26 practice sets · Page 1 of 2
While operating on variable frequency supplies, the AC motor requires variable voltage in order to
improve the capabilities of the inverter
protect the insulation
avoid effect of saturation
protect thyristor from dV / dt
Which speed control method preferred for constant torque drive?
Mechanical loading system
Field control
Armature voltage control
None of these
Which of the following are electrical braking methods ?
regenerative
plugging
dynamic
All of the above
Which braking is not possible in series motor?
Counter current braking
Regenerative braking
Dynamic braking
Rheostat braking
What type electric drive is used in cranes?
Individual
Multimotor
Group
Both A and C
What are the constituents in speed time curve of train?
Constant speed
Coasting
Initial acceleration
All of the above
The slip of an induction motor during DC rheostatic braking is
2 + s
2 - s
1 - s
s
The power input to a 3 - F induction motor is 60 kW and stator loss is 1 kW the rotor cu loss per phase is
slip × 69 / 3
slip × 50 / 3
slip × 59 / 3
1
The heating time constant of an electrical machine gives an induction of its
overload capacity
rating
cooling
short time rating
The concept of V/f control of inverters driving induction motors resuls in
reduced magnetic loss
constant torque operation
speed reversal
hormonic elimination
The basic elements of a electric drive are
electrical motor and control system
electric motor
control system
None of these
Speed control by variation of field flux results in
variable power drive
constant power drive
constant torque drive
None of these
Polarity of supply voltage is reversed in which type of braking?
Plugging
Regenerative braking.
Dynamic braking
None of these
In which braking back emf exceeds supply voltage?
Plugging
Regenerative
Dynamic
None of these
In industries which electrical braking is preferred?
Dynamic braking
Regenerative braking
Plugging
None of these
In case of kiln drives, starting torque is
almost equal to running torque
more than double of the running torque
more than triple of the running torque
less than running torque
In 4 quadrant operation of a hoist 3rd quadrant represents
forward braking
reverse motoring
reverse braking
forward motoring
High braking torque produced in
regenerative braking
plugging
dynamic braking
None of these
Full form of VVVF control
variable VAr voltage frequency
variable voltage VAr frequency
VAr variable voltage frequency
variable voltage variable frequency
For an IM to operate in braking region slip should be always
is equal to 1
less than zero
greater than 1
None of these
