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8/18/2019 EMMI LAB MANUAL_correct.pdf
1/41
Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
Exp. No:
Date:
CALIBRATION OF THREE PHASE ENERGYMETER
AIM
To calibrate the given three phase static energy meter at upf
(i) By direct loading.
(ii) By phantom loading
APPARATUS REQUIRED
SL NO. APPARATUS SPECIFICATION QUANTITY
1. Energy meter 1no.
2. Wattmeter 2no.
3. Voltmeter 1no.
4. Ammeter 1no.
5. 3φ autotransformer 1no.
6. 3φ r esistive load 1no.
7. Rheostat 1no.
8. Stop Watch 1no.
< Students are expected to calculate instrument ranges based on the machine ratings before start of
experiment and get it approved before connections are made>
8/18/2019 EMMI LAB MANUAL_correct.pdf
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
CIRCUIT DIAGRAM
(i) Direct Loading
Fig. 1
(ii) Phantom Loading
Fig. 2
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
PRINCIPLE
In order to check the calibration of a three phase energy meter, reading of energy meter has
to be compared with that of standard instrument. For determining the true energy consumption a
standard wattmeter and an accurate stop watch is used. From the calculated true energy, the error and
percentage error in the energy meter is determined.
(i) Direct Loading
In direct loading, current coil of energy meter and wattmeter are connected to a three phase
supply in series with a loading device, where as in each phase pressure coils of energy meter are
connected altogether to neutral wire. The pressure coils of two wattmeters are connected to Y phase.
By adjusting the auto transformer take the reading of voltmeter which connected in between two phases
as 415V. Supply is given to the circuit. Then by adjusting the loading device required current had got
on the ammeters. Then energy consumption (measured power) is got by observing the time taken for
3 revolutions of energy meter. True energy is calculated from wattmeter reading and time indicated inthe stop watch.
Measured Power = ∗ ∗1000 Watts
K = Energy meter constant in rev/kWh
N = Number of revolutions made by energy meter disc
t = Time for N revolutions of energy meter disc
% error =( . . . ∗ 100) , where M.P is measured power and T.P is true power.(ii) Phantom loading
Calibration is done by phantom loading of three phase energy meter. In phantom loading
using standard wattmeter, the current coil is fed from a low voltage supply and pressure coil
by rated voltage. Hence total power required for conducting the test is small.
Measured Power = ∗ ∗1000 Watts
K = Energy meter constant in rev/kWh
N = Number of revolutions made by energy meter disc
t = Time for N revolutions of energy meter disc
% error =( . . . ∗ 100) , where M.P is measured power and T.P is true power.
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
PROCEDURE
(i) Direct Loading
Connections are made as shown in the fig (1). Autotransformer is kept at minimum position
and the supply is switched on. Autotransformer is adjusted to apply rated voltage in the circuit. Then by adjusting the loading devices the required current readings are made on ammeters. Different
Wattmeter readings and the time taken for 3 revolutions of the energy meter using a stopwatch are
noted. The true reading is obtained from the wattmeter reading.
(ii) Phantom Loading
Connections are made as shown in fig (2). Autotransformer is kept at minimum position and
the supply is switched on. Autotransformer is then varied and different currents are passed through
the current coil of the energy meter. All the meter readings, wattmeter reading for all currents and
time taken for three revolutions of the disc are noted.
OBSERVATION
(i) Direct Loading
Sl
no.
Voltmeter
Reading
(V)
Ammeter
Reading
(A)
W1
(W)
W2
(W)
T.P=
W1+W2(W)
Time for 3
revolutions
(sec)
M.P
(W)
Error=M.P - T.P
(W)
% error=.−.
. ×1
8/18/2019 EMMI LAB MANUAL_correct.pdf
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
(ii) Phantom Loading
l
o.
Vol
tme
ter
Readin
g
(V)
Am
mete
r
Reading
(A)
W1
(W)
W2
(W)
T.P=
W1+W2
(W)
Time
for 3
revol
utions
(sec)
M.P
(W)
Error
=
M.P-
T.P(W)
% error=
.−.
