[SOLVED] Can someone explain ac system with grounded neutral?

panic mode

Joined Oct 10, 2011
2,111
when it comes to potential, ground is just a reference.... if you are 6ft tall when standing on a side walk, you are still 6ft when standing on a balcony on 3rd floor, or 18th floor, or when deep in a basement... but distance to reference (ground level) is changing depending where you stand.

voltage is just that, it is a difference between two potentials. potentials may not be the same, depending what you use as a reference but... this difference (like your height) is the same regardless what elevation you measure from. in case of ungrounded secondary, none of terminals are grounded. this is called floating. trying to measure potential to one of them relative to ground can produce any readings, but voltage between those terminals (the difference) is still going to be the same.

grounding is used for several reasons, one of them is to make sure all potentials you may accidentally get in contact with, are reasonably close to OUR reference (regardless where you stand, you are at earths potential). there may be a transformer 15kV to 230V. touching 230V is bad but... not as bad as touching 15kV. transformers windings can be isolated from each other so secondary can float. if you touch either ONE of secondary terminals, nothing will happen since no circuit is created. if there is a fault or leakage to ground, one of the secondary terminals may be at or near 0V (relative to ground). then touching the other terminal you will be in contact with 230V and this is not fun.

but suppose that mentioned fault or leakage is not to ground... so secondary is not grounded and it is floating. if the fault connects one point of secondary (any point, could be one of terminals or some point on the winding) to a point on primary, then the voltage between two secondary terminals is still the same 230V but... they will be at a new potential from ground... up to 15kV different. and this is a far bigger problem. to avoid such severe problem grounding is used. then in case of fault like this, primary current would be huge and trip fuse or breaker. because of one fault, we purposely we created another, to remove power and keep circuit safe(r) - at the expense of replacing cheap fuse or having to reset some breaker.


and i do not suggest one should be touching live circuits, things like that happen accidentally and often don't end well.
 
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MisterBill2

Joined Jan 23, 2018
11,593
For most transformers the no-load voltage ratio is the same as the turns ratio. As power is drawn from the secondary the voltage tends to drop a bit, because the efficiency is less than 100%.
 
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