Question

1. [20 points] Choose the right answer. a) If phase current of a wye-connected three-phase system is equal to Ipu, then the line current of the same system is equal to V3 pu. i. True ii. False b) A synchronous generator is supplying power to a load with unity power factor at 60 Hz. The load is suddenly disconnected (tripped). What would happen to the internal generated voltage, EA? i. Same as before ii. Increase iii. Decrease c) What is the winding configuration of the below three-phase transformer? I Yes 3 i. ii. ili. iv. Y-Y Y-A A-Y A-A d) Three single-phase, 15 kVA, 460V/120V, 60 Hz transformers are connected to form a three-phase, 460V/120V transformer bank. What is the turns-ratio of the three-phase transformer bank? i. 3.83 ii. 6.64 iii. 2.21 e) An increase in field current of a synchronous motor increases the magnitude of internal induced voltage, Ex but does not affect the real power supplied by the motor. i. True ii. False

Answer 1

a) In wye connection of three phase system, h ł if phase current IPU then line Current will 01150 equal to Ipu Hence, Given Answer is false ” Te b) In Synch, generator, When load is suddenly off, Load and generated voltage are not dependenz Hence, When load is suclebenly off then, internal generated voltage En will be same as abefore. Vip elle k Above given winding confin for 30 transformer is Dor je Delta -star Connection. dy for three Single phase 460/120V connected, three phase banis transformer turns ratio toil) be equal to Nj Vi 400 M2 120 Hence Answer is 3.83 3.83 V2 the An increase in field current of Synchronous motor Increases magnitude of internal induced voltage (En) & en dors not affect the real power supplied by motor Ans True.