delta

Hi, I have to on-off switch a AC load, which delta connected 3 phase AC source. Consider the load that will be switched on-off is Z1. To achieve on-off switch, I think use zero cross triac opto driver and triac for both Phase-R and Phase-Y. But I am confused. When Phase-R reaches zero point...

To solve this question all I know is I had to change the delta source to star shape (wye), then to find the current is using ohm law's with the voltage divided by the impedance which in the same line I'm confused with this question, does the position of the source in delta and impedance matter...