Question

a) [1 mark] Pulsating magnetic field in the air gap of a single-phase induction motor A. Results in a zero starting torque B. Becomes a rotating magnetic field at the speeds above zero C. Can be represented by two magnetic fields rotating in opposite directions D. Both A and C are true E. All of A, B and C are true b) [1 mark] In a properly designed capacitor start single-phase induction motor A. The auxiliary winding current lags the main winding current by 90° at the start B. The auxiliary winding remains connected to provide smooth torque C. The starting torque could be as high as 300% of the rated torque D. The direction of the rotation cannot be changed by interchanging the auxiliary winding terminals because of the series capacitor E. All of the above are true c) [1 mark] In North America, a three-phase distribution transformer connection A. is made so that LV side voltages always lags 30° behind HV side voltages B. is made so that HV side voltages always lags 30° behind LV side voltages C. can be of Dy1 vector group D. B is true but vector group should be Dy11 E. Both A and C are true d) [1 mark] A 30 MVA, 66 kV/11 kV, \Delta-\Delta three-phase transformer bank consist of three single phase transformers. One of the transformers is required to remove for maintenance. With the remaining two transformers, A. Up to 17.3 MVA of 3-phase power can be supplied without interruption. B. Up to 20 MVA of 3-phase power can be supplied without interruption. C. Up to 21.2 MVA of 3-phase power can be supplied without interruption. D. Up to 30 MVA of 3-phase power can be supplied without interruption. E. Power cannot be supplied to a three-phase load..

a) [1 mark] Pulsating magnetic field in the air gap of a single-phase induction motor
A. Results in a zero starting torque
B. Becomes a rotating magnetic field at the speeds above zero
C. Can be represented by two magnetic fields rotating in opposite directions
D. Both A and C are true
E. All of A, B and C are true
b) [1 mark] In a properly designed capacitor start single-phase induction motor
A. The auxiliary winding current lags the main winding current by 90° at the start
B. The auxiliary winding remains connected to provide smooth torque
C. The starting torque could be as high as 300% of the rated torque
D. The direction of the rotation cannot be changed by interchanging the auxiliary
winding terminals because of the series capacitor
E. All of the above are true
c) [1 mark] In North America, a three-phase distribution transformer connection
A. is made so that LV side voltages always lags 30° behind HV side voltages
B. is made so that HV side voltages always lags 30° behind LV side voltages
C. can be of Dy1 vector group
D. B is true but vector group should be Dy11
E. Both A and C are true
d) [1 mark] A 30 MVA, 66 kV/11 kV, \Delta-\Delta three-phase transformer bank consist of three single
phase transformers. One of the transformers is required to remove for maintenance. With the
remaining two transformers,
A. Up to 17.3 MVA of 3-phase power can be supplied without interruption.
B. Up to 20 MVA of 3-phase power can be supplied without interruption.
C. Up to 21.2 MVA of 3-phase power can be supplied without interruption.
D. Up to 30 MVA of 3-phase power can be supplied without interruption.
E. Power cannot be supplied to a three-phase load..

Added by James N.

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