.×100
Power
consumed by
Wattmeter
Power
consumed byEnergymeter
Total
Power
=
T.P+C.C+
P.C(W)
C.C (W)
P.C (W)
C.C (W)
P.C (W)
SAMPLE CALCULATION
(i) Direct Loading
Time for 3 revolutions of energy meter disc = ------------------sec
Energy meter constant, K= ---------------------rev/kWh
Measured Power = ∗ ∗1000 Watts = -------------------W
True Power = W1+W2 = ---------------W
% error = ( . . . ∗ 100)
(ii)
Phantom Loading
Time for 3 revolutions of energy meter disc = ------------------sec
Energy meter constant, K= ---------------------rev/kWh
Measured Power = ∗ ∗1000 Watts = -------------------W
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
True Power = W1+W2 = ---------------W
% error = ( . . . ∗ 100) = ----------------Power loss in wattmeter current coil = 2*I2R = --------------W
Power loss in wattmeter pressure coil = 2*V2/R= ----------------W
Power loss in energy meter current coil = 2*I2R = --------------W
Power loss in energy meter pressure coil = 2*V2/R= ----------------W
Total Power = T.P +C.C+P.C = --------------W
Power Savings = True power obtained from direct loading- Total power consumed in
phantom Loading
= ------------W
RESULT
The given three phase energy meter is calibrated at upf by direct loading and phantom loading.
INFERENCE
Exp No:
Date :
8/18/2019 EMMI LAB MANUAL_correct.pdf
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
CALIBRATION OF SINGLE PHASE ENERGYMETER
AIM
To calibrate the given single phase static energy meter at upf by direct loading and phantom
loading using standard wattmeter and draw the error and calibration curve.
APPARATUS REQUIRED
SL NO. APPARATUS SPECIFICATION QUANTITY
1. Energy meter 1no.
2. Wattmeter 1no.
3. Voltmeter 1no.
4. Ammeter 1no.
5. 1φ autotransformer 1no.
6. Rheostat 1no.
7. Resistive load 1no.
8. Stop Watch 1no.
< Students are expected to calculate instrument ranges based on the machine ratings before start of
experiment and get it approved before connections are made>
CIRCUIT DIAGRAM
(i) Direct Loading
Fig. 1
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
(ii)
Phantom Loading
Fig. 2
PRINCIPLE
In order to check the calibration, single phase energy meter is compared with that of standard
instrument. For determining the true energy consumption a standard wattmeter and an accurate stop
watch is used. From the calculated true energy the error and percentage error in the energy meter is
determined. The given energy meter can be calibrated for different loads by comparing the measured
value of power obtained from it and the wattmeter reading. The wattmeter gives the true power.
In direct loading, the load voltage appears across the pressure coil. Hence the energy meter
and wattmeter reads the actual value of energy and power dissipated in the load.
Phantom loading is employed for testing energy meter of high capacity. The phantom loading
method is usually used for calibration of single phase or three phase energy meter. Here external loadis not connected and the current and pressure coils are supplied separately so that it will consume
only less power. In this connection the voltage across pressure coil will be supply voltage even if the
autotransformer is in minimum position and current coil is supplied from a separate low voltage
supply.
For checking the calibration of energy meter at upf, the current coils of energy meter and
wattmeter are connected in series to the supply(R phase) through an autotransformer, which reduces
the voltage to a low value. The pressure coils are connected directly to the supply to the same phase(R
phase).
Energy meter constant, K= 900 rev/KWh which means
900 revolutions = 1 kWh
= 1*1000*3600
ie, one revolution = 1000∗3600 900 = 4000 W
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
For ‘N’ revolutions, power = 4000 N W
Time ‘t’ in second is required for N revolutions.
Power expected in one second = 4000 WTrue power = Wattmeter reading
Measured Power = 4000 W% error =( . . . ∗ 100)
PROCEDURE
(1)
Direct loading of energy meter at upf condition.
Made the connections as shown in the fig(1). Supply is switched on and apply full voltage (230 V)
by using autotransformer while keeping the load resistance in the circuit as minimum as possible. Switch
on the load and the voltmeter, ammeter, wattmeter readings and time taken for 3 revolutions of the
energy meter are noted. Experiment is repeated for various load currents up to rated value.
(2) Phantom loading of energy meter at upf condition.
Keep the autotransformer in minimum position and switch on the supply. Keep the rheostat at
constant value throughout the experiment. Give a voltage so that the ammeter readings do not exceed
the rated current. Take readings for different current by adjusting the autotransformer.
