Question

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 resistance will be
connected in series with the armature winding (with the field
winding remaining directly across the 220-V supply). The resistance
will then be automatically adjusted in steps so that the armature
current does not exceed 200 percent of rated current. The step size
will be determined such that, until all the external resistance is
switched out, the armature current will not be permitted to drop
below rated value. In other words, the machine is to start with 200
percent of rated armature current and as soon as the current falls
to rated value, sufficient series resistance is to be cut out to
restore the current to 200 percent. This process will be repeated
until all of the series resistance has been eliminated.

a) Find the maximum value of the series resistance.

b) How much resistance should be cut out at each step in the
starting operation and

c) At what speed should each step change occur?

PLEASE SHOW ALL WORKING!!!

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
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A 230-V DC shunt motor has armature circuit resistance of 0.25 ?
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The full-load armature current of a 5 hp, 150 V shunt dc motor
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of the motor are ????F = 125 ? and ???????? = 0.15, respectively.
At a random speed of 1800 rpm magnetization curve of the motor has
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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 230 V, 250 rpm, 100 A separately excited dc motor has
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