Indian Engineering Services (IES) Objective Questions and Answers:Machines1

Indian Engineering Services Objective Questions and Answers

1) Match the Following   ( IES- 2003)

      List I                                        List II 

A. Transformer                           1. Slip Test

B. DC Motor                               2. Blocked Rotor Test

C. Alternator                               3. Sumpner's Test

D. Induction Motor                      4. Swinburne's Test

Codes:

         A          B          C         D

a)      3           4          1         2

b)      4           3          2         1

c)      3           4          2         1

d)      4           3          1         2

2) Possible three to three phase transformer connection for parallel operation is: ( IES- 2002)

a) Delta-Star to Delta-Star

b) Delta-Delta to Delta-Star

c) Star-Star to Delta-Star

d) Delta-Star to Star-Delta

3) Stepper Motors are widely used for  ( IES- 2002)

a) Very high power requirement

b) Very high speed operation

c) Very low speed operation

d) Control system applications

4) Armature torque of a d.c motor is a function of which of the following factors ( IES- 2003)

1. Speed

2. Field Flux

3. Armature Current

4. Residual Magnetism

Select the correct answer

a) 2 and 3

b) 1 and 4

c) 3 and 4

d) 1 and 2

5) The dummy coils in the DC machine are useful to

a) Increase the efficiency of the machine

b) Improve the commutation

c) Reduce the armature reaction

d) Maintain mechanical balance

6) The synchronous reactance is the ( IES- 2003)

a) Reactance due to armature reaction of the machine

b) Reactance due to the leakage flux

c) Combined reactance due to leakage flux and armature reaction

d) Reactance either due to armature reaction or leakage flux

7) The crawling in the induction motor is due to  ( IES- 2003)

a) Improper design of the stator laminations

b) Low voltage supply

c) Improper design of rotor laminations

d) Harmonics developed in the motor

8) In an Induction motor, when the number of stator slots is equal to an integral multiple of rotor slots  ( IES- 2003)

a) There must be a discontinuity in the torque slip charcteristics

b) A high starting torque will be available

c) The maximum torque will be high

d) The machine may fail to start

Answers:

(1) a (2) a (3) d (4) a

(5) d (6) c (7) d (8) d

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Indian Engineering Services (IES) Objective Questions and Answers:Machines

1) A self excited d.c shunt generator, driven by its prime mover at the rated speed fails to build up the voltage across its terminals at no load. What reason can be assigned for this? (IES 2006)

a) The initial shunt field mmf does not assist the residual magnetism

b) The field circuit resistance is higher than the critical resistance

c) One of the inter-pole connection is removed

d) Brush axis slightly shift from the geometrical neutral axis of the machine

2) Wave winding is employed in a dc machine of: (IES 2006)

a) High current and low voltage rating

b) Low current and high voltage rating

c) High current and high voltage rating

d) Low current and low voltage rating

3) The resultant flux density in the air gap of a synchronous generator is the lowest during: (IES 2006)

a) Open circuit

b) Solid short circuit

c) Full load

d) Half load

4) If the load of an Induction motor is increased from no load to full load, its slip and the power factor will respectively (IES 2006)

a) decrease, decrease

b) decrease, increase

c) increase, decrease

d) increase, increase

5) A single phase Induction motor is running at N rpm. Its synchronous speed is Ns. If its slip with respect to forward field is 's', what is the slip with respect to the backward field is: (IES 2006)

a) s

b) -s

c) (1-s)

d) (2-s)

6)  Match the following: (IES 2003)

List I                                                List II

A. DC Motor                        1. Circle Diagram

B. DC Generator                  2. V-Curves

C. Alternator                        3. Open circuit characteristics

D. Induction Motor                4.Speed-Torque characteristics

Codes:

         A          B          C         D

a)      4           3          1         2

b)      3           4          2         1

c)      4           3          2         1

d)      3           4          1         2

7)  A smaller air gap in a polyphase induction motor helps to: (IES 2004)

a) reduces the chances of crawling

b) Increases the starting torque

c) reduces the chances of cogging

d) reduce the magnetising current

8) If the supply voltage of the induction motor is reduced by 10%. By what percentage approximately will the maximum torque decreases? (IES 2004)

a) 5%

b) 10%

c) 20%

d) 40%

 Answers:

(1) b (2) b (3) b (4) d

(5) d (6) c (7) d (8) c

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