Longitudinal mutation quantity direction protection method based on positive, negative and zero sequence impedance

Abstract

The invention provides a longitudinal mutation quantity direction protection method based on positive, negative and zero sequence impedance. Aiming at a practical UHVDC layered access project, an electromagnetic transient model is built in PSCAD to obtain the positive, negative and zero sequence impedance characteristics of a back side DC system in case of commutation failure; and a longitudinal mutation quantity direction protection method based on the zero sequence impedance is put forward according to the protection principle of the mutation quantity direction element through combination ofthe characteristics of the positive, negative and zero sequence impedance of the back side DC system. As for the mutation quantity phase direction element and the phase difference direction element,the positive and negative sequence impedance of the back side system at the protection installation position are required to be equal so that the positive sequence impedance of the back side system isaccurately measured; as for the mutation quantity sequence direction element, the positive, negative and zero sequence impedance of the back side system at the protection installation position can beaccurately measured, and the phase angle of the positive, negative and zero sequence impedance of the back side system and the phase angle of the line sequence impedance are required to be equal andthus the fault direction can be accurately judged.

Description

technical field [0001] The invention belongs to the field of protection of an AC system under an AC-DC hybrid UHV DC layered access mode, and in particular relates to a method for protecting the direction of a longitudinal sudden change based on positive, negative, and zero-sequence impedances. Background technique [0002] For a long time, there has been serious spatial heterogeneity between my country's energy consumption and resource endowment, and large-scale, long-distance power transmission requirements have promoted the continuous construction and development of EHV DC projects. At present, East China and South China have formed a multi-infeed DC system, and the supporting capacity of the receiving end grid is facing a severe test. In order to solve this problem from the perspective of the grid structure, domestic scholars took the lead in proposing a method of connecting UHV DC to the AC grid in layers , that is, the high-end and low-end converters of the DC inverter...

AI Technical Summary

Problems solved by technology

Compared with multi-infeed DC, the topological structure of the hierarchical hybrid system at the receiving end is more complex, and the coupling between AC and DC systems is more serious

It is particularly worth noting that the interaction between the hybrid systems at the receiving end may lead to cascading failures, which is also the crux of the current situation of "strong direct and weak AC" in some power grids in my country

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