Download lab 03: dc series motor

EKT 451/4 APPLIED ELECTRICAL ENGINEERING
LAB 03: DC SERIES MOTOR
LAB 03: DC SERIES MOTOR
3.0
OBJECTIVES
1.
2.
3.1
To operate a DC Series Motor.
To study the speed characteristics of the no-load motor against current.
EQUIPMENTS
DC Series Motor
DC Drive
Contactor
Selector Switch
DC Voltmeter
Multimeter
DC Ammeter
Handheld Tachometer
Cable
3.2
INTRODUCTION
DC machines are conveniently used when the speed of the loads need to be
adjusted. The magnetizing characteristic shows the variation of the magnetic flux
in the machine with the field current to be similar as the relationship between the
open-circuit (OC) armature voltage and the field current, when the machine is
driven at a constant speed (as a generator). This relationship is referred to as the
open-circuit or magnetizing characteristic.
A DC Series Motor field windings consist of a relatively few turns connected in
series with the armature circuit. In a Series Motor, the armature current, field
current and line current are all of the same values. The Kirchhoff’s Voltage Law
equation for this motor is given in equation 1.
VT = EA + IA (RA + RS)
(1)
Where VT is supply voltage, EA is armature voltage, RA is armature resistance,
Rs is field resistance and IA the motor current.
Motor on No-load condition
E=N
E1 N1
(2)
1
SEMESTER II (2007)
EKT 451/4 APPLIED ELECTRICAL ENGINEERING
LAB 03: DC SERIES MOTOR
N = E (N1) ≈ V (N1)
E1
E1
(3)
The terminal characteristic of a DC Series Motor is different from that of the DC
Shunt Motor. The basic behavior of a series dc motor is due to the fact that the
flux is directly proportional to the armature current, at least until saturation is
reach. As the load on the motor increases, its flux increases too. As seen earlier,
an increase in flux in the motor causes a decreased in the speed. The result is that
a series motor has a sharply drooping torque-speed characteristic.
3.3
PRE-LAB INTRODUCTION (BACKGROUND REVIEW)
This Pre-Lab Introduction on the background review of above-mentioned
laboratory title and objectives should be prepared by each student before entering
this laboratory session. Marks will be given during the laboratory sessions.
Students are not allowed to perform any experimental works before completing
this section.
3.4
PROCEDURE
Warning:
1.
High voltages are used in this laboratory experiment.
Do not make any connection with the Power ON.
Please ask the Teaching Engineer or the Technician to check your circuits
before turning on the supply for all the tests.
Connect the circuit as shown in Figure 3.1 and Figure 3.2.
DC
Drive
A
+
Contactor
M
Figure 3.1 – Circuit Diagram
2
SEMESTER II (2007)
EKT 451/4 APPLIED ELECTRICAL ENGINEERING
LAB 03: DC SERIES MOTOR
L
Selector
Switch
A1
240V
Contactor A2
N
Figure 3.2 – Control Circuit
2.
Write down all the rated of the Series DC motor shown on the rating plate
in a table. These ratings should not exceed at any time during the
laboratory exercises.
3.
Please inform to the teaching engineer or technician when need to check
the connections.
4.
Switch on the power supply to DC drive, firstly at the main switch and
then by using the selector switch to START to engaged the contactor.
5.
Slowly turn the potentiometer on the DC drive and observe the variation
of the motor speed.
6.
Using the handheld tachometer, measure the speed rotation of the motor
and prepare for data collection.
7.
Set and record the speed at different values, the corresponding voltage and
current values.
8.
After finish taking the measurement, please switch off all power supplies
before disconnect the wiring.
9.
Plot the speed against current and the speed against voltage in the graph
paper.
10.
Take into account the armature resistance. Calculate the speed
corresponding to the different values of current. Use the rated voltage
180V and the rated speed 1500rpm under the rated load conditions as the
base values for this calculation. Use an equation 2 to calculate the values
of speed.
11.
Plot the graph of calculated values of speed using equation 2 against
current on the same graph sheet as the experimental values.
3
SEMESTER II (2007)
EKT 451/4 APPLIED ELECTRICAL ENGINEERING
LAB 03: DC SERIES MOTOR
L1
L2
L3
A2
A1
Figure 3.3 – Wiring diagram for training kit - module
REPORT
Laboratory report should be prepared individually and submitted within two days.
Your report contents should include the followings:
3.5. Results (Calculations, Graphs, Tables etc)
3.6. Discussions
3.7. Conclusions
3.8. References
4
SEMESTER II (2007)