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DAVIET
ELECTRICAL DEPARTMENT
DAV Institute of Engineering& Technology,
Jalandhar
www.davietjal.org
Department of Electrical Engineering
Name of Lab: Basic Electrical Engineering
CODE: BTEE102-18
(Laboratory Manual)
CAY : 2019-20
Basic Electrical Engineering Lab Manual
Page | 1
DAVIET
ELECTRICAL DEPARTMENT
Vision of the Department: We, the department of Electrical Engineering, perceive amalgamation of
academia, research and industry paving the way to zenith for innovative, competent and self sustainable
professionals.
Mission of the Department:
M1. To create and sustain environment of learning in which Electrical engineering graduates acquire
knowledge and implement it professionally with due consideration of ethical and economical issues.
M2. To produce innovative, vibrant leaders and entrepreneurs in core and allied fields to minimize skill gap
between academia & industry.
M3. Transforming the Department of Electrical Engineering into nationally recognized Centre of Excellence.
PEOs
1. Graduates will have Technical, Analytical abilities & skills suitable to cater the need of Industry &
Society.
2. Graduates will have successful career in core and inter disciplinary fields.
3. Graduates will follow professional ethics and generate an attitude of research oriented continuous
learning.
PSOs
1. Graduates will have knowledge of principles, design and performance & testing of static & dynamic
electrical machines.
2. Graduates will gain knowledge and acquire skills for analysis, operation, control and protection of
electrical power system for generation, transmission, distribution & utilisation.
3. Graduates will gain knowledge of instrumentation, control & automation and powertronics applicable
in core and related fields.
POs
After the successful completion of undergraduate course, Electrical Engineering, Graduates will be able to:
PO1. Apply the knowledge of mathematics, science, engineering fundamentals, and an engineering
specialization for the solution of complex engineering problems.
PO2.
Identify, formulate, research literature, and analyse complex engineering problems reaching
substantiated conclusions using first principles of mathematics, natural sciences, and engineering sciences.
Basic Electrical Engineering Lab Manual
Page | 2
DAVIET
ELECTRICAL DEPARTMENT
PO3. Design solutions for complex engineering problems and design system components or processes that
meet the specified needs with appropriate consideration for public health and safety, and cultural, societal, and
environmental considerations.
PO4. Use research-based knowledge and research methods including design of experiments, analysis and
interpretation of data, and synthesis of the information to provide valid conclusions.
PO5. Create, select, and apply appropriate techniques, resources, and modern engineering and IT tools,
including prediction and modelling to complex engineering activities, with an understanding of the
limitations.
PO6. Apply reasoning informed by the contextual knowledge to assess societal, health, safety, legal, and
cultural issues and the consequent responsibilities relevant to the professional engineering practice.
PO7. Understand the impact of the professional engineering solutions in societal and environmental contexts,
and demonstrate the knowledge of, and need for sustainable development.
PO8. Apply ethical principles and commit to professional ethics and responsibilities and norms of the
engineering practice.
PO9. Function effectively as an individual, and as a member or leader in diverse teams, and in
multidisciplinary settings.
PO10. Communicate effectively on complex engineering activities with the engineering community and with
the society at large, such as, being able to comprehend and write effective reports and design documentation,
make effective presentations, and give and receive clear instructions.
PO11. Demonstrate knowledge and understanding of the engineering and management principles and apply
these to one’s own work, as a member and leader in a team, to manage projects and in multidisciplinary
environments.
PO12. Recognize the need for, and have the preparation and ability to engage in independent and life-long
learning in the broadest context of technological change.
Basic Electrical Engineering Lab Manual
Page | 3
DAVIET
ELECTRICAL DEPARTMENT
LIST OF EXPERIMENTS
1. To verify Ohm’s Law and its limitations.
2. To verify Kirchhoff’s Laws.
3. To measure the resistance and inductance of a coil by ammeter-voltmeter method
4. To find voltage-current relationship in a R-L series circuit and to determine the power factor of the circuit.
5. To verify the voltage and current relations in star and delta connected systems.
6. To measure power and power factor in a single- phase AC circuit.
7. To verify series and parallel resonance in AC circuits.
8. To observe the B-H loop of ferromagnetic core material on CRO.
9. To use a bridge rectifier for full- wave rectification of AC supply and to determine the relationship
between RMS and average values of the rectified voltage.
10. To measure the minimum operating voltage, current drawn, power consumed, and the power factor of a
fluorescent tube light.
11. To connect measuring analog and digital instruments to measure current, voltage, power and power factor.
12. To obtain the characteristics of a transistor under common base (CB) and common emitter (CE)
configuration.
13. To perform open- and short circuit tests on a single- phase transformer and calculate its efficiency.
14. To start and reverse the direction of rotation of a (i) DC motor (ii) Induction motor
15. Determining of voltage regulation of transformer by directly loading
16. Study of starters for (i) DC motor (ii) Induction motor
Basic Electrical Engineering Lab Manual
Page | 4
DAVIET
ELECTRICAL DEPARTMENT
Laboratory Outcomes
1. Get an exposure to common electrical components and their ratings.
2. Make electrical connections by wires of appropriate ratings.
3. Understand the usage of common electrical measuring instruments.
4. Understand the basic characteristics of transformers and electrical machines.
5. Get an exposure to the working of power electronic converters.
List of experiments/demonstrations:
1. Basic safety precautions. Introduction and use of measuring instruments – voltmeter, ammeter, multimeter, oscilloscope. Real-life resistors, capacitors and inductors.
2. Measuring the steady-state and transient time-response of R-L, R-C, and R-L-C circuits to a step change in
voltage (transient may be observed on a storage oscilloscope). Sinusoidal steady state response of R-L,
and R-C circuits – impedance calculation and verification. Observation of phase differences between
current and voltage. Resonance in R-L-C circuits.
3. Transformers: Observation of the no-load current waveform on an oscilloscope (non-sinusoidal waveshape due to B-H curve nonlinearity should be shown along with a discussion about harmonics). Loading
of a transformer: measurement of primary and secondary voltages and currents, and power.
4. Three-phase transformers: Star and Delta connections. Voltage and Current relationships (line-line
voltage, phase-to-neutral voltage, line and phase currents). Phase-shifts between the primary and
secondary side. Cumulative three-phase power in balanced three-phase circuits.
5. Demonstrate of cut-out sections of machines: dc machine (commutator-brush arrangement), induction
machine (squirrel cage rotor), synchronous machine (field winging - slip ring arrangement) and singlephase induction machine.
6. Torque Speed Characteristic of separately excited dc motor.
7. Synchronous speed of two and four-pole, three-phase induction motors. Direction reversal by change of
phase-sequence of connections. Torque-Slip Characteristic of an induction motor. Generator operation of
an induction machine driven at super-synchronous speed.
8. Synchronous Machine operating as a generator: stand-alone operation with a load. Control of voltage
through field excitation.
9. Demonstration of (a) dc-dc converters (b) dc-ac converters – PWM waveform (c) the use of dc-ac
converter for speed control of an induction motor and (d) Components of LT switchgear.
Basic Electrical Engineering Lab Manual
Page | 5
DAVIET
ELECTRICAL DEPARTMENT
Mapping of COs with Pos
SNO
DESCRIPTION
PO
MAPPING
Get an exposure to common electrical components and their ratings
PO1,PO2,PO4,P
O6,PO10,PO12
2
Make electrical connections by wires of appropriate ratings
PO1,PO6,PO12
3
Understand the usage of common electrical measuring instruments
PO1,PO2,PO6,PO12
1
4
5
Understand the basic characteristics of transformers and electrical machines PO1,PO2,PO3,PO12
Get an exposure to the working of power electronic converters
Basic Electrical Engineering Lab Manual
PO1,PO2,PO6,PO12
Page | 6
DAVIET
ELECTRICAL DEPARTMENT
Introduction of the Lab.
