GATE EE : Electrical Machines National Champion Test for ESE & GATE EE Exams

Question 1

In a stepper motor, the detent torque means

Question 2

In case of an armature controlled separately excited dc motor drive with closed loop speed control, an inner current loop is useful because it

Question 3

How many 200W/220V incandescent lamps connected in series would consume the same total power as a single 100W/220V incandescent lamp?

Question 4

In a DC machine, which of the following statements is true?

Question 5

The speed/torque regimes in a dc motor and the control methods suitable for the same are given respectively in Group II and Group I

Question 6

A dc series motor fed from rated supply voltage is overloaded and its magnetic circuit is saturated. The torque-speed characteristic of this motor will be approximately represented by which curve of the following figure?
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Question 7

For a given stepper motor, the following torque has the highest numerical value.

Question 8

The following motor definitely has a permanent magnet rotor

Question 9

The condition for maximum efficiency of transformer

Question 10

A 240 V/120 V, 12 kVA auto-transformer has 96.2% efficiency at full-load and unity power-factor. The full-load efficiency at 0.85 pf lagging when connected to a load across 360V would be

Question 11

A 50 kW synchronous motor is tested by driving it by another motor. When the excitation is not switched on, the driving motor takes 800W. When the armature is short-circuited and the rated armature current of 10 A is passed through it, the driving motor requires 2500 W. On open-circuiting the armature with rated excitation, the driving motor takes 1800W. Calculate the efficiency of the synchronous motor at full load. Neglect the losses in the driving motor.

Question 12

The figure above shows coils 1 and 2, with dot markings as shown, having 4000 and 6000 turns respectively. Both the coils have a rated current of 25 A coil 1 is excited with single phase, 400V, 50 Hz supply.

The coils are to be connected to obtain a single phase, 400/1000 V, auto-transformer to drive a load of 10kVA. Which of the options given should be exercised to realize the required auto-transformer?

Question 13

The figure above shows coils 1 and 2, with dot markings as shown, having 4000 and 6000 turns respectively. Both the coils have a rated current of 25 A coil 1 is excited with single phase, 400V, 50 Hz supply.

In the autotransformer obtained in Question 57, The current in each coil is

Question 14

Transformer is a device which transforms __________ at one level to ___________ at required higher/lower/same level.

Question 15

Which one of the following is the correct statement?
In a 3-phase induction motor, the resultant flux is of a constant nature and is

Question 16

In a split phase motor, the running winding should have

Question 17

A 3-phase 50 Hz square wave (6-step) VSI feeds a 3-phase, 4 pole induction motor. The VSI line voltage has a dominant 5^th harmonic component. If the operating slip of the motor with respect to fundamental component voltage is 0.04, the slip of the motor with respect to 5^th harmonic component of voltage is _____.

Question 18

The figure shows the per-phase equivalent circuit of a two-pole three-phase induction motor operating at 50 Hz. The “air-gap” voltage across the magnetizing inductance, is 210 V rms and the slip, s, is 0.05. The torque (in Nm) produced by the motor is ________.

Question 19

The speed of a 4-pole induction motor is controlled by varying the supply frequency while maintaining the ratio of supply voltage to supply frequency (V/f) constant. At rated frequency of 50 Hz and rated voltage of 400 V its speed is 1440 rpm. Find the speed at 30 Hz, if the load torque is constant.

Question 20

Which of the points on the torque-speed curve of the induction motor represents operation at a slip greater than 1?

Question 21

The required load torque line intersects the resultant torque-speed characteristic of a 3-

squirrel cage induction motor as points P, Q and R as shown in the figure below. Which is/are the stable operating point (s)?

Question 22

When the applied rated voltage per phase is reduced to one half, the starting torque of a three-phase squirrel cage induction motor becomes

Question 23

A wound rotor induction motor runs with a slip of 0.03 when developing full load torque. Its rotor resistance is 0.25 ohm per phase. If an external resistance of 0.50 ohm per phase is connected across the slip rings. What is the slip for full torque?

Question 24

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,

Question 25

Consider the following statements:
Skewing of rotor slots in a 3-phase induction motor (cage rotor) may
1) introduce additional leakage reactance
2) eliminate slot harmonies
Which of these statements is/are correct?

Question 26

What is the operating slip of a 400 V, 50 Hz, 6-pole, 3-phase induction motor, while the speed is 936 r.p.m. with a 400 V, 48 Hz, 3-phase supply?

Question 27

Which of the following parameters in an induction motor influences the magnetizing reactance to the maximum extent?

Question 28

Under no load condition, if the applied voltage to an induction motor is reduced from the rated voltage to half the rated value,

Question 29

The direct axis and quadrature axis reactances of a salient pole alternator are 1.2 p.u and 1.0 p.u respectively. The armature resistance is negligible. If this alternator is delivering rated kVA at up of and at rated voltage then its power angle is

Question 30

A synchronous generator is feeding a zero power factor (lagging) load at rated current. The armature reaction is