ELECTRICAL SCIENCE
Jan- May’2012
Compiled by:
Prachi Dewan
Manisha Mittal
Gitanjali Chopra
ECE Department
GTBIT
1
LIST OF
EXPERIMENTS
(Electrical Science Lab-I) ETEC -112
Branch:- EEE /ECE
Sl. No. Experiment
Page No.
1 Introduction to various Basic Instruments 3-9
of Electrical Science
10-12
2 To verify Superposition Theorem
3 To verify Thevenin Theorem and find out 13-15
Thevenin’s Equivalent circuit using DC
Sources
16-18
4 To verify Maximum Power Transfer
Theorem for DC source
19-21
5 To study R-L-C series circuit and draw
its phasor diagram
22-25
6 Measurement of energy and calibration
of single phase Energy meter with
Wattmeter
26-29
7 To perform open circuit test and short
circuit test on single phase transformer
8 Load test on a single phase transformer, 30-31
regulation and efficiency
2
EXPERIMENT 1: Introduction to various Basic Instruments of
Electrical Science
AIM: Introduction to various Basic Instruments of Electrical Science
OBJECTIVE: Introduction to various Supply Systems, Ammeter, Voltmeter,
Wattmeter, Energy meter, Tachometer, Rheostat, Loading Devices, Transformer.
APPARATUS REQUIRED: Demonstration of various instruments like Ammeter,
Voltmeter, Wattmeter, Energy Meter, Tachometer, Rheostat, Various Capacitors, Various
Resistors, AC and DC Power Supply.
THEORY OF EXPERIMENT:
AMMETER
Ammeter is employed for measuring of current in a circuit and connected in series in the
circuit. As ammeter is connected in series, the voltage drop across ammeter terminals is
very low. This requires that the resistance of the ammeter should be as low as possible.
The current coil of ammeter has low current carrying capacity whereas the current to be
measured may be quite high. So for protecting the equipment a low resistance is
connected in parallel to the current coil and it is known as shunt resistance
Analog Ammeter
3
VOLTMETER
(a) Voltmeter is employed to measure the potential difference across any two points
of a circuit. It is connected in the parallel across any element in the circuit. The
resistance of voltmeter is kept very high by connecting a high resistance in series
of the voltmeter with the current coil of the instrument. The actual voltage drop
across the current coil of the voltmeter is only a fraction of the total voltage
applied across the voltmeter which is to be measured.
Analog voltmeter
WATTMETER
The measurement of real power in AC circuits is done by using an instrument using
Wattmeter. The real power in AC circuits is given by expression
VI cos 
where, cos  is power factor.
A wattmeter has two coils, namely, current coil and pressure coil. The current coil (CC)
is connected in series with the load and the pressure coil (PC) is connected across the
load. Watt meters are available in dual range for voltages as well as for current
4
Internal Cicuit of Wattmeter
Wattmeter
ENERGYMETER
Energy meter is an instrument which is used to measure the consumption of electric
energy in a circuit (DC or AC). It measures energy in kWh. The essential difference
between a energy meter and a wattmeter is that the former is fitted with some type of
registration mechanism where by all the instantaneous readings of power are summed
over a definite period of time whereas the latter indicates the value at particular instant
when it is read.
Energy Meter
TACHOMETER
Tachometer is an instrument to measure the speed in (revolutions per minute
(r.p.m.)).The speed of a rotating shaft is measured by inserting the tapered projected part
of the tachometer into the tapered hole in the rotating shaft speed of which is to be
measured.
5
Tachometer
RHEOSTAT
Rheostats are made up of high resistivity material, like, nickel-chromium iron alloy
closely wound over a circular tube. These are available both in single tube and double
tube. Inter-turn insulation is provided to avoid short circuiting of turns. The tube of
rheostat is made of insulating material, like asbestos. These are employed at places where
resistance of a circuit is to be varied without breaking the circuit.
LOADING DEVICES
The most commonly used loading devices are (1) lamp Bank (2) loading Rheostat. Lamp
Bank load consists of number of lamps connected to form a load. These are suitably
connected and controlled by a no. of switches. The switches are provided in a manner so
that it should be possible to switch on any required no. of lamps at a time.
A loading rheostat type of load consists of no. of identical resistive elements. These
elements are connected in series or parallel. The rheostat is made up of high resistivity
material such as like nickel-chromium. The elements of the load can be designed to take
1A, 2A or 4 A of current.
