Difference Between Thyristor Switching And Relay Switching

Thyristor means may be Fast switching devices. Is it right

Chuck it in a search engine and see what it says!

A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. It acts exclusively as a bistable switch, conducting when the gate receives a current trigger, and continuing to conduct while the voltage across the device is not reversed (forward-biased).

Thyristor - Wikipedia, the free encyclopedia

From a practical standpoint, it also depends on what type of tourist or you are referring to. The basic common thyristor used most often is an SCR, which can only be used on AC. That's because it can be gated on, but current will continue to flow after the gate is turned off until the voltage crosses zero. So you can't use it in DC because the voltage will not cross zero (unless you have some other switch). On a relay, it can switch AC or DC, although the ratings will be different between them.

scr's can and have been used with DC in older TV sweep circuits and electric forklifts for power control just to name 2 uses.

Yes, they CAN be used in DC like that because there is ANOTHER device somewhere in the circuit that cuts off power flow through the cathode. But they cannot be used AS a relay all by themselves with DC, and the OP was relating an SCR to a relay contact.

Not quite correct.

SCRs are often used on DC without any other switch to turn them off.

They are commonly used in flash circuits where the gate is triggered by a UJT, timer pulse, etc. and then turns itself off and resets when the voltage across it (normally provided by a charged capacitor) falls below the hold voltage.

I would suggest that their greatest advantages over relays are their speed of operation, lack of arcing, lack of contact bounce, lack of maintenance requirements and relative cheapness. Their major disadvantage is their inability to control multiple circuit operations via the same device as can a relay.

"... and resets when the voltage across it (normally provided by a charged capacitor) falls below the hold voltage."

Again, SOMETHING ELSE has to interrupt the flow of the power through the cathode. In this case, it is the source itself going away by decaying. Same effect. But again, consider the context of the question; that is NOT a "relay" type of situation.