A flexible grounding system high resistance grounding fault line selection method based on zero sequence current amplitude ratio

Abstract

The application discloses a flexible grounding system high-resistance grounding fault line selection method based on a zero sequence current amplitude ratio and belongs to the flexible grounding system fault line selection field. The existing single-phase grounding fault protection method of the flexible grounding system has the problems of low transition resistance resistance and complex operation, and therefore, the application provides a flexible grounding system single-phase high-resistance grounding fault line selection method based on a zero sequence current amplitude ratio. The method only needs to obtain the amplitudes of the zero sequence currents of each line before and after the input of a parallel small resistor, is not affected by the polarity reverse connection of a zero sequence current transformer and phase measurement error, does not need transverse comparison between fault information, has the advantages of strong transition resistance resistance, high reliability, low requirement on the precision of a transformer and easy implementation. In addition, the influence of the measurement dead zone of a zero sequence current transformer on the criterion is solved through reasonable design of an algorithm.

Description

Technical Field

[0001] This invention relates to the field of fault location in flexible grounding systems, and specifically to a method for fault location in high-resistivity grounding systems based on the zero-sequence current amplitude ratio. Background Technology

[0002] Flexible grounding systems are a new type of grounding system proposed by my country's power supply departments after summarizing long-term operation and management experience with resonant grounding systems and the experience of promoting and using low-resistance grounding systems. They combine the advantages of high power supply reliability of resonant grounding systems with the strong ability of low-resistance grounding systems to suppress fault overvoltages. Currently, flexible grounding systems have been widely adopted in the Southern Power Grid region of my country. The "Technical Guidelines for 20kV and Below Power Grid Equipment" issued by China Southern Power Grid Co., Ltd. in 2016 indicated that flexible grounding systems could be adopted for 10kV (20kV) distribution systems after technical demonstration and analysis to improve reliability. Subsequently, the State Grid Corporation of China also successively issued relevant technical specifications, further clarifying the application specifications of this type of grounding method.

[0003] Currently, flexible grounding systems mainly use the protection methods of low-resistance grounding systems to construct single-phase grounding protection. Among these, time-delay zero-sequence overcurrent protection is the most widely used. However, time-delay zero-sequence overcurrent protection needs to be set to avoid the maximum capacitive current of the system, resulting in a high operating threshold and a maximum withstand resistance of less than 140Ω. Even with improved zero-sequence overcurrent protection, the reliable withstand resistance is only 760Ω. In reality, grounding faults caused by broken or fallen distribution conductors or aging cable insulation can result in transition resistance values ​​as high as several thousand ohms, making it difficult for existing protection methods to meet the requirements of rapid and reliable fault clearing. Furthermore, most existing research methods only focus on whether the protection installed on the faulty line can operate correctly, neglecting whether the protection on the healthy line can reliably not operate. After the parallel small resistor is connected, the zero-sequence current of the healthy line is very weak. The measurement error and measurement dead zone of the zero-sequence current transformer may lead to failure in criterion calculation or misjudgment. Moreover, existing protection methods do not fully exploit the information of fault changes, resulting in a cumbersome judgment process, a large amount of accurately collected signals, and susceptibility to interference from multiple factors. Therefore, with the widespread use of flexible grounding systems, it is urgent to conduct research on line selection for high-resistance grounding faults in flexible grounding systems. Summary of the Invention

[0004] To address the challenges mentioned in the background section, this invention proposes a flexible grounding system high-resistivity grounding fault location method based on the zero-sequence current amplitude ratio.

[0005] This invention achieves the above-mentioned technical objectives and effects through the following technical solution: a method for selecting high-resistance grounding faults in a flexible grounding system based on the zero-sequence current amplitude ratio, comprising the following steps:

[0006] Step 1: Identify the line with the largest capacitance to ground within the system, calculate the ratio of this line's capacitance to the total capacitance to ground in the system, and determine the line selection threshold. ;

[0007] Step 2: Detect the fault under resonant grounding conditions, and activate the protection system once the fault initiation conditions are met;

[0008] Step 3: Record the amplitude of the zero-sequence current in each line before the parallel small resistor is connected;

[0009] Step 4: After a 1-second delay, if the fault start-up conditions are still met, connect the parallel small resistor and proceed to Step 5; if the fault start-up conditions are no longer met, return to Step 2.