6
Loading Rheostat
VAROIUS SUPPLY SYSTEM
(a) A.C supply systems: There are two types of supply.
(i)
Single phase-230V: In this system we have two wires, one is known as
phase/line and the other is neutral. Voltage between them is 230 V.
(ii)
Three phase - 400 V (line to line): In his system we have three wires, one for
each phase or line. In case the fourth wire is there it is neutral. While voltage
between two phases/lines is 400 V, between any phase/line and neutral it is
230 V.
(b) DC Supply System
There are two type of D.C supply system
(i)From battery: We use rectifiers for 6V or 12V D.C supply current.
(ii)From generator
DC Supply
7
AC Supply
MULTIMETER
Multimeter is a measuring instrument used to measure the current ,voltage and
resistance.These can be used to troubleshoot many electrical equipments such as
domestic appliances,power supplies etc.
TRANSFORMER: A transformer is a static device which consists of two or more
stationary electric circuits interlinked by a common magnetic circuit for the purpose of
transferring electrical energy between them. The transfer of electric energy takes place
from one circuit to another circuit without change in frequency. Transformer may be for
stepping up voltage from low to high or stepping down voltage from high to low.
Single Phase Transformer
8
Auto Transformer
REFERENCES
Books
1.”Electrical Science” by J. B. Gupta
2. “A Text book of Electrical Technology” by B. L. Thereja Vol-11
3.”Electrical Engineering Fundamentals” by Del Toro
4.”Electric Circuits” by James Nelson (Pearson publication)
5.”Basic Electrical Engg.” By DC Kulshreshtha, TMHill.
URL’s
1. www.brighthub.com
2. www.allaboutcircuits.com
3. www.howstuffworks.com
4. www.nptel.iitm.ac.in
LAB TUTORIALS
1. What are the basic measuring instruments for measuring electrical quantities?
2. What is the working principle of wattmeter and an energy meter?
3. What are the various safety measures to be taken while performing practical work in
electrical science lab?
4. Discuss various types of resistors and capacitors?
5 Define the term ideal current and ideal voltage source?
9
EXPERIMENT 2: Verification of Superposition Theorem
AIM: To verify Superposition Theorem.
OBJECTIVE: To apply the principle of Superposition Theorem for electrical network
containing independent DC sources.
APPARATUS: Digital multi-meter, power supply, resistance (wire wound),
Connecting Wires
THEORY OF EXPERIMENT:
Superposition theorem states that in a linear network containing several independent
sources, the overall response at any point in the network equals the sum of responses due
to each independent source considered separately with all other independently sources
made inoperative(short circuited). To make a source inoperative, it is short circuited
leaving behind its internal resistance if it is a voltage source, and it is open circuited
leaving behind its internal resistance if it is a current source.
In most electrical circuit analysis problems, a circuit is energized by a single independent
energy source. In such cases, it is quite easy to find the response (i.e., current, voltage,
power) in a particular branch of the circuit using simple network reduction techniques
(i.e., series parallel combination, star delta transformation, etc.).
However, in the presence of more than one independent source in the circuit, the response
cannot be determined by direct application of network reduction techniques. In such a
situation, the principle of superposition may be applied to a linear network, to find the
resultant response due to all the sources acting simultaneously.
10
The superposition theorem is based on the principle of superposition. The principle of
Superposition states that the response (a desired current or the voltage) at any point in the
linear network having more than one independent source can be obtained as the sum of
responses caused by the separate independent sources acting alone. The validity of
principle of superposition means that the presence of one excitation sources does not
affect the response due to other excitations.
PROCEDURE:
1. Connect the DC power supply to resistance R1.Adjust voltage of supply to 10V.
2. Connect another DC supply to resistance R2. Adjust voltage to 5 V.
3. Connect the DC ammeter(mA) to resistance R3.
4. Now remove the left hand side of supply and measure and record the current
through R3.
I3=___ma
5. Remove another supply and measure and record the current through R3.
I3’=__ma.
6. Now apply both the supplies and measure the current in R3 i.e. I3’’.
Now I3’’= I3+ I3’
OBSERVATION TABLE:
Calculated Values
I3’
I3
I3’’
Observed Values
V1=10V
V2=5V
V1=10V
V2=0V
V1=0V
V2=5V
I3
I3’
I3’’
CALCULATIONS:
I3 “(Observed) =I3+I3 ‘
11
I3 “ (Calculated)=?(by solving using KVL)
% Error=(Observed Value-Calculated Value)/Calculated Value
RESULT:
The percentage error is found to be__%.
