1
GATE EE 2018
+2
-0.6
A transformer with toroidal core of permeability $$\mu$$ is shown in the figure. Assuming uniform flux density across the circular core cross-section of radius r $$\ll$$ R, and neglecting any leakage flux, the best estimate for the mean radius R is
A
$${{\mu V{r^2}N_P^2\omega } \over I}$$
B
$${{\mu I{r^2}{N_P}{N_S}\omega } \over V}$$
C
$${{\mu V{r^2}N_P^2\omega } \over {2I}}$$
D
$${{\mu V{r^2}N_P^2\omega } \over {2V}}$$
2
GATE EE 2018
Numerical
+1
-0
A separately excited dc motor has an armature resistance R$$a$$ = 0.05⁡Ω. The field excitation is kept constant. At an armature voltage of 100 V, the motor produces a torque of 500 Nm at zero speed. Neglecting all mechanical losses, the no-load speed of the motor (in radian/s) for an armature voltage of 150 V is _____ (up to 2 decimal places).
3
GATE EE 2018
Numerical
+2
-0
A 200 V DC series motor, when operating from rated voltage while driving a certain load, draws 10 A current and runs at 1000 r.p.m. The total series resistance is 1 Ω. The magnetic circuit is assumed to be linear. At the same supply voltage, the load torque is increased by 44%. The speed of the motor in r.p.m. (rounded to the nearest integer) is ________
4
GATE EE 2018
Numerical
+2
-0
A 3-phase 900 kVA, 3 kV / $$\sqrt 3$$ kV (Δ/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).
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