The mission of the Electrical Department is to enhance knowledge and educate students in latest technologies
used in industry and power sector. We are committed to generate, disseminate and preserve knowledge and to
use it to bear the world’s great challenges. The labs of electrical engineering departments are well equipped
with latest equipments/tools/instruments and machines to cater to the requirements of engineers and
researchers.
Basic components like capacitors, resistors, inductors, diodes, light emitting diode (led) and transistors can be
divided into 2 categories: (i) Passive components like resistors and capacitors and (ii) Active components like
diodes and transistors. The difference between the above two categories is that active components can
generate energy whereas passive components can not generate energy. In other words active components can
increase power of a signal whereas passive components often cause the power to be lost.
Some components like resistors have their values marked on them whereas others like transistors do not have
any value marking but have a type number on them. One has to refer to datasheets to get to know the value of
the unmarked component. Besides component values, they are also characterized by their ratings for e.g.
maximum current value that a component can stand without being burnt out.
Basic Electrical Engineering Lab Manual
Page | 7
DAVIET
ELECTRICAL DEPARTMENT
List of the Equipment’s with description & Cost:
S.No
Name of
Equipment/Set up
1.
AmmeterDC(0-5A)
Attachment
details
Bill No. &
Date
Make
Oty
Unit
Cost
Total
Cost
6729,17/8/
2K
M/s sanjay
biological
measurements
03
120/-
391.68/-
-----------------2
AmmeterDC(0-10A)
------------------
6734,18/8/
2K
M/s sanjay
biological
measurements
03
120/-
391.68/-
3
AmmeterAC(0-5A)
------------------
6734,18/8/
2K
M/s sanjay
biological
measurements
03
195/-
636.48/-
4
AmmeterAC(0-10A)
------------------
6734,18/8/
2K
M/s sanjay
biological
measurements
03
195/-
636.48/-
5
Voltmeter AC(050V)
------------------
6734,18/8/
2K
M/s sanjay
biological
measurements
03
195/-
636.48/-
6
Voltmeter AC(0250V)
------------------
6734,18/8/
2K
M/s sanjay
biological
measurements
03
195/-
636.48/-
7
Voltmeter AC(0500V)
------------------
6734,18/8/
2K
M/s sanjay
biological
measurements
03
195/-
636.48/-
8
Voltmeter DC(0300V)
------------------
6734,18/8/
2K
M/s sanjay
biological
measurements
03
120/-
391.68/-
9
Voltmeter AC(015V)
------------------
5439,13/08
/03
M/s Anand
Elect,40499,404
96
02
950/-
1900/-
10
Voltmeter AC(030V)
------------------
5439,13/08
/03
M/s Anand
Elect,49894,408
96
02
950/-
1900/-
11
Voltmeter AC(075V)
------------------
5439,13/08
/03
M/s Anand
Elect,40293,379
51
02
950/-
1900/-
Basic Electrical Engineering Lab Manual
Page | 8
DAVIET
ELECTRICAL DEPARTMENT
Basics of Electrical Engineering Laboratory
Laboratory In-charge:
Email:[email protected]
Phone:
Lab Assistant: Mr. Tejinder Singh
Email: [email protected]
Phone: 9814947600
Basic Electrical Engineering Lab Manual
Page | 9
DAVIET
ELECTRICAL DEPARTMENT
Safety Precautions
1. SAFETY is of paramount importance in the Electrical Engineering Laboratories.
2. Electricity NEVER EXCUSES careless persons. So, exercise enough care and attention in handling
electrical equipment and follow safety practices in the laboratory. (Electricity is a good servant but a
bad master).
3. Avoid direct contact with any voltage source and power line voltage. (Otherwise such contact may
subject you to electrical shock).
4. Wear laboratory-coat and avoid loose clothing. (Loose clothing may get caught on an
equipment/instrument and this may lead to an accident particularly if the equipment happens to be a
rotating machine)
5. Girl students should have their hair tucked under their coat or have it in a knot.
6. Do not wear any metallic rings, bangles, bracelets, wristwatches and neck chains. (When you move
your hand/body, such conducting items may create a short circuit or may touch a live point and
thereby subject you to electrical shock).
7. Be certain that your hands are dry and that you are not standing on wet floor. (Wet parts of the body
reduce the contact resistance thereby increasing the severity of the shock).
8. Ensure that the power is OFF before you start connecting up the circuit. (Otherwise you will be
touching the live parts in the circuit)
9. Get you circuit diagram approved by the staff member and connect up the circuit strictly as per the
approved circuit diagram.
10. Check power chords for any sign of damage and be certain the chords use safety plugs and do not
defeat the safety feture of these plugs by using ungrounded plugs.
11. When using connection leads, check for any insulation demage in the leads and avoid such defective
leads.
12. Do not defeat any Safety devices such as fuse or circuit breaker by shorting across it.
13. Switch on the power to your circuit and equipment only after getting them checked up and approved
by the staff member.
14. Take the measurement with one hand in your pocket.
15. Do not make any change in the connection without the approval of the staff member.
16. In case you notice any abnormal condition in your circuit (like insulation heating up, resistor heating
up etc).
17. Switch off the power to your circuit immediately and inform the staff member.
18. Keep hot soldering iron in the holder when not in use.
Basic Electrical Engineering Lab Manual
Page | 10
DAVIET
ELECTRICAL DEPARTMENT
ELECTRICAL SYMBOLS
Symbol
Component name
Meaning
Wire Symbols
Electrical Wire
Conductor of electrical current
Connected Wires
Connected crossing
Not Connected Wires
Wires are not connected
Switch Symbols and Relay Symbols
SPST Toggle Switch
Disconnects current when open
SPDT Toggle Switch
Selects between two connections
Pushbutton Switch (N.O)
Momentary switch - normally open
Pushbutton Switch (N.C)
Momentary switch - normally closed
DIP Switch
DIP switch is used for onboard configuration
SPST Relay
Relay open / close connection by an electromagnet
SPDT Relay
Jumper
Close connection by jumper insertion on pins.
Solder Bridge
Solder to close connection
Ground Symbols
Earth Ground
Used for zero potential reference and electrical shock protection.
Basic Electrical Engineering Lab Manual
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DAVIET
Chassis Ground
ELECTRICAL DEPARTMENT
Connected to the chassis of the circuit
Digital / Common Ground
Resistor Symbols
Resistor (IEEE)
Resistor reduces the current flow.
Resistor (IEC)
Potentiometer (IEEE)
Adjustable resistor - has 3 terminals.
Potentiometer (IEC)
Variable Resistor /
Rheostat (IEEE)
Adjustable resistor - has 2 terminals.
Variable Resistor /
Rheostat (IEC)
Trimmer Resistor
Preset resistor
Thermistor
Thermal resistor - change resistance when temperature changes
Photoresistor / Light
dependent resistor (LDR)
Photo-resistor - change resistance with light intensity change
Capacitor Symbols
Capacitor
Capacitor is used to store electric charge. It acts as short circuit with AC
and open circuit with DC.
Capacitor
Polarized Capacitor
Electrolytic capacitor
Polarized Capacitor
Electrolytic capacitor
Basic Electrical Engineering Lab Manual
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DAVIET
Variable Capacitor
ELECTRICAL DEPARTMENT
Adjustable capacitance
Inductor / Coil Symbols
Inductor
Coil / solenoid that generates magnetic field
Iron Core Inductor
Includes iron
Variable Inductor
Power Supply Symbols
Voltage Source
Generates constant voltage
Current Source
Generates constant current.
AC Voltage Source
AC voltage source
Generator
Electrical voltage is generated by mechanical rotation of the generator
Battery Cell
Generates constant voltage
Battery
Generates constant voltage
Controlled Voltage Source
Generates voltage as a function of voltage or current of other circuit
element.
Controlled Current Source
Generates current as a function of voltage or current of other circuit
element.
