A method for selecting single-phase ground fault line in distribution network based on the sum of absolute values ​​of mutual differences

Abstract

The present invention discloses a method for selecting a line for a single-phase grounding fault in a distribution network based on the absolute value sum of mutual differences. Three lines are selected at random to estimate their capacitive current to the ground. When a single-phase grounding fault occurs in the distribution network, the absolute value sum of the first half-wave sampling values ​​of the three lines is calculated, and the ratio of the intermediate value and the estimated capacitive current value corresponding to it is selected; based on the ratio and the magnitude of the zero-sequence voltage, different methods for calculating the absolute value sum of mutual differences and line selection criteria are selected. When the conditions are met, the line selection criteria are calculated based on the absolute value sum of mutual differences of half-wave direct sampling values; when the conditions are not met, if it is a distribution network with an ungrounded neutral point, the line selection criteria are calculated based on the absolute value sum of mutual differences of full-wave direct sampling values; when it is a distribution network with a grounded neutral point through an arc suppression coil, the line selection criteria are calculated based on the absolute value sum of mutual differences of full-wave direct sampling values ​​after power correction based on the sampling values; the line corresponding to the maximum value of the line selection criteria is the fault line; the present invention is simple and accurate in calculation.

Description

Technical Field

[0001] The invention belongs to the technical field of power system automation, and particularly relates to a single-phase grounding fault line selection method for a distribution network based on the sum of mutual difference absolute values. Background Art

[0002] The line selection for single-phase ground fault in distribution network has always been a difficult problem for relay protection. Since the fault characteristics are relatively complex, the fault types are many, and the fault components are relatively small, the accuracy of line selection for ground fault is seriously affected.

[0003] To this end, a large number of power workers have also proposed some line selection methods based on the characteristics of zero-sequence components after grounding faults. These line selection methods mainly include: line selection methods based on zero-sequence current quantity based on the characteristics of zero-sequence components after grounding faults; line selection methods based on zero-sequence energy analysis; line selection methods based on wavelet analysis; line selection methods based on injection signal characteristics, etc. However, all of the above methods have certain limitations, such as low accuracy, uncertain frequency of zero-sequence current transient components, and complex amplitude and phase calculations. Therefore, the research on the single-phase grounding fault line selection method of distribution network based on the absolute value of the sum of mutual differences, which is simple to calculate, easy to implement and popularize, has important research value for improving the safety and reliability of distribution network operation. Summary of the invention

[0004] In order to solve the technical problems raised by the above-mentioned background technology, the present invention provides a single-phase grounding fault line selection method for distribution network based on the sum of mutual difference absolute values, so as to overcome the shortcomings of traditional single-phase grounding fault line selection in distribution network, solve the problems of uncertain frequency of transient component of zero-sequence current and complex amplitude and phase calculation, and realize accurate line selection of various types of single-phase grounding faults in distribution network.

[0005] In order to achieve the above technical objectives, the technical solution of the present invention is:

[0006] The method for selecting a single-phase ground fault line in a distribution network based on the sum of absolute values ​​of mutual differences comprises the following steps:

[0007] S1. Number the lines according to the structure of the distribution network and the number of lines, and determine the value of M;

[0008] S2. Select any three lines, estimate the ground capacitance current of the three lines according to the basic data of the three lines, and save them;

[0009] S3, judging whether a single-phase grounding fault occurs in the distribution network by detecting the magnitude of the zero-sequence voltage of the distribution network, and if a single-phase grounding fault occurs, proceeding to the next step;

[0010] S4, calculate the sum of the absolute values ​​of the sampling points of the first half-wave of the selected three lines, and0·1 ,I 0·2 ,I 0·3 ;

[0011] S5, with I 0·1 ,I 0·2 ,I 0·3 The value after removing the maximum and minimum values ​​of the three data is taken as the reference value I0. The estimated capacitance current of the line corresponding to I0 is recorded as I c ;

