Question

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 there in the machine, (b) What is its induced voltage (c) Find the emf per turn of the coil. [3 marks]

(c) (i)Draw the speed vs load curve of a dc shunt motor and a dc series motor [1 mark]

(ii) Draw torque vs load curve of a dc separately excited motor. [1 marks]

(iii) Why the demagnetization in a dc motor is more dangerous when compared to a dc generator? Note that the demagnetization occurs due to the armature reaction in a dc machine.

Answer #1

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...

1) A DC machine induces an EMF of 240 v at 1500 rpm. Find the
developed torque for an armature current of 25A.
2) Draw and explain all characteristics of d.c. Shunt motor.
3) State accessitivity of 3 point starter.
4) A four pole wave connected dc armature has 50 slots with 10
conductors per slot. The armature is rotated at 1000 rpm of the
useful flux per pole is 30mwb, calculate the amount of EMF
induced.
5) A 6...

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

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 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 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...

A shunt-wound DC motor with the field coils and rotor connected
in parallel (see the figure) (Figure 1)operates from a 130 VV DC
power line. The resistance of the field windings, RfRfR_f, is 201
ΩΩ . The resistance of the rotor, RrRrR_r, is 4.10 ΩΩ . When the
motor is running, the rotor develops an emf EEEMF. The motor draws
a current of 4.88 AA from the line. Friction losses amount to 47.0
WW .
a)
Compute the field current...

Q.1: Choose the correct answer (and expalin) for the
follwoings:
Minimum number of coils for 400 V, 6-pole lap connected de
machine for a maximum voltage of 15 V between adjacent commutator
segments should be
(a) 80 (b) 160 (c) 200 (d) 400
The armature resistance of a 6-pole lapp wound de machine is
0.05 Q. If the aramture is re-wound using a wave winding, then the
armature resistance will be
(a) 0.452 (b) 0.30 (c) 0.15 (d)
0.102
A...

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