WorksheetsIV SEM 23198 EE-402 ELECTRICAL MACHINES-II
Total questions: 42
Worksheet time: 21mins
What is the relationship between speed, frequency, slip and poles?
(a)
At standstill, what is the value of slip of a induction motor?
1
0
0.01
5%
What is the following ratio in terms of slip? P2:Pc:Pm=?
1:1-s:s
1:s:1-s
s:1:1-s
s:1-s:1
What is the condition for maximum torque?
(a)
rotor efficiency in terms of slip?
s
1
0
1-s
The speed of Induction motor is .....
equal to synchronous speed
independent of synchronous speed
less than synchronous speed
greater than synchronous speed
Which of the following motors are not self-starting?
Synchronous motor
3-ph Induction motor
1-ph induction motor
DC shunt motor
What is the direction of rotation of a shaded pole motor?
shaded part to unshaded part of the pole
unshaded part to shaded part of the pole
Phase to neutral
Neutral to phase
Which of the following is most suited for traction purposes?
DC shunt motor
DC series motor
DC compound motor
None of the above
Load angle is the angle between....
Back emf and armature current
Back emf and resultant emf
resultant emf and applied voltage
back emf and applied voltage
Which of the following is used for power factor correction?
Alternator
DC motor
Synchronous motor
Any of the above
Back emf in a synchronous motor depends on .....
excitation but not speed
speed but not excitation
neither speed nor excitation
both speed and excitation
V curve is plotted between.....
armature current and power factor
armature current and field current
power factor and field current
power factor and back emf
In a DC generator, field is on ..... and armature is on .....
stator and rotor
rotor and stator
both on rotor
both on stator
The exciter of an alternator is actually a .....
DC generator
AC generator
DC motor
AC motor
What is the distribution factor of a concentrated winding?
0
negative
1
2
The armature reaction for unity power factor is .....
demagnetising
cross-magnetising
magnetising
no effect
The process of connecting an alternator in parallel with another alternator or with common busbar is called (a)
In bright and dark lamp method, synchronization is done when _____
one lamp is dark and one lamp is bright
two lamps are dark and one lamp is bright
two lamps are bright and one lamp is dark
all lamps are dark
If the power factor of an alternator is zero lagging, the armature reaction is _____
cross magnetising
inductive
Alternators in general have _____
Stationary armature and revolving field system
stationary field system and revolving armature
stationary armature and stationary field system
revolving armature and revolving field system
If an alternator has 12 poles and produces 60 Hz frequency, what is its speed?
500 rpm
1500 rpm
1000 rpm
600 rpm
Number of slip rings used in a 3-ph alternator are _____
3
6
2
0
For proper parallel operation, the 3-ph alternators must have the same _____
speed
voltage rating
KVA rating
excitation
The load sharing between two alternators can be changed by varying the _____
field current
power factor of the alternator
mechanical input to the alternator
speed of the alternator
In a 3-ph slip ring induction motor, brushes are connected to _____
external star connected resistor
dc supply
3-ph ac supply
equalising coils
The operation of an induction motor is based on _____
lenz's law
ampere's law
principle of mutual induction
principle of self-induciton
The torque developed by an induction motor depends upon _____
rotor resistance
rotor emf
slip
all the above
The speed of a squirrel cage induction motor can be changed by _____
pole changing
rotor resistance control
cascade control
none of the above
In a split phase induction motor, auxiliary winding should have _____
high resistance and low reactance
high reactance and low resistance
high resistance and high reactance
low resistance and low reactance
in a split phase motor _____
the starting winding is connected through a centrifugal switch
the running winding is connected through a centrifugal switch
the starting and running windings are connected through a centrifugal switch
the starting and running windings are connected permanently in the machine
The power factor of an induction motor is usually _____
lagging
leading
unity
can't say
Which of the following motors is generally used in toys?
DC shunt motor
universal motor
shaded pole motor
capacitor motor
If synchronous reactance increases, the size of the alternator _____
increases
decreases
remains constant
can't say
cylindrical pole type rotors are generally used with prime movers of _____
medium speed
low speed
high speed
any speed
the power factor of an alternator depends upon _____
speed
excitation
losses
type of load
an alternator will have emf closer to sine waveform when it has _____
distributed winding in full pitch coils
distributed winding in short pitch coils
concentrated winding in full pitch coils
concentrated winding in short pitch coils
an infinite busbar has _____
constant voltage
constant frequency
constant speed
both a and b
stator and rotor fields rotate simultaneously and together in _____
synchronous generator
synchronous motor
alternator
DC motor
when a synchronous motor is rotating at synchronous speed, damper winding produces _____
high torque
low torque
no torque
medium torque
direction of rotation of a 3-ph system can be reversed by reversing _____
pole polarity
field current
none of these
phase sequence
the armature current of a synchronous motor is high for _____
lagging pf
leading pf
upf
lagging and leading pfs
