PYQs Based test 9: Electrical Machines

A 3-phase, 50 Hz generator supplies power of 3 MW at 17.32 kV to a balanced 3-phase inductive load through an overhead line. The per phase line resistance and reactance are 0.25 Ω and 3.925 Ω respectively. If the voltage at the generator terminal is 17.87 kV, the power factor of the load is ________.

A three phase synchronous generator is to be connected to the infinite bus. The lamps are connected as shown in the figure for the synchronization. The phase sequence of bus voltage is R – Y – B and that of incoming generator voltage is R’ – Y’ – B’.



It was found that the lamps are becoming dark in the sequence Lₐ – L${}_b$ – L${}_c$. It means that the phase sequence of incoming generator is

The starting line current of a $415V,3-phase$, delta connected induction motor is $120A$, when the rated voltage is applied to its stator winding. The starting line current at a reduced voltage of $110V$, in ampere, is _________.

A 120 V DC shunt motor takes 2 A at no load. It takes 7 A on full load while running at 1200 rpm. The armature resistance is 0.8 Ω and the shunt field resistance is 240 Ω. The no load speed, in rpm is

A 3-phase 900 kVA, 3 kV/$\sqrt{3}$ kV (∆/Y), 50 Hz transformer has primary (high voltage side) resistance per phase of 0.3 Ω and secondary (low voltage side) resistance per phase of 0.02 Ω. Iron loss of the transformer is 10 kW. The full load % efficiency of the transformer operated at unity power factor is _______ (up to 2 decimal places).