If an emf at slip frequency is injected at an angle with existing rotor induced emf, then the ___________

power factor improves and speed changes

power factor worsens and speed changes

A constant torque variable power drive of induction machine has ___________

variable air gap flux, constant slip

constant slip, constant air gap flux

If a 3-phase induction motor is fed from the rotor short circuiting the stator terminals, frequency of the current flowing in the short-circuited stator is?

frequency corresponding to the rotor speed

Torque-slip characteristic of an induction motor is linear in the smaller slip values, because ___________

rotor resistance is equal to stator resistance

effective rotor resistance is very large compared to reactance

rotor resistance is equal to stator resistance

rotor resistance is equal to rotor reactance

rotor reactance almost equal to stator reactance

For 3-phase induction motor, as load increases from no load towards the full load then the ___________

power factor increases till 40% load and then decreases

Due to the line to ground fault, phase a in the induction motor phase supply gets cut, then machine ___________

continues to run with reduced slip

continues to run with excessive supply current

continues to run with reduced slip

Choose from the below which can be obtained by the equivalent circuit of an electrical machine?

Temperature coefficients of the machine components

Complete performance characteristics of the machine

Temperature coefficients of the machine components

Type of protection to be used in the machine

Design parameters of the windings

A 3-phase slip ring IM is has its copper bars replaced by the aluminium bars in the machine. With the above change ___________

starting torque increases, maximum torque remains same, smT remains same

starting torque increases, maximum torque remains same, smT increase

starting torque increases, maximum torque remains same, smT remains same

starting torque increases, maximum torque remains increases, smT increase

starting torque decreases, maximum torque remains same, smT decrease

A 3-phase induction motor is fed at the stator at a frequency f. If the rotor speed is Nr and synchronous speed is Ns, then the absolute speed of the resultant flux in space is?

(Ns+Nr) if the flux rotates in the same same direction as the rotor

(Ns-Nr) if the flux rotates in the same same direction as the rotor

12 + Mcqs in Starting of Polyphase Induction Motors-II in Electrical Machines Page 1 McqOptions

1.	If an emf at slip frequency is injected at an angle with existing rotor induced emf, then the ___________
A.	power factor only improves
B.	speed changes
C.	power factor improves and speed changes
D.	power factor worsens and speed changes
Answer» B. speed changes

Discussion

2.	A constant torque variable power drive of induction machine has ___________
A.	constant air gap flux.
B.	constant slip
C.	variable air gap flux, constant slip
D.	constant slip, constant air gap flux
Answer» E.

Discussion

3.	If a 3-phase induction motor is fed from the rotor short circuiting the stator terminals, frequency of the current flowing in the short-circuited stator is?
A.	slip frequency
B.	supply frequency
C.	zero
D.	frequency corresponding to the rotor speed
Answer» B. supply frequency

Discussion

4.	Torque-slip characteristic of an induction motor is linear in the smaller slip values, because ___________
A.	effective rotor resistance is very large compared to reactance
B.	rotor resistance is equal to stator resistance
C.	rotor resistance is equal to rotor reactance
D.	rotor reactance almost equal to stator reactance
Answer» B. rotor resistance is equal to stator resistance

Discussion

5.	For 3-phase induction motor, as load increases from no load towards the full load then the ___________
A.	power factor improves
B.	power factor remains same
C.	power factor varies linearly
D.	power factor increases till 40% load and then decreases
Answer» B. power factor remains same

Discussion

6.	Due to the line to ground fault, phase a in the induction motor phase supply gets cut, then machine ___________
A.	continues to run with excessive supply current
B.	continues to run with reduced slip
C.	stalls
D.	all of the mentioned
Answer» B. continues to run with reduced slip

Discussion

7.	If one of the supply fuses blows off and gets open circuited, then for the connected induction machine continues to run with increased slip.
A.	True
B.	False
Answer» B. False

Discussion

8.	Choose from the below which can be obtained by the equivalent circuit of an electrical machine?
A.	Complete performance characteristics of the machine
B.	Temperature coefficients of the machine components
C.	Type of protection to be used in the machine
D.	Design parameters of the windings
Answer» B. Temperature coefficients of the machine components

Discussion

9.	A center ammeter connected to the rotor end circuit of a 6-pole,50 Hz, induction motor makes 45 complete oscillations in a minute. Then the rotor speed and the speed of stator field w.r.t. rotor is?
A.	985, 15
B.	970, 1000
C.	985, 985
D.	985, 970
Answer» B. 970, 1000

Discussion

10.	A 3-phase slip ring IM is has its copper bars changed by the aluminium bars in the machine. With the above change ___________
A.	starting torque remains same
B.	starting torque increase
C.	starting torque decrease
D.	maximum torque increase
Answer» B. starting torque increase

Discussion

11.	A 3-phase slip ring IM is has its copper bars replaced by the aluminium bars in the machine. With the above change ___________
A.	starting torque increases, maximum torque remains same, smT increase
B.	starting torque increases, maximum torque remains same, smT remains same
C.	starting torque increases, maximum torque remains increases, smT increase
D.	starting torque decreases, maximum torque remains same, smT decrease
Answer» B. starting torque increases, maximum torque remains same, smT remains same

Discussion

12.	A 3-phase induction motor is fed at the stator at a frequency f. If the rotor speed is Nr and synchronous speed is Ns, then the absolute speed of the resultant flux in space is?
A.	Ns
B.	(Ns+Nr) if the flux rotates in the same same direction as the rotor
C.	(Ns-Nr) if the flux rotates in the same same direction as the rotor
D.	Nr
Answer» B. (Ns+Nr) if the flux rotates in the same same direction as the rotor

Discussion

Explore topic-wise MCQs in Electrical Machines.

If an emf at slip frequency is injected at an angle with existing rotor induced emf, then the ___________

A constant torque variable power drive of induction machine has ___________

If a 3-phase induction motor is fed from the rotor short circuiting the stator terminals, frequency of the current flowing in the short-circuited stator is?

Torque-slip characteristic of an induction motor is linear in the smaller slip values, because ___________

For 3-phase induction motor, as load increases from no load towards the full load then the ___________

Due to the line to ground fault, phase a in the induction motor phase supply gets cut, then machine ___________

If one of the supply fuses blows off and gets open circuited, then for the connected induction machine continues to run with increased slip.

Choose from the below which can be obtained by the equivalent circuit of an electrical machine?

A center ammeter connected to the rotor end circuit of a 6-pole,50 Hz, induction motor makes 45 complete oscillations in a minute. Then the rotor speed and the speed of stator field w.r.t. rotor is?

A 3-phase slip ring IM is has its copper bars changed by the aluminium bars in the machine. With the above change ___________

A 3-phase slip ring IM is has its copper bars replaced by the aluminium bars in the machine. With the above change ___________

A 3-phase induction motor is fed at the stator at a frequency f. If the rotor speed is Nr and synchronous speed is Ns, then the absolute speed of the resultant flux in space is?