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

Question 1

It is advisable to use auto-transformer if the transformation ratio is

Question 2

Assertion (A) : In a d.c. generator even though the armature magnetic field is in quadrature with the main magnetic field each considered alone the resultant magnetic field due to interaction of both the fields is shifted backwards by certain angle from the geometrical neutral axis depending upon the load.
Reason (R) : In a d.c. generator, the trailing pole tips get magnetically saturated as the load reaches its rated value

Question 3

It the armature current is increased to double its previous value and the time of commulation is halved, how will the teactance voltage vary?

Question 4

Neglecting all losses how is the developed torque (T) of a dc separately excited motor operating under constant terminal voltage, related to its output power (P)?

Question 5

A 4-pole, separately excited, wave wound DC machine with negligible armature resistance is rated for 230 V and 5 kW at a speed of 1200 rpm. If the same armature coils are reconnected to form a lap winding, what is the rated voltage (in volts) and power (in kW) respectively at 1200 rpm of the reconnected machine if the field circuit is left unchanged?

Question 6

Which one of the following curves represents the speed-torque characteristic of a d.c. series motor?

Question 7

Which one of the following statements is correct for the ideal field excitation during starting in case of shunt and compound motors?

Question 8

Consider the following statements :
In the figure below, the curves pertain to the dc motor.

1) Speed Vs armature-current characteristic of a dc shout.
2) Torque Vs armature-current charac- teristic of dc shunt motor
3) Speed Vs armature current characteristic of dc series motor
4) Torque Vs armature-current charac- teristic of dc series motor.
What is the correct sequence of characteristics?

Question 9

A separately excited dc motor is started using a 4-phase ac/dc controlled rectifier using 'Soft starting'. For limiting the starting current, it is required that firing angle should be

Question 10

The speed of a dc motor is related to the back emf and flux in the following ways:

Question 11

A capacitor-start single-phase induction motor is used for:

Question 12

Which one of the following is the type of single phase induction motor having the highest power factor at full load?

Question 13

A single phase induction motor is running at N rpm. Its synchronous speed is N_s. If its slip with respect to forward field is s, what is the slip with respect to the backward field?

Question 14

Match List-I with List-II and select the correct answer using the code given below the lists:
List-I
A) General purpose split phase FHP motor
B) General purpose capacitor start FHP motor
C) Permanent split capacitor start FHP motor
D) Shaded pole FHP motor
List-II
1) Refrigerators
2) Hair dryers
3) Unit heaters
4) Fans, blowers

Question 15

For a given applied voltage and current, the speed of a universal motor will be

Question 16

A 4 KVA, 400 V/200 V single phase transformer has resistance of 0.02 p.u. and reactance of 0.06 p.u. The resistance and reactance referred to high voltage side are:

Question 17

Conditions for parallel operation of transformer are:
1) The same voltage ratio
2) The same per unit impedance
3) The same polarity
4) The same phase sequence
5) The relative phase displacement
Which are the absolutely essential conditions?

Question 18

If the percentage impedance of the two transformers working in parallel are different then

Question 19

Three single phase 11000/220 V trans-formers are connected to form 3-phase transformer bank. High voltage side is connected in star, and low voltage side is in delta. What are the voltage ratings and turn ratio of 3-phase transformer?

Question 20

Match List-I (Test) with List-II (Quantities) and select the correct answer using the code given below the lists:
List-I
A. O.C. Test
B. S C Test
C. Sumpner’s Test
D. Load Test
List-II
1) Copper loss and iron loss
2) Total losses
3) Iron loss
4) Copper loss

Question 21

1. Statement (I): Large power transformer testing under full load current is not possible.
Statement (II): Short circuit test of transformer gives indication of copper loss.

Question 22

The voltage regulation of a transformer having 2% resistance and 5% reactance, at full load, 0.8 pf lagging is

Question 23

In a transformer, if the iron losses and copper losses are 40.5 kW and 50 kW respectively. Then at what fraction of load will be efficiency be maximum?

Question 24

Which three-phase connection can be used in a transformer to introduce a phase difference of 30^o between its output and corresponding input line voltages?

Question 25

When one transformer is removed from a bank of 30 kVA transformer, the capacity of the resulting 3-phase trans-former corresponding input line voltages?

Question 26

The full-load copper loss and iron loss of a transformer are 6400 W and 5000 W, respectively. What are the above copper loss and iron loss, respectively at half-load?

Question 27

When are eddy-current losses in a transformer reduced?

Question 28

Match List-I (DC machine quantity) with List-II (Relation) and select the correct answer using the code given below the lists :

Question 29

The armature MMF waveform of a dc machine is

Question 30

A dc motor operated from a type A chopper is switched to type B chopper. How does the motor operate when type A and B are in operation respectively?