Biblio

In recent years, there have been situations in which the zero-sequence protection of the transformer has been incorrectly operated due to the converter transformer energizing or fault recovery. For converter transformers, maloperation may also occur. However, there is almost no theoretical research on the zero-mode inrush currents of converter transformers. This paper studies the characteristics of the zero-mode inrush currents of the converter transformers, including the relationship between the amplitude and attenuation characteristics of the zero-mode inrush currents of converter transformers, and their relationship with the system resistance, remanence, and closing angle. First, based on the T-type equivalent circuit of the transformer, the equivalent circuit of the zero-mode inrush current of each transformer is obtained. On this basis, the amplitude relationship of the zero-mode inrush currents of different converter transformers is obtained: the zero-mode inrush current of the energizing pole YY transformer becomes larger than the YD transformer, the energized pole YD becomes greater than the YY transformer, and the YY transformer zero-mode inrush current rises from 0. It is also analyzed that the sympathetic interaction will make the attenuation of the converter transformer zero-mode inrush current slower. The system resistance mainly affects the initial attenuation speed, and the later attenuation speed is mainly determined by the converter transformer leakage reactance. Finally, PSCAD modeling and simulation are carried out to verify the accuracy of the theoretical analysis.

Interface transformer used in asynchronous networking was a kind of special transformer which's different from normal power transformer. During no-load switch-in, the magnitude of inrush current will be high, and the waveform distortion also be severity. Maybe the protections will be activated, even worse may lead the lockdown of the DC system. In this paper, field-circuit coupled finite element method was used for the study of transient characteristic of no-load switch-in, remanence simulation methods were presented. Quantitative analysis of the effect of closing making angle and core remanence on inrush current peak value, meanwhile, the distribution of magnetic field inside the tank during the transient process. The result indicated that the closing making angle and core remanence have obvious effect on inrush current peak value. The research results of this paper can be used to guide the formulation of no-load switch-in strategy of interface transformer, which was of great significance to ensure the smooth operation of HVDC Flexible system.