Important MCQ on Electrical Machines - 7
Important multiple choice questions on Electrical
Machines
1.
To eliminate the single phasing
torque in an ac servomotor, the rotor must have
a)
Both high resistance and
reactance.
b)
High resistance.
c)
High reactance.
d)
Large air-gap
2.
If a single-winding
single-phase motor is running in a particular direction
a)
Both the rotating fields
(rotating in opposite directions) have the same strength.
b)
Forward rotating field is
slightly stronger than the backward field.
c)
Forward rotating field is much
stronger than the backward field.
d)
Backward
field is stronger than the forward field.
3.
A single-winding single phase
motor has
a)
Low starting torque
b)
Zero starting
torque
c)
High starting torque
d)
Starting torque equal to
full-load torque
4.
A single phase stator winding
when excited with ac voltage produces
a)
A single rotating field
rotating at synchronous speed
b)
Two rotating
fields rotating at synchronous speed in opposite directions
c)
Two rotating fields rotating in
the same direction at different speeds.
d)
Two rotating fields rotating in
opposite direction with different speeds.
5.
In a shaded-pole induction
motor, the rotor runs from
a)
Shaded portion to the unshaded
portion of the pole while the flux in the former leads that of the latter.
b)
Shaded portion to the unshaded
portion of the pole while the flux in the former lags that in the latter.
c)
Unshaded portion to the shaded
portion while the flux in the former leads that in the latter.
d)
Unshaded
portion to the shaded portion while the flux in the former lags that in the latter.
6.
An ideal synchronous motor has
no starting torque because the
a)
Rotor is made up of salient
poles
b)
Relative velocity between the
stator and the rotor mmf’s is zero
c)
Relative
velocity between stator and rotor mmf’s is not zero
d)
Rotor winding is highly reactive
7.
An induction motor having full
load torque at 60 Nm, when delta connected develops a starting torque of 120Nm.
For the same supply voltage, if the motor is change to star connection, the
starting torque developed will be
a)
40 Nm
b)
60 Nm
c)
90 Nm
d)
120 Nm
8.
The torque speed
characteristics of a repulsion motor resembles which of the following dc motor
characteristic?
a)
Separately excited
b)
Shunt
c)
Series
d)
Compound
9.
In a dc machine the angle
between the stator and rotor field is
a)
45 degrees
b)
90 degrees
c)
Depends upon the load
d)
180 degrees
10.
Open slots are used in dc
machine armature because
a)
Of the ease with which the
winding can be placed inside the slots
b)
It increases the induced emf
per coil
c)
It reduces the armature voltage
drop
d)
It reduces
the coil reactance emf and hence aids in commutation
Comments
a) Rotor is made up of salient poles
b) Relative velocity between the stator and the rotor mmf’s is zero
c) Relative velocity between stator and rotor mmf’s is not zero
d) Rotor winding is highly reactive
the correct answer id (b) not (c)