Answer / tango

basically to obtain the desired voltage at the secondary side
tap is used , the voltage variations at the primary side
results the variations at the secondary side according to
transformation ratio, if the voltage at primary side is more
than rating then no of tuns to be reduced and vice versa if
voltage is less so the no of turns has to be increased so as
to get the exact rated voltage at the primary side.
hence to keep voltage at the rated one needs tap changer for
altering the no of turns. Tap changing is done normally for
+5% to -5%, but some times upto -10% in steps of either 2.5%
or 1.25%.

Answer / apoorv

there are different tap changers in transformers. diff. taps have diff. no. of turns , therefore suitable voltage output can be obtained , allowing good voltage regulation.

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