WorksheetsDC Drives
Total questions: 17
Worksheet time: 9mins
. In a separately excited dc motor, constant horsepower control of speed is achieved by variation and constant torque control by variation
armature current, armature voltage
field current, armature voltage
field voltage, field current
armature voltage, field current
. In the armature control method, if the applied armature voltage Va is decreased
by a large amount, then the motor.
speed gets reduced
gets overloaded
is constrained to work as a generator
quickly comes to a standstill
During the discontinuous conduction mode of a drive with armature control
using a single-phase converter, the reduction in ωm for an increase in Ia will be
that for the continuous mode.
more than
equal to
less than
independent of
An inner current control loop along with an outer speed loop gives response for a change in the ac supply voltage as compared to a simple speed control loop
slower
the same
quicker
much slower
In a closed-loop drive with four-quadrant operation, the master controller performs the function of and the slave controller helps in.
smooth changeover of conduction from one rectifier to the other, switching the appropriate rectifier into conduction
smooth changeover of conduction from one rectifier to the other, sudden changeover of conduction from one rectifier to other
sudden changeover of conduction from one rectifier to the other, smooth changeover of conduction from one rectifier to the other
switching the appropriate rectifier into conduction, smooth changeover of conduction from one rectifier to the other
For a dc motor, the region of discontinuous conduction in the speed–torque plane is with chopper control than that with rectifier control
greater
much lesser
lesser
much greater
Regenerative braking of a separately excited dc motor using dc chopper control gives that using rectifier control.
better performance than
inferior performance than
the same performance as
much inferior performance as compared to
In a speed control system incorporating an outer speed loop and an inner current loop, the drive response becomes sluggish in the discontinuous conduction mode because.
the field response is slower than that with continuous conduction
the output of the speed controller is smaller than that in continuous conduction
the combined gain of the firing circuitry and the rectifier is smaller than that with continuous conduction
the combined gain of the firing circuitry and the rectifier is larger than that with continuous conduction
During the regenerative braking operation of a chopper-based dc drive, energy
transfer takes place.
from the load at high voltage to the source at low voltage
from the source at high voltage to the load at low voltage
from the source at low voltage to the load at high voltage
from the load at low voltage to the source at high voltage
Dc drives that use series motors are more advantageous than drives that employ separately excited motors because they facilitate .
high starting torque
frequent starting
frequent torque overloads
all of the above
In a dc drive supplied by a single-phase ac source and a rectifier, discontinuous conduction can be avoided by .
decreasing the frequency of the ac supply
adding a capacitor in series with the armature of the dc motor
increasing the frequency of the ac supply
adding an inductor in series with the armature of the dc motor.
A three-phase, full-wave controlled rectifier feeds a separately excited dc motor. The data are Td = 140 Nm, Ia = 60 A, and ωm = 65 rad/s. With these data, the back emf of the motor will be nearly V.
102
178
152
194
A three-phase, full-wave controlled rectifier feeds a separately excited dc motor and the data are Eb = 150 V, ωm = 75 rad/s, and Ia = 56 A. With these data, the torque of the motor will be Nm.
168
108
184
112
A dc drive consisting of a three-phase, full-wave controlled rectifier together
with a separately excited dc motor has the following data: Ra = 0.2 ohm, Kbφf = 0.8.With these data the slope of the speed–torque curve will be nearly rad/Nm s.
-0.31
-0.48
-0.36
-0.27
A dc drive consisting of a three-phase, full-wave controlled rectifier together
with a separately excited dc motor has the following data: Va = 160 V, Kbφf = 0.75. With these data the intercept of the speed–torque curve on the ω-axis will be nearly rad/s.
254
213
198
176
In a separately excited dc motor, constant horsepower control of speed is achieved by armature voltage variation and constant torque control by field current variation.
True
False
During the speed control of a dc motor by armature control, if there is a large decrease in the applied armature voltage Va, then the motor will be constrained to work as a generator.
True
False
