1
GATE EE 2010
+1
-0.3
A single-phase transformer has a turns ratio of 1:2, and is connected to a purely resistive load as shown in the figure. The magnetizing current drawn is 1 A, and the secondary current is 1 A. If core losses and leakage reactances are neglected, the primary current is
A
1.41 A
B
2 A
C
2.24 A
D
3 A
2
GATE EE 2010
+2
-0.6
A balanced star-connected and purely resistive load is connected at the secondary of a star-delta transformer as shown in the figure. The line-to-line voltage rating of the transformer is 110 V/220 V. Neglecting the non-idealities of the transformer, the impedance 'Z' of the equivalent star-connected load, referred to the primary side of the transformer, is
A
(3 + j0) Ω
B
(0.866 − j0.5) Ω
C
(0.866 + j0.5) Ω
D
(1 + j0) Ω
3
GATE EE 2010
+1
-0.3
A balanced three-phase voltage is applied to a star-connected induction motor, the phase to neutral voltage being V. The stator resistance, rotor resistance referred to the stator, stator leakage reactance, rotor leakage reactance referred to the stator, and the magnetizing reactance are denoted by $$r_s,\;r_r,\;r_s,\;r_r\;and\;X_m$$, respectively. The magnitude of the starting current of the motor is given by
A
$$\frac V{\sqrt{\left(r_s+r_r\right)^2+\left(x_s+x_r\right)^2}}$$
B
$$\frac V{\sqrt{r_s^2+\left(r_s+X_m\right)^2}}$$
C
$$\frac V{\sqrt{\left(r_s+r_r\right)^2+\left(X_m+x_r\right)^2}}$$
D
$$\frac V{\sqrt{r_s^2+\left(X_m+x_r\right)^2}}$$
4
GATE EE 2010
+2
-0.6
A separately excited $$dc$$ machine is coupled to a $$50Hz,$$ three-phase, 4-pole induction machine as shown in the figure. The dc machine is energized first and the machines rotate at $$1600$$ $$rpm.$$ Subsequently the induction machine is also connected to a $$50Hz,$$ three-phase source, the phase sequence being consistent with the direction of rotation. In steady state
A
both machine act as generators
B
the $$dc$$ machine acts as a generator, and the induction machine acts as a motor
C
the $$dc$$ machine acts as a motor, and the induction machine acts as a generator
D
both machines act as motors
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