OBSERVATIONS
(1) Direct loading
Sl
No.
Voltmeter
Reading
(V)
Ammeter
Reading
(A)
True
Power
(W)
Time for 3revolutions
(Sec)
Measured
Power
(W)
Error=
M.P-T.P
(W)
% error=
.−.. ×100
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
(2) Phantom loading
Sl
No.
Volt
meter
Read
ing(V)
Ammet
er
Readin
g(A)
True
Power
(W)
Time
for 3revoluti
ons(Sec)
M.P
(W)
Error=
M.P-
T.P
(W)
% error=.−.
. ×100Power
consumed by
wattmeter
Power
consumed by
energymeter
Total
power (W)=
T.P+C.C+P.C
C.C
(W)
P.
C
(W)
C.C
(W)
P.C
(W)
SAMPLE CALCULATION
(i)
Direct Loading
True Power = Wattmeter reading = ---------------------W
K= 900 rev/KWh
Number of revolution of energy meter disc, N = 3
Time for 3 revolutions of energy meter disc, t = --------------sec
Measured power =∗∗
∗ = -------------------W
% error = ( . . . ∗ 100) = (ii) Phantom Loading
True Power = Wattmeter reading = ---------------------W
K= 900 rev/KWh
Number of revolution of energy meter disc, N = 3
Time for 3 revolutions of energy meter disc, t = --------------sec
Measured power =∗∗
∗ = -------------------W
8/18/2019 EMMI LAB MANUAL_correct.pdf
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
% error = ( . . . ∗ 100) = Power loss in wattmeter current coil = I2R = --------------W
Power loss in wattmeter pressure coil = V2/R= ----------------W
Power loss in energy meter current coil = I2R = --------------W
Power loss in energy meter pressure coil = V2/R= ----------------W
Total Power = T.P +C.C+P.C = --------------W
Power Savings = True power obtained from direct loading- Total power consumed in
phantom Loading
= ------------W
RESULT
The single phase energy meter is calibrated at upf by direct and phantom loading.
INFERENCE
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
Exp No:
Date :
CALIBRATION OF SINGLE PHASE ENERGYMETER AT 0.5 pf
AIM
To calibrate the given single phase static energy meter at 0.5 pf lag and lead by phantom
loading.
APPARATUS REQUIRED
SL NO. APPARATUS SPECIFICATION QUANTITY
1. Energy meter 1no.
2. Wattmeter 1no.
3. Voltmeter 1no.
4. Ammeter 1no.
5. 1φ autotransformer 1no.
6. Rheostat 1no.
7 Stop Watch 1no.
< Students are expected to calculate instrument ranges based on the machine ratings before start of
experiment and get it approved before connections are made>
CIRCUIT DIAGRAM0.5 pf lag
Fig. 1
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8/18/2019 EMMI LAB MANUAL_correct.pdf
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
(i) 0.5 pf lag
Connections are made as shown in the fig (1). Supply is switched on and apply full voltage (230 V)
by using autotransformer while keeping the load resistance in the circuit as minimum as possible. Switch
on the load and the voltmeter, ammeter, wattmeter readings and time taken for 3 revolutions of the
energy meter are noted. Experiment is repeated for various load currents up to rated value.
(iii) 0.5 pf lead
Connections are made as shown in the fig (2). Supply is switched on and apply full voltage (230
V) by using autotransformer while keeping the load resistance in the circuit as minimum as possible.
Switch on the load and the voltmeter, ammeter, wattmeter readings and time taken for 3 revolutions
of the energy meter are noted. Experiment is repeated for various load currents up to rated value.
OBSERVATIONS
(i) 0.5 pf lag
Sl
No.
Voltmeter
Reading
(V)
Ammeter
Reading
(A)
True
Power
(W)
Time for 3
revolutions
(Sec)
Measured
Power
(W)
Error=
M.P-T.P
(W)
% error=
.−.. ×100
(ii) 0.5 pf lead
Sl
No.
