Answer / dinesh

1. Star-Star(Y-Y) Connections.I gives line voltage √3 times
phase voltage. It is economical for small high voltage
transformers as the number of turns per phase and the amount
of insulation required is less. There is no phase shift
between primary and secondary voltages. The drawback is that
the neutral is unstable because of third harmonic component
in the exciting current.


2. Delta-Delta (Δ - Δ ) Connections. The arrangement is
generally used in systems which carry large currents on low
voltages and specially when continuity of service is to be
maintained even though one of the phases develops fault.
There is no phase displacement between primary and secondary
voltages. There is no distortion of flux as the third
harmonic component of magnetizing current can flow in the
delta connected primary windings without flowing in the line
wires. The conductor is required of smaller x-section as the
phase current is 1/√3 times of the line current. No
difficulty is experienced due to unbalancing of loads on the
secondary side. The disadvantages are that more insulation
is required and the voltage appearing between windings and
core will be equal to full line voltage in case of earth
fault on one phase.


(techie.dinesh@gmail.com)

Answer / mohd saaim

in star-star T/F primary windings are connected in star
connection and secondry winding sme as well
in delta-deltaT/F primary windings are connected in delta
connection and secondry winding sme as well

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