[0012] S6. Determine the method for calculating the line selection criterion for each single-phase grounding fault;

[0013] S7, when the conditions set in step S6 are met, the line selection criterion P is calculated based on the absolute value sum of the mutual differences of the half-wave direct sampling values. 0·i ;

[0014] S8. When the condition set in step S6 is not met, different fault criterion calculation methods are used for different neutral point grounding methods of the distribution network; if the distribution network is a neutral point ungrounded method, the line selection criterion is calculated based on the absolute value sum of the mutual differences of the full-wave direct sampling values; when the distribution network is a neutral point grounded method via an arc suppression coil, the line selection criterion is calculated based on the absolute value sum of the mutual differences of the full-wave sampling values ​​after power correction;

[0015] S9. Use the maximum line selection criterion method to select the faulty line, that is, the line corresponding to the maximum value of the line selection criterion is the faulty line.

[0016] Furthermore, in step S6, according to formula (2) as a setting condition, the corresponding absolute value of the mutual difference and the calculation method of the line selection criterion are determined for each single-phase grounding fault in the distribution network;

[0017]

[0018] Further, in step S6, when the conditions set in formula (2) are met, the line selection criterion P is calculated based on the absolute value sum of the direct sampling values ​​of the first half wave. 0·i ;

[0019]

[0020] Furthermore, when the conditions set by formula (2) are not met, different line selection criterion calculation methods are used for different neutral point grounding methods of the distribution network;

[0021] When the neutral point of the distribution network is not grounded, the line selection criterion P is calculated based on the absolute value sum of the mutual difference of the full-wave direct sampling value. 0·i , as shown in formula (4):

[0022]

[0023] When the neutral point of the distribution network is grounded through an arc suppression coil, the line selection criterion P is calculated by using the absolute value sum method of the mutual difference after power correction based on the full-wave sampling value. 0·i , as shown in formula (5):

[0024]

[0025] Among them: F 0·i is the power correction factor.

[0026] Beneficial effects brought by adopting the above technical solution: The present invention is a new method for realizing fault line selection by directly using the value of the zero-sequence current sampling point of the single-phase grounding fault in the distribution network. The present invention can effectively solve the problems of uncertain frequency of the transient component of zero-sequence current, complex amplitude and phase calculation when the neutral point is not grounded and the neutral point is grounded through an arc suppression coil in various single-phase grounding faults in the distribution network, and can effectively improve the accuracy of single-phase grounding fault line selection in the distribution network, and has the characteristics of simple calculation, easy implementation and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of the present invention;

[0028] Figure 2 is a schematic diagram of the distribution network;

[0029] Figure 3 This is a schematic diagram of a phase A grounding fault on the neutral point ungrounded distribution network L2;

[0030] Figure 4 This is a schematic diagram of a phase A grounding fault on the distribution network L2 where the neutral point is grounded via an arc suppression coil;

[0031] Figure 5 It is the zero-sequence current waveform (transient) of each line when an A-phase arc grounding fault occurs on the neutral point ungrounded distribution network L2;

[0032] Figure 6 It is the zero-sequence current waveform (transient) of each line when an A-phase arc grounding fault occurs on the neutral point grounded distribution network L2 through an arc suppression coil;

[0033] Figure 7 It is the zero-sequence current waveform of each line when a phase A grounding fault occurs on the neutral point ungrounded distribution network L2 (steady state);

[0034] Figure 8 It is the zero-sequence current waveform (steady state) of each line when a phase A grounding fault occurs on the distribution network L2 with the neutral point grounded through an arc suppression coil. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0036] The present invention proposes a method for selecting arc ground fault lines in distribution networks based on a sampling value method. Figure 1 As shown, the following steps are included:

[0037] Step 1: Number the lines according to the structure of the distribution network and the number of lines;

[0038] Step 2: Select any three lines (such as lines L1, L2, and L3), and estimate the ground capacitance current of these three lines according to the basic data such as the line type (overhead line, cable), cross-sectional area, and length, and save them. The estimated capacitance current is recorded as: I c·1 ,I c·2 ,I c·3 ;

[0039] Step 3: Determine whether a single-phase grounding fault occurs by detecting the zero-sequence voltage on the secondary side of the voltage transformer of the distribution network. If so, start fault line selection.

