Problem 103-1
Source:
Issue 12 - Page 128 - HUGHES, Austin - Book:
Electric Motors and Drives - 3rd Edition - Ed. Elsevier - 2006.
Suppose a 250 V DC motor with an armature resistance equal to RA = 1 Ω and it's spinning
no load, drawing a current of 2 A at a rotation of 1800 rpm. Estimate the friction torque.
Problem 103-2
Source:
Problem 14 - Page 128 - HUGHES, Austin - Book:
Electric Motors and Drives - 3rd Edition - Ed. Elsevier - 2006.
Suppose, in the previous problem, the motor running at full load and consuming a current equal to 32 A.
Calculate the motor speed at full load and the torque developed by the machine.
Problem 103-3
Source: Problem prepared by the website author.
A DC motor in the shunt configuration, fed by a line voltage of 380 V, has a
armature current of 125 A. Considering the field resistance equal to 110 Ω and the resistance of
armature equal to 0,2 Ω, determine:
Problem 103-5
Source: Problem prepared by the website author.
A shunt DC motor has the following characteristics: 50 HP / 380 V. It has compensation windings and
armature resistance equal to 0.1 Ω. In the field circuit we have Raj + RF = 100 Ω.
Under nominal voltage the no-load speed is 1,200 rpm and having an armature current equal to 5 A.
At full load and at rated voltage, the line current is equal to 93.8 A assuming a 5% reduction in flux
due to the armature reaction in relation to the no-load value. Find the engine speed when at full load.
Problem 103-6
Source: Problem prepared by the website author.
A DC motor in series configuration consumes a current of 15 A when powered by
a voltage of 220 V. If the armature resistance is equal to 0.75 Ω and the stator resistance is
0.55 Ω, find the value of the electromotive force EA.
Problem 103-7
Source:
Example 9-1 - page 405 - FITZGERALD, A. E. - Book:
Electric Machinery - 5th Edition - Ed. McGraw-Hill - 1990.
A DC machine in independent excitation configuration has a power of 125 kW at a voltage of 125 V and operates at a speed 3,000 rpm with a constant field current, such that the open-circuit armature voltage is equal to 125 V. Armature resistance is equal to 0.02 Ω.
Find the armature current, the power absorbed by the machine from the supply network, the mechanical power
and the torque, when:
Problem 103-8
Source:
Example 4.1 - page 135 - SEN, P.C. - Book:
Principles of Electric Machines and Power Electronics - 3rd Edition - Ed. Wiley - 2014.
A 4 pole DC machine has an armature with a radius equal to 125 mm and an effective length of 250 mm.
The poles cover 75% of the periphery of the armature. The armature winding has 33 coils and each coil has
7
turns
. Coils are accommodated in 33 slots. The magnetic flux density, B, at each pole is
0.75 T. Considering the armature winding as overlapping, determine:
a) the constant, Ka of the machine.
b) the induced armature voltage, EA, when the rotor turns at 1,000 rpm.
c) the power, Pm, developed by the machine when the armature current is 400 A .
d) the current in the coils and the electromagnetic torque developed.
Problem 103-9
Source:
Example 4.1 - page 135 - SEN, P.C. - Book:
Principles of Electric Machines and Power Electronics - 3rd Edition - Ed. Wiley - 2014.
Calculate what is asked below, using the data from the previous problem (Problem 103-8) and considering the winding as
wave wound. Consider that the current in the coil remains at the value calculated in the previous problem.
a) the constant, Ka of the machine.
b) the induced armature voltage, EA, when the rotor turns at 1,000 rpm.
c) the power, Pm, developed by the machine when the armature current is 400 A .
d) the current in the coils and the electromagnetic torque developed.
Problem 103-10
Source: Problem prepared by the website author.
In a DC motor in shunt configuration, the armature has a resistance of 0.28 Ω and a voltage drop
on the 2 V brushes. A voltage of 130 V is applied across the armature terminals. Calculate the armature current when:
a) the rotor speed produces an induced voltage of 120 V;
b) when applying an additional load, the speed drops and the induced voltage reduces to 114 V.
c) in the condition of item a) the engine was running at 1,400 rpm. Calculate the new engine speed in the case of item
b)
.
Problem 103-11
Source:
Adapted from Example 42.2 - page 872 - HUGHES, Austin - Book:
Electrical and Electronics Technology - 10th Edition - Ed. Pearson - 2008.
A 4 pole motor is fed with a voltage of 440 V and draws an armature current of 50 A. The
armature resistance is equal to 0.28 Ω. The armature winding is wavy type and has
888
conductors
. The flow in the machine is 0.023 Wb. Calculate:
Problem 103-12
Source: Problem prepared by the website author.
Suppose a DC motor that has a characteristic magnetization curve given by the following equation:
EA = - 0.000005
F2 + 0.073 F + 5
. The field winding has 800 turns and for the speed of
1,500 rpm requires a field current of 5 A. In this case, the armature current is 100 A. Despise the
armature reaction and take the armature resistance equal to 0.18 Ω. Find:
a) the induced voltage EA in the machine and the supply voltage VT of the engine.
b) if the field current is reduced to 4.5 A what is the new induced voltage and armature current?
c) the power developed by the machine in item a) and b).
Problem 103-14
Source: Problem prepared by the website author.
A DC electric motor, in the independent configuration, operates with a constant field current and is rotating at 1,400 rpm. Powered with a voltage of 200 V the armature current is 12 A. When we reduce the load
on the motor shaft, maintaining the same supply voltage, the armature current became 7 A. Assume that the motor has an armature resistance of 0.12 Ω. Determine:
a) the new engine speed;
b) the power developed by the motor when IA = 12 A;
c) the power developed by the motor when IA = 7 A;
d) the torque developed by the engine in both cases.
