Research on the Influence Factors of Inrush Current in Ultra-High Voltage Converter Transformers

The ultra-high voltage converter transformer is the important equipment of the ultra-high voltage direct current transmission system. During the no-load closing process of a converter transformer, there might be significant inrush current. The residual magnetism of iron core is a key factor affecting the magnitude of the inrush current generated during the no-load closing process. If circuit breaker option closing device of the converter transformer is not perfectly matched with the residual magnetism of iron core, it may generate excessive inrush current, which might even reach 8 to 10 times rated current of the converter transformer, and seriously affecting the stable operation of the converter transformer and HVDC system. According to engineering cases of inrush current in converter transformers, this article analyzes the principle of inrush current generation in converter transformers. By establishing an electromagnetic transient mathematical model of inrush current, the influence laws of AC system impedance, inherent characteristic parameters of converter transformers, connection way of converter transformers, residual magnetism of iron core, and equalizing capacitance of circuit breakers on inrush current in converter transformers are studied, and providing proposes for suppressing inrush current in converter transformers.