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ENT 289 Drive and Power Electronics
Laboratory Manual
Drive and Power Electronics
(ENT289)
Session 2011/2012
Semester 1
Experiment No. 1:
Separately Excited DC Generator
(Laboratory Manual)
Name
:___________________________________________
Matric No.
:__________________
School of Mechatronic Engineering
Universiti Malaysia Perlis
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ENT 289 Drive and Power Electronics
Laboratory Manual
Lab1 – Separately-Excited DC Generator (using Electrical Machine Trainer)
Objectives:
To investigate and understand the relationship between theoretical and experimental
result for separately-Excited DC Generator.
2.
3.
Part and Equipments:
2.1)
DC Compound Motor
2.2)
DC Separately Excited Electromotor (DC Generator)
2.3)
DC Meter (30423010)
2.4)
DC Motor Control unit (30421157)
2.5)
Tachometer
2.6)
Bulbs (30111093)
2.7)
Connector wires
2.8)
Multimeter
Introduction:
A generator is a machine that converts mechanical energy into electrical energy by using the
principle of magnetic induction. This principle is explained as follows:
Whenever a conductor is moved within a magnetic field in such a way that the conductor cuts
across magnetic lines of flux, voltage is generated in the conductor.
SEPARATELY EXCITED GENERATORS receive current for field coils from an outside
source such, as a battery or another dc generator. A separately excited DC generator is the
generator that requires an external Direct Current (DC) source for excitation. Since the output
voltage may be controlled more easily and over a wide range (from zero to a maximum), this
type of excitation finds many applications.
Figure 1: Separately Excited DC Generator
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ENT 289 Drive and Power Electronics
Laboratory Manual
Voltage Generation
There is a definite relationship between the direction of the magnetic flux, the direction of
motion of the conductor and the direction of the induced EMF. Figure 2 shows the motion of the
conductor perpendicular to the magnetic field. The voltage and current output are perpendicular
to both the motion of the conductor and the magnetic field.
Figure 2: Voltage Generation
To illustrate this with Fleming's right hand rule, the thumb and first two fingers of the right hand
are extended at right angles to one another, the thumb will indicate the direction of motion of the
conductor, the forefinger will indicate the direction of the magnetic field, and the middle finger
will indicate the direction of voltage or current. Applying this rule, one can see that the current
will reverse if the motion of the conductor changes from down to up. This is true even though the
magnetic field does not change position.
Value of Generated Voltage
The EMF at any instant of time is proportional to the number of turns in the coil times rate of
change of flux. The C.G.S. (centimeter gram second) unit of EMF known as the abvolt is defined
as that value induced, in a coil of one turn, when the flux linking with the coil is changing at the
rate of one line or Maxwell per second; or as that value induced when magnetic flux is being cut
by the conductor at the rate of one line per second. A volt is equal to 108 abvolts or an abvolt is
equal to 10-8 volts. Therefore, the instantaneous value of voltage is expressed as:
e = N x (dϕ / dt) x 10-8
where:
e = voltage
N = the number of turns
dϕ / dt = the rate of change of the flux
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ENT 289 Drive and Power Electronics
Laboratory Manual
Procedure:
4.1)
Connect the circuit as shown in Figure 1. But, for the first circuit, the connection is using
no load (bulb). Make sure that all connection is correct before proceed to the next step.
4.2)
Switch ON DC Meter and DC Motor Control unit.
4.3)
Adjust the DC voltage from Variable DC Voltage Board until the Rotate Speed Meter
shows 300rpm.
4.4)
Record the values of DC Current Meter and DC Voltage Meter that show in DC Motor
Control Unit for input value in Table 1. Record the value for output (current and voltage)
using DC meter or Multimeter in Table 1.
4.5)
Repeat step 4.3 for different value of rpm stated in Table 1.
4.6)
Slowly turn down the speed of motor before switch off the panel.
4.7)
Switch OFF the DC Meter and DC Motor Control unit.
4.8)
Repeat step 4.1 to 4.5 for ONE bulb, TWO bulbs, THREE bulbs and FOUR bulbs. Use
the parallel connection for two and more bulbs. Record the data in Table 2, 3, 4 and 5.
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ENT 289 Drive and Power Electronics
Laboratory Manual
Figure 1: Connection diagram
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