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jinxnao
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Thyristor as an Isolating Device

04/08/2016 3:21 PM

Hello. what is your opinion and knowledge on thyristors used in power circuits ? Say we use them in medical areas and criticial loads.As far as I know they are not reliable as isolation devices and not allowed in transfer or changeover switches. But there are many applications which use them as switch. What are the requirements related to isolation capabilities of switches. Semiconductors can be used in medical isolated power systems or not ? Of course I mean in changeover side of the panels.Do you know any respectable company using thyristors (sts) in medical isolated power panels?

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Tornado
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#1

Re: Thyristor as an Isolating Device

04/08/2016 3:45 PM

Incompetent question.

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tcmtech
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#2

Re: Thyristor as an Isolating Device

04/08/2016 4:05 PM

yes.
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Tornado
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#3
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Re: Thyristor as an Isolating Device

04/08/2016 4:11 PM

I might be wrong, but dollars to donuts that something besides thyristors is doing any isolating.

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JRaef
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#4

Re: Thyristor as an Isolating Device

04/08/2016 4:22 PM

Thyristors, and the surge protection devices they need to survive (RC Snubber for example), will "leak" voltage. It is very low current, depending on the design of the protective devices but will usually show up on a digital meter as line voltage potential. That makes them wholly unsuitable as isolation devices, meaning when used in power circuits, must be used with an "air gap" device of some sort ahead of them.

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Peterpipper
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#7
In reply to #4

Re: Thyristor as an Isolating Device

04/09/2016 12:22 AM

Are sure about that? Surge protection?

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marcot
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#9
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Re: Thyristor as an Isolating Device

04/09/2016 11:56 AM

Jraef is correct. All semiconductors leak some current but thyristors also need dv/dt protections that increase the leakage by a lot. You end up with uA to mA of leakage.

A concrete example are the PLC AC outputs made with triac that will activate sensitive coils relays even when off. We always need to use "bulky" isolation relays on those outputs.

It looks like you need a real galvanic isolation switch in your application. Something that opens the circuit with a mm or two of air.

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PWSlack
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#5

Re: Thyristor as an Isolating Device

04/08/2016 5:37 PM

They are not permitted as isolators under British Standard 7671. And there is no opinion in it.

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TonyS
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#8
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Re: Thyristor as an Isolating Device

04/09/2016 2:56 AM

What regulation number?

Look up "electrical separation" for what is being discussed here.

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PWSlack
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#10
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Re: Thyristor as an Isolating Device

04/11/2016 3:30 AM

There is no opinion in any regulation number.

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Rixter
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#6

Re: Thyristor as an Isolating Device

04/08/2016 8:01 PM

I don't know if this is what you are looking for, but opto isolators are generally used when you want to send a signal between two circuits that are not electrically connected. It basically consists of a package with a LED connected to the transmit side and a phototransistor connected to the receive side.

https://en.wikipedia.org/wiki/Opto-isolator
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ci139
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#11
In reply to #6

Re: Thyristor as an Isolating Device

04/11/2016 8:04 AM

sorry i spoke ► (you must have missed your coffe) it´s an ~AC (i assume) thus [Solid-state relay]

(i won´t credit the further) as far as i know the Thyristors can´t be swithed off from 2N×"quarter-phase" , "quarter-phase" = T(au)/4 = 1/(4·f) ~ e.g. a possible over voltage conditions ...

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ci139 (1); JRaef (1); marcot (1); Peterpipper (1); PWSlack (2); Rixter (1); tcmtech (1); TonyS (1); Tornado (2)

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