GATE EE 2015 Set 2 — Question 53
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Power Electronics → AC-DC Converters → Semi & Full Converters (1φ)
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Question
A balanced (positive sequence) three-phase AC voltage source is connected to a balanced, star connected load through a star-delta transformer as shown in the figure. The line-to-line voltage is 230 V on the star side, and 115 V on the delta side. If the magnetizing current is neglected and A, then what is the value of in Ampere?
Correct answer
(A) 50 30^
Solution
Turns ratio
Star side: winding (phase) voltage V. Delta side: winding voltage = line voltage V.Winding connections (from the figure)
The primary windings are star-connected with dotted ends at . On the delta side, winding 1 runs from (dot) to , winding 2 from (dot) to , and winding 3 from (dot) to .Let be the delta winding currents leaving their dotted ends. For a balanced positive-sequence system, .KCL at terminal A
Winding 1 delivers into node and winding 3 draws from it:Primary current (magnetizing current neglected, )Check: the magnitude also follows from power balance, A.Answer: (A)
Star side: winding (phase) voltage V. Delta side: winding voltage = line voltage V.Winding connections (from the figure)
The primary windings are star-connected with dotted ends at . On the delta side, winding 1 runs from (dot) to , winding 2 from (dot) to , and winding 3 from (dot) to .Let be the delta winding currents leaving their dotted ends. For a balanced positive-sequence system, .KCL at terminal A
Winding 1 delivers into node and winding 3 draws from it:Primary current (magnetizing current neglected, )Check: the magnitude also follows from power balance, A.Answer: (A)
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