An ac phase control circuit by thyristor is widely used in industry, The characteristics of the singlephase circuit with series RLC elements are numerically analyzed, and is reported the interesting phenomenon of step-up voltage without transformer. However, the performance of three phase phase control circuit with series RLC elements is not made clear. In this paper, the performance of three-phase
control circuit of a balanced and an unbalanced load with series RLC elements is described. The analytical programs with each load are developed, and it is clarified that the calculated by this analytical program agree well with the measured. The calculated results, e.g. waveforms, RMS values of voltage and current, power, and power factor are illustrated and discussed the step-up phenomenon in three phase.