Download single phase energy meter

Vignan’s University, Vadlamudi
Electrical Measurements Lab
Exp-1
TESTING & CALIBRATION OF
SINGLE PHASE ENERGY METER
Aim:
To test and calibrate a single-phase energy meter.
Apparatus:
Sl.No
Apparatus
Range
Type
Quantity
1.
Voltmeter
0-300V
MI
1No.
2.
Ammeter
0-10A
MI
1No.
3.
Loading rheostat
3KW
-
1No.
4.
Energy meter
15A,240V
Analog
1No.
5.
Stop clock
----
Analog
1No.
6.
1-
Auto 230V/
1No.
0-270V,10A
Transformer
Theory :
The energy meter is calibrated by finding error in the meter under different load
conditions. In energy meter, there are two fluxes produced by currents, flowing in the series
and shunt windings. These alternating fluxes produce emfs in the metallic disc. These emfs
inturn circulate eddy currents in the disc. Thus there are two fluxes and two eddy currents and
therefore two torques are produced. Total torque is the sum of the torques.
The speed of rotation of the disc is proportional to power.
Energy consumed = Number of revolutions/Meter Constant
1
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Circuit diagram:
Model graph (Indaicative Only) :
%error
IL(A)
0
2
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Procedure:
1. Connect the circuit as per the circuit diagram.
2. Apply rated voltage i.e., 230V to the energy meter by varying auto transformer.
3. Switch on the load & vary the load in steps.
4. For each step note down the time taken for 20 revolutions of the disc
using stop clock..
5. Note down the ammeter and voltmeter readings for each step.
6. Repeat the procedure until 10A of load current is reached.
7. Calculate the percentage error.
8. Plot a graph between load current and percentage error taking the load
current on x-axis and percentage error on y-axis.
Observations:
Meter constant K = ______ rev/KWh
S.
No
Current
in amps
IL(A)
Voltage
in volts
V(V)
No.of
revoluti
ons(N)
Time taken for Actual
20 revolutions Energy
= VI LT
Secs
Hrs(T)
(Wh)
Total
energy
recorded
=N/K×1000
(Wh)
%
error
1
2
3
4
5
3
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Sample calculations:
Voltage =
Current =
Time for 20 revolutions =
Energy measured (actual in Wh) = VILT =
Energy recorded =
%error =
No. of revolutions
KWh
meter cons tan t
energy measured by energy meter  actual energy consumed
x100
actual energy consumed
Precautions:
1.Initially the autotransformer should be kept in minimum position.
2.Initially load resistance should be kept in minimum position.
3.Time taken for 20 revolutions must be determined accurately.
Result :
4
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Exp-2
CALIBRATION OF DYNAMOMETER TYPE 1-PHASE
POWER FACTOR METER
Aim :
To calibrate a dynamometer type power factor meter.
Apparatus :
S.No
Apparatus
Range
Type
Quantity
1
Ammeter
0-10A
MI
1No.
2
Voltmeter
0-300V/ 150V
MI
3No.
3
Powerfactor meter
250V / 10A
D.M.T
1No.
4
1- auto transformer
230V/0-270V,10A
1No.
5
1- loading rheostat
3KW,230v
1No.
6
1- loading inductor
230V,15A
1No.
7
SPST Switch
1NO.
Theory:
Single phase dynamometer type power factor meter consists of a fixed coil which is
split into two parts which carries a current of test circuit.
Two identical pressure coils are pivoted on spindle of the moving system. One
pressure coil has a resistance in series and other has an inductance in series. The two coils are
connected across the voltage of the circuit.
Current through one pressure coil will be in phase with the voltage and that of the
other coil lags by 90 degrees. The torques due to these two coils is in opposite to each other.
The pointer will stop when the two torques are equal.
The deflection of the instrument depends on phase difference between the main
current and currents in the two pressure coils.
5
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Circuit diagram :
Model graph (Indaicative Only) :
% error
IL(A)
6
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Procedure :
1. Connect the circuit as per circuit diagram.
2. Initially keep the autotransformer in minimum position & close the supply DPST
switch.
3. Initially keep the inductive load in minimum position & close the SPST switch across
it.
4. Vary the variac until voltmeter connected across it reads rated voltage.
5. Vary the resistive load until ammeter shows maximum possible reading ( 9.5A)
6. Note down the readings of all the meters.
7. Open the SPST switch connected across inductive load.
8. Increase the inductive load in steps.
9. Note down the readings of all the meters at each step.
10. Calculate the percentage error for each step.
11. Plot a graph between IL and percentage error.
7
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Observations :
S.No
Voltage
applied
VS
(Volts)
IL
(A)
Voltage
Across
R(VR)
(volts)
Voltage
Across
L(VL)
(volts)
Reading of
meter
Cos
(measured
value)
pf Power Factor
Angle
=Tan- 1(VL/VR)
Actual Value
of pf meter
Cos
% error=
Cos  Cos
Cos
×100
1
2
3
4
5
Sample calculations:
Applied voltage Vs=
Voltage across inductor VL=
Voltage across resistor VR =
Power Factor Angle  = Tan-1 (VL/VR) =
Cos  =
Cos  =
% error =
Result:
8
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Exp-3
KELVIN’S DOUBLE BRIDGE – MEASUREMENT OF RESISTANCE
Aim:
To determine the resistance of given unknown resistor..
