The question can be replied in three conditions
When earthing is perfect and (a) neutral is solidly
earthed at transformer end then the volatge between erath &
neutral is zero and earth and phase is the same as between
earth & neutral in all conditions whether all pahases are
perfect or one of them faulty. and between earth and phase
is the same as neutral and earth i.e. nominal value when
system is healthy
(b) when neutral earthing is not solid but with resistance
then Voltage between neutral and earth will be zero in case
of balanced load on all three phases and it may rise max.
upto a value equal to phase value if there is fault on one
of the phase,depending upon the value of earthing
resistance of the neutral earthing. Value of earth to phase
will be nominal value if system is balanced and healthy,
and may go max upto phase to phase voltage if there is
fault on one of the phases and mind it again value in case
fault will depend on fault resistance.
In nut cell we can say that min. value between neutral and
earth will be zero volt and max. will be nominal voltage
(e.g 230 volt in indian LT supply case) and voltage between
neutral and phase will be nominal voltage is system is
balanced and healthy and mind it in case of fault it may go
down min. to zero value and max to phase to phase voltage!
and that is what great abt electrical enineering.
Regarding answer 11, i think in case the Neutral to Earth
voltage is high, it means there is an unbalanced load in
the three phases (in case of 3 phase supply) or the neutral
is not proper. Either way, there is a chance of current
flowing back into the circuit because of improper neutral
or earth not properly grounded, resulting in equipment burn-
outs in case of a surge. These equipments need not be
switched on and will burn-out in case of fault. Thus it is
recommended to keep the voltage between Neutral and earth
as low as possible.
Can a 50-Hz designed transformer be used at 60-Hz system?
Is the same remains true, when a 60-Hz designed transformer
be used at 50-Hz system? Consider only frequency variation.
The voltage remains as rated value in all cases.
Justify the answer.