Electrical Machine - IES Academy
Electrical Machine - IES Academy
Electrical Machine - IES Academy
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India’s No. 1<br />
<strong>IES</strong> <strong>Academy</strong><br />
Case II: Unequal Voltage Ratios<br />
Transformer<br />
Chapter-1<br />
1. In case of unequal voltage ratios, a circulating current will flow which will boost lower<br />
voltage magnitude and buck higher voltage magnitude so that the two transformers have<br />
same terminal voltage.<br />
2. The currents in the two transformers will be unequal:<br />
1 1<br />
Ia = + Icand<br />
Ib = − Ic<br />
2 2<br />
3. The two transformers will operate<br />
at different power factors. The<br />
effect of circulating current is to<br />
reduce the power factor and<br />
increase the current shared by the<br />
transformer having greater no-load<br />
induced e.m.f. At the same time,<br />
the power factor of the second<br />
transformer with smaller no-load<br />
induced e.m.f. is increased and the<br />
current shared by it is decreased.<br />
4. In case of unequal voltage ratios, a<br />
circulating current will flow which<br />
will boost lower voltage magnitude<br />
and buck higher voltage magnitude<br />
so that the two transformers have<br />
same terminal voltage.<br />
5. The currents in the two<br />
transformers will be unequal:<br />
1 1<br />
Ia = + Icand<br />
Ib = − Ic<br />
2 2<br />
6. The two transformers will operate at different power factors. The effect of circulating<br />
current is to reduce the power factor and increase the current shared by the transformer<br />
having greater no-load induced e.m.f. At the same time, the power factor of the second<br />
transformer with smaller no-load induced e.m.f. is increased and the current shared by it<br />
is decreased.<br />
Auto - Transformers<br />
When the primary and secondary windings are electrically connected so that a part of the<br />
winding is common to the two, the transformer is called an auto-transformer. Unlike a two<br />
winding transformer, in an auto- transformer the two windings are not electrically isolated.<br />
They are used particularly economical where the voltage-ratio required is small (less than 2)<br />
and electrical isolation of the two windings is not essential. The major applications are<br />
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