DISCUSSION:
The % error is found to be in the range within 10%.The percentage error is due to
observational errors, tolerance errors, calibration of instruments, etc. However,
superposition theorem cannot be applied to non-linear network and network containing
only dependent sources.
CONCLUSION:
The superposition theorem is verified.
REFERENCES:
Books:
1. Fundamentals of Electrical engineering by Ashfaq Husain.
2. A Textbook of Electrical Technology by B.L Thereja.
3. Electrical Science by J. B. Gupta
4. ”Basic Electrical Engg.” By DC Kulshreshtha, TMHill.
URLS:
1. www.brighthub.com
2. www.allaboutcircuits.com
3. www.howstuffworks.com
4. www.nptel.iitm.ac.in
LAB TUTORIALS
1. What are the advantages and disadvantages of using superposition Theorem?
2. Why superposition theorem is not applied to non-linear circuits?
3. Can superposition theorem be applied to circuit having A.C sources? If yes, then what
will be its requirements?
4. How can superposition theorem be applied to network containing both independent
and dependent sources?
12
EXPERIMENT 3: Verify Thevenin Theorem and find out
Thevenin’s Equivalent circuit using DC Sources
AIM: To verify Thevenin Theorem and find out Thevenin’s Equivalent circuit using DC
Sources.
OBJECTIVE: To apply the principle of Thevenin Theorem for electrical network
containing independent DC sources and to find out Thevenin’s Equivalent circuit.
APPARATUS:
Digital Multi-meter, Power Supply, Resistance (wire wound),
Connecting Wires
THEORY OF EXPERIMENT:
Sometimes, we wish to determine the response in a single load resistance in a network.
Thevenin Theorem enables us to replace the remainder of the network by a simple
equivalent circuit. Determining response in the load resistance, then becomes easier. The
use of Thevenin Theorem is specially very helpful and time saving when we wish to find
the response for different values of load resistance. Thevenin Theorem states that current
through a load resistance connected across any two points of an active network can be
obtained by the formula:
IL=Vth/(Rth+RL)
Where Vth is the open circuit voltage at the terminals of RL when RL is disconnected and
Rth is the equivalent resistance viewed from the output terminals when all the sources
replaced by their internal resistance only(short circuit the voltage sources).
PROCEDURE:
1. Connect the DC power supply to resistance R1. Adjust voltage of supply to 10V.
2. Connect another DC supply to resistance R2. Adjust voltage to 5 V.
3. Now remove the resistance RL and measure Vth (open circuit voltage) by setting
meter in range 0 to 20V .
13
4. Remove both the sources . Set your meter to measure the resistance in hundreds
of ohms range. Calculate Rth
5. Now the Thevenin’s equivalent circuit is as in figure.
OBSERVATION TABLE:
Calculated Values
Vth
Rth
IL
Observed Values
Vth
Rth
IL
CALCULATIONS:
IL=Vth /(Rth+RL)
Where Vth is the open circuit voltage at the terminals when disconnected, Rth is the
equivalent resistance viewed from the output terminals when all the sources are replaced
by their internal resistance. IL is the current through resistance RL.
Percentage Error= [(Observed-Calculated)/Calculated]*100
The percentage error is to be found for the current flowing in the load resistance.
RESULT:
The percentage error is found to be__%.
DISCUSSION:
The % error is found to be in the range within 10%.The percentage error is due to
observational errors, tolerance errors, calibration of instruments. Moreover, it can be seen
that Thevenin Theorem can’t be applied to network containing only dependent sources.
14
CONCLUSION:
The Thevenin Theorem is verified and the Thevenin’s equivalent circuit is obtained.
.
REFERENCES:
.Books
1.”Electrical Science” by J. B. Gupta
2. “A Text book of Electrical Technology” by B. L. Thereja Vol-11
3.”Electrical Engineering Fundamentals” by Del Toro
4. “A Text book of Electrical Technology” by B. L. Thereja Vol-1
5.”Basic Electrical Engg.” By DC Kulshreshtha, TMHill.
URL’s
1. www.brighthub.com
2. www.allaboutcircuits.com
3. www.howstuffworks.com
LAB TUTORIALS
1. What are the advantages and disadvantages of using Thevenin Theorem?
2. Why Thevenin Theorem is not applicable to non-linear circuits?
3. Can Thevenin Theorem be applied to circuit having A.C sources? If yes, then what is
the difference in using DC sources?
