Improved single-phase earth fault line selection method and system

Abstract

The invention relates to an improved single-phase earth fault line selection method and system, and belongs to the technical field of power distribution automation. According to the scheme, judgment is performed according to the maximum value and the minimum value of the transient zero-sequence current and the maximum value and the minimum value of the transient zero-sequence voltage derivative; when the maximum value appears earlier than the corresponding minimum value, the maximum value is marked as a first value, and when the maximum value appears later than the minimum value, the maximum value is marked as a negative first value; and when the sum of the mark of the zero-sequence voltage derivative and the mark of the zero-sequence current is 0, judging that the line is a fault line. And the accuracy of the line selection device in the electromagnetic complex environment is improved. The improved single-phase earth fault line selection method is simpler and more effective, the fault line can be selected only by comparing the positions of the maximum value and the minimum value of the transient zero-sequence current and the transient zero-sequence voltage, and compared with a traditional correlation coefficient calculation method, the calculation amount is greatly reduced.

Description

Technical Field

[0001] The invention relates to an improved single-phase ground fault line selection method and system, belonging to the technical field of power distribution automation. Background Art

[0002] At present, there are many methods and line selection devices for single-phase grounding fault detection in the prior art, which are divided into steady-state quantity method and transient quantity method according to the type of signal used.

[0003] Steady-state quantity methods include zero-sequence current amplitude, phase comparison method, zero-sequence current amplitude and phase ratio method, harmonic analysis method, power direction method, negative sequence current method, etc. In general, the defects of the line selection method based on steady-state quantity are that the steady-state characteristic value is small, difficult to be detected, prone to misjudgment, and mostly affected by the neutral point grounding method.

[0004] Transient quantity methods include the first half-wave method, energy method, wavelet analysis method, etc. Although the transient component of the grounding capacitor current is often dozens of times larger than the steady-state value when single-phase grounding occurs, the line selection method based on transient signals is highly sensitive and is not affected by arc suppression coils, but most of the existing methods need to be improved. For example, the first half-wave method is based on the assumption that the grounding fault occurs at the moment when the phase voltage is close to the maximum value, and is only valid within the first half-wave; the wavelet analysis algorithm is relatively complex; the energy method does not make full use of transient signals.

[0005] Moreover, the zero-sequence component of a single-phase grounding fault in a small current grounding system is weak and difficult to detect, the electromagnetic environment near the fault point is complex, there are many factors that affect the fault characteristics, and the amount of fault characteristics included in the algorithm used is small, resulting in a low accuracy rate for the line selection device. Summary of the invention

[0006] The purpose of the present invention is to provide an improved single-phase grounding fault line selection method and system to solve the problems of complex single-phase grounding fault detection algorithm and insufficient use of transient signals in the prior art.

[0007] To achieve the above object, the solution of the present invention includes: The technical solution of an improved single-phase grounding fault line selection method of the present invention is judged according to the maximum and minimum values ​​of the transient zero-sequence current and the maximum and minimum values ​​of the transient zero-sequence voltage derivative; when the maximum value appears earlier than the corresponding minimum value, it is marked as the first value, and when the maximum value appears later than the minimum value, it is marked as the negative first value; when the sum of the mark of the zero-sequence voltage derivative and the mark of the zero-sequence current is 0, the line is judged to be a fault line.

[0008] Furthermore, after determining that a line fault occurs, the determination result is combined with the determination result of the active component direction method, and the result is output if they are consistent; otherwise, the determination is made based on the top three transient currents in the line from largest to smallest. If the largest transient current among the three transient currents is smaller than the set multiple of any other transient current, the result is based on the determination result of the active component direction method.

[0009] Furthermore, when every line fails, it is determined to be a bus failure.

[0010] Furthermore, the set multiple is 1.5 times.

[0011] Beneficial effects of the present invention: The present invention proposes an improved transient direction method, which is simpler and more effective. It only needs to compare the positions of the maximum and minimum values ​​of the transient zero-sequence current and the transient zero-sequence voltage to select the fault line. Compared with the traditional method of calculating the correlation coefficient, the amount of calculation is greatly reduced.

[0012] At the same time, the method of the present invention is further combined with the active component method in the steady-state quantity method to realize multi-criteria comprehensive line selection. When a single-phase grounding fault occurs in the distribution network system, the fault can be detected quickly and effectively, greatly improving the accuracy of single-phase grounding fault line selection.

[0013] A technical solution of an improved single-phase grounding fault line selection system of the present invention includes a processor, which is used to execute a computer program to implement the following steps: judging according to the maximum value and minimum value of the transient zero-sequence current and the maximum value and minimum value of the transient zero-sequence voltage derivative; when the maximum value appears earlier than the corresponding minimum value, it is marked as a first value, and when the maximum value appears later than the minimum value, it is marked as a negative first value; when the sum of the mark of the zero-sequence voltage derivative and the mark of the zero-sequence current is 0, judging that the line is a fault line.

