Why generally the transformer primary is connected in star
& secondary in delta

Answer Posted / 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.

Is This Answer Correct ?    19 Yes 4 No



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