15
EXPERIMENT 4: To verify Maximum Power Transfer Theorem
for DC source
AIM: To verify Maximum Power Transfer Theorem for a DC source.
OBJECTIVE: To understand the concept of Maximum Power Transfer Theorem to
the network consisting of a fixed internal resistance RS and a variable load resistance RL
and if maximum power is drawn by the network then it is to be proved that RL = RS.
APPARATUS: one fixed resistor, one variable resistor, digital multi-meter, DC Power
supply, connecting wires.
THEORY OF EXPERIMENT::This theorem is applicable for analyzing
communication networks. According to this theorem”A resistive load will draw the
maximum power from a network when the load resistance is equal to the resistance of the
network as viewed from its output terminals, with all energy sources removed leaving
behind their internal resistances.” If RL is the load resistance connected across terminals a
and b which consist of variable DC supply and internal resistance is RS, then according to
this theorem, the load resistance will draw maximum power when it is equal to RS i.e. RL
= RS.
And the maximum power drawn= V2oc/4 RL
Where, Voc is the open circuit voltage at the terminals from which RL is disconnected.
The variable resistor taken should be larger than fixed resistor. Then only power can be
calculated.
PROCEDURE:
1. Connect the circuit as shown in Figure.
2. Measure the value of load current (IL) for different (suitable) values of load resistance
and record them in observation table. By suitable value means that the value of R L should
be equal to, more than and less than RS.
16
3. Repeat step 2 for different value of supply voltage (Vs).
4. Also note down the reading in voltmeter connected across RL.Let it be V.
5. Calculate the value of power accordingly. You will notice that the power goes on
increasing as RL is increasing and after few observations it goes on decreasing.
6. Note down the maximum power and at that point calculate the value of RL. This RL
should be equal to Rs.
7. Draw a Graph Between PL and RL.
OBSERVATION TABLE
S.No
Supply
IL(Load
Voltage(VS)
Current)
V(Voltage)
RL=V/IL
P=IL2*RL
CALCULATION
RL=V/IL
P=IL2 RL
Note the maximum power point and hence determine the resistance RL. This RL is
comparable with RS. These come out to be same.
RESULT:
The maximum power transfer theorem is verified as RL=RS
DISCUSSION
It can be analyzed that at maximum power, the value of load resistance is equal to
internal resistance.
CONCLUSION
The value of load resistance comes out to be almost equal to the internal resistance of the
network.
REFERENCES
1. Fundamentals of Electrical engineering by Ashfaq Husain.
2. A Textbook of Electrical Technology by B.L Thereja.
17
3. ”Basic Electrical Engg.” By DC Kulshreshtha, TMHill.
URLS:
1. www.nptel.iitm.ac.in
2. www.electronics-tutorials.ws/dccircuits
3 www.openbookproject.net
4. www.mhhe.com
5. www.opamp-electronics.com
6. www.electronicsteacher.com
LAB TUTORIALS
1. Define power transfer efficiency in Maximum Power Transfer Theorem?
2. What are the practical applications of Maximum Power Transfer Theorem?
3. Can Maximum Power Transfer Theorem be applied to A.C sources?
4. What is the expression of η when RL=RS?
18
EXPERIMENT 5: To study R-L-C series circuit and draw its
phasor diagram
AIM: To study R-L-C series circuit and draw its phasor diagram.
OBJECTIVE:
To study the AC R-L-C series circuit and analyze the phase
relationship between voltage and current.
APPARATUS: Ammeter (0-1A), Resistor, Inductor and Capacitor, Variac,
Connecting Wires and Digital Multi-meter.
THEORY OF EXPERIMENT: Consider an AC circuit containing resistance of R
ohms, inductance of L henries and capacitance of C farads connected in series, as shown
in circuit diagram. Let the current flowing through the circuit be of I ampere and supply
frequency be f Hz.
(a) Voltage drop across resistance Vr =IR in phase with I.
(b) Voltage drop across inductance Vl=
L leading I by radians or 900.
(c) Voltage drop across capacitance, Vc = I/
C lagging behind I by
radian or 900.
Vl and Vc are 1800 out of phase with each other (or reverse in phase), therefore, when
combined by parallelogram they cancel each other. The circuit can either be effectively
inductive or capacitive depending upon which voltage drop ( Vl or Vc) is predominant.