[0010] Step 5: If the zero-sequence current amplitude of a certain line reaches the operating threshold of the improved zero-sequence overcurrent protection, disconnect the line and return to step 2; otherwise, record the zero-sequence current amplitude of each line after the parallel small resistor is connected.

[0011] Step 6: If the recorded zero-sequence current amplitude data is less than If A, then the original record data will be overwritten as 0A;

[0012] Step 7: If the recorded value of the zero-sequence current amplitude of a certain line is 0A before and after the parallel small resistor is connected, then the line is considered a healthy line by default.

[0013] Step 8: Calculate the zero-sequence current amplitude ratio for lines that do not meet the requirements of Step 7. , respectively Lines with values ​​greater than or less than the line selection threshold are classified as healthy lines and faulty lines, respectively.

[0014] Furthermore, the formula for calculating the line selection threshold in step 1 is as follows:

[0015]

[0016] Where v is the system detuning degree, The proportion of the line with the largest capacitance to ground in the system to the total capacitance to ground in the system.

[0017] Furthermore, in step 4, the moment when the parallel small resistor is connected is the instant when the system zero-sequence voltage crosses zero.

[0018] Furthermore, in step 6, if the recorded zero-sequence current amplitude data is less than... If A is selected, the original record data will be overwritten as 0A.

[0019] Furthermore, in step 7, if the recorded value of the zero-sequence current amplitude of a certain line is 0A before and after the parallel small resistor is put into operation, the line is considered to be a healthy line by default.

[0020] Furthermore, in step 8, the zero-sequence current amplitude of any line i is compared with... for:

[0021]

[0022] in, These represent the zero-sequence current amplitude of any line i in the system before and after the parallel small resistor is connected.

[0023] Furthermore, the line selection method in step 8 is as follows:

[0024] Step 8.1, if the zero-sequence current amplitude ratio of the line is greater than The line was determined to be a sound line.

[0025] Step 8.2, if the zero-sequence current amplitude ratio of the line is less than or equal to The circuit was determined to be faulty.

[0026] The high-resistance grounding fault selection method for flexible grounding systems based on the zero-sequence current amplitude ratio disclosed in this invention has the advantages of strong resistance to transition resistance, easy implementation, low requirements for the accuracy of the current transformer, and no influence from the reverse polarity of the zero-sequence current transformer. Moreover, it only requires measuring the amplitude of the zero-sequence current of each line, without the need for complex phase calculations, thus avoiding the influence of phase measurement errors and asynchronous sampling. In addition, through the operation of steps 6-7, the influence of the measurement dead zone of the zero-sequence current transformer on the fault selection effect of this invention can be eliminated. Attached Figure Description

[0027] Figure 1 This is an operation flowchart of a high-resistance grounding fault location method for flexible grounding systems based on the zero-sequence current amplitude ratio.

[0028] Figure 2 This is a simulation topology diagram of a 10kV flexible grounding system.

[0029] Figure 3 This is a waveform diagram showing the changes in zero-sequence voltage and zero-sequence current after a high-resistance grounding fault occurs in a flexible grounding system. Detailed Implementation

[0030] The following will provide a more detailed description of the actual operation process and simulation effects of the present invention, in conjunction with the accompanying drawings and simulation data.

[0031] A flexible grounding system high-resistivity grounding fault location method based on zero-sequence current amplitude ratio, such as... Figure 1 As shown, the specific process includes the following steps:

[0032] Step 1: Identify the line with the largest capacitance to ground within the system, calculate the ratio of this line's capacitance to the total capacitance to ground in the system, and determine the line selection threshold. ;

[0033] Step 2: Detect the fault under resonant grounding conditions, and activate the protection system once the fault initiation conditions are met;

[0034] Step 3: Record the amplitude of the zero-sequence current in each line before the parallel small resistor is connected;

[0035] Step 4: After a 1-second delay, if the fault start-up conditions are still met, connect the parallel small resistor and proceed to Step 5; if the fault start-up conditions are no longer met, return to Step 2.

