Small current grounding line selection device CT polarity error judgment method

Abstract

The invention discloses a small current grounding line selection device CT polarity error judgment method. The method comprises the following steps that when a grounding fault occurs, a fault branch zero sequence current is determined based on a fault line selected by a device; instantaneous values of all branch currents are recorded by the device sampling wave recording function; and all instantaneous values of all branch currents are calculated and compared, if prescriptive features are not met, branch CT polarity error exiting is determined, line selecting result is not reliable, and the condition is displayed on the device. Based on the premise that isolated neutral system small current grounding line selection device adopts zero sequence CT to obtain zero sequence currents of brancheson a bus, and with combination of the line selection results of the line selection device, the conclusion of whether zero sequence CT inverse connection in the branch existing is obtained through analysis and calculation of characteristics of each branch current when the single-phase grounding fault occurs in the branch.

Description

technical field [0001] The invention relates to the technical field of neutral point ungrounded systems, in particular to a method for judging CT polarity errors of a small current grounding line selection device. Background technique [0002] In the medium-voltage distribution network, single-phase ground faults account for more than 80% of the total faults. When a single-phase ground fault occurs, it is particularly important to accurately select the fault line. Therefore, the small current grounding line selection device has been obtained in the distribution network. a wide range of applications. [0003] At present, the small-current grounding line selection devices of almost all manufacturers in the market need to sample and analyze the zero-sequence current of the line for relevant diagnosis. The correct polarity of the zero-sequence CT has become a crucial factor affecting the accuracy of line selection. a factor. [0004] In view of the characteristics of the zero-...

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Problems solved by technology

[0004] In view of the characteristics of the zero-sequence current, it is very small when there is no ground fault, so it is often impossible to ac

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