Let us consider the case when Vl is greater than Vc.
Phase angle
=
between voltage and current is given by:-
Vl –Vc /Vr.
Power factor of the circuit is given by:= R/Z = R/
Power consumed in the circuit, P= I²R or VI cos .
19
PROCEDURE:
1. Connect the circuit as shown in the circuit diagram.
2. Measure the voltage supplied by variac (V1).
3. Measure the circuit current (I) using AC ammeter.
4. Note down the voltage drop across R, L and C by digital multi-meter.
5. Change the input voltage and then again note down the voltage drop (at least 5 readings)
6. Draw the phasor diagram between Vl , Vc , and Vr and calculate the phase.
OBSERVATION TABLE
Vi
Vr
VL
Vc
IA
R
XL
XC
Z
Cos
CALCULATIONS
1. R = Vr/I
2. XL= VL/I
3. Xc= VC/I
4. Cos
= R/Z
5. Z =
6. Draw a phasor diagram showing voltage between Vr, VL and Vc and calculate its phase
angle.
RESULT:
The value of Z is …….. and the value of  (phase angle) and power factor is ………
DISCUSSION
The RLC series circuit has been analyzed and it can be predicted that the circuit has
leading power factor. The main precaution to be taken while performing the experiment
is that the value of resistance should be small otherwise resonance will take place.
REFERENCES
1. Fundamentals of Electrical engineering by Ashfaq Husain.
2. A Textbook of Electrical Technology by B. L. Thereja.
3.
Electrical Science by J. B. Gupta
4. ”Basic Electrical Engg.” By DC Kulshreshtha, TMHill.
20
URLS:
1. www.nptel.iitm.ac.in
2. www.electronics-tutorials.ws/dccircuits
3. www.openbookproject.net
4. www.mhhe.com
5. www.opamp-electronics.com
LAB TUTORIALS
1. What do you understand by the term power factor in reference to AC circuits ?.
2. What is the importance of power factor?
3. What do you mean by a lagging power factor?
4. What do you mean by a leading power factor?
21
EXPERIMENT 6: Measurement of energy and calibration of
Single Phase Energy Meter with Wattmeter
AIM: Measurement of energy by an energymeter and to calibrate a single phase energy
meter with wattmeter.
OBJECTIVE: In this experiment our objective is to calibrate the energy meter with a
standard wattmeter and hence calculate the error between actual energy consumed and
recorded energy.
Energy Meter
APPARATUS:
1. single phase induction type Energy meter (0-5A, 240 V, 2400-1000-3600)
2. moving Iron Wattmeter (300V, 10A).
3. loading Rheostat (2.5kW, 250V).
4. MI ammeter (0-5A).
5. MI Voltmeter (0-300V)
6. Stop Watch.
THEORY OF EXPERIMENT:
Energy meter is an instrument which measures electrical energy. It is also known as watt
hour (Wh) meter. It is an integrating meter. There are several types of energy meters.
Single phase induction type energy meters is very commonly used to measure electrical
22
energy consumed in domestic and commercial installations. Electrical energy is measured
in kilo watt hours (kWh) by these energy meters.
In this experiment the purpose is to calibrate the energy meter. This means we have to
find out the error/ correction in the energy meter readings. This calibration is possible
only if some other standard instrument is available to know the correct reading.
Wattmeter:- Wattmeter is an instrument
which measures instantaneous power
consumed by a circuit . It consists of two coils:1. Fixed coil, divided in two parts is connected in series with load and produces a
flux proportional to the current.
2. Movable coil is suspended on the pivot and jeweled bearings, produces the flux
proportional to the voltage across the load. Deflection of the pointer is the result
of the change in the mutual inductance between the fixed and the moving coils.
PROCEDURE:
1. Connect the circuit as shown in figure and apply a rated constant AC voltage.
2. Switch on one of the loads.
3. Record the time taken for 10 revolutions of the disc of the energy meter with the
help of stop watch.
4. Take voltmeter, ammeter and wattmeter readings.
5. Repeat for more number of readings (4 readings) for different loads.
6. Record the readings as per table.
7. Note the multiplication factor of the wattmeter.
23
OBSERVATION TABLE
Revolutions per kWh= 2400
IA
Power in
Time required for
Actual energy by
Recorded
%
watts (P)
10 revolutions
wattmeter E =
energy kwh by
error
(secs)
reading in wattmeter
energy
x multiplying factor
meter=No. of
revolutions /
2400
CALCULATION
1. Energy by wattmeter = wattmeter reading x multiplying meter factor xtime for 10
revolutions
2. Energy by energy meter = (No. of Revolutions / 2400 (in kWh)
3. %error = (E by wattmeter – E by energy meter) * 100 / E by wattmeter.
