Effect of Voltage Transformation Ratio on the Kilovoltampere Rating of Delta-Connected Autotransformer for 12-Pulse Rectifier System

This paper presents the effect of voltage transformation ratio on the kilovoltampere rating of delta-connected autotransformer for 12-pulse rectifier system and gives an optimal configuration of the autotransformer with minimal kilovoltampere rating and the least windings. According to the phasor diagrams and the relation between the output voltage and input voltage of the autotransformer under different connection ways, the effect of voltage transformation ratio on current through windings is analyzed, and corresponding expressions and waveforms of the currents are also obtained. Consequently, a relation between the position parameter and output power is established, and based on the relation, the effect of winding configuration on the kilovoltampere rating of the autotransformer is analyzed, which can be used to obtain the optimal configuration. From the theoretical analysis, an autotransformer with optimal configuration and minimal equivalent kilovoltampere rating is designed. Some simulated and experimental results show the correctness of the theoretical analysis.