Meter Symbols
Voltmeter
Measures voltage. Has very high resistance. Connected in parallel.
Ammeter
Measures electric current. Has near zero resistance. Connected serially.
Basic Electrical Engineering Lab Manual
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DAVIET
ELECTRICAL DEPARTMENT
Ohmmeter
Measures resistance
Wattmeter
Measures electric power
Lamp / Light Bulb Symbols
Lamp / light bulb
Lamp / light bulb
Generates light when current flows through
Lamp / light bulb
Diode / LED Symbols
Diode
Diode allows current flow in one direction only - left (anode) to right
(cathode).
Zener Diode
Allows current flow in one direction, but also can flow in the reverse
direction when above breakdown voltage
Schottky Diode
Schottky diode is a diode with low voltage drop
Varactor / Varicap Diode
Variable capacitance diode
Tunnel Diode
Light Emitting Diode
(LED)
LED emits light when current flows through
Photodiode
Photodiode allows current flow when exposed to light
Transistor Symbols
NPN Bipolar Transistor
Allows current flow when high potential at base (middle)
PNP Bipolar Transistor
Allows current flow when low potential at base (middle)
Basic Electrical Engineering Lab Manual
Page | 14
DAVIET
ELECTRICAL DEPARTMENT
Darlington Transistor
Made from 2 bipolar transistors. Has total gain of the product of each gain.
JFET-N Transistor
N-channel field effect transistor
JFET-P Transistor
P-channel field effect transistor
NMOS Transistor
N-channel MOSFET transistor
PMOS Transistor
P-channel MOSFET transistor
Misc. Symbols
Motor
Electric motor
Transformer
Change AC voltage from high to low or low to high.
Electric bell
Rings when activated
Buzzer
Produce buzzing sound
Fuse
The fuse disconnects when current above threshold. Used to protect circuit
from high currents.
Fuse
Bus
Bus
Contains several wires. Usually for data / address.
Bus
Optocoupler / Optoisolator
Optocoupler isolates connection to other board
Basic Electrical Engineering Lab Manual
Page | 15
DAVIET
ELECTRICAL DEPARTMENT
Loudspeaker
Converts electrical signal to sound waves
Microphone
Converts sound waves to electrical signal
Operational Amplifier
Amplify input signal
Schmitt Trigger
Operates with hysteresis to reduce noise.
Analog-to-digital
converter (ADC)
Converts analog signal to digital numbers
Digital-to-Analog
converter (DAC)
Converts digital numbers to analog signal
Crystal Oscillator
Used to generate precise frequency clock signal
Antenna Symbols
Antenna / aerial
Transmits & receives radio waves
Antenna / aerial
Dipole Antenna
Two wires simple antenna
Logic Gates Symbols
NOT Gate (Inverter)
Outputs 1 when input is 0
Basic Electrical Engineering Lab Manual
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DAVIET
ELECTRICAL DEPARTMENT
AND Gate
Outputs 1 when both inputs are 1.
NAND Gate
Outputs 0 when both inputs are 1. (NOT + AND)
OR Gate
Outputs 1 when any input is 1.
NOR Gate
Outputs 0 when any input is 1. (NOT + OR)
XOR Gate
Outputs 1 when inputs are different. (Exclusive OR)
D Flip-Flop
Stores one bit of data
Multiplexer / Mux 2 to 1
Connects the output to selected input line.
Multiplexer / Mux 4 to 1
Demultiplexer / Demux 1
to 4
Connects selected output to the input line.
Basic Electrical Engineering Lab Manual
Page | 17
DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 1
AIM: To verify Ohm’s Law and Its limitation.
OBJECTIVE: (1) To show that ratio of applied voltage to current in a circuit is constant when physical
conditions do not change, it represents Ohm’s law.
(2)When temperature changes the ratio of voltage to current doesn’t remain constant but it
changes because resistance of the circuit changes.
APPARATUS REQUIRED:
1.) D.C. Source (6 V or 12V)
2.) One D.C. voltmeter of range……..
3.) One D.C. ammeter of range……..
4.) One rheostat Rh of rating.
5.) Resistive load RL
6.) Switch i.e. double pole single throw.
7.) Connecting leads.
CIRCUIT DIAGRAM:
Fig. 1(a)
THEORY: The relation between voltage and current is explained by Ohm’s law. Ohm’s law states that
current flowing through a circuit or conductor is directly proportional to the voltage applied across it provided
the physical conditions like temperature etc. remain the same, i.e. I α V.
Fig. 1(b)
Basic Electrical Engineering Lab Manual
Page | 18
DAVIET
ELECTRICAL DEPARTMENT
LIMITATIONS OF OHM’S LAW: Ohm’s law doesn’t hold good if the temperature of the circuit of
resistance changes.
PROCEDURE:
1.)
2.)
3.)
4.)
5.)
6.)
Connect the apparatus as per the circuit shown in fig. 1(a).
Get the connections checked by the teacher in charge.
Switch-ON the supply through switch S.
Insert whole of the resistance of rheostat in the circuit and take the reading of voltmeter and ammeter.
Change the value of Rh in steps and take the reading of voltmeter and ammeter.
Record the observations in the observation table.
OBSERVATIONS:
S.NO.
VOLTMETER
READING IN VOLT (V)
AMMETER READING IN
AMPERE (A)
RESISTANCE IN OHM
RL = V/I
1.
2.
3.
4.
5.
From the Observations plot a graph with suitable scale, taking voltage on X-axis and current on Y-axis.
CONCLUSION: The ratio of applied voltage across the circuit to current flowing through it remains constant
provided that physical conditions like temperature don’t change.
Basic Electrical Engineering Lab Manual
Page | 19
DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 2
AIM: To verify the Kirchhoff’s Law.
OBJECTIVE: To make the students familiar with the Kirchhoff’s laws which are very important for the
solution of electric network.
APPARATUS REQUIRED:
1.) Two D.C. voltage source E1 and E2 (6V or12V)
2.) Three D.C. ammeters (A, A1 and A2)
3.) Three variable resistors R1, R2, R3 variable carbon resistors.
4.) Five D.C. voltmeters VE1, VE2, V1, V2, V3 (or digital multimeter).
5.) One rheostat Rh
6.) Main Switch (S) and two single way switches S1 and S2.
7.) Connecting leads etc.
CIRCUIT DIAGRAM:
Fig. 2(a) & 2(b)
THEORY: Kirchhoff’s First Law: It states that at any junction, sum of incoming currents is equal to the sum
of outgoing currents.
Kirchhoff’s Second Law: It states that in any closed mesh or circuit the algebraic sum of all the e.m.f.’s plus
the sum of all the voltage drops is equal to zero, i.e. according to fig. 2(b).
In circuit ABCDA;
E1 - I1R1 - (I1+I2) R3 = 0 or VE2 – V1 – V3 = 0 or
VE1 = V1 + V3
Basic Electrical Engineering Lab Manual
and
Page | 20
DAVIET
ELECTRICAL DEPARTMENT
In circuit FEBCF,
E2 – I2R2 – (I1 + I2)R3 = 0
or VE2 – V2 – V3 = 0
or VE2 = V1 + V3
PROCEDURE:
1.)
2.)
3.)
4.)
5.)
6.)
Connect the apparatus as per the circuit shown in fig. 2(a) and 2(b).
Get the connections checked by the teacher in charge.
Switch-ON the switch S and take the readings of three ammeters.
Change the value of Rh in steps and take the readings of A, A1, and A2.
For the verification of Kirchhoff’s Second Law switch on the switch S1 and S2.
Take the readings of different voltmeters VE1, V1, V2, V3 and VE2 or measure the voltages across various
terminals with the help of digital multimeter and note down them in the observation table.
7.) Change the value of the resistors R1, R2 and R3 in steps and take the readings of voltmeters VE1, V1, V2,
V3 and VE2 each time.