RESULT:
The % error is found to be …….%.
DISCUSSION:- The single phase energy meter is calibrated with wattmeter by
varying the loads and it can be found that the percentage error between actual and
recorded energy is very less.
REFERENCES
Books:
1. Fundamentals of Electrical engineering by Ashfaq Husain.
2. A Textbook of Electrical Technology by B. L Thereja.
3. “Basic Electrical Engg.” By DC Kulshreshtha, TMHill.
24
URLS:
1. www.nptel.iitm.ac.in
2. www.electronics-tutorials.ws/dccircuits
3. www.openbookproject.net
4. www.mhhe.com
5. www.opamp-electronics.com
LAB TUTORIALS
1. What do you mean by calibration of an instrument?
2. Where are the induction type energy meters used?
3. How many coils exist and what are their functions in an induction type energy meter?
4. How many terminals does an energy meter have?
25
EXPERIMENT 7: To perform open circuit test and short circuit
test on single phase transformer
AIM: To perform open circuit test and short circuit test on a single phase transformer.
OBJECTIVE:
To perform open circuit and short circuit tests and calculate the
equivalent circuit parameters Cu losses and Iron losses.
APPARATUS: Single phase Transformer (2kVA), AC Ammeter (0-10 A) AC
voltmeter (0-300 V), Wattmeter (10A, 300V), Connecting leads , Variac(230/270V, 20
A).
THEORY OF EXPERIMENT:
The performance of a transformer can be calculated on the basis of its equivalent circuit
which contains four main parameters, the equivalent resistance R01 as referred to primary
(or secondary R02), the equivalent leakage reactance X01 as referred to primary. These
constants or parameters can be easily determined by two tests, i.e. open circuit test and
short circuit test. These are very economical and convenient, because they furnish the
required information without actually loading the transformer.
The purpose of the Open Ckt. Test is to determine no load loss or core loss and no load
I0 which is helpful in finding X0 and R0. One winding of the transformer usually high
voltage winding is left open and the other is connected to its supply of normal voltage
and frequency. A wattmeter (W), Voltmeter (V) and ammeter (A) are connected in the
low voltage winding, i.e., primary winding in the present case. With normal voltage
applied to the primary, normal flux will be setup in the core, hence normal iron losses
will occur which are recorded by the wattmeter. As in the primary no load current I0 is
small, Cu loss is negligibly small in primary and nil in secondary. Hence, the wattmeter
reading represents practically the core loss under no load condition.
26
For short circuit test, one winding usually the low voltage winding, is short- circuited
by a thick conductor (or through an ammeter which may serve the additional purpose of
indicating rated load current).
A low voltage (usually 5 to 10% of normal primary voltage) at correct frequency is
applied to the primary and is gradually and cautiously increased till full- load current is
flowing both in primary and secondary (as indicated by the respective ammeters).
Since, in this test, the applied voltage is a small percentage of the normal voltage, the
mutual flux ø produced is also a small percentage of its normal value. Hence, core losses
are very small with the result that the wattmeter reading represents the full load Cu loss
or i2 R loss for the whole transformer, i.e. sum of both primary and secondary Cu losses..
The equivalent impedance of the transformer under short- circuit condition, if Vsc is the
voltage required to circulate rated load currents, is then given by Z01= Vsc/I1.
PROCEDURE:
OPEN CIRCUIT:1. Switch on the supply, increase the supply in an orderly manner (rated voltage) to
2kVA of transformer.This test is performed on low voltage winding and high
voltage winding is open.
2. Note down the readings of wattmeter, voltmeter and ammeter.
3. Compute the value of cos
, R0 and X0.
SHORT CIRCUIT:1. For short circuit test short the secondary winding.This test is perfomed on high
voltage winding,low voltage winding is short circuited.
2. Increase the voltage applied slowly so that the current flowing in the transformer
winding equals the rated value.
3. Record the readings of ammeter, voltmeter and wattmeter; which correspond to
short- circuit current, corresponding applied voltage and power with full load
current flowing under short circuit condition respectively.
