Question

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

Answer #1

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...

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 5-kW, 220-V shunt motor has an armature resistance of 0.15 ?
and a field-circuit resistance of 100 ?. The motor delivers rated
output power at rated voltage when its armature current is 20 A.
When the motor is operating at rated voltage, the speed is observed
to be 1000 r/min when the machine is loaded such that the armature
current is 15 A. In order to protect both the motor and the dc
supply under starting conditions, an external...

A 230-V DC shunt motor has armature circuit resistance of 0.25 ?
and field circuit resistance of 115 ?. At
full load armature draws a current of 38 A and the speed is
measured at 1050 rpm. Find the developed
torque.
The field rheostat is now changed so that total field resistance is
144 ?. Find the speed under this condition.
Assume that the armature current does not change. Assuming the
rotational losses amount to 600 W, find the
efficiency...

Design of DC Motor Starter
In order for a dc motor to function properly, it must be protected
from physical
damage during the starting period. At starting conditions, the
motor is not rotating,
and armature generated voltage EA = 0 V. Since the internal
resistance of a normal DC
motor is very low, a very high current flows. It is possible for a
motor to be severely
damaged by such currents, even if they last for only a moment.
A...

Design of DC Motor Starter In order for a dc motor to function
properly, it must be protected from physical damage during the
starting period. At starting conditions, the motor is not rotating,
and armature generated voltage EA = 0 V. Since the internal
resistance of a normal DC motor is very low, a very high current
flows. It is possible for a motor to be severely damaged by such
currents, even if they last for only a moment. A...

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...

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...

In order for a dc motor to function properly, it must be
protected from physical damage during the starting period. At
starting conditions, the motor is not rotating, and armature
generated voltage EA = 0 V. Since the internal resistance of a
normal DC motor is very low, a very high current flows. It is
possible for a motor to be severely damaged by such currents, even
if they last for only a moment.
A solution to the problem of...

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