Answer / t eswara rao

For lighting loads, neutral conductor is must and hence the
secondary must be star winding. and this lighting load is
always unbalanced in all three phases. To minimize the
current unbalance in the primary we use delta winding in the
primary. So delta / star transformer is used for lighting loads.

Answer / naheru arun

i think there are mainly two resone
1. in a big sub station or in company power supply is used
for plant load (which is generally use only 3 phase neutral
is not used)this supply also used for plant lighting which
is require neutral to obtain this neutral we use Delta Star
transformer which is also called isolation transformer
2. Delta star transformer is used to isolated secondary
side earth fault (which is common in lighting circuit) from
primary side.

Answer / guest

delta-star transformers are used for lighting loads
because in delta side primary side the voltages fed are in
phase (R-Y-B) and thus on the secondary side the star
connection aims at equal currents in all the phases in case
of 3 phase thus equal current flows and thus the lighting
intensity is not disturbed for the lighting loads.

Answer / p krishna teja

in delta connection there is no common point ( i:e no
netural) for lighting we need netural line for
maintaining voltage difference. so star connection is need
for lighting .

on delta connection 3 phase we can only get 415 volts as
there is no netural line we cant use individual phase .
But in stare connection 3 phase ther is flexibility of
using individual phases with common netural 230 volts.

Answer / ravi

Bcoz to obtain Phase to Netural Voltage..

Answer / b.b.barah nalco

I agree with Mr. P Krishna Teja but one thing is there, to minimize the fault current secondary winding should be star connection and minimize the watt loss.

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Dear all, I just want to ask an expert on this forum for some insights. For the magnetic balance test, when applied voltage on a Delta-Star transformer e.g. Dyn11, the following relationships apply for HV side: 1.  H1-H2 = H2-H3 H3-H1 2.  H2-H3 = H3-H1 H1-H2 3.  H3-H1 = H1-H2 H2-H3 For the LV side also: 4.  X1-X0 = X2-X0 X3-X0 5.  X2-X0 = X3-X0 X1-X0 6.  X3-X0 = X1-X0 X2-X0 Is there a similar pattern for Y-d, Y-Y, D-d? And how about Y-z, D-z, Z-y transformers? I've tested a YNzn5 transformer and for LV side I don't see the pattern. In this particular case I got for LV side the following (see values below): H1-H0  H2-H0  H3-H0    X0-X1  X0-X2  X0-X3 128.0  119.9  7.2      29.2   13.3   15.8 70.7   128.4  59.2     23.4   22.0   3.6 7.2    120.1  128.1    13.4   29.3   15.8 What is the relationship here for LV? For row 1 I see the relationship, for row 3 I also see but it's shifted, but for row 2 I don't see such relationship. Any suggestions, answers, someone?

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