Voltmeter
Reading
(V)
Ammeter
Reading
(A)
True
Power
(W)
Time for 3
revolutions(Sec)
Measured
Power
(W)
Error=
M.P-T.P
(W)
% error=
.−.. ×100
SAMPLE CALCULATION
(i) 0.5 pf lag
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
True Power = Wattmeter reading = ---------------------W
K= 900 rev/KWh
Number of revolution of energy meter disc, N = 3
Time for 3 revolutions of energy meter disc, t = --------------sec
Measured power =∗∗
∗ = -------------------W
% error = ( . . . ∗ 100) = (ii) 0.5 pf lead
True Power = Wattmeter reading = ---------------------W
K= 900 rev/KWh
Number of revolution of energy meter disc, N = 3
Time for 3 revolutions of energy meter disc, t = --------------sec
Measured power =∗∗
∗ = -------------------W
% error = ( . . . ∗ 100) = RESULT
The single phase energy meter is calibrated at 0.5 pf lag and lead by phantom loading.
INFERENCE
Exp No:
Date :
CALIBRATION OF SINGLE PHASE ENERGYMETER AT 0.866 pf
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
AIM
To calibrate the given single phase static energy meter at 0.866 pf lag and lead using phase
shifting transformer.
APPARATUS REQUIRED
SL NO. APPARATUS SPECIFICATION QUANTITY
1. Energy meter 1no.
2. Wattmeter 1no.
3. Voltmeter 1no.
4. Ammeter 1no.
5. 1φ autotransformer 1no.
6. Rheostat 1no.
7 Stop Watch 1no.
< Students are expected to calculate instrument ranges based on the machine ratings before start of
experiment and get it approved before connections are made>
CIRCUIT DIAGRAM
(i) 0.866 pf lag
` Fig.1
(i) 0.866 pf lead
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
Fig. 2
Exp. No:
Date:
8/18/2019 EMMI LAB MANUAL_correct.pdf
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
MEASUREMENT OF SELF AND MUTUAL INDUCTANCE
AIM:-
To determine self inductance, mutual inductance and coefficient of coupling of coupled coil.
APPARATUS REQUIRED
SL NO APPARATUS SPECIFICATION QUANTITY
1. Iron cored coils (Transformer 1φ) 1no.
Voltmeter 1no.
3. Voltmeter 1no.
4. Voltmeter 1no.
5. Ammeter 1no.
6. Ammeter 1no.
7. Autotransformer 1no.
8. DC regulated power supply 1no.
9. Rheostat 1 no.
< Students are expected to calculate instrument ranges based on the machine ratings before start of
experiment and get it approved before connections are made>
CIRCUIT DIAGRAM
Additive Polarity
Fig. 1
Subtractive Polarity
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
Fig. 2
To measure resistance of Primary coil
Fig. 3
To measure resistance of Secondary coil
Fig. 4
PRINCIPLE
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
Inductance is the property of a circuit element by which energy is capable of being stored in
a magnetic flux field and any circuit element exhibit the property of inductance is called an inductor.
Self Inductance of a coil is the property by which it opposes any flux through it. Mutual
inductance of a coil is the ability to produce an EMF in the neighboring coil by induction, when the
current in the first coil changes.
Consider two magnetically coupled coils of self inductance and . Let M be the mutualinductance of the coils connected in series so that flux is produced by current I through the coils are
in the same direction, then the effective inductance
= + + 2MIf coils are connected such that the flux produced by the current in opposite direction, then
effective inductance
= + - 2MTherefore mutual inductance M= ( - ) / 4Coupling Coefficient k = M / √ In the first case, if and are the applied voltage and current, then = / , = √ , = 2⁄ , where is the DC resistance of primarycoil.
Similarly for the second case
= / , = , = 2⁄ , where is the DC resistance of secondarycoil.
/ = / )2 From the above equations , , M and k can be found out. The experimental determinations ofthe above parameters are carried out for a pair of transformer winding.
PROCEDURE
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
For determining the inductance of transformer coil, connections are made as shown in figure
(1) when the windings are connected in series for additive polarity. Supply is switched on and the
rated voltage is applied in the circuit by adjusting the auto transformer. The Voltmeter and Ammeter
readings are noted. Then the terminals of the coils are interchanged as shown in the figure (2) for
subtractive polarity. Auto transformer is adjusted to give a voltage to the primary and all other
readings are taken.(It is desirable to keep V2 constant for both aiding and opposing).