[0036] Step 5: If the zero-sequence current amplitude of a certain line reaches the operating threshold of the improved zero-sequence overcurrent protection, disconnect the line and return to step 2; otherwise, record the zero-sequence current amplitude of each line after the parallel small resistor is connected.

[0037] Step 6: If the recorded zero-sequence current amplitude data is less than If A, then the original record data will be overwritten as 0A;

[0038] Step 7: If the recorded value of the zero-sequence current amplitude of a certain line is 0A before and after the parallel small resistor is connected, then the line is considered a healthy line by default.

[0039] Step 8: Calculate the zero-sequence current amplitude ratio for lines that do not meet the requirements of Step 7. , respectively Lines with values ​​greater than or less than the line selection threshold are classified as healthy lines and faulty lines, respectively.

[0040] Furthermore, the formula for calculating the line selection threshold in step 1 is as follows:

[0041]

[0042] Where v is the system detuning degree, The proportion of the line with the largest capacitance to ground in the system to the total capacitance to ground in the system.

[0043] Furthermore, in step 4, the moment when the parallel small resistor is connected is the instant when the system zero-sequence voltage crosses zero.

[0044] Furthermore, in step 6, if the recorded zero-sequence current amplitude data is less than... If A is selected, the original record data will be overwritten as 0A.

[0045] Furthermore, in step 7, if the recorded value of the zero-sequence current amplitude of a certain line is 0A before and after the parallel small resistor is put into operation, the line is considered to be a healthy line by default.

[0046] Furthermore, in step 8, the zero-sequence current amplitude of any line i is compared with... for:

[0047]

[0048] in, These represent the zero-sequence current amplitude of any line i in the system before and after the parallel small resistor is connected.

[0049] Furthermore, the line selection method in step 8 is as follows:

[0050] Step 8.1, if the zero-sequence current amplitude ratio of the line is greater than The line was determined to be a sound line.

[0051] Step 8.2, if the zero-sequence current amplitude ratio of the line is less than or equal to The circuit was determined to be faulty.

[0052] Simulation verification

[0053] A simulation model was built using a Real-Time Digital Simulation System (RTDS) to verify the effectiveness and applicability of the proposed method. The simulation topology of the 10kV flexible grounding system is shown below. Figure 2 As shown in the diagram, the line length is marked, G is an infinite power source, and a small resistor R is connected in parallel. N The Ω is 10Ω, the system detuning degree v is -8%, and L p The value is 0.237H, and S is a switch that controls the connection or disconnection of the parallel small resistor. The positive-sequence and zero-sequence parameters of the overhead line resistance are 0.178Ω / km and 0.250Ω / km, respectively; the positive-sequence and zero-sequence parameters of the overhead line inductance are 1.210mH / km and 5.540mH / km, respectively; the positive-sequence and zero-sequence parameters of the overhead line capacitance are 0.015uF / km and 0.008uF / km, respectively; the positive-sequence and zero-sequence parameters of the cable line resistance are 0.27Ω / km and 2.70Ω / km, respectively; the positive-sequence and zero-sequence parameters of the cable line inductance are 0.255mH / km and 1.020mH / km, respectively; and the positive-sequence and zero-sequence parameters of the cable line capacitance are 0.376uF / km and 0.280uF / km, respectively.

[0054] Line 1 has the largest capacitance to ground within the system, with a ratio of 26.09% to the total capacitance to ground of the system. The system detuning degree is -8%, therefore the line selection threshold... It is 4.26.

[0055] Table 1. Ratio of zero-sequence current amplitude for each line when ground faults occur with different resistance values. 1000 67.08 67.11 67.09 0.74 67.09 Line 4 2000 86.44 86.43 86.48 0.96 86.44 Line 4 3000 93.64 93.64 93.62 1.03 93.64 Line 4 5000 100.32 100.28 100.29 1.09 100.33 Line 4 10000 108.19 108.20 108.25 1.12 108.22 Line 4

[0056] The fault location in the table is 10km away from the busbar on line 4. The data in the table shows that the faulty line is clearly distinguishable from the healthy line, proving that the present invention can be applied to single-phase grounding faults with different resistance values.

