Direct-current single-pole ground fault determination method of flexible direct-current power transmission system

Abstract

The invention discloses a direct-current single-pole ground fault determination method of a flexible direct-current power transmission system. Voltages to ground of positive and negative direct-current buses of a direct-current side are obtained; if an absolute value of one voltage value is less than a low-voltage limiting value and an absolute value of the other voltage value is larger than a high-voltage limiting value and a condition that duration time is larger than a set screening time is met, a single-pole ground fault is determined to occur in a direct-current bus corresponding to the voltage value with the absolute value less than the low-voltage limiting value. According to the invention, on the basis of the changing feature of the voltage during the direct-current single-pole ground fault development process, the voltages to ground of the positive and negative direct-current buses are selected as direct-current single-pole ground fault identification parameters. Besides, overtime of the voltage parameter is also used as another main criterion, thereby improving the fault identification accuracy and avoiding wrong determination caused by other faults. With the method, the direct-current single-pole ground fault of the flexible direct-current power transmission system of the modularized multi-level converter can be identified rapidly and accurately.

Description

technical field [0001] The invention belongs to the technical fields of flexible power transmission and distribution of electric power systems, power electronics and user electric power, and in particular relates to a method for judging DC unipolar grounding faults in flexible DC transmission systems of modular multilevel converters. Background technique [0002] With the development of fully-controlled power electronic devices and the application of power electronic technology in power systems, the flexible DC transmission technology based on voltage source converters has been paid more and more attention. Modular multi-level converter is a kind of voltage source converter in the application of flexible direct current transmission system. It is composed of multiple half-bridge sub-modules connected in a certain way. By separately controlling the input of IGBT components of each sub-module The cut-off state makes the AC voltage output by the converter close to a sine wave, r...

AI Technical Summary

Problems solved by technology

The only judgment condition of this judgment method is the voltage of the positive and negative DC bus bars. The judgment condition is relatively simple, and misjudgment is easy to occur. Although the threshold value meets the voltage judgment conditions, there is no DC unipolar ground fault in fact, resulting in misjudgment

Therefore, the reliability of this discrimination method is low. In order to improve system reliability, protection timeliness, and operation and maintenance efficiency, it is urgent to propose an efficient and universally applicable DC unipolar grounding system for flexible DC transmission systems with modular multilevel converters. Fault identification method

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