To measure the resistance of the coils, connections are made as shown as figure (3) and (4)
and dc supply is switched on. The rheostat is adjusted for different values of Ammeter and Voltmeter
reading. R = ⁄ After obtaining the voltages and currents, inductance , , M and coupling coefficient k
for a pair of transformer windings are determined.
OBSERVATION
Aiding Circuit
Z A(Ω)
Opposing Circuit
Z B(Ω)
V(V) V 1(V) V 2(V) I(A) V(V) V 1(V) V 2(V) I(A)
Resistance Measurement
Transformer PrimaryWinding
Transformer SecondaryWinding
V(V) I(A) R P (Ω) V(V) I(A) RS (Ω)
Sample Calculation
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
= / = ------------- = √ = ------------- = 2⁄ = ------------- = / = -------------
= = ------------- = 2⁄ = -------------M = ( - ) / 4 = -------------
= + + 2M = -------------
= + - 2M = ------------- + = 2 ( + = -------------( + = ( + ) / 2 = -------------
/ = / )2 = / )2 From the above equations the values of , , M and k are calculated.
RESULT
Self inductance, Mutual inductance and Coefficient of coupling for a pair of transformer
windings are determined.
Self inductance of coil 1, = -------------Self inductance of coil 2 , = -------------Mutual inductance , M = -------------
Coefficient of Coupling, k = ---------------
INFERENCE
Expt No:
Date:
8/18/2019 EMMI LAB MANUAL_correct.pdf
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
MEASUREMENT OF B-H CURVE USING CRO
AIM
To study the hysteresis loop of a given specimen
APPARATUS REQUIRED
SL NO. APPARATUS SPECIFICATION QUANTITY
1. Hysteresis loop module ITB-026A 1
2. CRO 1
< Students are expected to calculate instrument ranges based on the machine ratings before start of
experiment and get it approved before connections are made>
PRINCIPLE
Magnetic field is a phenomenon where under certain conditions, energy or force transfer canoccur through space. it can be established only by its effective which is used to determine the
magnetic property of the materials.
Hysteresis loop is nothing but a plot of flux density ‘B’ versus magnetizing for ‘H’. Many
other parameters can be determined from this loop. The hysteresis in any process is the
nonconformity of the loading and unloading curve of the process. The reason for occurrence of
hysteresis is that of all energy that has been pumped in to the system during the loading period, is
not being recovered completely due to losses in the system.
The a-b-c-d-e-f-a curve is called hysteresis curve for the magnetic material.
BR is the residual flux density. This is what enables the creation of permanent magnets. The
magnetic force HD is required coerce the material to reduce its flux density level to zero is called
coercive force. The unit for magnetic force ‘H’ is ampere turn per meter At/m. flux density B is
called Tesla (Wb/m2) or gauss. One gauss is 10,000 gauss
Thus the hysteresis loop is often called B-H curve. The understanding of B-H curve is
extremely importance in design of transformer, chokes, coils and inductors
PROCEDURE
(iii)
Connect the variable power supply to the input terminals.
(iv) Connect the X input of the CRO to the terminal T3
(v) Connect the Y input of the CRO to the terminal T6
(vi) Keep the CRO in XY mode
(vii) Hysteresis loop appears as in figure
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
(viii) Vary the input AC voltage and calculate VX , VY and tabulate the readings.
(ix) Tabulate the VX and VY from CRO
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
OBSERVATION
SL.NO. VX VY I1 H B
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
FORMULAE
VX = R 1 * I1 VX=0.22 * I1
I1= VX/0.22
H=N1I1 / L
VY= (1/C) (N2AS/R 2) B
B= VYCR 2/ N2AS
Where
R 1= 0.22 ohms (from manufacturer)
L= length of magnetic path= 0.1139m
N1= no. of turns in primary=2475
N2= no. of turns in secondary+102
As= area of the specimen+0.00045m2
R 2= 4700Ω (from manufacturer)
C= 10μF (from manufacturer)
RESULT
Thus the graph is plotted between B and H
INFERENCE
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CIRCUIT DIAGRAM
a)
Calibration of voltmeter
Fig (1)
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
Expt No:
Date:
VERNIER POTENTIOMETER
AIM
To calibrate the given voltmeter, ammeter and wattmeter using Vernier potentiometer and
hence draw the calibration curve.
