commutation transformer core. K set is the transition protection action threshold that should be preset before closing the circuit breaker. The unit of P is MW. r It is the percentage of saturation flux. According to the obtained residual magnetism and load parameters, the real-time appropriate protection action threshold can be calculated according to this formula.

[0075] The extreme cases of large residual magnetism and large load, large residual magnetism and small load, small residual magnetism and large load, and small residual magnetism and small load, as well as the case where the system half-load residual magnetism is half of the saturation residual magnetism, are selected respectively, and the action difference between the traditional protection threshold and the dynamic protection threshold is compared.

[0076] Table 3 Comparison of protection thresholds under special load and residual magnetism conditions

[0077]

[0078]

[0079] From Table 3, it can be found that the dynamic protection threshold can be used to correctly operate when the load is not small. The size of the load will affect the amplitude of the harmonics, and the size of the residual magnetism will affect the size of the action coefficient. The situation of extremely small load in the DC transmission system is relatively rare, and more working conditions may still be the state of the last column and the first column of the table. Therefore, compared with the traditional protection action threshold, the dynamic protection action threshold is more advantageous for the scenario where the commutation transformer and the inrush current cause the misoperation of the broadband harmonic protection.

[0080] Considering the situation where a fault occurs in the transient state of the DC transmission system, a fault is set to occur 0.2s after closing the switch, and the new protection action threshold is observed compared with the traditional static threshold. The residual magnetism is selected as 0.4 of the saturation value and the load is half load. At this time, the calculated dynamic protection threshold should be 9.74%.

[0081] Table 4 Comparison of fault protection thresholds during inrush current

[0082]

[0083] The harmonics generated by the short circuit between three-phase lines and the ground fault have little impact and last for a very short time. Therefore, when a single-phase short circuit fault with the smallest impact occurs, the traditional protection action threshold cannot be fully dealt with. In engineering, a combination of multiple protection behaviors is generally used to deal with various types of faults. According to the above table, it can be found that when dealing with a fault during the inrush current of the converter transformer, the dynamic protection threshold is consistent with the traditional static protection threshold action state. In other words, the method of dynamically increasing the threshold for the transition process does not bring new disadvantages to the protection.

[0084] Combining the verification of the above two aspects, it can be concluded that the dynamic protection action threshold can effectively deal with the situation of false operation of broadband harmonic protection during the inrush current generated by the closing of the converter transformer. Compared with the traditional static protection action threshold, the dynamic protection threshold also adds new problems. At the same time, the dynamic protection threshold also avoids the possibility of missing action in response to faults caused by blindly increasing the static action threshold.

[0085] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0086] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A broadband harmonic protection optimization method based on dynamic threshold, characterized in that: include: When the air-drop transformer performs the opening operation, the current amplitude and the opening angle at the opening moment are recorded; The residual magnetism is determined according to the current amplitude at the time of the opening and the opening angle, and the dynamic protection action threshold is determined according to the input value and load size of other residual magnetism generating scenarios. The protection action threshold currently used is the single-pole action threshold; Before the air-drop transformer is closed, the current protection action threshold of the protection system is set to the transition action threshold, and the auxiliary criterion is combined to monitor whether the attenuation of the commutation transformer inrush current is completed; If the attenuation of the commutation transformer surge current has been completed, the current protection action threshold is changed from the transition action threshold to the bipolar action threshold.

2. The broadband harmonic protection optimization method based on dynamic threshold according to claim 1 is characterized in that: The opening angle is determined by the opening moment.

3. The broadband harmonic protection optimization method based on dynamic threshold according to claim 1 is characterized in that: The calculation process of the dynamic protection action threshold is: Calculating the residual magnetism according to the current amplitude at the opening moment and the opening angle; Obtaining artificial input values ​​of residual magnetism based on other residual magnetism-generating scenarios, and monitoring load size in real time; The residual magnetism of the commutation transformer core is determined according to the manual input value and the residual magnetism size, and the dynamic protection action threshold is calculated according to the residual magnetism of the commutation transformer core and the load size, and the single-pole action threshold is determined as the current protection action threshold.

4. The method for optimizing broadband harmonic protection based on dynamic threshold according to claim 1, characterized in that: The auxiliary criterion is a second harmonic criterion.

5. The method for optimizing broadband harmonic protection based on dynamic threshold according to claim 1, characterized in that: The calculation formula of the transition action threshold is: K set =1.2×(6.03308-0.00379P+1.24772×10 -5 P 2 -1.532×10 -8 P 3 -1.17068×10 -10 P 4 +2.6435×10 -13 P 5 -4.48865B r +34.51635B r 2 <h2 style=";text-align:left;direction:ltr">-16.62417B<h2 style=";text-align:left;direction:ltr"> r <h2 style=";text-align:left;direction:ltr"> 3 <h2 style=";text-align:left;direction:ltr"> -19.5764B<h2 style=";text-align:left;direction:ltr"> r <h2 style=";text-align:left;direction:ltr"> 4 <h2 style=";text-align:left;direction:ltr"> +15.32452B<h2 style=";text-align:left;direction:ltr"> r <h2 style=";text-align:left;direction:ltr"> 5 <h2 style=";text-align:left;direction:ltr"> ) Among them, P represents the load size, B r Indicates the residual magnetism of the commutation transformer core.

6. A broadband harmonic protection optimization system based on dynamic threshold, characterized in that: include: A data acquisition unit is used to record the current amplitude and the opening angle at the time of the opening when the air-drop transformer performs the opening operation; A trip state threshold determination unit, used to determine the residual magnetism according to the current amplitude at the trip moment and the trip angle, and to determine the dynamic protection action threshold according to the input value and load size of other residual magnetism generating scenarios. The currently adopted protection action threshold is a single-pole action threshold; The transition state threshold determination unit is used to set the current protection action threshold of the protection system to the transition action threshold before the air-dropped transformer performs the closing operation, and monitor whether the attenuation of the commutation transformer inrush current is completed in combination with the auxiliary judgment criteria; The closing state threshold determination unit is used to change the current protection action threshold from the transition action threshold to the bipolar action threshold if the attenuation of the commutation transformer inrush current has been completed.

7. An electronic device, characterized in that: It comprises a memory and a processor, the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to execute the broadband harmonic protection optimization method based on dynamic threshold according to any one of claims 1-5.

8. A computer-readable storage medium, characterized in that: It stores a computer program, which, when executed by a processor, implements the broadband harmonic protection optimization method based on dynamic threshold as described in any one of claims 1 to 5.

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