DEPARTMENT OF CIVIL ENGIEERING SCE&T, RAHIM’YAR’KHAN
BASIC ELECTRICAL TECNOLOGY (1ST SEMESTER, FIRST YEAR) EXPERIMENT # 06
Name: Irfan Munir Roll No: 15CE25
Lab Instructor’s Signature:........... Date....................
Common Base Characteristics
Objective:
To construct a set of common base input and output characteristic curves based on practical
measurement
Equipment:
DC Supply
Transistor C828
Digital Multimeter
Connecting wires
Bread board
Resistors 4.7KΩ, 22KΩ, 1KΩ
Circuit Diagram:
Procedure:
To measure transistor’s common base characteristics, connect the circuit as shown above
Adjust Vcc to obtain Vcb of 5V
Adjust Vee to obtain Vbe of 0V
Measure and record Ve to determine emitter current Ie
Repeat the procedure for all values of Vbe in the corresponding column of table
Repeat the above procedure for each value of Vcb
Vcb = 5 volts Vcb = 15 volts Vcb=25 volts
Sr Vb V Vb V V
No. e e Ie=Ve/Re e e Ie=Ve/Re Vbe e Ie=Ve/Re
1 0 0 0
2 0.2 0.2 0.2
3 0.3 0.3 0.3
4 0.4 0.4 0.4
5 0.5 0.5 0.5
6 0.6 0.6 0.6
Input Characteristics:
To determine common base output characteristics, connect the circuit as shown
Adjust Vee to obtain Ie of 1mA (Ve=1V)
Adjust Vcc to obtain the desired values for both Vcb and Ie
Measure and record Vc which is used to calculate Ic
Ie=1mA Ie=2mA Ie=3mA Ie=4mA Ie=5mA
Sr V V Ic=Vc/R V V V Ic=Vc/R
No. Vcb c Ic=Vc/Rc c c c Ic=Vc/Rc c Ic=Vc/Rc c c
1 -0.65
2 -0.5
3 0
4 5
5 10
6 15
7 20
Repeat above procedure for all values of Ie in the table
Output Characteristics:
DEPARTMENT OF CIVIL ENGIEERING SCE&T, RAHIM’YAR’KHAN
BASIC ELECTRICAL TECNOLOGY (1ST SEMESTER, FIRST YEAR) EXPERIMENT # 07
Name: Irfan Munir Roll No: 15CE25
Lab Instructor’s Signature:........... Date....................
Objective:
To study main parts of a DC Machine and Its Construction Detail.
Apparatus:
D.C Machine (Motor Generator Sets)
Yoke, Poles, Armature, Commutator, Brushes.
Theory:
Almost every mechanical movement that we see around us is accomplished by an electric
motor. Electric machines are a means of converting energy. Motors take electrical energy and
produce mechanical energy. Electric motors are used to power hundreds of devices we use in
everyday life. Motors come in various sizes. Huge motors that can take loads of 1000’s of
Horsepower are typically used in the industry. Some examples of large motor applications
include elevators, electric trains, hoists, and heavy metal rolling mills. Examples of small motor
applications include motors used in automobiles, robots, hand power tools and food blenders.
Electromechanical Energy Conversion
An electromechanical energy conversion device is essentially a medium of transfer between an
input side and an output side. Three electrical machines (DC, induction and synchronous) are
used extensively for electromechanical energy conversion. Electromechanical energy conversion
occurs when there is a change in magnetic flux linking a coil, associated with mechanical motion.
Electric Motor
The input is electrical energy (from the supply source), and the output is mechanical energy (to
the load).
Electric Generator
The Input is mechanical energy (from the prime mover), and the output is electrical energy.
A DC Machine is comprised of following main parts
1. Yoke or Frame
2. Magnetic Poles
3. Armature
4. Commutator
5. Carbon Brushes
Yoke or Frame
It is circular in shape and consists of even number of salient poles bolted inside of circular
frame. The yoke is usually made of solid cast steel.
Fig: Yoke
Magnetic Poles
In small machines the poles are made with yoke and both are of cast iron. In big machines poles
are made of laminated steel sheets which are riveted together under hydraulic pressure.
Field coils are mounted on the poles and carry the D.C exciting current. It spreads flux over
large area.
Armature
It is cylindrical core keyed to the machine shaft and rotates between the field poles. It consists
of slotted soft-iron laminations (about 0.4 mm to 0.6 mm thick) that are stacked to form a
cylindrical core. The laminations are insulated from each other by thin layer of insulating
material so that they do not come in contact with each other. The laminations are slotted to
accommodate and provide mechanical security to the armature winding.
The slots of the armature core hold insulated conductors that are connected in a suitable manner
and is called the armature winding. This is the winding in which working e.m.f is induced.
Commutator
A commutator is a mechanical rectifier which converts the alternating voltage generated in the
armature winding into direct voltage across the brushes. The commutator is made of copper
segments insulated from each other by suitable insulating material and mounted on the shaft of
the machine. The armature conductors are soldered to the commutator segments in a suitable
manner to give rise to the armature winding.
Brushes
The purpose of the brushes is to ensure electrical connections between the rotating commutator
and stationary external load circuit. The brushes are made of carbon and rest on the
commutator. Carbon brushes are employed to reduce sparking and provide better commutation.
Review Questions:
Q. 01: Why laminated core is used in D.C Machine?
Ans.:________________________________________________________________________
_____________________________________________________________________________
______________________________________________________________
Q.02: What is the function of commutator?
Ans.:________________________________________________________________________
_____________________________________________________________________________
______________________________________________________________
Q.03: What is the function of Carbon Brushes?
Ans.:________________________________________________________________________
___________________________________________________________________
DEPARTMENT OF CIVIL ENGIEERING SCE&T, RAHIM’YAR’KHAN
BASIC ELECTRICAL TECNOLOGY (1ST SEMESTER, FIRST YEAR) EXPERIMENT # 08
Name: Irfan Munir Roll No: 15CE25
Lab Instructor’s Signature:........... Date....................
Objective:
To understand different types of DC Machines
1. Separately Excited DC Machine
2. Shunt Excited DC Machine
3. Series Excited DC Machine
Apparatus:
1. DC Machine (Motor Generator Set)
2. DC Power Supply
3. Connecting Leads
4. Voltmeter
5. Ammeter
Circuit Diagram:
Theory:
DC Machines are classified according to manner in which armature circuit is connected to the field
circuit. So there are following main types
1. Separate Excited DC Machine
2. Shunt Excited DC Machine
3. Series Excited DC Machine
In a separate excited DC Machine the armature and field circuits are supplied by separate voltage
sources. In a shunt excited DC Machine both circuits are connected in parallel to each other. In a series
excited DC Machine both the field and armature circuits are connected in series to each other. These
connections are shown in the circuit diagram.
In this lab exercise our aim is to achieve above stated connections.
Procedure:
Make connections according to the given circuit diagram for each type of machine
separately.
Review Questions:
Q. 01: How should a generated be started?
Ans.:________________________________________________________________________________
_____________________________________________________________________________________
______________________________________________
Q.02: how about a series generator ?
Ans.:________________________________________________________________________________
_____________________________________________________________________________________
______________________________________________
Q.03: What is the procedure of shutting down a generator?
Ans.:________________________________________________________________________________
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