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 />
Transformer<br />
Chapter-1<br />
If one of the transformers is disconnected, it results in open-delta connection. It can supply a<br />
balanced load.<br />
In the delta/delta connection if one of the transformers is disconnected, the resulting<br />
connection is known as open-delta. Supposing the b-phase transformer is removed, and the<br />
open-delta is excited from balanced 3-phase supply, then the voltage Vb 1<br />
b 2<br />
= Vbc does not<br />
change as it equals – (Vca + Vab); thus the voltage on the secondary side still remain balanced<br />
3-phase. If the maximum allowable secondary phase current is Iph, the transformer can handle<br />
VA of<br />
Sopen-delta = 3 VI<br />
ph<br />
Which for normal delta/delta connection is<br />
Sdelta = 3VIph<br />
Thus the open-delta connection has a VA rating of 1/<br />
delta/delta connection.<br />
3 = 0.58 of the rating of the normal<br />
The maximum allowable secondary phase current is Iph, the transformer can handle VAopen-delta<br />
= √3 VIph = S'<br />
For normal (Δ/Δ) Connection, VA delta = 3VIph = S<br />
S '<br />
S = √<br />
13<br />
= 0.58<br />
Star/Delta (Yd) Connection – (+30° and –30° connections<br />
are obtained)<br />
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