Question

a)Explain the shunt excitation and compound excitation of DC generator.

b)A 240V compound DC motor has the armature, series field and
shunt field resistances are

0.22 Ω, 0.04 Ω and 200 Ω respectively. On full load, the line
current is 17.5 A and the motor runs at 1800 rpm. (short
shunt)

i) Draw the diagram and the power flow of the motor.

ii) Find the back EMF of the motor.

iii) Find the mechanical power developed.

iv) Find the output power if the rotational losses are 250W.

v) Find the output torque.

vi) Determine the overall efficiency.

Answer #1

A 25-hp, 240V, DC shunt motor has
armature and field resistances of 0.2 ? and 120 ?, respectively. At
no load and rated voltage, the motor draws a line current of 5A and
its speed is 1250 rpm.
When driving a certain load, the
input to the motor is 15KW. For this condition, find:
a.The speed of the motor
b.The developed torque
The efficiency of the motor at this load

Q3: (a) Determine the terminal voltage of a dc shunt generator
which develops an e.m.f. of 240V and has an armature current of 50
A on load. Assume the armature resistance is 0.04Ω. [3 marks]
(b) A lap wound armature is used in a 4-pole dc machine and 70
coils on the armature each containing 10 turns. The flux per pole
in the machine is 40 mWb and the machine rotates at 500 rpm; (a)
How many current paths are...

A dc shunt generator runs at 500 rpm at 200 V. It is delivering
50,000 W .
The armature resistance is 0.02 Ω and the field resistance is 40
Ω.
Calculate the emf generated. Assume brush drop of 1V per
brush.
Show all steps and circuit diagram if needed.

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 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...

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...

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 long-shunt compound generator running at 1000 r.p.m.
supplies 22 kW at a terminal voltage of 220 V. The resistance of
the armature, shunt field and series field are 0.05 Ω, 110 Ω, and
0.06 Ω respectively. The overall efficiency at the above load is 88
%. Find (i) Cu losses (ii) iron and friction losses and (iii)
torque exerted by the prime mover.

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