Electrical Drives And Controls Set 1 MCQs

Q1 | Which motor is preferred for Jaw crushers?

wrim
scim
belt slip ring im
dc shunt motor

Answer: belt slip ring im

Explaination:
belt slip ring im is preferred for the operation of jaw crushers. a high starting is provided by the belt ring im. slip rings are used to add external resistance.

Q2 | A high starting torque is offered by the Belt Conveyors.

true
false

Answer: true

Explaination:
the belt conveyors can provide continuous-flow transportation. the amount of material transported on a conveyor system depends upon belt speed, belt width.

Q3 | Which starting method is the worst method in Induction motor?

direct online starting
autotransformer starting
reactance starting
star-delta starting

Answer: reactance starting

Explaination:
the reactance starting method is the worst method in an induction motor. it uses the concept of the potential divider. the losses are very high in case of reactance starting method.

Q4 | Explanation: Intermittent duty cycle has frequent on load and off-loads period. The on-load period and off-loads periods are too

frequency changer
frequency remover
time period remover
dc machine

Answer: frequency changer

Explaination:
the induction motor is also known as frequency changer. the stator frequency can be changed using the slip concept. the rotor frequency of im is slip×(stator frequency).

Q5 | The capacity of the Crane is expressed in terms of tonnes.

true
false

Answer: true

Explaination:
cranes are used to carry or lift the heavy loads. the capacity of a crane is expressed in terms of tonnes. 1 tonne is equal to 1000 kg.

Q6 | 1800 second rated motors are used for

heavy duty cranes
light duty cranes
medium duty cranes
intermittent duty cranes

Answer: medium duty cranes

Explaination:
medium duty crane motor is used to develop high starting torque. they provide the output for a specified interval of time without exceeding a specified temperature.

Q7 | Calculate the frequency of the rotor side of the IM if the value of slip is 0.34 and the supply frequency is 70 Hz.

23.8 hz
22.7 hz
24.5 hz
23.1 hz

Answer: 23.8 hz

Explaination:
the frequency of the rotor side is low as compared to supply frequency. the rotor frequency is slip×(supply frequency)=.34×70=23.8 hz.

Q8 | frequency is 2 Hz.

50 hz
49 hz
45 hz
51 hz

Answer: 50 hz

Explaination:
the frequency of the stator side is high as compared to the rotor side. the stator frequency is (rotor frequency) ÷ slip = 2÷.04 = 50 hz.

Q9 | values of the capacitor and inductor are 4 F and 4 H.

.25 rad/sec
.26 rad/sec
.28 rad/sec
.29 rad/sec

Answer: .25 rad/sec

Explaination:
during resonance condition xl=xc. the value of the resonant frequency is 1÷√lc=1÷√16=.25 rad/sec. the voltage across the capacitor and inductor becomes equal.

Q10 | Calculate the value of the angular acceleration of the Heavy duty crane using the given data: J = 5 kg-m2, load torque = 30 N-m, motor torque = 80 N-m.

10 rad/s2
20 rad/s2
30 rad/s2
50 rad/s2

Answer: 10 rad/s2

Explaination:
using the dynamic equation of motor j×(angular acceleration) = motor torque – load torque: 5×(angular acceleration) = 80-30=50, angular acceleration=10 rad/s2.

Q11 | motor torque = 2 N-m.

45 rad/s2
the machine will fail to start
30 rad/s2
51 rad/s2

Answer: the machine will fail to start

Explaination:
using the dynamic equation of motor j×(angular acceleration) = motor torque – load torque: .541×(angular acceleration) = 2-10=-8, angular acceleration=-14.78 rad/s2. the load torque is greater than the motor torque. the motor will fail to start.

Q12 | The direction of the single-phase IM can be reversed by using which one of the method?

by interchanging the supply terminals
by removing the capacitor
by changing the direction of auxiliary winding current
by removing the main winding

Answer: by interchanging the supply terminals

Explaination:
the direction of the single- phase im can be reversed by changing the direction of auxiliary winding or main winding current.the net torque developed in the im is imiasin(Φ).

Q13 | Which motor is preferred for overhead traveling cranes?

intermittent periodic motor
continuous duty motor
slow speed duty motor
short time rated motor

Answer: intermittent periodic motor

Explaination:
intermittent periodic motor is preferred for overhead traveling cranes.

Q14 | conditions where electric motors are being used?

thermography
geography
seismography
anthropology

Answer: thermography

Explaination:
thermography is used to detect heat patterns. it uses an infrared rays camera. this test is used to determine the conditions where electric motors are being used.

Q15 | What is the range of size of the motor (kW) for efficiency nearly equals to 90%?

15-150
0-2
3-15
150-250

Answer: 15-150

Explaination:
as the size of the motor increases its speed decreases. the range of size of the motor (kw) for efficiency nearly equals to 90 % is 15-150. the efficiency increases as the size increases.

Q16 | Calculate the heat loss in the electric motor for time interval 0-5 sec using the following data: Ia=2 A, Ra=.8Ω.

16 j-sec
14 j-sec
12 j-sec
10 j-sec

Answer: 16 j-sec

Explaination:
the heat loss can be calculated using the joule law of heating effect. the

Q17 | sec.

.641
.334
.293
.417

Answer: .293

Explaination:
one british thermal unit is equal to .293 watt. 1 btu/h is the amount of energy requires to increase the temperature of one pound of water by 1℉.

Q18 | Overloading can be prevented using

over-current protection
speed protection
over frequency protection
oversize protection

Answer: over-current protection

Explaination:
overloading can be prevented using over-current protection. it will detect the over-current and interrupt the supply.

Q19 | Full form of IDMT is

inverse definite minimum time
inverter definite minimum time
inverter definite maximum time
insert definite minimum time

Answer: inverse definite minimum time

Explaination:
idmt stands for inverse definite minimum time over-current relay. it has both the characteristics of inverse over- current and definite time over-current relay.

Q20 | The most common cause of motor failure is

overloading
low resistance
contamination
over-heating

Answer: low resistance

Explaination:
the most common cause of motor failure is low resistance. overheating, corrosion can damage the insulation of the windings which leads to low resistance.

Q21 | Full form of THD is

total harmonic diverter
total harmonic digital
total harmonic distortion
total harmonic discrete

Answer: total harmonic distortion

Explaination:
thd stands for total harmonic distortion. it measures the harmonic distortion in the signal. according to ieee-1992, only 5% of thd is valid.

Q22 | Calculate the compensator rating required for a sec(Φ)=1.

0.64 p.u
0.21 p.u
0.57 p.u
0 p.u

Answer: 0 p.u

Explaination:
the compensator rating can be calculated using the relation qp.u=√1-

Q23 | Calculate the value of Voltage ripple factor if the Form factor is 1.1.

45.8 %
46.2 %
47.5 %
49.9 %

Answer: 45.8 %

Explaination:
voltage ripple factor measures the harmonics on the dc side of the converter. the value of voltage ripple factor is √f.f2-1=45.8 %. the form factor is vr.m.s÷vavg.

Q24 | Calculate the value of THD if the

76 %
75 %
74 %
73 %

Answer: 75 %

Explaination:
thd measures the harmonics distortion in the signal. the value of thd is

Q25 | Full form of VRF.

voltage ripple factor
voltage revert factor
volume ripple factor
volume revert factor

Answer: voltage ripple factor

Explaination:
voltage ripple factor measures the harmonics on the dc side of the converter. the value of voltage ripple factor is √f.f2-1. the form factor is vr.m.s÷vavg.