Question

A separate excited DC motor is running at 1000 rpm when the
armature voltage is 600 V. The motor has a field constant Kphi = 4
V.sec and the armature resistance of the motor is 0.8 Ohms.

i. Calculate the value of the resistance of the dynamic braking at
full load. The armature current should be limited to 200 % of the
rated value.

ii. If the motor operates in regenerative braking at a speed of
1200 rpm, calculate the armature current.

iii. If the terminal voltage is reversed and reduced to 90 V, calculate the steady-state speed of the motor.

iv. Calculate the terminal voltage required to block (stop) the rotor. v. Sketch the speed-torque characteristics and show all operating conditions.

Answer #1

A 230 V, 250 rpm, 100 A separately excited dc motor has
an armature resistance of 0.5 Ω. The motor is connected to 230 V dc
supply and rated dc voltage is applied the field winding. It is
driving a load whose torque-speed characteristic is given
by
TL = 500 − 10ω where ω is the speed in rad/sec and TL is
the load torque in N-m. Find
(a) the steady state speed at which the motor will drive
the...

A dc motor has an armature resistance of 1 ?, and
K? = 3 Vsec. When the motor’s terminal voltage is
adjusted to 320 V, the motor speed is 1000 r/min. A
TVR braking is applied,
a) Calculate the value of the braking resistance that
would reduce the maximum braking current to twice
the rated current.
b) Calculate the new motor steady state speed if the
load is bidirectional and braking resistance is taken
off.

A separately excited DC motor has the following parameters:
field resistance = 250 ?, armature resistance = 0.03 ?, terminal
voltage = 250 V and field voltage = 250 V. Initially the machine
runs at 1000 rpm with the terminal voltage = 250 V and armature
current = 120 A. a) find the speed of the motor if the load torque
dropped to 50% of its original value, b) find the speed of the
motor if the armature voltage is...

A 220 V, 960 rpm, 20 A separately excited DC motor has
armature resistance and inductance of 1.2 ohms and 50 mH
respectively. Motor is controlled by a single phase half controlled
rectifier with source voltage of 230 V, 50Hz.
(a) Calculate no load speeds and speeds and developed torques on
the boundary between continuous and discontinuous conduction for ą
= 45°, 90° and 135°.
(b) Calculate and plot speed torque curve for ą = 45°.

A 200 V DC, 1,800 RPM shunt connected motor has an armature
resistance of 0.4 ohm and a brush resistance of 0.4 ohm; brush
voltage drop of 6.0 V, independent of load. The resistance of the
shunt field is 230 ohm. The full load rated line current is 40 A.
When the motor is operated at no load the line current is 5 A and
the speed is 1750 RPM.
Calculate speed at rated load
Calculate speed at .3 rated...

The full-load armature current of a 5 hp, 150 V shunt dc motor
is 30 A. The field (shunt) resistance and the armature resistance
of the motor are ????F = 125 ? and ???????? = 0.15, respectively.
At a random speed of 1800 rpm magnetization curve of the motor has
measured and is shown in the table below. ????0 (V) armature
voltage 10 90 110 140 170 185 ???????? (A) field (shunt) current 0
0.82 1 1.2 1.7 2.88 Calculate...

A 100 hp, 250 V, 1200 rpm DC shunt motor
with an armature resistance of 0.03 ? and a field
resistance of 41.67 ?. The motor has compensating
windings, so armature reactance can be ignored.
Mechanical and core losses may be ignored also. The
motor is driving a load with a line current of 126 A and
an initial speed of 1103 rpm. The magnetization curve is
shown in the following figure.
1. What is the motor speed if the...

Question 2
The full-load armature current of a 5 hp, 150 V shunt dc motor
is 30 A. The field (shunt) resistance and the armature resistance
of the motor are ????F=125 ? and ????????=0.15, respectively. At a
random speed of 1800 rpm magnetization curve of the motor has
measured and is shown in the table below.
EO(V) armature voltage
10
90
110
140
170
185
IF (A) field (shunt) current
0
0.82
1
1.2
1.7
2.88
Calculate the following:
a....

A 152 V DC shunt motor has an armature resistance of 0.3ohm, a
brush voltage drop of 2 V, the rated full load current is 70 A.
A) calculate the current at the instant of starting as a
percentage of full load current
B) calculate the value of starting resistance of limit the motor
current at the instant of starting to 150 percent of the rated load
current

A 3-phase 50Hz 2-pole 440V (L-L rms) induction motor drive has a
rated speed of 2955 rpm and rated torque of 35 Nm. This motor
drives a load with a torque characteristic that increases linearly
with speed such that it equals the load torque at the rated speed.
It draws a current of 3.0 A(rms) per phase at the rated voltage at
a power factor of 0.81 (lagging). The stator resistance Rs = {r_s}
ohms. At the rated operating speed,...

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