[0057] Table 2. Ratio of zero-sequence current amplitudes for each line when ground faults occur at different resistance values ​​on the busbar. 1000 67.28 67.29 67.1 67.29 67.31 No action 2000 86.56 86.55 86.56 86.54 86.56 No action 3000 93.69 93.68 93.67 93.67 93.67 No action 5000 100.22 99.55 100.21 100.18 100.19 No action 10000 107.56 107.57 107.54 107.57 107.59 No action

[0058] As can be seen from the data in the table, when a bus fault occurs, the ratio of the zero-sequence current amplitude of each line is much greater than the line selection threshold. Therefore, the protection installed on each line can reliably not operate, indicating that the present invention can be applied to the bus fault conditions of a flexible grounding system.

[0059] Figure 3 This diagram shows the changes in zero-sequence voltage waveforms of some intact lines, the faulty line, and the system when a 3000Ω ground fault occurs 10km from the busbar on line 4. Observe... Figure 3 It can be observed that after the parallel small resistor is connected, the amplitude of the zero-sequence current in the faulty circuit 4 hardly changes, while the amplitudes of the zero-sequence current in the healthy circuits 1 and 5 drop sharply, far below the values ​​of the parallel small resistor. Therefore, when recording this data, record it as 0A.

[0060] It should be noted that there is no measurement dead zone for zero-sequence current transformers in the simulation environment. Therefore, when calculating the ratio of zero-sequence current amplitude for each line in Tables 1 and 2, for ease of presentation and understanding, the operation in steps 6-7 was not performed to reduce the zero-sequence current amplitude below a certain value. Line A, overwrite the original record data with 0A.

[0061] The above description and embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for selecting the fault location of a high-resistivity grounding system based on the zero-sequence current amplitude ratio, characterized in that, Specifically, the following steps are included: Step 1: Identify the line with the largest capacitance to ground within the system, and calculate the ratio of this line's capacitance to the total capacitance to ground of the system. Based on this ratio and the system detuning degree v, the line selection threshold is calculated. : Step 2: Detect the fault under resonant grounding conditions, and activate the protection system once the fault initiation conditions are met; Step 3: Record the amplitude of the zero-sequence current in each line before the parallel small resistor is connected; Step 4: After a 1-second delay, if the fault start-up conditions are still met, connect the parallel small resistor and proceed to Step 5; if the fault start-up conditions are no longer met, return to Step 2. Step 5: If the zero-sequence current amplitude of a certain line reaches the operating threshold of the improved zero-sequence overcurrent protection, disconnect the line and return to step 2; otherwise, record the zero-sequence current amplitude of each line after the parallel small resistor is connected. Step 6: If the recorded zero-sequence current amplitude data is less than If A, then the original record data will be overwritten as 0A; Step 7: If the recorded value of the zero-sequence current amplitude of a certain line is 0A before and after the parallel small resistor is connected, then the line is considered a healthy line by default. Step 8: Calculate the zero-sequence current amplitude ratio for lines that do not meet the requirements of Step 7. , respectively Lines with values ​​greater than or less than the line selection threshold are classified as healthy lines and faulty lines, respectively.

2. The method for selecting high-resistance grounding faults in flexible grounding systems based on zero-sequence current amplitude ratio as described in claim 1, characterized in that, If the recorded zero-sequence current amplitude data in step 6 is less than A, overwrite the original record data with 0A.

3. The method for selecting high-resistance grounding faults in flexible grounding systems based on zero-sequence current amplitude ratio as described in claim 1, characterized in that, If, in step 7, the recorded value of the zero-sequence current amplitude of a certain line is 0A before and after the parallel small resistor is put into operation, the line is considered to be a healthy line by default.

4. The method for selecting high-resistance grounding faults in flexible grounding systems based on zero-sequence current amplitude ratio as described in claim 1, characterized in that, The zero-sequence current amplitude ratio in step 8 : in, These represent the amplitudes of the zero-sequence current of any line i in the system before and after the parallel small resistor is connected.

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