OBSERVATION: (1) For verification of Kirchhoff’s Law;
S. NO.
AMMETER READING IN
AMPERE
A1 = I1
A2 = I 2
A=I
THEORETICAL MEASURED
CURRENT
CURRENT
I = I1+I2
I=A
1.
2.
3.
Check that measured current must be equal to theoretical current, i.e. Ammeter reading of ammeter A =
reading of ammeter A1 + reading of ammeter A2.
(2) For verification of Kirchhoff’s second Law;
S.NO.
VE1=E1
VE2=E2
OBSERVATIONS
VERIFICATION
V1=I1R1 V2=I2R2 V3=(I1+I2)R3 VE1=V1+V2 VE2=V2+V3
1.
2.
3.
CONCLUSION: (1) The readings tabulated in observation table-1 show that in an electrical network
incoming currents are equal to the outgoing currents at a junction.
(2) The readings tabulated in observation table-2 show that in a closed circuit or mesh the algebraic sum
of all the e.m.f.’s plus the algebraic sum of all the voltage drops is equal to zero.
Basic Electrical Engineering Lab Manual
Page | 21
DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 3
AIM: To measure the resistance and inductance of a coil by ammeter-voltmeter method.
OBJECTIVE: To make the students familiar, how to determine the parameters of an ac single-phase series
circuit.
APPARATUS REQUIRED:
1.) Single-phase 230V ac Supply.
2.) One choke coil.
3.) A single-phase auto-transformer or variac.
4.) One A.C. ammeter of range ……
5.) One A.C. voltmeter of range ……
6.) One A.C. wattmeter of range ……
7.) Connecting leads etc.
CIRCUIT DIAGRAM:
Fig. 3
THEORY:
Power in an ac circuit, P = V2/R =W
Resistance of the choke, R = V2/W
Impedance of the choke, Z = V/I
Inductive reactance of the choke, XL = √ (Z2 – R2)
Inductance of the choke, L = XL/2πf Henry
Basic Electrical Engineering Lab Manual
Page | 22
DAVIET
ELECTRICAL DEPARTMENT
PROCEDURE:
1.) Connect the apparatus as per the circuit shown in fig. 3.
2.) Get the connections checked by the teacher in charge.
3.) Set the variac to give almost 25% of the supply voltage to the circuit.
4.) Take the reading of wattmeter (W), ammeter (A) and voltmeter (V) and record them in the observation
table.
5.) Make the calculations to get the value of R and L.
6.) Change the setting of variac and repeat the steps (4) and (5).
7.) Again change the setting of variac and repeat the steps (4) and(5).
OBSERVATION TABLE:
S.NO.
OBSERVATIONS
W
I
CALCULATIONS
V
R = V2/W
Z = V/I
XL = √ (Z2 – R2) L = XL/2πf
1.
2.
3.
RESULT: The value of R and L comes out to be the same in all the three settings.
Basic Electrical Engineering Lab Manual
Page | 23
DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 4
AIM: To find the voltage, current relationship in a R-L series circuit and to determine the power factor of the
circuit.
APPARATUS REQUIRED:
S.NO
1.
2.
3.
4.
5.
6.
7.
8.
NAME OF APPARATUS
VARIAC(Single Phase)
Resistive load
Inductive load
AC voltmeter
AC Ammeter
Wattmeter(single phase)
DPIC main switch
Connecting Leads
RANGE
0-260 V
0-10 A
0-10 A
0-300 V
0-10 A
0-1 KW
32V
-----
QUANTITY
1
1
1
1
1
1
1
As per requirement
THEORY: When only resistive load is connected with AC supply then the power factor remains Unity but
when inductive load is connected with AC supply then the power factor reduces, it can be ½ i.e. efficiency of
single phase system reduces to 50% which effects our electricity consumptions well as AC Efficiency. But
many stages RL series circuit is used for eg. Street light. So when a resistance and an inductor both are
connected in series then this type of circuit is called RL Series circuit and total resistance of both is called
impedance. And is denoted by Z and its units are Ohm.
So:- Current flowing through an AC circuit is given as I=V/Z
Where V is the AC supply voltage and Z is the impedance of the circuit in ohms.
Power factor of an AC supply is given by cosΦ=P/VI
Where P is the power of the given load circuit in watts, V is the voltage applied to the circuit in the
Volts and I is the current in amperes flowing through the circuit.
And the angle Φ is known as relation between V and I and its value can be calculated by following
Formula:- Φ =
(P/VI)
CIRUCIT DIAGRAM:
Fig. 4
Basic Electrical Engineering Lab Manual
Page | 24
DAVIET
ELECTRICAL DEPARTMENT
PROCEDURE: Do as follows:
1.) Make the connections of Variac, ammeter, wattmeter, voltmeter, load, as shown in circuit diagram.
2.) Connect this circuit to the main single phase supply.
3.) Take the readings of ammeter, wattmeter, voltmeter for every 50V setting of Variac in the
Observation table as given below.
4.) Note down 5-6 readings.
OBSERVATION AND CALCULATION:
S.NO. VOLTMETER AMMETER POWER(P) COSΦ=P/VI
READING (V) READING(I) WATTS
1.
2.
3.
4.
5.
6.
(P/VI)
PRECAUTIONS:1. Connections should be right & tight.
2. Always take accurate reading.
3. Meters used should be without error.
4. Be alert while doing practical.
RESULT:1. Current I increase directly in proportion to applied voltage V.
2. Power factor of the circuit is approx. same throughout for a given load.
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Page | 25
DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 5
AIM: To verify the voltage and current relations in star and delta connected system.
APPPARTUS REQUIRED
S.NO.
NAME OF APPARATUS
Variac(3-phase)
1.
3-phase Balanced Resistive
2.
load
AC voltmeter
3.
AC Ammeter
4.
TPIC main switch
5.
Connecting leads
6.
RANGE
0-460V
0-10A
QUANTITY
1
1
0-500V
0-10A
32A
------
3
3
1
As per
requirement
THEORY:
When Star connections are done
Line voltage (VL)=√3 X Phase voltage (Vph)
Line current (IL) =Phase current (Iph)
When Delta connections are done
Line voltage (VL) =Phase voltage (Vph)
Line current (IL) =√3 X Phase current (Iph)
CIRCUIT DIAGRAM:
Fig. 6
PROCEDURE: Do as follows:
1. Make the connections of variac, ammeter, wattmeter and voltmeter & 3 –ph load, as shown in diagram.
2. Connect this circuit to the main single phase supply.
3. Take the reading of ammeter, wattmeter and voltmeter in the observation table as given below.
4. Note down 3-4 readings.
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DAVIET
ELECTRICAL DEPARTMENT
OBSERVATION AND CALCULATION:
Connections
S.No.
Voltmeter
Reading(VL)
Voltmeter
reading(Vph)
Ammeter
reading (IL)
Ammeter
reading(Iph)
1.
STAR
DELTA
2.
3.
4.
1.
2.
3.
4.
PRECAUTIONS:
1. Connections should be right & tight.
2. Always take accurate reading.
3. Meters used should be without error.
4. Be alert while doing practical.
RESULT:
When Star connections are done
Line voltage (VL) =√3 X Phase voltage (Vph)
Line current (IL) =Phase current (Iph)
When Delta connections are done
Line voltage (VL) =Phase voltage (Vph)
Line current (IL) =√3 X Phase current (Iph)
Basic Electrical Engineering Lab Manual
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DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO.6
AIM: To measure power and power factor in single phase ac circuit.
APPARATUS REQUIRED:
S.NO
1.
2.
3.
4.
5.
6.
7.
8.
