Reverse traveling wave differential protection method for flexible direct-current power grid grounded through metal return wire

Abstract

The invention provides a reverse traveling wave differential protection method for a flexible direct-current power grid grounded through a metal loop, and the method comprises the following steps: carrying out the fitting of a propagation function and characteristic impedance through a rational function based on a Marti frequency-variable parameter line model and an overhead line tower topology, and obtaining a time domain expression of the propagation function and the characteristic impedance; for a multi-terminal flexible direct-current power grid, collecting the voltage and current time domain values of a positive electrode, a negative electrode and a grounding electrode at two ends of a direct-current line, wherein electromagnetic coupling exists among lines of the positive electrode, the negative electrode and the grounding electrode; decoupling the lines into mutually independent 0-mode, 1-mode and 2-mode components through a decoupling matrix; employing the forward traveling waves and reverse traveling waves at the two ends of the line obtained through calculation, and performing calculating to obtain 0-mode, 1-mode and 2-mode components of a reverse traveling wave differential value by using the calculated forward traveling wave and reverse traveling wave at the two ends of the line; and according to the change rule of the reverse traveling wave differential value under different fault types, realizing the fault detection by using a starting 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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