GATE EE 2015 Set 2 — Question 61
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Electrical Machines → Three-Phase Transformers → Phase Shift & Clock Notation
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Question
Two three-phase transformers are realized using single-phase transformers as shown in the figure.
The phase difference (in degree) between voltages and is ______.
The phase difference (in degree) between voltages and is ______.
Correct answer
30 to 30
Solution
Upper bank: the primary windings are connected in delta, and the secondary windings are also connected in delta in the same way. For this - bank each secondary line voltage equals a winding voltage, which is in phase with the corresponding primary winding (line) voltage. So has shift with respect to the supply line voltage.Lower bank: the primary is delta-connected in the same way, but the secondary ends are joined together to form a star point, so this is a -Y bank. Here each secondary phase voltage is in phase with a primary line voltage, and the secondary line voltage isi.e. it is displaced by from the corresponding phase (and hence primary line) voltage.Both banks are fed from the same supply, so the phase difference between and isAnswer: 30
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