APPARATUS REQUIRED
SL NO. APPARATUS SPECIFICATION QUANTITY
1. Vernier potentiometer
2. STD cell
3. Fixed 2V supply
4. DC regulated power supply
5. Voltmeter
6. Galvanometer
7. Volt ratio box
8. Standard Resistance
9. Rheostat
10. Ammeter
< Students are expected to calculate instrument ranges based on the machine ratings before start of
experiment and get it approved before connections are made>
PRINCIPLE
The potentiometer is an instrument used for measurement of an unknown EMF or potential difference
by balancing it, wholly or partially by a known potential difference produced by the flow of a known
current in a network or circuit of known characteristics. Potentiometers are extensively used in
measurements where the precision required is higher than that can be obtained by ordinary deflection
instruments. EMFS are measured directly with a potentiometer in terms of the EMF of a standard
cell. By using, in addition, a standard resistor, current can also be measured. From the current and
voltage measurements, power can be calculated. The
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b) Calibration of ammeter
c)
Calibration of Wattmeter
Fig (2)
Fig (3)
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
potentiometer is widely employed for calibration of voltmeters, ammeters and wattmeters.
The potentiometer works on the principle of opposing the unknown EMF by a known EMF with the
– VE terminals of two EMFS connected together and also the +VE terminals connected together
through a galvanometer. Galvanometer gives no deflection if two EMFS are equal.
PROCEDURE
a) Standardization
The potentiometer is energized by giving a 2V dc supply to the terminals given in fig. The
selector switch is thrown to position ‘STD’ to include standard cell in the circuit. Range selector key
should be in position X0.1. In position X0.1, all dial readings should be multiplied by a factor 0.1 in
addition to factors shown near dials. The dials are adjusted to read standard cell voltage i.e. if standard
cell voltage is 1.0186, the first dial should read 10; the second dial 18 and third dial 60. The
galvanometer is connected to the terminal pair marked as ‘GALV’. The galvanometer key is pressed
and observed the galvanometer. The coarse, medium and fine rheostats are adjusted until the
galvanometer gets null deflection.
b)
Calibration of voltmeter
The voltmeter to be calibrated is connected across the variable dc source. The voltmeter is
connected to the high voltage side of volt ratio box. The low voltage side of volt ratio box is connected
to the potentiometer at appropriate terminals. The selector switch is thr own to ‘TEST’ position and
voltage at output of volt ratio box is measured using potentiometer. Then the true value of voltage
across voltmeter can be determined by multiplying the voltage at low voltage side of the volt ratio
box by multiplication factor. The voltmeter reading is noted. The ratio of difference between
measured value and true value is the percentage error. The errors at various voltmeter readings are
calculated.
% Error = − × 100
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
OBSERVATIONS
a) Calibration of voltmeter
Sl
No.
Volts
V
X1 ×0.1 X2 ×0.001 X3 ×0.00001 V(V) − × 100
b)
Calibration of ammeter
Sl
No.
Current I X1×0.1 X2×0.001 X3×0.00001 V I =/ − × 100
c) Calibration of Wattmeter
Sl
No V Wind X1
×0.1
X2
×0.001
X3
×0.00001E1
X1
×0.1
X2
×0.001
X3
×0.00001E2
I= 2/
Wact
W−WW× 100
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a)
Calibration of ammeter
An Ammeter to be calibrated is connected in series with a standard resistance R s of suitable value.
The current supplied by a D.C. supply passes through ammeter as well as standard resistance R s.
using D.C. potentiometer; a voltage across standard resistance can be measured. Thus, current
flowing through R s (and ammeter also) is given by,
I =R ; where Vs = voltage across Rs measured using potentiometer
Rs = resistance of standard resistor
Since the resistance of standard resistance is known accurately and also the voltage across Rs is
measured using standardized potentiometer, the method of calibrating ammeter is very accurate. If
the actual current Iact and the current indicat5ed by ammeter Iind are not matching, error is
indicated. The percentage error is given by
% error =−
× 100 ; where Iind = current indicated by ammeter and Iact = I =R
The calibration curve of ammeter can be obtained by plotting % error against the reading of
ammeter i.e. Iind.
