Isolation transformer

[wkyong]

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

1)why we need to bond secondary neutral to earth?what is the purpose of it?

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

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

 

[laktronics]

Hi,
The neutral is grounded to establish a known phase voltage with respect to earth which is treated as an equipotential surface available every where. By grounding the neutral, you remove any earth based common mode voltage that may appear on the phase conductors. In the absence of the earthing, the phase conductors can get charged to any high voltage with respect to earth and can pose danger to anybody who comes in contact with it. By grounding, all such picked up charges find a return path to earth, thus preveting buid up of high voltage on conductors with respect to earth.

If you use a floating secondary locally, with a proper grounded shield from primary, you will not get shock touching the secondary connections due to primary voltage, but again, if the secondary connections are long, it can still pick up extraneous charges e.g., from lightning and can pose danger. Also in this case the RCCB will not trip, since the differential current which it monitors does not get affected and it is the common mode voltage that causes the shock.

Regards,
Laktronics