[0040] When U0≥U 0zd When , it is judged that a single-phase grounding fault has occurred. Where U0 is the effective value of the zero-sequence voltage monitored in the substation; U 0zd is the zero-sequence voltage setting value;

[0041] Step 4: Calculate the sum of the absolute values ​​of the sampling points of the first half-wave of the three selected lines; as shown in formula (1):

[0042]

[0043] Where: N is the number of sampling points in one cycle; T is the conversion coefficient, which is determined by factors such as zero-sequence mutual inductor, sampling circuit, and A / D bit number, and can be determined in advance; i 0·i (k) is the value of the kth sampling point of the i-th line;

[0044] Step 5: I 0·1 ,I 0·2 ,I 0·3 The value after removing the maximum and minimum values ​​of the three data is taken as the reference value I0, and the estimated capacitance current of the corresponding line is recorded as I c ;

[0045] Step 6: Determine the calculation method for the line selection criterion of the single-phase grounding fault in the distribution network according to the conditions described in formula (2);

[0046]

[0047] Step 7: When the conditions set in formula (2) are met, the line selection criterion P is calculated based on the absolute value sum of the mutual differences of the half-wave direct sampling values. 0.i ; Its formula is shown in (3):

[0048]

[0049] Step 8: When the conditions set in formula (2) are not met, different line selection criteria calculation methods are used for different neutral point grounding modes of the distribution network;

[0050] When the neutral point of the distribution network is not grounded, the line selection criterion P is calculated based on the absolute value sum of the mutual difference of the full-wave direct sampling value. 0·i , as shown in formula (4):

[0051]

[0052] When the neutral point of the distribution network is grounded through an arc suppression coil, the line selection criterion P is calculated by using the absolute value sum method of the mutual difference after power correction based on the full-wave sampling value. 0·i , as shown in formula (5);

[0053]

[0054] Among them: F 0·i is the power correction factor;

[0055] Step 9: Use the maximum line selection criterion method to select the faulty line. That is, the line corresponding to the maximum value of the line selection criterion is the faulty line.

[0056] The present invention is described below by way of examples.

[0057] Figure 2 For the distribution network shown, it is assumed that the setting value of the zero-sequence voltage is 10% of the rated phase voltage. When the zero-sequence voltage is greater than this value, it is considered that a single-phase grounding fault has occurred.

[0058] according to Figure 2 , lines L1~L5 are defined as lines.

[0059] (1) An arc ground fault occurs on phase A of line L2. Figure 3 As shown, at this time: U0≥U 0zd , start selecting the fault line.

[0060] According to the values ​​of the zero-sequence current sampling points detected on each line, the line selection criteria of lines L1 to L5 are calculated as shown in Table 1:

[0061] Table 1

[0062] line L1 L2 L3 L4 L5 <![CDATA[Line selection criterion P 0·i > 2642.06 8068.14 2764.85 2565.15 2553.00

[0063] (2) A phase ground fault occurs on line L2. Figure 3 As shown, it does not satisfy: U0≥U 0zd , and the system neutral point is not grounded, start selecting the fault line.

[0064] According to the values ​​of the zero-sequence current sampling points detected on each line, the line selection criteria for lines L1 to L5 are calculated as shown in Table 2:

[0065] Table 2

[0066] line L1 L2 L3 L4 L5 <![CDATA[Line selection criterion P 0·i > 757.02 2737.83 805.40 740.89 757.00

[0067] (3) A phase ground fault occurs on line L2, such as Figure 4 As shown, it does not satisfy: U0≥U 0zd , and the system neutral point is grounded through the arc suppression coil, and the fault line is selected.

