PYQs Based test 9: Electrical Machines

A 220 V, 10 kW, 900 rpm separately excited DC motor has an armature resistance Rₐ = 0.02 Ω. When the motor operates at rated speed and with rated terminal voltage, the electromagnetic torque developed by the motor is 70 Nm. Neglecting the rotational losses of the machine, the current drawn by the motor from the 220 V supply is

The power input to a 500 V, 50 Hz, 6-pole, 3-phase induction motor running at 975 RPM is 40 kW. The total stator losses are 1 kW. If the total friction and windage losses are 2.025 kW, then the efficiency is _____%

A cylindrical rotor synchronous generator with constant real power output and constant terminal voltage is supplying 100 A current to a 0.9 lagging power factor load. An ideal reactor is now connected in parallel with the load, as a result of which the total lagging reactive power requirement of the load is twice the previous value while the real power remains unchanged. The armature current is now A (rounded off to 2 decimal places).

A three-winding transformer is connected to an AC voltage source as shown in the figure. The number of turns are as follows: $N_1=100,N_2=50,N_3=50$. If the magnetizing current is neglected, and the currents in two windings are ${\bar{I}}_2=2\angle 30^{\circ }Aand{\bar{I}}_3=2\angle 150^{\circ }A$, then what is the value of the current ${\bar{I}}_1$ in Ampere?

A star connected 400 V, 50Hz, 4 pole synchronous machine gave the following open circuit and short circuit test results:

Open circuit test: $V_{OC}=400V$ (rms, line – to – line) at field current $I_f=2.3A$

Short circuit test: $I_{SC}=10A$ (rms, phase) at field current $I_f=1.5A$

The value of per phase synchronous impedance in Ω at rated voltage is ____________