NAME OF APPARATUS
VARIAC(Single Phase)
Resistive load
Inductive load
AC voltmeter
AC Ammeter
Wattmeter(single phase)
DPIC main switch
Connecting Leads
RANGE
0-260 V
0-10 A
0-10 A
0-300 V
0-10 A
0-1 KW
32V
-----
QUANTITY
1
1
1
1
1
1
1
As per requirement
THEORY: When only resistive load is connected with AC supply then the power factor remains Unity but
when inductive load is connected with AC supply then the power factor reduces, it can be ½ i.e. efficiency of
single phase system reduces to 50% which effects our electricity consumptions well as AC Efficiency. But
many stages RL series circuit is used for eg. Street light. So when a resistance and an inductor both are
connected in series then this type of circuit is called RL Series circuit and total resistance of both is called
impedance. And is denoted by Z and its units are Ohm.
So:- Current flowing through an AC circuit is given as I=V/Z
Where V is the AC supply voltage and Z is the impedance of the circuit in ohms.
Power factor of an AC supply is given by cosΦ=P/VI
Where P is the power of the given load circuit in watts, V is the voltage applied to the circuit in the
Volts and I is the current in amperes flowing through the circuit.
And the angle Φ is known as relation between V and I and its value can be calculated by following
Formula:- Φ =
(P/VI)
CIRUCIT DIAGRAM:
Fig. 7
PROCEDURE: Do as follows:
1.) Make the connections of Variac, ammeter, wattmeter, voltmeter, load, as shown in circuit diagram.
2.) Connect this circuit to the main single phase supply.
3.) Take the readings of ammeter, wattmeter, voltmeter for every 50V setting of Variac in the
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DAVIET
ELECTRICAL DEPARTMENT
Observation table as given below.
4.) Note down 5-6 readings.
OBSERVATION AND CALCULATION:
S.NO. VOLTMETER AMMETER POWER(P) COSΦ=P/VI
READING (V) READING(I) WATTS
1.
2.
3.
4.
5.
6.
(P/VI)
PRECAUTIONS:1. Connections should be right & tight.
2. Always take accurate reading.
3. Meters used should be without error.
4. Be alert while doing practical.
RESULT:1. Current I increase directly in proportion to applied voltage V.
2. Power factor of the circuit is approx. same throughout for a given load.
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DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 7
AIM: To verify the series and parallel resonance in AC circuits.
OBJECTIVE: To make the students familiar with RLC- series and parallel resonance.
APPARATUS REQUIRED:
1.
2.
3.
4.
5.
6.
7.
Single phase ac supply.
Signal generator to supply variable frequency to the circuit.
A choke coil having resistance and inductance.
An electrolytic capacitor (ac).
An ac ammeter
A variable resistance Rh (Rheostat)
Connecting leads.
CIRCUIT DIAGRAM:
Fig. 8(a)
Fig. 8(a.1)
Fig. 8(b.1)
Fig. 8(b)
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DAVIET
ELECTRICAL DEPARTMENT
THEORY: At resonance, XL=XC
2πfL = 1/2πfC; fr = 1/2πLC then impedance, Zr = R
 Current is maximum at resonance in RLC series circuit.
In RLC parallel circuits, the current will be minimum at resonance.
PROCEDURE:
1.
2.
3.
4.
5.
Make the connections as per circuit diagram as shown in fig. a.
Get the connections checked by the teacher in charge.
Bring the needle of signal generator to minimum (zero) frequency.
Switch ON the power supply to the signal generator.
Increase the frequency supplied to the circuit gradually and records the ammeter readings in the
observation table.
6. Note the value of frequency on the signal generator against maximum current; it represents the
resonance of frequency.
7. Switch OFF the supply bring the needle of signal generator to zero, change the value of Rh and repeat
the steps 4,5 and 6.
8. Switch OFF the supply and change the connections as shown in fig.b.
9. Repeat the experiment, by changing the frequency get minimum value of current.
10. Record the readings in the table for parallel ac circuits.
OBSERVATION TABLE:
S.NO.
RHEOSAT SET FORRh1
RHEOSAT SET FOR Rh2
RHEOSAT SET FOR Rh3
Reading of
signal
generator (f)
Reading of
signal
generator (f)
Reading of
signal
generator (f)
Reading of
ammeter (I)
Reading of
ammeter (I)
Reading of
ammeter (I)
FOR SERIES RESONANCE CIRCUIT
1.
2.
FOR PARALLEL RESONANCE CIRCUIT
1.
2.
RESULT: In all the three settings, the value of resonance frequency comes out to be the same because
resonance frequency is independent of circuit resonance.
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DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 8
AIM: To observe the B-H loop of a ferromagnetic core material on CRO.
APPARATUS: CRO, Ferromagnetic material.
THEORY:
In ferromagnetic material, the magnetic flux density B increases with the applied field strength H, according
to the law:
B=µ0(m+ H)
B=µH
When a magnetic material is magnetized the curve obtained between flux density B and magnetizing force H
is called Hysteresis curve.
CIRCUIT DIAGRAM:
Fig. 9
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DAVIET
ELECTRICAL DEPARTMENT
PROCEDURE:
1. As the magnetizing force H is kept on the increasing, the flux density the flux density also increases.
2. Now H is reduced and B will also start reducing but now it will choose separate path.
3. In order to remove this H is to be reduced again i.e. increased negatively .It makes B zero where H is
OD.
4. Now if H is kept on increasing in its reverse direction, to its maximum value, then we can say curve is
DP.
5. Now again if magnetizing force is removed, the B will not become zero and its value will be OQ.
6. Now if magnetizing force is reduced to make flux density zero again, then it is to be reversed again
and a value of OR H will make flux density zero.
7. If H will be kept on increasing then it will again reach to be L point, thus the curve covers a complete
path i.e. OLMDPQRL. This curve is called hysteresis curve.
OBSERVATION AND CALCULATION:
S.NO.
CURRENT
FORWARD DIRECTIONS
FLUX
DENSITY
REVERSE DIRECTIONS
FLUX
DENSITY
1
2
PRECAUTIONS:
1. All the connections should be kept tightly.
2. Handle all the apparatus very gently.
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DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 9
AIM: To use a bridge rectifier for full-wave rectification of AC
determine the relationship between RMS and average values of the rectified voltage.
supply
and
to
OBJECTIVE: i) To make the students familiar with the full wave rectifier.
ii) How dc is obtained at the output of a bridge rectifier.
APPARATUS REQUIRED:
1.
2.
3.
4.
5.
6.
7.
Single phase ac supply.
230/12V, single phase transformer.
Four diodes ( say IN4005-4 in number)
Load resistance.
Multimeter to read rms (ac) voltage at input and average (dc) voltage at the output.
One electrolytic capacitor as a filter.
Connecting leads.
CIRCUIT DIAGRAM:
Fig. 10
THEORY: During the +ve half cycle diode D1 and D3 conduct and current flows from M’ to L’ whereas
during –ve half cycle diode D2 and D4 conduct and current flows from M’ to L’. Thus, full wave is rectified.
But this output contains ripples which are suppressed by filter capacitor C placed parallel to the load.
Rms value is obtained by connecting multimeter leads across A’B’ (ac setting)
Average value is obtained by connecting multimeter leads across M’L’ (dc setting)
Vrms= 0.707Vm and Vave= 0.637Vm
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DAVIET
ELECTRICAL DEPARTMENT
PROCEDURE:
1.
2.
3.
4.
Make the connections as shown in the circuit diagram.
Get the connections checked by the teacher in charge.
Switch ON the single phase ac supply to the circuit.
Measure the voltage across terminal A’B’ as rms value of voltage and voltage across M’L’ as average
value of voltage and record this value in the observation table.
5. Switch OFF the supply and dismantle the circuit.
OBSERVATION:
Voltage across terminal A’B’, Va’b’ = Vrms =………….
Voltage across terminal M’L’, Vm’l’= Vavg =………….
RESULT: Vrms > Vavg.
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DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 10
AIM: To measure minimum operating voltage, current drawn, power consumed and power factor of a
fluorescent tube light.
