As an example : A 1:1 ratio and1 primary 1 secondary isolation transformer

1)why we need to connect a secondary winding to earth?what is the purpose of it?

2)if we are not doing so what would happen?will it generate noise?

3)if accidently human body touching any secondary windings of isolation transformer ,would it trip off the Residual current circuit breaker(RCCB) placed at the input primary?

 

1 i don't think you realy need to do that but the voltage level is on both wires a diferent potential as earth (floating) so it could be potentialy deadly

2 can't answer this question

3 since the primary is still a closed circuit without a leakage to the earth the RCCB wil not activate no mater what you do ate the secondary side

Robert-Jan

 

If you don't ground/earth either of the secondary wires, touching one of them while grounded/earthed yourself will not cause a shock since there is no ground/earth reference for the secondary. There is a point where I would not ever consider testing that theory though, such as a 1:1 isolation transformer in a 13KV system! I'm not that "ballsy"!

High-end transformers used in laboratory test and measurement equipment, military, audio and communications equipment many times have a shield between primary and secondary that is grounded/earthed to reduce noise transmitted between primary and any secondary windings. Isolation transformers rarely have this shield.

Industrial control transformers have varying ratios including 1:1 and often have one side of the secondary grounded/earthed as part of the standard electrical precautions of having all exposed metal parts grounded/earthed. That way, if a "hot" wire comes loose and touches the enclosure, a blown fuse results.

I assume that an "RCCB" is the same as the ground fault circuit interruptor (GFCI) here in the States. Since the secondary of the transformer is electrically isolated from the hot wire, there can be no ground fault current (current that's flowing somewhere outside of the hot wire) through the transformer, so it will not trip. Now, if there's LEAKAGE between the primary and secondary, then YES, it will trip, doing exactly what it's supposed to do: protecting you from a faulty component (the transformer).

Dean

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Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

 

I've already answered this question in another thead. Please do not post quetion more than once.

http://www.electro-tech-online.com/g...ansformer.html

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