FAKULTEIT INGENIEURSWESE
FACULTY OF ENGINEERING
Elektriese Aandryfstelsels 324 / Electrical Drive Systems 324
Tutoriaal 3 / Tutorial 3
20 en 21 Februarie 2014 / 20 and 21 February 2014
Die volgende probleme uit Chapman 5uit moet gedoen word en aan die dosent aan diens gewys word voor
16:00 om vir die Tutoriaal afgemerk te word.
The following problems from Chapman 5ed shall be done and shown to the lecturer on duty before 16:00
in order to be signed off for the Tutorial.
Problems 8-1 to 8-12 refer to the following dc motor:
Prated
VT
RA
=
=
=
22,38 kW
240 V
0,19 Ω
IA,rated
nrated
RF
=
=
=
109 A
1 800 rpm
75 Ω
Rotational losses (mechanical and core losses combined) can be ignored
Magnetization curve as shown in Figure P8-1
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In Problems 8-1 through 8-7, assume that the motor described above can be connected in shunt. The equivalent
circuit of the shunt motor is shown in Figure P8-2.
P8-1 If the resistor Radj is adjusted to 175 Ωwhat is the rotational speed of the motor at no-load conditions?
P8-2 Assuming no armature reaction, what is the speed of the motor at full load? What is the speed regulation
of the motor?
P8-3 If the motor is operating at full load and if its variable resistance Radj is increased to 250 Ω, what is the
new speed of the motor? Compare the full-load speed of the motor with Radj = 175 Ωto the full-load
speed with Radj = 250 Ω. (Assume no armature reaction, as in the previous problem.)
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P8-5 If Radj can be adjusted from 100 to 400 Ω, what are the maximum and minimum no-load speeds possible
with this motor?
P8-22 The magnetization curve for a separately excited dc generator is shown in Figure P8-7. The generator
is rated at 6 kW, 120 V, 50 A, and 1800 r/min and is shown in Figure P8-8. Its field circuit is rated at 5 A.
The following data are known about the machine:
RA
Radj
=
=
0,18 Ω
0 to 40 Ω
VF
RF
=
=
120 V
20 Ω
Answer the following questions about this generator, assuming no armature reaction.
(a) If this generator is operating at no load, what is the range of voltage adjustments that can be achieved
by changing Radj ?
(b) If the field rheostat is allowed to vary from 0 to 30 Ωand the generator’s speed is allowed to vary
from 1 500 to 2 000 r/min, what are the maximum and minimum no-load voltages in the generator?
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