OBJECTIVE: i) To observe that a fluorescent tube light does not glow at low voltages, it required sufficient
voltage.
ii) It never operates unity power factor.
APPARATUS REQUIRED:
1. Single Phase 230V ac supply.
2. One fluorescent tube set with tube, choke and starter.
3. One single phase auto transformer or variac.
4. One ac wattmeter.
5. One ac ammeter.
6. One ac voltmeter.
7. Connecting leads.
CIRCUIT DIAGRAM:
Fig. 11
THEORY: Fluorescent tube glows only at sufficient supply voltage. It operates at less than unity power
factor.
Power factor, cos$ = W/ V*I.
PROCEDURE:
1.
2.
3.
4.
5.
6.
7.
8.
Make the connections as per the circuit diagram shown in fig.
Get the connections checked by the teacher in charge.
Set the variac at the zero input voltage.
Switch ON the ac supply through switch S.
Increase the voltage across the tube circuit gradually till tube starts glowing continuously.
Record the voltage, current and power in the observation table.
Switch OFF the supply and bring the variac at zero position.
Switch ON the supply and increase the voltage gradually and record the voltmeter, ammeter and
wattmeter reading when tube starts glowing continuously.
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DAVIET
ELECTRICAL DEPARTMENT
9. Repeat the experiment 3 to 4 times.
10. Switch OFF the supply and dismantle the circuit.
OBSERVATION TABLE:
S.NO.
OBSERVATIONS
V
I
W
CALCULATIONS
p.f., cosΦ=W/VI
1.
2.
3.
RESULT:
1. Every time, the tube starts glowing continuously almost at the same voltage which is slightly than its rated
voltage i.e. 230V. But it does not glow at lower voltages that are why it is binding on the supplier to supply
power at +- 6% of the rated voltage.
2. Tube never operates at unity p.f., it always operates at a p.f. less than unity.
Basic Electrical Engineering Lab Manual
Page | 37
DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 12
AIM: To obtain the characteristics of a transistor under common base and common emitter configuration.
APPARATUS REQUIRED
S.NO.
NAME OF APPARATUS
Experiment kit
1.
2
3.
4.
Transistor
resistor
dc ammeter
5.
dc voltmeter
6.
Connecting Leads
RANGE
NPN
transistor
NPN
100Ω,0.5W
0 -A
0 -A
0 – 1.5V
0 - 10V
-------
QUANTITY
1
1
1
1 each
1 each
As per
requirement
THEORY:
Transistor is a three semiconducting layers, two junction device, which is used for weak signal’s
amplication .The input is connected in forward biased, whereas the output junction is reversed biased.
When we draw the curve between collector current and collector emitter voltage with respect to Ib then
following three regions appear;
(1)Saturation region:
When Vce increases, IC increases from zero to near saturation value of Ib .When Vce is reduced ,Ic doesn’t
reduced. In this region input as well as junctions is forward biased.
(2)Active region:
When Vce is increased further output junction is reversed biased . the transistor operates in active region and
Ic increases Vce fiased . the transistor operates in active region and Ic increases Vce for constant value of
Ib.In this region the input junction is forward biased and output junction is reversed biased.The value of Ic can
be changed by changing the value of Ib.
(3)Cutoff region:
When Ib =0,still some Ic =Iceo flows in the collector region. This is independent of Ib or Vce.
In this region both the junctions are reversed biased.
TRANSISTORS CHARACTERISTICS
INPUT CHARACTERISTICS:
In common base configuration, the curve plotted b/w the emitter current Ie and the emitter base voltage
Veb.At constant collector-base voltage Veb,is called input characteristics. Then input dynamics resistance:
Ri=∆Veb at constant Veb
∆ Ie
OUTPUT CHARACTERISTICS
In common base configuration ,the curve plotted b/w the collector current Ic and the collector base voltage
Vcb ,at constant emitter current Ie is called Output characteristics.
Then output dynamic resistance:
Ro=∆Vcb at constant Ie
∆Ic
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DAVIET
ELECTRICAL DEPARTMENT
For both the characteristics,we may determine dc and ac current amplification factor:
αac = ∆Ic at constant Vcb
∆Ie
αde = Ic at constant Vcb
Ie
CIRCUIT DIAGRAM:
Fig. 17
OUTPUT CHARACTERISTICS:
In common base configuration, the curve plotted b/w collector current Ic and the collector base
voltage Vcb ,at constant emitter current Ie is called is output characteristic then output dynamic resistance:
Ro = ∆ Vcb
at constant Ie
∆Ic
I or both the characteristics, may determine dc and ac current amplification factor:
αac = ∆Ic at constant Vcb
∆Ie
αdc = Ic at constant Vcb
Ie
PROCEDURE:
1. Make the connections as per circuit diagram.
2. Set both the power supplies at zero.
3. Switch on the AC input to both the power supplies.
4. For input characteristics fix end voltage Vcb=5V
5. Now increase the Veb voltage in steps of 0.05 V and note down the corresponding value of emmiter
current Ie and record them in the observation table.
6. Draw the input characteristics taking Veb on X axis and Ie on Y axis.
7. Repeat the steps for Vcb=10 V.
8. For output, fix Ie = mA ie , keeps the input circuit open.Change the collector base voltage Vcb in steps
and note down the corresponding values of Ic in observation table.
9. Draw the output characteristics taking Vcb on X axis and Ic on Y axis.
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DAVIET
ELECTRICAL DEPARTMENT
OBSERVATION AND CALCULATION:
A. FOR INPUT CHARACTERISTICS
CHARACTERISTICS S.NO.
VCB=5V
VOLTMETER AMMETR
READING
READING
(VEB)VOLTS
(IE)mA
1.
FOR INPUT
2.
3.
4.
VCB=10V
VOLTMETER AMMETER
READING
READING
(VEB)VOLTS
(IE)mA
B.FOR OUTPUT CHARACTERISTICS
CHARACTERISTICS
S.NO.
IE=0 mA
VOLTMETER
READING
(VCB)VOLTS
AMMETER
READING
(IC)mA
IE=2mA
VOLTMETER
READING
(VEB)VOLTS
AMMETER
READING
(IE)mA
IE=4mA
VCB
VOLTS
IC
mA
1.
FOR OUTPUT
2.
3.
4.
PRECAUTIONS:
1. Connections should be right and tight.
2. Always take accurate reading.
3. Meters used should be without error.
4. Be alert while doing practical.
Basic Electrical Engineering Lab Manual
Page | 40
DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 13
AIM: To perform open circuit & short circuit tests of a single phase transformer. Also find the transformation
ratio & efficiency.
A.FOR OPEN CIRCUIT TEST:
APPARATUS REQUIRED:
S.NO.
NAME OF APPARATUS
Variac(3-phase)
1.
1-Phase transformer
2.
AC voltmeter
3.
Wattmeter
4.
AC Ammeter
5.
DPIC main switch
6.
Connecting leads
7.
RANGE
0-270V
2kv A
0-300V
0-1000W
0-1 A
32 A
-------
QUANTITY
1
1
2
1
3
1
As per
requirement
THEORY:
When open circuit test is performed, the secondary side of the transformers on no load. The primary
is supplied at its rated voltage, since there is no current in the secondary, a very small current flows through
primary. So copper loses are negligible &the wattmeter gives only iron loses.
CIRCUIT DIAGRAM:
Fig. 18(a)
PROCEDURE: Do as follows:
1. Make the connections of variac ,ammeter,voltmeter&a single-phase transformer
as shown in circuit diagram.
2. Set the Variac to zero position.
3. Switch on the power supply.
4. Increase the variac voltage till rated primary voltage is reached.
5. Take the reading of ammeter,wattmeter,voltmeter in the observation table as given
below.
6. Now find transformation ratio.
Basic Electrical Engineering Lab Manual
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DAVIET
ELECTRICAL DEPARTMENT
OBSERVATION AND CALCULATION
S.NO.
