Low current neutral grounding malfunction detection and positioning device and method

Abstract

The invention relates to a device and a method for detecting and positioning small current earthing fault. The device comprises a slave computer and a host computer composed of a CPU module, a DSP, a pre-loop unit module, a A / D conversion module, a memory module, a display and keyboard operation module as well as a communication module; wherein, the pre-loop unit module, the A / D conversion module, the CPU module and the DSP are connected in sequence; the memory module, the display and keyboard operation unit module and the communication module are respectively connected with the CPU; the host computer is connected with the communication module. The CPU module collects the analog signal of the zero-sequence voltage of the bus and the zero-sequence current of each line, and adjusts the value in proportion to the amplitude range so that the device can deal with. The analog signal is turned into digital signal recognized by the computer module, and analyzed by the DSP to judge whether the fault occurs or not. If the fault occurs, then the DSP gives the line selection result, saves the fault information and transfers the line selection result to the host computer for fault alarm.

Description

technical field [0001] The invention belongs to the technical field of power transmission and transformation, and in particular relates to a device and method for detecting and locating a small current grounding fault. Background technique [0002] In my country's distribution network, the 66kV and 35kV power grids mainly adopt the neutral point grounding method through the arc suppression coil, and the 3kV~10kV power grid mainly adopts the neutral point ungrounded method. Resistance grounding method. When a single-phase ground fault occurs in this system (generally accounting for more than 70%), the problem of grounding line selection has not been well resolved because the current at the fault point is very small and the arc is unstable. At present, the five popular line selection methods in China include the power direction method, the harmonic analysis method (namely, the group ratio amplitude ratio method), the fifth harmonic method, the signal injection method and the w...

AI Technical Summary

Problems solved by technology

When a single-phase ground fault occurs in this system (generally accounting for more than 70%), the problem of grounding line selection has not been well resolved due to the small current at the fault point and unstable arc.

However, the active component in the fault current is also very small, and it is easily affected by factors such as the unbalanced current in the zero-sequence current filter. This method cannot reach 100% accuracy in principle. Judging the result that multiple lines are grounded or none of them can be judged

[0004] (2) Harmonic analysis method: The harmonic analysis method adopts the group amplitude and phase ratio method of the zero-sequence steady-state signal after single-phase grounding. Since the amplitude and phase ratios use the relative principle, in an ungrounded system, this The application effect of this method is better, but in the arc-suppression coil grounding system, due to the compensation effect of the arc-suppression coil, the line selection method will fail, and this method cannot effectively solve the zero-sequence current caused by CT imbalance.

The fifth harmonic method solves the fault line selection problem of the neutral point through the arc suppression coil system. One of its shortcomings is that the fifth harmonic content in the fault current only accounts for about 1 / 10 of the fundamental wave. Under the circumstances, the value will be smaller, which is easy to cause misjudgment

In addition, we believe that the domestic small current grounding line selection device still has the following problems: For example, there are serious congenital defects in the hardware circuit design that lead to low operating reliability of the device; field installation wiring problems; the selection of the system with arc suppression coil The line is more difficult and easy to misjudgment; the current market of this type of product is uneven, etc.

[0009] Based on the above analysis, it can be seen that this field is still in the research stage in China at present, and there is no recognized and effective product for small current line selection and positioning devices, but the demand for this function by power companies is very urgent

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