Calibration of Wattmeter
For the calibration of a Wattmeter, a low voltage supply is given to the current coil (CC)
whose current can be adjusted by using a rheostat R h in series with low voltage supply and a high
voltage supply is given across the potential coil (PC). The voltage is stepped down by volt-ratio box.
A voltmeter measures voltage V and ammeter measures current I which gives true power as,
Wind = V I
This value can be compared with a value indicated by watt meter. If two values are not matching, a
positive or negative error is indicated which is given by,
% error =W−W
W × 100
RESULT
The given voltmeter, ammeter and wattmeter were calibrated the using vernier potentiometer
and hence the calibration curve were drawn.
INFERENCE
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
Expt.No.
Date:
WHEATSTONE BRIDGE AND KELVIN’S DOUBLE BRIDGE
AIM
a) To use wheatstone bridge for the measurement of medium resistance
b) To use Kelvin Double bridge for the measurement of low resistance.
APPARATUS REQUIRED
SL No APPARATUS SPECIFICATION QUANTITY
1. Wheatstone Bridge 1 no.
2. Voltmeter 1 no.
3. Voltmeter 1 no.
4. Rheostat 1 no.
5. Kelvin Double Bridge 1 no.
6. Galvanometer 1 no.
7. DC regulated power supply 1 no.
8. Ammeter 1 no.
9. Ammeter 1 no.
< Students are expected to calculate instrument ranges based on the machine ratings before start of
experiment and get it approved before connections are made>
CIRCUIT DIAGRAM
Wheatstone Bridge
Fig.1
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
Fig.2
PRINCIPLE
a) Wheatstone Bridge
This is the best and common method of measuring medium resistances (1Ω to 0.1MΩ).Majority of the electrical apparatus and equipments have resistances within these limits and hence
the wheat stone bridge is a very useful instrument for resistance measurement.
The General circuit arrangement is given in the figure (1), where P and Q are two known fixed
resistances, S being a known variable resistance and R be the unknown resistance (i.e. voltmeter
or rheostat). At balanced condition, no current flows through the galvanometer, and the unknown
resistance R is given by R = .The arms P and Q are the ratio arms of decade dial is provided in the portable bridge
for this purpose. S is the known standard resistance whose values may be varied. Decade dials in
different ranges are provided in the portable bridges. The product of the range selector ( ) andthe total value of variable resistance (S) gives the unknown resistance R.
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
Kelvin Double bridge
Fig .4
Fig .3
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
Kelvin Double Bridge
This method is the best available for the precise measurement of low resistances (less than
1Ω). It is a development of the wheat stone bridge by which the errors due to contact and lead
resistance are eliminated. Kelvin Double Bridge is suitable for measuring resistance fitted withfour terminals i.e. two current terminals C1 and C2 and two potential terminals P1 and P2. This is
to reduce contact and lead resistances completely. It incorporates the idea of a second set of ratio
arms. Hence the name double bridge and the use of four terminals.
Figure (2) shows the schematic diagram of Kelvin’s double bridge. The first set of ratio arms
is Q and M. The second set of ratio arms q and m is used to connect the galvanometer to a point
at the appropriate potential between Q and M to eliminate the effect of connecting lead resistance
between the known resistance R and standard resistance S. In the figure (2), R is the low resistance
to be measured (i.e. resistance of ammeter, given length of wire etc.), S is the standard variable
resistance and Q, M, q and m are four non inductive resistances, one pair of each (M and m Or
Q and q) are variable. These are connected to two sets of ratio arms which are used for range
selection. The ratio ⁄ is kept same as ⁄ under balanced condition. These ratios along withS being varied until zero deflection of the galvanometer are obtained. Then ⁄ = ⁄ = ⁄ or R = ⁄ × S. So the product of ratio arms ⁄ and variable resistance S gives the unknownresistances.
PROCEDURE
a) Wheatstone bridge circuit is shown in figure ( 1 ). Initially, set the four knobs of the decade
resistance box at zero position. Then adjust the galvanometer pointer to zero by using ‘SET
ZERO’ knob after checking the position of key 10, which should be in the normal raised position
and connect the given voltmeter to the external terminal ( 3 and 4) of the bridge.[Ensure that the
terminals 1 and 2 and also 7 and 8 are shorted.]. The range selector ( ) is properly selected andresistance S (i.e. by varying the four decade resistances) is varied and the galvanometer is
checked. This is continued until the balanced condition of the bridge is obtained. The readings
of the range selector and the four dials of the variable resistance S are noted. The experiment is
repeated for different values of range selector.