[0068] According to the values ​​of the zero-sequence current sampling points detected on each line, the line selection criteria for lines L1 to L5 are calculated as shown in Table 3:

[0069] Table 3

[0070] line L1 L2 L3 L4 L5 <![CDATA[Line selection criterion P 0·i > 28243.84 110836.88 28390.26 28278.49 29000.40

[0071] From the above criteria, it can be seen that the method of the present invention can accurately select the faulty line;

[0072] in Figure 5 It is the zero-sequence current waveform (transient) of each line when an A-phase arc grounding fault occurs on the neutral point ungrounded distribution network L2; Figure 6 It is the zero-sequence current waveform (transient) of each line when an A-phase arc grounding fault occurs on the neutral point grounded distribution network L2 through an arc suppression coil; Figure 7 It is the zero-sequence current waveform of each line when a phase A grounding fault occurs on the neutral point ungrounded distribution network L2 (steady state); Figure 8 It is the zero-sequence current waveform (steady state) of each line when a phase A grounding fault occurs on the distribution network L2 with the neutral point grounded through an arc suppression coil.

[0073] The embodiments are only for illustrating the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A single-phase ground fault line selection method for distribution network based on the sum of absolute values ​​of mutual differences, characterized by: The following steps are involved: S1. Number the lines according to the structure of the distribution network and the number of lines; S2. Select any three lines, estimate the ground capacitance current of the three lines according to the basic data of the three lines, and save them; S3, judging whether a single-phase grounding fault occurs in the distribution network by detecting the magnitude of the zero-sequence voltage of the distribution network, and if a single-phase grounding fault occurs, proceeding to the next step; S4, calculate the sum of the absolute values ​​of the sampling points of the first half-wave of the selected three lines, and 0·1 ,I 0·2 ,I 0·3 ; S5, with I 0·1 ,I 0·2 ,I 0·3 The value after removing the maximum and minimum values ​​of the three data is taken as the reference value I0. The estimated capacitance current of the line corresponding to I0 is recorded as I c ; S6. Determine the method for calculating the line selection criterion for each single-phase grounding fault; S7, when the conditions set in step S6 are met, the line selection criterion P is calculated based on the absolute value sum of the mutual differences of the half-wave direct sampling values. 0·i ; S8. When the condition set in step S6 is not met, different fault criterion calculation methods are used for different neutral point grounding methods of the distribution network; if the distribution network is a neutral point ungrounded method, the line selection criterion is calculated based on the absolute value sum of the mutual differences of the full-wave direct sampling values; when the distribution network is a neutral point grounded method via an arc suppression coil, the line selection criterion is calculated based on the absolute value sum of the mutual differences of the full-wave sampling values ​​after power correction; S9, select the faulty line by using the maximum line selection criterion method, that is, the line corresponding to the maximum value of the line selection criterion is the faulty line; Wherein, in step S6, according to formula (2) as the setting condition, the corresponding absolute value of the mutual difference and the calculation method of the line selection criterion are determined for each single-phase grounding fault of the distribution network; Among them, in step S6, when the conditions set by formula (2) are met, the line selection criterion P is calculated based on the absolute value sum of the direct sampling values ​​of the first half wave. 0·i ; i 0.i (k), i 0.j (k)——the kth zero-sequence current sampling value of the i-th and j-th lines respectively; Among them, when the conditions set by formula (2) are not met, different line selection criteria calculation methods are used for different neutral point grounding methods of the distribution network; When the neutral point of the distribution network is not grounded, the line selection criterion P is calculated based on the absolute value sum of the mutual difference of the full-wave direct sampling value. 0·i , as shown in formula (4): Where: M is the total number of distribution network lines; N is the number of sampling points in one power frequency cycle; When the neutral point of the distribution network is grounded through an arc suppression coil, the line selection criterion P is calculated by using the absolute value sum method of the mutual difference after power correction based on the full-wave sampling value. 0·i , as shown in formula (5): Among them: F 0·i is the power correction factor.

Images