Answer / mpn

Who told you that primary is always connected in star and
secondary in delta? In general you can say that one side is
connected in star and the other in delta (for this also,
there are exceptions). Delta winding provide a closed path
as indicated in the Answer#1. Which side is star is decided
by the voltage level and the requirement of neutral. For
example, in a 220KV/11KV transformer, primary(ie;220KV
side )will be star because they can give graded insulation
on the star side and save money.This is possible because
near the earthed star point, the voltage encountered by the
coil is low, hence they need not be insulated for the full
voltage. As you move away from the star point, voltage keep
on increasing and hence the insulation shall be rated for
higher and higher voltage.
In a 11KV/415V transformer, you need a 4 wire system (3
phase and neutral)on the LT side because you have to feed
single phase loads also. Hence 11KV side will be delta and
LT side will be star(solidly grounded).
There are cases in which you have to give star on primary
as well as secondary for purpose of phase matching. In such
cases, you may give a tertiary winding connected in delta
for providing the closed path for reasons explained in Ans
#1.

Answer / naresh

transformer generally consistsof primary star connected &
secondary delta connected.star connection consists of 3
phase & 1 neutral wire ,so that each phase voltage is equal
to1.732 times the line voltage.similarly on secondary side
more current is required to drive the load ,it is provided
by delta connection,phase current =1.732 times line
current.for this reason transformer is connected so.

Answer / iamdon

Primary side is that side of transformer through which
source of power is connected and secondary side is that
side through which load is connected.Star on primary side
has a neutral point which is grounded for protection
purpose.Delta on secondry side ensure that in case of
unbalance the zero sequence current would circulate in
delta and would not flow in line of secondry side.

Answer / raul

its absolutely wrong dat most of d times the primary is
star connected and sec is delta connected...........the
connections depends upon d type of service
required........i.e star-delta is used as step down
transformer, delta-star as step up transformer.........star-
star is rarely used until required due to disturbance
caused in d neighbouring communication system .......

Answer / mothe ravi kiran

i think the reason behind this is that we know that vp=vl/1.732 and il=ip for star connection....similarly for delta connection vp=vl and ip=il/1.732....means we can say that line current is i.732 times the phase current in delta connection ......and we dont want more line current at the recieving side because this leads to more losses and due to heavy current our transformer cud be burn,it can be happen only in that case if we connect our secondary side in star although in some app.we need its reverse also........thats why we always connect primary side of transformer in star and secondary side in delta........thank you... 

Answer / ashish

there are several reasons for which such star-delta configuration are used the two reasons are already discussed in ans no.#1&no.#3 also in some cases for eg in multipulse inverter phase difference are required so such configuration gives a phase difference of 30degree.

Answer / rekha goley

i think the reason behind this is that we know that vp=vl/1.732 and il=ip for star connection....similarly for delta connection vp=vl and ip=il/1.732....means we can say that line current is i.732 times the phase current in delta connection ......and we dont want more line current at the recieving side because this leads to more losses and due to heavy current our transformer cud be burn,it can be happen only in that case if we connect our secondary side in star although in some app.we need its reverse also........thats why we always connect primary side of transformer in star and secondary side in delta........thank you...

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