Why the Transformer connection is changing in different transformer?(Like Star

Why the Transformer connection is changing in different
transformer?(Like Star & Delta,Delta & Delta,Star &
Star,Delta Star)

From that connection where it is used?

Question Posted / asmoorthi2000

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Why the Transformer connection is changing in different transformer?(Like Star & Delta,Delta &a..

Answer / j.b.

(1) in the star - star connection 57.7% of the line voltage
is impressed upon each winding, but full line current flows
in each winding. power cicruits supplied from a star -star
bank often create serious distrubance in communication
circuits in their vicinity. It is seldom used.
(2) The Delta Delta connction is often used for moderate
voltages. An advantage of this connection is that if one
transformer gets damaged or if removed from service,the
remaining two can be operated in open delta or V-V
connection, but the capacity of the bank is reduced to
57.7% of what it was with all threee phase are in working.
(3)The Star Delta connction is suitable for step down a
high voltage. In this case, the primary is designed for
57.7% of the high tension lines.
(4) Delta Star connction is commonly used to step the high
voltage.