Kelvin Double bridge circuit is shown in figure ( 3 ). Provision has been given in
the bridge for current terminals (C and C1) and potential terminals (P and P1) separately. But
when connecting the unknown resistance having two terminals (like ammeters), they are
connected to only C and C1 while C to P and C1 to P1 are short circuited. An external dc power
supply (at ‘CURRENT INPUT’ terminal) and a galvanometer (between G1 and G2) are
connected. After setting the CURRENT SWITCH to NOMAL and adjusting the current to the
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
required value, select a proper value for range multiplier. Then vary the resistance S by adjusting
the decade dials. This is continued until the balanced condition of the bridge is obtained. The
readings of the range selector and the four dials of the variable resistance S are noted. The
experiment is repeated for the REVERSE CURRENT SWITCH condition also. The mean of the
two readings should be taken as the correct value.
OBSERVATIONS
a) For Wheatstone bridge
Sl
No.
S1 × 1000 S2 × 100 S3 ×10 S4 × 1 R3 = S1+S2+S3+S4 R =
b) For Kelvin Double bridge
Sl No.
Remarks ⁄ S1 S2 S = S1 + S2 R = ⁄ × S
RESULT
1. Resistance of Voltmeter =
2. Resistance of Ammeter =
INFERENCE
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
Expt.No.
Date:
B - H CURVE USING SINGLE PHASE TRANSFORMER
AIM
To plot the B- H characteristics of a transformer core.
APPARATUS REQUIRED
SL No APPARATUS SPECIFICATION QUANTITY
1. Autotransformer 1 no.
2. Voltmeter 1 no.
3. Ammeter 1 no.
4. Wattmeter 1 no.
5. Transfomer 1 no.
< Students are expected to calculate instrument ranges based on the machine ratings before start of
experiment and get it approved before connections are made>
CIRCUIT DIAGRAM
Fig. 1
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
Expt.No.
Date:
DETERMINATION OF HYSTERISIS LOOP
AIM
To trace the hysteresis loop using CRO.
APPARATUS REQUIRED
SL NO. APPARATUS SPECIFICATION QUANTITY
1. Hysteresis loop module ITB-026A 1
2. CRO 1
< Students are expected to calculate instrument ranges based on the machine ratings before start of
experiment and get it approved before connections are made>
CIRCUIT DIAGRAM
Fig. 1
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Dept. of Electrical & Electronics Engg. College of Engineeri ng, Kidangoor
PRINCIPLE
Magnetic field is a phenomenon where under certain conditions, energy or force transfer can
occur through space. it can be established only by its effective which is used to determine the
magnetic property of the materials.
Hysteresis loop is nothing but a plot of flux density ‘B’ versus magnetizing for ‘H’. Many
other parameters can be determined from this loop. The hysteresis in any process is the
nonconformity of the loading and unloading curve of the process. The reason for occurrence of
hysteresis is that of all energy that has been pumped in to the system during the loading period, is
not being recovered completely due to losses in the system.
The a-b-c-d-e-f-a curve is called hysteresis curve for the magnetic material.
BR is the residual flux density. This is what enables the creation of permanent magnets. The
magnetic force HD is required coerce the material to reduce its flux density level to zero is called
coercive force. The unit for magnetic force ‘H’ is ampere turn per meter At/m. flux density B is
called Tesla (Wb/m2) or gauss. One gauss is 10,000 gauss
Thus the hysteresis loop is often called B-H curve. The understanding of B-H curve is
extremely importance in design of transformer, chokes, coils and inductors
PROCEDURE
(i) Connect the variable power supply to the input terminals.
(ii) Connect the X input of the CRO to the terminal T3
(iii)
Connect the Y input of the CRO to the terminal T6(iv) Keep the CRO in XY mode
(v) Hysteresis loop appears as in figure
(vi) Vary the input AC voltage and calculate VX , VY and tabulate the readings.
(vii) Tabulate the VX and VY from CRO
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