Page 78 - Power Electronic Control in Electrical Systems

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Power electronic control in electrical systems 67

Fig. 2.40 Voltage phasor diagrams of polyphase transformers.

Note that the voltage and current ratios are affected by the connection. For
example in a Yd1 transformer with N 1 turns per phase on the high-voltage winding
and N 2 turns per phase on the low-voltage winding, the ratio between phase voltages
p
is N 1 /N 2 , but the ratio between line±line voltages is 3 N 1 /N 2 , while the ratio
p
between line currents is (N 1 /N 2 )/ 3. The impedance referral ratio is therefore
2
3(N 1 /N 2 ) .