Small current grounding anti-error line selection method based on five-temporal phase-ground incremental current

Abstract

The invention provides a small current grounding anti-error line selection method based on five-temporal phase-ground incremental current. The method comprises the following steps: 1) calculating andcomparing whether zero sequence current sudden change amount is larger than a preset value or whether grounding phase current sudden change amount is larger than K1S times of non-grounding phase current sudden change amount, and qualitatively judging whether suspected grounding or electric leakage occurs; 2) calculating and comparing whether subtranient phase-ground incremental current of some phase is larger than a corresponding preset value and larger than K1S times of that of the other two phases, and judging whether to accumulate the times of suspected faults; 3) calculating and comparingwhether post-transient phase-ground incremental current of the phase is larger than K2S times of that of the other two phases, and preliminarily judging whether the phase is a grounding line groundingphase, or whether the phase is an intermittent leakage circuit leakage phase according to subtranient failure times within 3 seconds; 4) calculating semi-cycle phase-ground incremental current phasedifference or three-phase current of two non-fault phases at the eighth cycle after fault as dual anti-error judgment; and 5) detecting and comparing whether the grounding phase phase-ground incremental current obtained after fault for 5 seconds is larger than KHS times of non-grounding phase phase-ground incremental current, and monitoring whether the fault persists.

Description

technical field [0001] The invention relates to a small current grounding line selection method for a distribution network, in particular to a small current grounding anti-misselection line method based on five-temporal phase-to-ground incremental current. Background technique [0002] In the existing typical monitoring technology methods for small current single-phase grounding of distribution network, there are the following problems: [0003] 1. The traditional monitoring technology is to compare the steady-state zero-sequence current value and power direction of different branch lines of the same power bus after a ground fault, and determine the maximum zero-sequence current amplitude and zero-sequence power direction from the line pointing to the bus. for the faulty line. This technology can be used in principle in the distribution network lines that were not equipped with arc suppression coils in the past, but after the distribution network is equipped with arc suppre...

AI Technical Summary

Problems solved by technology

This technology can be used in principle in the distribution network lines that were not equipped with arc suppression coils in the past, but after the distribution network is equipped with arc suppression coils, the post-steady-state zero-sequence current amplitudes of different branch lines of the same power bus are similar to ground faults , zero-sequence power in the same direction, it is difficult for this traditional monitoring technology to distinguish faulty lines from non-faulty lines

[0004] 2. The zero-sequence current mutation comparison method solves the line selection problem of single-phase grounding between the multiple radiation lines of the same busbar in the distribution network equipped with arc suppression coils, but the grounding or occurrence of image 3 (a) shows the operational disturbance oscillation zero-sequence current and Figure 4 (a) When the induced disturbance oscillates the zero-sequence current, there is a problem of misjudgment and false alarm for the non-grounded line

This method can theoretically be applied to multi-branch radiating lines under the same busbar, but it only uses the method of mathematically deriving the phase current mutation to distinguish between load changes and single-phase grounding, and it is difficult to distinguish, for example, transformer excitation inrush current from those containing non-periodic components. The difference between single-phase grounding current; the method of setting and obtaining the harmonic ratio and similarity coefficient of three-phase current mutation according to different conditions on site is not suitable for single-phase grounding of voltage zero phase, and the application is more complicated; image 3 (b) shows the sudden change of operational disturbance oscillation phase current and Figure 4 When the induced disturbance oscillating phase current mutation amount shown in (b) is large, there is also the problem of misjudgment and false alarm for non-grounded lines

[0006] 4. The intelligent grounding distribution system with low resistance at the neutral point of the power supply combined with the soft switch of the three-phase metallic grounding of the busbar can effectively suppress the resonant overvoltage that may be caused by continuous low-resistance single-phase grounding, but the system adopts the traditional staged zero-sequence The grounding line selection for current protection is not suitable for single-phase grounding with high and medium resistance, and this scheme must transform the delta connection of many distribution network power transformers into star connection, and the implementation cost of the scheme is high

[0007] 5. Other low-frequency signal injection methods and small current single-phase grounding detection technology are also good for low-impedance grounding detection, but they are not suitable for high- and high-impedance single-phase grounding, and medium-voltage signal injection equipment needs to be added. A certain degree of low-frequency current impact on distribution network lines, on the other hand, also brings new medium-voltage equipment safety management risks and engineering implementation troubles to the distribution network site

[0008] 6. The grounding detection technology using wavelet analysis is easy to misjudge and report when the load fluctuates; the traveling wave fault location technology has a good theoretical effect in detecting single-line single-phase grounding, but it is not suitable for distribution networks with complex structures.

[0009] Summarize the problems existing in the existing similar technical methods of grounding monitoring, the most important of which is the high probability of misjudgment and false alarm; according to research and analysis, the root cause is that the temporal signals of grounding characteristics used by all these discrimination methods are single, and it is difficult to identify the true grounding. Pseudo-single-phase grounding

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