Answer / dolphinopera

if the three phase
load is unbalanced (ie)
the impedance me
three phases are not
equal, a circulating
current will be
produced, hence this
current should flow
through the neutral.
otherwise the
winding will damage.

Answer / rvg

if the three phase load is unbalanced, there will be a
voltage between the common point (star system) and earthed
ground( system ground), known as Neutral shift voltage. So
if you are short circuiting these, there will be a current.

Ir+Iy+Ib=Io not Zero for unbalanced loads.

Answer / prabhu

Due to unbalance of load

Answer / pravesh

in electrial system we can sy that neutral is the return
path of the elctivity as if there is any immbalance of the
supply or unbalanced load then some current flows through
the neutal , and if the system is balanced then only no
current flows through the neutral , in single phase supply
there is no current in neutral until there is disbalance
from incoming side or the equipment is faulty.

Answer / marshal mothers

Balanced loading in 3 phase system is only achieved in
factory settings, in distribution system loads keep on
flactuating during the day hence loading keeps varying
throughout the day

Answer / ashokreddy r

In single phase systems current flows thro the neutral as
it is the return path
In three phase systems w.r.t individual phases there is
neutral current .(Ir0,Iy0,Ib0)
For balanced system Ir0+Iy0+Ib0=0
For unbalanced system Ir0+Iy0+Ib0 not equal to zero

Answer / ashok kumar saini

Due to unbalance load on 3Ph .

Answer / sumesh s l

even though the system is balanced third harmonics gets
added up.(r-phase sin3wt,y phase/b phase :sin3*(+/-120wt)
same as sin3wt.that is all harmonics component of 3 and
multiple of 3 added up...so neutral current may not be zero..
for more information mail me at sumeshsl@gmail.com or
eeo8m107@smail.iitm.ac.in

Answer / onkar singh

i think it occours only in case of unbalancing. i.e if a
suddern unbalancing of load occours then a particular
neutral to ground voltage forms that forces unbalancing
current to flow in the neutral to counteract the
unbalancing of load.

Answer / ujjwal karki

1. As per the theory, No current should be flowing in the neutral. But this is theoretically possible when the load in each phase are perfectly balanced. As the switching patterns of each loads in 3 phases are not exactly the same, some amount of neutral current is likely to flow through the neutral.

2.Another likely cause as to why there is current flowing in the neutral is due to the effect of harmonics. Lets take an example of transformer. The Hysteresis loss in transformer causes a non-sinusoidal exciting current to flow which mainly comprises of third and fifth harmonics. Since the line-line third harmonic voltage is zero, these current can only flow through the neutral wire or around the mesh winding.(If these harmonic current donot get a path to flow, the flux in transformer is not sinusoidal and the output voltage is non sinusoidal as well!!). Hence, high current might be flowing in neutral and there is even the provision of doubling the size of neutral wire to prevent its overheating.

what is second harmonic, how is effect transformer ?.

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