Fakulti:
FAKULTI KEJURUTERAAN ELEKTRIK
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Nama Matapelajaran : MAKMAL KEJ. ELEKTRIK
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Kod Matapelajaran
: SEE 2742
No. Prosedur
:2
: Julai 2008
: 2008
: PK-UTM-FKE-(O)-10
SEE 2742
FAKULTI KEJURUTERAAN ELEKTRIK
UNIVERSITI TEKNOLOGI MALAYSIA
KAMPUS SKUDAI
JOHOR
ELECTROTECHNIC LABORATORY
SEPARATELY EXCITED DC GENERATOR
(Experiment 5)
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1
FAKULTI KEJURUTERAAN ELEKTRIK
UNIVERSITI TEKNOLOGI MALAYSIA
ELECTROTECHNIC LABORATORY
EXPERIMENT: 5
TITLE
1.
: SEPARATELY EXCITED DC GENERATOR
Aim:
To study the characteristics and performance of a separately excited dc generator.
2.
Theory:
When a load is connected to the generator terminal output, the characteristic
obtained is as shown in the graph below:
The characteristics can be shown with the following equation:
V = E - IaRa
where,
V = generator terminal output voltage
E = induced voltage
Ia = armature current
Ra = armature resistance
2
Field and armature winding for a separately excited dc generator are as shown in
the diagram below.
When the field current is being increased from zero until it reaches its limit,
therefore the relationship obtain for induced voltage E at the generator armature
and the field current If is as shown below:
Induced armature voltage E can be measured at the generator output terminal by
opening the switch connected to the load. In other words, the induced voltage is
equal to the no load voltage. The armature speed is set at fixed value.
3
3.
Equipments:
i.
ii.
iii.
iv.
v.
vi.
vii.
4.
Two poles machine DCM-250 as a motor.
Two poles machine DCM-250 as a generator.
Volt meter.
Ampere meter.
Variables resistor ED-5101 as a load.
Power supply ED-5119.
Tachometer (for measuring the speed).
Procedure:
i.
The circuit connection is as shown in Figure 1.0.
DCM – 250 (MOTOR)
DM- 250(GENERATOR)
Figure 1.0
ii.
Connect the L1 and L2 terminals for motor DCM-250 to the output
terminal DC 0~125V, 4A power supply ED-5119. Then connect the L1
and L2 terminals for generator DM-250 to the output terminal DC
0~150V, 1A. All the supply knobs must be set at the zero position (turn
anti clockwise direction) before starting the motor and the generator.
4
iii.
Switch OFF the load ED-5101. Ask for the instructor to check all the
circuit connections before you switch ON the power supply.
iv.
Switch ON the supply ED-5119, to start the motor you have to turn the
knob in clockwise direction slowly, and then adjust the knob so that the
speed of 1750 rpm can be achieved.
v.
Then turn the power supply knob slowly so that field current IF flows
through the field generator winding. Gradually increase the field current IF
from 0 to 0.5 A. Make sure that the speed is always constant. Record the
induced voltage E at every different value of field current in Table 1.0.
vi.
Reduce the field current IF to zero. Next adjust the speed to half
(approximate 875 rpm) of the actual speed. Repeat step (v).
vii.
Fixed the field current at 0.4 A and gradually change the generator speed
from 0 to 1750 rpm. Record the induced voltage E for each changes of the
speed in Table 2.0.
viii.
Next step with the field current fixed at 0.4 A, the speed also fixed at 1750
rpm, gradually introduce the load by switching ON the resistor load switch
(ED-5101). Starting with resistor 1200 ohm, record the load current Ia and
generator terminal voltage V. The load current is actually armature
current. Record all the reading for different values of load resistance in
Table 3.0.
ix.
Reduce the motor speed until it reaches zero, field current IF is also set to
zero, switch OFF the power supply and disconnect the motor DCM-250
and the generator DM-250 connections.
x.
Refer to Figure 2.0; the connection is only on the (DM-250. Make sure
no connection on the motor (DM-250). This experiment is to determine
the value of generator armature resistance.
xi.
Gradually increase the supply voltage until the volt meter reads 3 Volt.
Record the ampere meter reading and then calculate the armature
resistance using basic Ohm’s Law.
5
Figure 2.0
6