4. Compute the value of short circuit impedance and resistance.
27
OBSERVATION TABLE
For Open- Circuit test:-
V1
I0
W
cos
X0
R0
X01
R01
CALCULATIONS:W=V1 I0 cos
Therefore, X0 = V1/ I , R0= V1/ Iw
Where Iw= I0 cos
,I
= I0
sin
OBSERVATIONS:For Short Circuit test:-
V
I
W
CALCULATION
For Short Circuit Test:W= I ²R01
R01 =W/I²
28
Z01
Z01= V/ I
X012= (Z01²- R01²)
RESULT:
The Cu loss is obtained to ………W and iron loss is ………W.
DISCUSSION: The open circuit and Short circuit test have been performed and
various parameters like R0, X0, Z01 and X01 are calculated and losses of transformer i.e.
iron and copper loss can be determined.
REFERENCES
Books:
1. Fundamentals of Electrical engineering by Ashfaq Husain.
2. A Textbook of Electrical Technology by B. L Thereja.
3. Basic Electrical Engg.- By DC Kulshreshtha, TMHill.
URLS:
1. www.nptel.iitm.ac.in
2. www.electronics-tutorials.ws/dccircuits
3. www.openbookproject.net
4. www.mhhe.com
5. www.opamp-electronics.com
LAB TUTORIALS
1. Why indirect testing of large size transformers is necessary?
2. When a transformer is energized what types of losses occur in the magnetic frame
of the transformer?
3. What do you understand by all day efficiency of a transformer?
4. What type of losses are ignored in the short circuit test on a transformer?
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EXPERIMENT 8: Load test on a single phase transformer and
calculate regulation and efficiency
AIM: Perform a load test on a single phase transformer and determine its regulation and
efficiency.
APPARATUS: Single phase Transformer 2kVA, AC Voltmeter (0-300 V), AC
ammeter (0-10A), wattmeter (unity pf, 0-10 A, 0-300V), Connecting wires, single phase
variable resistive load.
THEORY OF EXPERIMENT:
Load test: The input to the transformer is observed with the help of wattmeter. Let it be
W1. The output of the transformer is calculated from the product of the voltage (V) and
current (I) in the secondary of the transformer. The load is taken a resistive and therefore
power factor is unity.
Hence η (efficiency) of transformer = output/ input x 100
= (V * I) x 100/w1
Voltage Regulation: With the increase in load on the transformer, there is a change in its
terminal voltage. The voltage falls if the load power factor is lagging. It increases if
power is leading. The change in secondary terminal voltage from full load to no load,
expressed as a percentage of full load voltage is called the percentage voltage regulation
of the transformer. If E is the no load terminal voltage and V is the full load terminal
voltage then % Regulation = (E- V) x 100 / V.
PROCEDURE:
1. Connect the circuit as shown in Figure.
2. Apply full load and note down the readings of wattmeter, voltmeter, and ammeter.
3. Decrease the load and note down the readings.
4. Calculate efficiency and regulation with rated and half rated load.
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OBSERVATION TABLE
Wl
Vl
I2
V2
CALCULATION
η = (V2 I2 / W1) * 100
% Reg = (E – V) * 100 / V where E is secondary no load voltage
DISCUSSION:- By calculating the voltage regulation the figure of merit which
determines the voltage characteristics of a transformer can be determined. By actual
loading transformer efficiency can’t be determined with high precision since the losses
are of the order of only 1 to 4%. The best and accurate method of determining the
efficiency of a transformer would be to compute losses from open circuit and short circuit
test and then determine the efficiency.
REFERENCES
Books:
1. Fundamentals of Electrical engineering by Ashfaq Husain.
2. A Textbook of Electrical Technology by B. L Thereja.
3. Electrical Science by J. B. Gupta.
4. Electrical Engineering Fundamentals by Del Toro.
5. ”Basic Electrical Engg.” By D C Kulshreshtha, T M Hill.
URLS:
1. www.nptel.iitm.ac.in
2. www.electronics-tutorials.ws/dccircuits
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3. www.openbookproject.net
4. www.mhhe.com
LAB TUTORIALS
1. What does the reading of wattmeter indicate in case of short- circuit test on
transformer?
2. How do the copper losses vary with load on a transformer?
3. What is the magnitude of no load current as compared to full load current?
4. What is the power factor of a transformer under no load condition?
5. Differntiate between “all day efficiency” and “power effiency” of a transformer.
6. How an autotransformer differs from a two winding transformer?
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