PRIMARY SIDE
SECONDAR
Y SIDE
CURRENT POWER VOLTAGE
IO
WI
VS
VOLTAGE
VP
TRANSFORMATION
RATIO,
K=VS/VP
1.
2.
3.
4.
5.
PRECAUTIONS:
1. Connections should be right &tight.
2. Always take accurate reading.
3. Meters used should be without error.
4. Be alert while doing practical.
RESULT:
In open circuit test we find iron loses.
B.FOR SHORT CIRCUIT TEST:
APPARATUS REQUIRED:
S.NO. NAME OF APPARATUS
Variac(3-phase)
1.
1-phase transformer
2.
AC voltmeter
3.
Wattmeter
4.
AC Ammeter
5.
DPIC main switch
6.
Connecting leads
7.
RANGE
0-270V
2kv A
0-300 V
0-1000W
0-10a
32A
------
QUANTITY
1
1
1
1
2
1
As per requirement
THEORY:
When short circuit test is performed , the secondary side of the transformer is short circuited. The
primary is supplied at very less voltage, since there is heavy current in the secondary, a very large current
flows through primary .so copper loses occurs & the wattmeter gives only copper loses.
CIRCUIT DIAGRAM:
Fig. 18(b)
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DAVIET
ELECTRICAL DEPARTMENT
PROCEDURE: Do as follows:
1. Make the connections of variac, ammeters, voltmeter and a single phase transformer, as shown in
circuit diagram.
2. Set the variac to zero position.
3. Switch on the power supply.
4. Increase the variac voltage till rated secondary current is reached.
5. Take the readings of ammeter, voltmeter, wattmeter, in the observation table as given below.
6. Now find efficiency of transformer.
OBSERVATION AND CALCULATION:
S.NO.
PRIMARY SIDE
VOLTAGE
CURRENT
POWER
VSC
ISC
WCU
SECONDARY
SIDE
CURRENT
1.
2.
3.
4.
5.
6.
7.
PRECAUTIONS:
1. Connection should be right & tight.
2. Always take accurate reading.
3. Meters used should be without error.
4. Be alert while doing practical.
RESULT: In short circuit test we find copper losses.
Basic Electrical Engineering Lab Manual
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DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 14.a
AIM: To connect, start and reverse the direction of rotation of three-phase induction Motor.
APPARATUS REQUIRED:
S.NO.
APPARATUS
REQUIRED
3 ph induction motor
1.
Connecting Leads
2.
3.
4.
5.
6.
DOL Starter
TPIC main switch
AC voltmeter
AC Ammeter
RANGE
QUANTITY
5hp,415V
-----
1
As per
requirements
1
1
1
1
32 Amp
0-500V
0-20Amp
THEORY:
When motor is connected to a three-phase supply through a DOL Starter (Direct Online Starter) or a Star delta
Starter, then the motor should run in anticlock wise direction but/Many times motor runs clockwise. So, it is
desired to change its DOL. So, for the same we have to interchange any two supply terminal of the motor to
make its direction anti-clockwise. The starter’s main function is to protect the motor from overload condition
and it also provides easy ON-OFF the motor so it is necessary to use a starter. In this practical we have used a
DOL starter, which runs a three-phase 3hp motor, whose circuit diagram is as shown.
CIRCUIT DIAGRAM:
Fig. 21
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DAVIET
ELECTRICAL DEPARTMENT
PROCEDURE: Do as follows:
1. Make the connections as per circuit diagram-1
2. Now switch on the power supply.
3. The direction of rotation (DOR) should be noted when motors starts.
4. Now if the direction is clockwise or it is required to change the direction of rotation of motor then the
interchange any two phases as shown in diagram-3.
5. Now note the new DOR of motor.
OBSERVATIONS & CALCULATIONS
S.NO.
IN FIRST STAGE
CONNECTIONS
DOR
1.
2.
3.
4.
IN SECOND STAGE
CONNECTIONS
DOR
PRECAUTIONS:
1. Make the connections as per circuit diagram.
2. Connections should be right & tight.
3. Note the direction of rotation carefully.
4. Do every procedure carefully.
RESULT: Now we have come to know how to change the DOR of any three phase induction motor by
interchanging any two supply terminals.
Basic Electrical Engineering Lab Manual
Page | 45
DAVIET
ELECTRICAL DEPARTMENT
EXPERIMENT NO. 14.b
AIM: To connect, start and reverse the direction of rotation of DC shunt motor.
OBJECTIVE: To make the students understand that a shunt motor is started through a starter and its
direction can be reversed by interchanging the connections of armature winding.
APPARATUS REQUIRED:
1. 250 V DC supply.
2. One 250V dc shunt motor of capacity……KW.
3. One double pole single throw (DPST) switch.
4. Connecting leads.
CIRCUIT DIAGRAM:
Fig. 21(a)
Fig. 21(b)
THEORY: A dc motor draws heavy current at the start if it is started without starter because back emf is
zero at start:
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DAVIET
I = V - E B/ R A
ELECTRICAL DEPARTMENT
and at start
IS = V – 0/ RA
To limit the current at start a resistance is added in the armature circuit called starter;
IS = V/ RA + RS
However, the starting resistance is taken out of circuit gradually as the motor picks up speed and back emf
(EB) is built up.
The direction of rotation of a motor depends upon the direction of torque developed in it i.e.:
Hence, the direction of rotation of a dc motor can be reversed if the connections of armature winding are
reversed.
PROCEDURE:
1. Make the connections as per the circuit diagram shown in fig.21(a)
2. Get the connections checked by the teacher in charge.
3. Switch on the dc supply through DPST switch.
4. Start the motor with the help of a starter and note the direction of rotation of the motor.
5. Switch OFF the supply.
6. Change the connections as shown in fig.21(b) and switch ON the supply.
7. Start the motor with the help of starter and note the direction of rotation.
8. Switch OFF the supply.
RESULTS:
1. Direction of rotation of motor with the connections as shown in fig.21 (a) = ……….. (Say clockwise).
2. Direction of rotation of motor with the connections as shown in fig.21 (b) = ……….. (Say anticlockwise).
Thus, the direction of rotation is reversed by interchanging the connection of armature winding.
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Experiment-15
Aim of experiment: To find efficiency & voltage regulation of a single phase transformer under
different loading conditions.
Equipment:
1. Single- Phase Transformer (2 Kva, 220 V/220 V)
-------------------
01
2. Voltmeter 0-300 V----------------------------------------------------------
02
3. Ammeter 0-10 A ----------------------------------------------------------
02
4. Wattmeter 0-2000 W--------------------------------------------------------
02
5. Variac 0-270 V--------------------------------------------------------------
01
6. Connecting leads.
Theory
A transformer is a static electrical machine which converts or transfers an electrical power from one
circuit to other.
A transformer is a static electrical machine which converts or transfers an electrical power from one
circuit to other. We know that there are certain relations between two voltages & the two currents in the
transformer. Also the volt ampere V1 . I1 ;V2 . I2 & the power V1 . I1 . Cos¢1 ; V2 . I2 . Cos¢2 remain the
same on the two sides of an ideal transformer.
Neglecting the no load current , the relations are:
V2/ V1 = N2 / N1 --------------------------------------- 1
I1/ I2 = N2 / N1 --------------------------------------- 2
V1. I1 = V2. I2 -------------------------------------- 3 & The power
V1 . I1 . Cos¢1 =V2 . I2 . Cos¢2 ------------------------------- 4
To verify the same, the transformer should be loaded & the quantities on the both sides are compared.
The working principle of a transformer is that the energy may be efficiently transferred from one coil to
another by means of varying magnetic flux, provided that both the set of coils are on a common magnetic
circuit. In a transformer the coil and the magnetic circuit all are stationary with respect to each other.
