Thyristor for Voltage Regulator

What sort of currents are we talking about here?

Operating voltage?

Circuit diagram(s)?

If you are designing it, why don't you know enough to answer these general questions regarding your application?

Use ans oscilloscope and proper probes to take waveforms and check the operation of "your design". Check the timings, the current levels etc... Come back to us with specific problems but don't ask about the whole science related to this application. We are not a university.

I would also advise using and oscilloscope and checking the waveform of both the gate drive and the output, as it could be a gate drive issue or something as simple as exceeding the parameters of the thyristor.

Additionally there are good thyristor application manuals available off thyristor manufacturer websites that go into great detail and should be able to answer your questions (once you narrow down what the problem appears to be in your circuit).