Thyristor Switching vs. Solid-State Relay Switching

Your description is one and the same thing.

Identify your solid state components.

Dear Sir,

Had discussed this problem with M/s Siemens and M/s Ducati and both confirmed that SSR and thyristor are different, but did not give reasons, hence this query, so if u can shed more light I will be grateful

In my experience, Thyristor is another name for SCR (Silicon Controlled Rectifier). An SCR is a three-terminal device that conducts in one direction once the voltage at the gate reaches a minimum voltage. Removal of the trigger voltage does NOT turn the device off; it will continue to conduct until the supply voltage approaches zero.

SSRs (Solid State Relays) use triacs or other devices (possibly a pair of SCRs) that conduct in either direction. I must confess that I've never tried to use a SSR to control a DC current, so I'm not sure if they stop conducting when the triggering voltage is removed, or whether they also require the zero-crossing of the AC waveform to stop conduction.

Its my understanding that SS is a generic term for semiconductors which can incorporate SCRs, Triacs, IGBTs, transistors etc. So unless you define which SS component is being used it does not help much.

Dual thyristors can give a better perfomance in some situations than a Triac.

• Thyristor switch will leave a voltage drop across. Over a year that could be so many LOST $$.
• "Solid state Relay" is a metal contact (old days in a telephone switching station-- remember?) pair operated by some logic Transistor/Thyristor -- across whose switching contacts the volts drop is next to zero.So you save on that score particularly on lethargic heavy power switching jobs.

But remember these:

Thyristor is controllable.In today's Digital world there is no escaping the Thyristor's

switching ON/OFF(Triac) capability in microseconds.

Metal relay takes upto a second to switch ON

Metal Relay cannot be recalled to BLOCK fast due to Inertia ,Hysterisis---

MM

"Solid state Relay" is a metal contact.

NO! A magnetic relay has metal contacts. There may be non-magnetic relays with metal contacts (I can imagine a piezoelectric one), but they are NOT Solid State.

By definition Solid State devices have no physically moving parts. Metal contacts can't change their connection state without physically moving. There are many ways to construct a solid state device that acts like a relay, but unless they use entirely solid state devices, they aren't Solid State Relays. The output terminals may be connections to SCRs, Triacs, Transistors, FETs, IGBTs, etc., none of which have metal contacts or moving parts.