Hell, you really are giving my crystal ball a workout here, and its only a cheap Chinese made one to start with that tells lies at times......lol.
Are you able to post a rough schematic of what the circuit is, because it just gets more confusing as it goes.
Ok..........180 what? Thyristors?? and if so are they all switched together at the same time.
There is likely many ways to do this and a relay could be one method but without knowing the circuit it could cause other problems, like with the relay contacts open the gates would be floating and this could cause unwanted effects.
A opto coupler can control several devices but it all depends on the current requirements of the devices.
Optos are small 4 or 6 pin packages and not over expensive, but to have to add 180 of them might be costly, perhaps a hex inverter like the 4069 would do the job, as a low on the input would give a high on the output and vice versa (inverted) but this is a 6 (hex) inverter package and would likely only control 6 devices, and if each device required its own control than thats 30 chips needed for 180.
You really need to give more information on the circuit, we dont mind if its hand drawn schematic or how your discription is, but dribs and drabs of information can only lead to poor answers in return. (hence my original reply)
Pete.