Step up and step down transformer have no grounding. Then why person standing on the ground would be electrocuted touching high voltage transmision line?
In IT grounding you can't get electrocuted touching single hot wire since no circuit is made.
And why TN grounding use no RCD? It's true that short circuit will draw great current due to low resistance from common ground thus circuit braker will quickly interupt. But when a person will touch hot wire braker will not interupt since low current will be flowing trough high resistance body.

 

Step up and step down transformer have no grounding. Then why person standing on the ground would be electrocuted touching high voltage transmision line? <some text deleted for clarity>

The isolated output of proper isolation transformers that step up or down are indeed not grounded -they are floating and only result in a very low current, perhaps 100's of microamps when touched by a grounded body or a ground wire for that mater, so no electrocution (your skepticism is well founded). That's the purpose of isolation transformers in the first place.

I did not understand the other question because I am not familiar with the "TN" and "RCD".

 

RCD = Residual Current Device (UK etc)
N.A. GFI.
Max.

 

if you follow Google they tell something about corona , electric field in the air, capacitors e.c. there - since i'm not about to get myself into this you likely have to help yourself - but the capacities are like to be blamed here

+something similar