[0014] Furthermore, after determining that a line fault occurs, the determination result is combined with the determination result of the active component direction method, and the result is output if they are consistent; otherwise, the determination is made based on the top three transient currents in the line from largest to smallest. If the largest transient current among the three transient currents is smaller than the set multiple of any other transient current, the result is based on the determination result of the active component direction method.

[0015] Furthermore, when every line fails, it is determined to be a bus failure.

[0016] Furthermore, the set multiple is 1.5 times.

[0017] Beneficial effects of the present invention: The improved single-phase grounding fault line selection system of the present invention can achieve the same beneficial effects as the above-mentioned improved single-phase grounding fault line selection method. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the correlation waveform diagram of transient zero-sequence voltage derivative and transient zero-sequence current; Figure 2 It is the transient waveform diagram of zero-sequence voltage derivative and zero-sequence current; Figure 3 It is the flow chart of the improved single-phase grounding fault line selection algorithm. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail in a clear and complete manner in conjunction with the accompanying drawings and embodiments.

[0020] The idea of ​​the present invention is to use the transient zero-sequence current data and the transient zero-sequence voltage derivative data correspondingly extracted from the transient waveform, and through the position relationship between the maximum value and the minimum value of the transient zero-sequence current (that is, the order in which the maximum value and the minimum value appear, the smaller the position value on the horizontal axis, the earlier it appears, that is, it appears first), to judge whether the transient waveform first appears upward as a positive wave and then a negative wave appears downward (the maximum value appears earlier than the minimum value) at the beginning, or whether the transient waveform first appears downward as a negative wave and then a positive wave appears upward (the maximum value appears later than the minimum value) at the beginning, and further judge whether the corresponding line has a single-phase grounding fault according to whether the transient zero-sequence current and the transient zero-sequence voltage derivative waveforms are in an opposite relationship to each other.

[0021] The present invention is further combined with the active component direction method to perform multi-criteria comprehensive line selection, thereby solving the problem that the line selection device has low accuracy due to the complex electromagnetic environment.

[0022] Method Example: An improved single-phase grounding fault line selection method of the present embodiment performs multi-criteria comprehensive line selection through an improved transient direction method and an active component direction method; the improved transient direction method judges the change trend and makes a single-phase grounding fault judgment in sequence through the chronological positions of the maximum and minimum values ​​of the transient zero-sequence current and the transient zero-sequence voltage derivatives; the judgment result of the improved transient direction method is combined with the judgment result of the active component direction method, and the result is output if the results are consistent; if the results are inconsistent, the transient process is judged to be obviously determined by the maximum transient current of the three transient currents being greater than or equal to the set multiple of any other transient current according to the top three transient currents ranked from large to small in the line; if it is obvious, the judgment result is based on the improved transient direction method, otherwise the judgment result is based on the active component direction method.

[0023] The present invention proposes an improved single-phase ground fault line selection method, which is mainly composed of an improved transient direction method and an active component direction method, which are both independent of each other and cooperate with each other. The specific implementation method is as follows: (1) Improved transient direction method.

[0024] As Figure 1 shown, based on the correlation between the derivative of the transient zero-sequence voltage and the transient zero-sequence current, the difference method is used to derive the sampled values of the zero-sequence voltage of each line to obtain the derivative of the zero-sequence voltage. Then, find and save the maximum value, minimum value and their respective occurrence positions in the transient waveform of the zero-sequence voltage derivative, denoted as U+, U-, WU+, WU-. Similarly, find and save the maximum value, minimum value and their respective occurrence positions in the transient waveform of the zero-sequence current, denoted as I+, I-, WI+, WI-. When the position value where the maximum value appears is less than the position value where the minimum value appears, it means that the transient waveform starts with a positive wave upwards first and then a negative wave downwards, and this situation is marked as 1; when the position value where the maximum value appears is greater than the position value where the minimum value appears, it means that the transient waveform starts with a negative wave downwards first and then a positive wave upwards, and this situation is marked as -1. Each line marks 1 or -1 for the change trends of the zero-sequence voltage derivative and the zero-sequence current respectively according to the above method. When the sum of the marks of the zero-sequence voltage derivative and the zero-sequence current is 0, then this line is defined as a faulty line; when each line is faulty, it is defined as a bus fault.

[0025] As Figure 2 shown, the position value where the maximum value of the zero-sequence current appears is less than the position value where its minimum value appears (i.e., WI+ < WI-), marked as 1 (i.e., WI = 1); the position value where the maximum value of the zero-sequence voltage derivative appears is greater than the position value where its minimum value appears (i.e., WU+ > WU-), marked as -1 (i.e., WU = -1); the sum of WI of the zero-sequence current and WU of the zero-sequence voltage derivative is 0 (i.e., WI + WU = 0), then this line is defined as a faulty line. When the sum of WI and WU of all lines is 0, it is defined as a bus fault.

[0026] (2) Active component direction method.

