Millisecond Zero Line Current and Large Line Current Phase Shifts from SCR Switching of Three-Phase Voltage Sources

Three-step switching by SCR at the line current zero points between different three-phase voltage sources causes significant line current phase shifts during the switching process, even for balanced resistive loads. It also causes a period of no current flow on one of the three-phase lines during the switching process. The phase shifts caused and the duration of the no current flow period is developed for various voltage ratios for balanced resistive loads. Extension of the results to reactive loads is addressed.