Electrical Drives And Controls Set 5 MCQs

Q1 | The effect of fringing increases as we

increase air gap

decrease air gap

increase in flux density

introduce more ferric core material

Q2 | is

main field distortion

shift in mna

reduction in main field

none of the mentioned

Q3 | If the students give a forward shift of 10° to the dc generator, then it

reduces flux per pole

improves flux per pole

increases the flux density in core

none of the mentioned

Q4 | A dc machine is run at rated speed in forward direction and then in backward direction. It is observed that, speeds of the rotation are different, then it leads to the conclusion of

incorrect brush placement

incorrect pole and core alignment

incorrect field supply

all of the mentioned

Q5 | For a dc machine, its commutator has a diameter of 50 c rotating at 1000 rpm. For a brush width of 1 cm, the time commutation taken by the machine will be

0.382 ms

0.456 ms

0.573 ms

0.312 ms

Q6 | An induction motor can be said analogous to

transformer

synchronous motor

universal motor

stepper motor

Q7 | A 3-phase induction motor with its rotor blocked behaves similar to a

transformer under short circuit of secondary terminals

transformer under open circuit of secondary

synchronous motor under slip test

synchronous motor under open circuit

Q8 | No load current in induction motor is 10- 20% of full load current and the no load current of transformer is 2-6%.

true

false

Q9 | no load estimated current for the machine?

12 a

20 a

30 a

5 a

Q10 | The no load current of the transformer is very less due to

mutual flux having low reluctance iron core

mutual flux having high reluctance iron core

leakage flux having low reluctance iron core

leakage flux having high reluctance iron core

Q11 | The no load current of the induction motor is high due to

long and high reluctance path between stator and rotor

mutual flux having moderate reluctance path between stator and rotor

leakage flux having low reluctance iron core

leakage flux having high reluctance iron core

Q12 | At no load induction motor has possible power factor as

0.2

0.5

0.65

Q13 | Mechanically air gaps in induction motor are kept very low to avoid

lower power factor

lagging nature

magnetizing current

all of the mentioned

Q14 | The low no load power factor

reduces full load operating pf

increases full load operating pf

reduces full load excitation voltage

increases full load excitation voltage

Q15 | An induction motor when started on load, it does not accelerate up to full speed but runs at 1/7th of the rated speed. The motor is said to be

locking

plumming

crawling

cogging

Q16 | The great advantage of the double squirrel-cage induction motor over single cage rotor is that its

efficiency is higher

power factor is higher

slip is larger

starting current is lower

Q17 | The rotor of 3-phase slip ring induction motor is fed from a 3-phase supply with its stator winding short circuited having rotor rotating clockwise at a speed of Nr, then the

speed of air gap field w.r.t. stator is ns-nr anticlockwise

speed of air gap field w.r.t. stator is ns-nr clockwise

speed of airgap field w.r.t rotor is ns clockwise

speed of airgap field w.r.t. stator is ns-nr clockwise

Q18 | (II) If a large 3–phase squirrel-cage induction motor with no load is started at full voltage, it will be damaged.

i is true, ii is false

i is true and ii is also true

i is false, ii is true

i and ii are false

Q19 | The PWM control of DC motor varies

linearly with speed

inversely with speed

parabolically with speed

exponentially with speed

Q20 | Ward-Leonard system of system of speed control is not recommended for

constant speed operation

wide speed

frequent-motor reversed

very slow speed

Q21 | Mark the wrong option. Which of the following cause and effect behaviour in speed control is correct when field resistance is increased.

decrease in flux

increase in armature current

increase in emf

decrease in speed

Q22 | resistance will

decrease the speed of motor

increase the speed of motor

not have signicant effect on speed

no effect

Q23 | by

armature voltage control

field resistance control

any of the methods

none of the mentioned

Q24 | must be ensured that

it is used on separately excited machine

it is used on shunt machine

it is used on series machine

any of the mentioned machine

Q25 | works well for speed

below, above

above, below

base speed.