Then as far as I can see, the triac will definitely blow up. The problem is due to the phase lead of the current through the capacitor.

When the gate drive is removed, the triac will turn off at the next capacitor current zero-crossing. The supply voltage will actually be at or near its peak value, so the capacitor will be charged to near peak supply voltage. During the next half-cycle the capacitor voltage will add to the (opposite sign) next voltage peak, bringing the total to about 678V. The triac you mention is 400V maximum blocking, so it will will break down.

Dear Adjuster;
does makeing series connection of 2 triacs solve this voltage issue?
regards

 

Sorry, but adding components will not help. The circuit is dangerous to mess with.

Despite several requests, we have not heard from you about what you are trying to do. The thread is getting closed. You are strongly advised to stop this project.

 

I agree that this is too dangerous, and would rather not comment further.