When the primary winding is connected to ac supply mains and a current flows through it and when the
secondry circuit is connected with the load then the current flows through the secondry winding. The
magnitude and the phase of the secondary current I2 w.r.t. secondary terminal voltage V2 will depend on the
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characteristics of the load i.e. current I2 will be in phase, lag behind and lead the terminal voltage V2
respectively when the load is non-inductive, inductive and capacitive.
Transformer efficiency :
We know that the rated capacity of a transformer is defined as the product of rated voltage and full
current on the output side. The power output depends on the power factor of the load. The efficiency may be
defined as the ratio of output power to input power & it is denoted by symbol η.
% Efficiency (η%) = output power x 100
Input power
= output power x 100
Output power +iron losses +copper losses
Voltage regulation of a transformer
We also know that the way in which the secondary voltage varies with the load depends on the load current,
the internal impedance and the load power factor. The change in secondary terminal voltage from no load to
full load at any particular load is termed the inherent regulation. It is usually expressed as a percentage or a
fraction of the rated no-load terminal voltage.
i.e. Percentage regulation = Terminal voltage on no load – terminal voltage on load
Terminal voltage on no load
= Voltage drop in transformer at load × 100
No-load rated voltage(secondary)
% voltage regulation = E2-V2 x 100
E2
Circuit diagram
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Procedure :
1. Make the connections as shown in figure.
2. Set the variac to its minimum value & keep all the switches of the load open.
3. Switch on the supply & adjust the variac output to the rated value.
4. Now switch on 25% load to get suitable currents & note down the readings of all connected meters
correspondingly in observation table.
5. Now further increase the load by 50%, 75% & 100 % respectively & note down the readings of all
connected meters correspondingly in observation table.
6. Now find efficiency & voltage regulation from readings.
7. Switch off the supply.
Observation & calculations:
S.no. Load
Observations
Primary side
V1
I1
W1
Calculations
Secondary side
V2
I2
W2
%efficiency(η%)
=
W2 x 100
W1
1
0%
2
25 %
3
50 %
4
75 %
5
100%
% voltage regulation
=
E2-V2 x 100
E2
Result
The % Efficiency (η%) = output power x 100
Input power
We also know that voltage regulation may be defined as the percentage change in voltage from no load to full
load voltage.
% voltage regulation = E2-V2 x 100
E2
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Precautions :
1. Do not touch any live terminal.
2. The reading should be accurate.
3. Don’t exceed the value of current, volts. & watts beyond range of meter.
4. Always remember alertness avoid accident.
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Experiment No. -16.a
Aim of Experiment : To Study D.C. Motor Starter.
Equipment Required:
1. 3-Point Dc Motor Starter --------------------------------------------
01
2. Shunt Wound Dc Motor 3hp, 230v, 1500rpm----------------------
01
3. Tachometer---------------------------------------------------------------- 01
4. Commecting Leads
Theory:
In the start when the DC motor armature is not rotating then a back emf is only induced in the
armature when it attains full speed. The armature resistant is very much lesser so in this case if we connect the
DC motor to direct mains then the starting current will be very much high (5 to 7 times the full load current)
which can damage the motor winding. So, for limiting the starting current and safe starting of the DC motor a
DC motor starter is required.
One of the DC motor starter i.e. 3-Point DC motor starter is as below :
3-Point Dc Motor Starter :
In a 3-POINT DC MOTOR STARTER there are additional facilities of no volt release & over
load release. It consists of a series starting resistance which is divided into several sections & are connected
with Brass studs. The connections of no volt release & over load release are done through brass arc (as shown
in fig ).
Initially, the starter arm is at OFF position i.e. Towards left . To start the motor, the DC supply is
switched-on .The starter arm is then moved to the right. When it comes in contact with stud no. 1,then the
field circuit is directly connected across the supply through brass arc. At the same time the entire resistance is
inserted in armature circuit . Some starting current flows through the armature, thus develops some torque &
the motor starts running. As the motor picks up speed, the starter arm is slowly moved towards right. Thus we
keep on moving across studs 2, 3,4,-----,etc., steadily cutting out the series resistance. Finally when arm is
brought to ON position, the resistance is totally cut-off & motor starts running at rated speed.
Following are the main parts of a 3-Point DC motor starter :
1. 3 connecting points –
a. L for main positive supply
b. A for armature connection
c. Z for field coil connection
2. A handle
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3. Overload coil or overload release
4. Studs
5. Resistance coils
6. No volt coil or no volt release.
Uses:
These starters are mainly used for a DC shunt motor
Circuit Diagram :
Procedure :
i)
Make the connections as per circuit diagram .
ii)
Now switch on the DC supply & start the DC SHUNT motor at 1st stead, note it with the help of a
tachometer.
iii) Now shift the handle to 2nd , 3rd , 4th studs & then last stud, till motor attains the rated speed .
iv)
Note it with the help of a tachometer in observation table.
v)
Switch off the load & supply in steps .
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Observations :
S.NO. STUD NO.
RPM
N
1.
2.
3.
Result: A DC motor starter limits the starting current and safely starts a DC motor and also protects the motor
from overload.
Precautions :
1. Connections should be right & tight.
2. Readings should be proper.
3. Don’t exceed the value of current, voltage beyond the range of meter & rheostats .
4. Don’t touch any live terminal.
5. Always remember Alertness Avoid Accident.
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Experiment No. -16.b
Aim of Experiment : To Study A.C. Induction Motor Starter.
Apparatus required:
i) Three-phase squirrel cage induction motor 7.5 H.P.
ii) Direct on line starter.
iii) Triple Pole Iron Clad (TPIC) Main Switch 63 Amp.
iv) Voltmeter 0 – 500 Volts.
v) Am-meter 0 – 100 Amp.
Theory: As the name indicates “Starter” is used to start and stop the motor. The starter is also used to protect
the motor and other connected equipment from sustained overload, under voltage, single phasing etc., and also
provide automatic control whenever require. We know that the motor acts as a transformer with secondary
winding (Rotor winding) short-circuited, when the motor is at stand-still position. When the motor is started
from stand-still position, high starting current will circulate in the rotor winding and simultaneously the stator
will start drawing heavy current from the supply mains. As a result of this heavy current, the system or line
voltage will be drastically reduced, which is objectionable from safety point of view. The other sensitive
equipment’s connected with same line may trip on low voltage. Therefore, large capacity motors (Above 5
H.P.) should be connected through such a mechanism, which can reduce the starting voltage. If the starting
voltage is reduced, the starting current drawn by the motor will be reduced automatically and thus the line
voltage will remains almost constant.
Direct On Line (D.O.L) Starter: The Direct On Line starter is used to connect the motor winding terminals
in delta connection directly instead of connecting in star first and then is delta position, as in case of StarDelta starter. When the on switch (Green Button) is pressed, the No-Volt-Coil (N.V.C.) will become an
electromagnet and pulls down the plunger down ward position. As a result of it, the motor winding will
connect across the three-phase supply and motor start running.
Observations:
The following points must be observed carefully during the working of the motors.
i) Observe the starting and running current drawn by the motor.
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ii) Observe the input voltage to the motor with the help of voltmeter and it should be around 440 volts.
iii) The motor should not make any abnormal sound or hum during the operation.
Precautions:
The following precautions must be observed while connecting and running the three phase induction motor
with the help of D.O.L. and Star Delta starter.
i) All the connections should be tight.
ii) The fuse wire of main switch or rating of MCB should be of proper size.
iii) Before connecting the motor on supply, check the leakage current or earth fault with the help of series test
lamp.
iv) Phase sequence test should be conducted carefully.
v) Connect the T.P.I.C. main switch, Starters and motor with proper earth wire to avoid leakage current
accidents.
vi) Connection plate should be carefully examined to connect the motor in Star or Delta position.
Results:
The student will be able to:
i) Check the motor’s phase sequence test.
ii) Connection of motor with starters.
iii) Observe the normal and abnormal sound of the motor.
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