Fault Identification Method of Neutral Point Ungrounded System

Abstract

The invention relates to a fault identification method for an isolated neutral system. According to the method, zero sequence voltage abrupt change amount detection is additional arranged in the initial phase of the algorithm and single-phase earth fault line selection is judged; then in order to reduce harmonic interference and accurately judge initial time of the fault, a negative sequence amount threshold value is set so that negative sequence amount of unbalance in normal operation is avoided; and non-earth fault line selection is judged according to the characteristics that zero sequence and negative sequence components do not exist in the system and high fault abrupt change current exists in the fault line when three-phase short circuit occurs. Group amplitude and phase comparison and zero sequence reactive power direction line selection methods are integrated in the aspect of algorithm, and variable threshold detection is additionally arranged so that interference of harmonic waves on the line selection process can be effectively reduced, and the complete fault identification method for the isolated neutral system is formed.

Description

technical field [0001] The invention belongs to the technical field of power transmission and transformation, in particular to a fault identification method for a neutral point ungrounded system. Background technique [0002] If the neutral point ungrounded system runs for a long time with a fault, the non-fault relative ground voltage will rise, which will accelerate the aging of the cable insulation, which may expand the fault and endanger the reliability of the power supply. Therefore, it is very necessary to find out the fault line in time and cut it off for the safe operation of the neutral point ungrounded system. [0003] At present, the common fault line selection methods of the neutral point ungrounded system include the zero-sequence reactive power direction method and the group-amplitude-phase method. The zero-sequence reactive power method has a small amount of calculation and good timeliness. Misjudgment, the result of grounding line selection is inaccurate for...

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Problems solved by technology

[0003] At present, the common fault line selection methods of the neutral point ungrounded system include the zero-sequence reactive power direction method and the group-amplitude-phase method. The zero-sequence reactive power method has a small amount of calculation and good timeliness, but it is easy to Misjudgment, the result of grounding line selection is inaccurate for lines with large grounding resistance and strong electromagnetic interference

The group ratio amplitude ratio method can overcome the randomness of the single-phase ground capacitance current in the neutral point ungrounded system to a certain extent, and avoid the influence caused by ground resistance and operation mode, but it may cause Line selection error, the line selection accuracy of these two methods in practical applications is not ideal

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