Galvanic Isolation in Series? Do they stack?

[DanielB33]

If I want 10KV dialectic isolation, and I have 1KV galvanic isolation downstream of my circuit, can I use 9KV galvanic isolation up stream and call the total 10KV?

Thanks.

 

[dorke]

Welcome to EP.

I think not.
It is like a chain composed of links,it is as strong as the weakest link right?
If the 9KV is subdued what good is the 1KV one for?
Please give more details

 

[DanielB33]

After looking into this more, I believe that the solution will work if we know the parasitic capacitance. Capacitance is the dominating parasitic in transformers, so the voltage division should stem from there. As long as we have a proper divider with the selected parts I think it will work. Thought?

 

[DanielB33]

And for details...I want to provide 5KV isolation through two 3.5KV barriers.

 

[dorke]

Not clear what you are trying to do.
Are you talking about mains isolation?

Here is some reading material and here is another for you.

 

[DanielB33]

Thanks for that. I am researching different methods of defibrillation protection. Applied mains is always a concern...but defib is a much more brutal test.

 

[Harald Kapp]

You need to discern between basic insulation and double or reinforced insulation.

• Basic insulation is a single barrier where, when this barrier breaks, the insulated (supposedly safe) side can have contact with the high potential side. Therefore a high risk of injury exists in case of a single fault. This is typically not allowed when humans can come in contact with the insulated (safe) side.
• Double insulation consists of (at least) two layers of insulation where each single layer is able to withstand the full potential difference. In this case, if one of the insulation layers fails, the second layer will still provide full insulation. Ths is typically regarded safe when humans can come in contact with teh insulated (safe) side.
  Double insulation is in many cases considered equivalent to double insulation. The difference being that only a single layer of insulation is used which has properties equivalent to double insulation (e.g. thicker material) which makes a complete failure of the insulation barrrier improbable.

IN addition the use of protective earth on the safe side needs to be considered such that in case of a failure of the insulation no dangerous potential can develop on the safe side. Usually this is achieved by a comparatively high short circuit current to protective earth which leads to a fuse being triggered and the dangerous potential thereby being disconnected.

Depending on the application different standards require different measures (e.g. different length of air gaps and creepage distances) as well as consideration of different detrimental effects (e.g. pollution, humidity, type of material, current tracking index CTI, overvoltage (measurement category) etc.).

A medical apparatus is as far as I know one of the most stringently regulated devices as it is used in direct contact with a human person. Therefore you need to look up the applicable standards and regulations and carefully evaluate your design with respect to the requirements of these standards!