Reverse Traveling Wave Differential Protection Method for Flexible DC Grid Grounded by Metal Return Line

Abstract

The invention provides a method for reverse traveling wave differential protection of a flexible DC power grid grounded through a metal return line, comprising the following steps: based on the Marti frequency-variable parameter line model and the topology of overhead line poles and towers, the propagation function and characteristic impedance are calculated using rational functions Fitting to obtain the time-domain expression of the propagation function and characteristic impedance; for the multi-terminal flexible DC power grid, the time-domain values ​​of the voltage and current of the positive, negative and ground electrodes at both ends of the DC line are collected, and there are Electromagnetic coupling, decoupled into mutually independent 0-mode, 1-mode and 2-mode components through the decoupling matrix; calculate the forward traveling wave and reverse traveling wave at both ends of the line; use the calculated forward traveling wave and For the reverse traveling wave, the 0-mode, 1-mode and 2-mode components of the reverse traveling wave differential value are calculated; according to the variation law of the reverse traveling wave differential value under different fault types, the fault detection is realized by using the start-up criterion.

Description

technical field [0001] The invention belongs to the field of relay protection of electric power systems, and in particular relates to a reverse traveling wave differential protection method suitable for a flexible DC power grid grounded through a metal loop. Background technique [0002] The flexible DC grid grounded by the metal return line is composed of a modular multilevel converter (Modular Multilevel Converter, MMC), a positive DC transmission line ring network, a negative DC transmission line ring network, and a metal return line grounding line ring for the ground electrode. net composition. The flexible DC grid has low damping characteristics, which makes the fault current rise rapidly and has no natural zero-crossing point. Limited by the development level of DC circuit breakers, DC line faults must be cleared within milliseconds, and fast and reliable identification of DC line faults has become a key issue. [0003] The traditional HVDC transmission system uses t...

AI Technical Summary

Problems solved by technology

However, these methods rely heavily on the training process, and in practice a large amount of training data is difficult to obtain

[0004] Most of the above improved methods use distributed parameter line models, ignoring the frequency-varying characteristics of transmission lines

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