[0027] Based on the half-wave Fourier algorithm, the fundamental wave components of the zero-sequence current and zero-sequence voltage are extracted. For an ungrounded neutral system, the zero-sequence current is advanced by 90° in phase, and the active component of the zero-sequence current is calculated according to the formula P = UIcos(φ + 90°); for a system with an arc suppression coil grounded at the neutral point, the zero-sequence voltage is advanced by 180° in phase, and the active component of the zero-sequence current is calculated according to the formula P = UIcos(φ + 180°). If P > 0, it is judged as a faulty line; if P < 0, it is judged as a non-faulty line; if all lines are judged as faulty lines, then it is a bus fault.

[0028] An improved single-phase grounding fault line selection method proposed by the present invention, as Figure 3 shown, combines the improved transient direction method and the active component direction method for multi-criterion judgment. The specific implementation process is as follows: (1) Real-time monitoring of zero-sequence voltage. If the zero-sequence voltage is greater than the set value, proceed to step 2). Otherwise, wait for the real-time monitoring of zero-sequence voltage to meet the conditions. (2) Extract the zero-sequence current and zero-sequence voltage data of each line, calculate the zero-sequence voltage derivative of each line, calculate WU and WI according to the improved transient direction method, find the three lines corresponding to the top three transient currents in the line from large to small, calculate the sum of WU and WI of the three lines, make a judgment based on the calculation results and save the results, and then go to step 3); (3) Calculate the active component of the zero-sequence current of each line, find the three lines corresponding to the top three transient currents in the line from large to small, and calculate P according to the neutral point grounding method, make a judgment based on the calculation results and save the results, and go to step 4); (4) Compare the judgment result of the improved transient direction method with the judgment result of the active component direction method. If the results are consistent, proceed to step 6); if the results are inconsistent, proceed to step 5); (5) Determine whether the transient process is obvious. The three transient currents I1, I2, and I3 ranked from largest to smallest in the line are used to determine whether the transient process is obvious. When I1 is greater than 1.5 times I2 or I3, the transient process is obvious and the judgment result of the improved transient direction method is adopted; otherwise, the transient process is not obvious and the judgment result of the active component direction method is adopted; after obtaining the judgment result of multiple criteria, proceed to step 6); (6) Take protective measures based on the judgment results, print, alarm and upload to the main station.

[0029] System Example: This embodiment provides a technical solution for an improved single-phase grounding fault line selection system, which is used to execute a computer program to implement the steps of the above-mentioned improved single-phase grounding fault line selection method.

[0030] Since the specific implementation process and principle of the improved single-phase grounding fault line selection system of this embodiment have been described in detail in the embodiment of the improved single-phase grounding fault line selection method, no further details will be given here.

Claims

1. An improved single-phase ground fault line selection method, characterized in that: Judge based on the maximum and minimum values ​​of the transient zero-sequence current and the maximum and minimum values ​​of the transient zero-sequence voltage derivative; when the maximum value appears earlier than the corresponding minimum value, it is marked as the first value, and when the maximum value appears later than the minimum value, it is marked as the negative first value; when the sum of the mark of the zero-sequence voltage derivative and the mark of the zero-sequence current is 0, the line is judged to be a fault line.

2. The improved single-phase grounding fault line selection method according to claim 1 is characterized in that: After determining a line fault, the determination result is combined with the determination result of the active component direction method, and the result is output if they are consistent; Otherwise, the judgment is made based on the top three transient currents in the line from largest to smallest. If the largest transient current among the three transient currents is smaller than the set multiple of any other transient current, the result shall be based on the judgment result of the active component direction method.

3. The improved single-phase grounding fault line selection method according to claim 2 is characterized in that: When every line fails, it is judged as a bus failure.

4. The improved single-phase grounding fault line selection method according to claim 2 is characterized in that: The setting multiple is 1.5 times.

5. An improved single-phase ground fault line selection system, comprising a processor, characterized in that: The processor is used to execute a computer program to implement the following steps: judging according to the maximum value and minimum value of the transient zero-sequence current and the maximum value and minimum value of the transient zero-sequence voltage derivative; when the maximum value appears earlier than the corresponding minimum value, it is marked as a first value, and when the maximum value appears later than the minimum value, it is marked as a negative first value; when the sum of the mark of the zero-sequence voltage derivative and the mark of the zero-sequence current is 0, judging that the line is a fault line.

6. The improved single-phase grounding fault line selection system according to claim 5 is characterized in that: After determining a line fault, the determination result is combined with the determination result of the active component direction method, and the result is output if they are consistent; Otherwise, the judgment is made based on the top three transient currents in the line from largest to smallest. If the largest transient current among the three transient currents is smaller than the set multiple of any other transient current, the result shall be based on the judgment result of the active component direction method.

7. The improved single-phase grounding fault line selection system according to claim 6 is characterized in that: When every line fails, it is judged as a bus failure.

8. The improved single-phase ground fault line selection system according to claim 6 is characterized in that: The setting multiple is 1.5 times.

Images