A small current grounding anti-misselection line method based on five-temporal phase-to-ground incremental current

Abstract

The method for preventing mis-selection of low-current grounding lines based on five-temporal phase-to-ground incremental current of the present invention includes (1) measuring and comparing whether the zero-sequence current abrupt change is greater than the set value or the ground phase current sudden change is greater than the amount k of the non-grounded phase. 1S If no, qualitatively determine whether the suspected grounding or leakage occurs; (2) Calculate and compare the incremental current of a certain phase sub-transient phase-to-earth is greater than the corresponding set value and greater than K of the other two phases 1S If no, determine whether to accumulate the number of suspected faults; (3) After the calculation and comparison, the transient incremental current value of this phase is larger than the value K of the other two phases. 2S If no, first judge whether it is the ground phase of the grounding line, or judge whether it is the leakage phase of the intermittent leakage line according to the number of sub-transient faults within 3 seconds; The phase difference or three-phase current is used for double anti-misjudgment; HS If no, monitor whether the fault persists.

Description

technical field [0001] The invention relates to a small-current grounding line selection method of a distribution network, in particular to a small-current grounding anti-misselection line method based on five-temporal phase-to-ground incremental currents. 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 adjacent lines in the closed loop network 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 (b) When the induced disturbance oscillating phase current mutation amount shown in (b), 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 low-current single-phase grounding detection technology are also good for low-resistance grounding detection, but they are not suitable for high-medium resistance 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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