Apparatus:
Sl.No
Apparatus
Range
1.
Kelvin’s double bridge ---
Type
Quantity
----
1No
trainer kit
2.
Unknown resistance
---
----
1 No
3.
Galvanometer
----
Spot light
1 No.
Theory:
Kelvin’s double bridge is used for the measurement of low resistances (of the order less
than 1).Wheatstone bridge is used for the measurement of medium resistances ranging from a
few ohms to several megaohms.
The lower limit for the measurement is set by the resistance of the connecting leads and
by contact resistance of the binding posts. The error caused by leads may be corrected fairly
well, but contact resistance presents a source of uncertainty that is difficult to overcome.
This is eliminated in the Kelvin’s double bridge by connecting the galvanometer to any
intermediate point of the known resistance(r) .Due to this, the resistance(r) is divided into two
parts i.e., second set of ratio arms(P,Q)
9
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Circuit diagram :
Procedure:
1. Connect the unknown resistance (DRB) between the terminals C1 and C2 and short circuit
the terminals P1 and C1, P2 and C2.
2. Connect the mains lead to 220V A.C. mains.
3. Choose the suitable range multiplier depending upon the magnitude of the unknown
resistance connected between terminals C1 and C2.
4. Press the push button provided on kit to bring both battery and galvanometer into the circuit
simultaneously.
5. Initially keep the slide wire at zero ohm position and vary the ‘variable standard resistance
(main dial)’ and multiplier until the ‘G’ deflection is minimized.
6. By varying the slide wire slowly, adjust the ‘G’ position to zero in initial and final positions
of ‘G’ switch for a particular value of sensitivity.
Note down the values of variable
resistance and slide wire resistance.
7. To eliminate errors, due to thermal e.m.f reverse the direction of the current using reversing
switch and take another reading as above. The mean of these two values will give the
correct value of unknown resistance
8. Calculate the unknown resistance at each step.
10
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Observations:
Variable
Resistance
S.
No
resistance r 
R
Normal
Unknown
slide wire
Multiply-ing
Factor(M)
Reverse
Normal
Revers
Resistance
X =(R+r )M
Normal
e
Reve
rse
1
2
Sample calculations:
Sensitivity=
Variable resistance R: Normal =
Reverse =
Slide wire resistance r: Normal =
Reverse =
Multiplying factor (M) =1
Unknown resistance, Normal X=(R+r )M =
Reverse X=,(R+r)M=
Precautions:
1.The galvanometer should not be operated in short circuit position.
2.While changing the sensitivity of the galvanometer, it should be set in
lock position.
Result :
11
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Exp-4
SCHERING BRIDGE
Aim:
To measure capacitance of an unknown capacitor and to determine its dissipating factor using
Schering bridge.
Apparatus:
1. Schering bridge kit -1 no.
2. Head phones
3. Connecting wires
Theory:
Schering bridge is used for the measurements of capacitance and dissipating factor. From
the balance, the equation to obtain the value of capacitance is
C=C1(R2/R1)
Since R1and C3 are fixed values, capacitance value can be obtained directly by varying R2.The
dissipation factor can be obtained directly from the equation
D1=C1r1
Circuit diagram:-
12
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
C = unknown capacitance
C1 = standard capacitance
C2= variable capacitance
R, R1 = non inductive resistances
R2 = variable non inductive resistance in parallel with C3
Procedure:1. Connect “AC supply” of 1k Hertz to the “supply” terminals and one unknown
capacitor on the kit with the terminals marked C in the circuit diagram and head
phone with the terminals marked D.
2. Set the resistance dial R to zero position and also set capacitance dial C 2 to zero
position. And also set resistance dial R1 at 1000 ohms.
3. Set the standard capacitor C1 to 0.01 μf position.
4. Now adjust the decade resistance dial R2 to minimize the sound in the head phone.
5. Note the value R1, R2 and C1 and calculate the value of unknown capacitor using
above formula.
6. Repeat the same experiment on another value of C1.
7. At each step find out the value of C
Where C = C1.R2 / R1
And dissipation factor D = 2 fCr1
where r1 = R1 x C2 / C1 and r1 is the resistance representing loss in C
Observations
S.no
R1()
R2()
C1(μF)
C2(μF)
C=
r1 =
D=
C1.R2 / R1
R1.C2 / C1
2fCr1
1
2
3
4
5
13
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Sample calculations:
Non-inductive resistance R1 =
Variable non-inductive resistance R2 =
Standard capacitance C1 =
Variable capacitance C2 =
Unknown capacitance C= C1.(R2 / R1) =
Internal resistance of C = r1= R1.(C2 / C1) =
Dissipation factor=2fCr1=
Result:Capacitance of given capacitor is
S.no
C
D
r1
1.
14
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Exp-5
MEASUREMENT OF 3-PHASE REACTIVE POWER USING
SINGLE PHASE WATTMETER
Aim :
To measure reactive power in a three-phase circuit using single phase wattmeter.
Apparatus :
Sl.No
Apparatus
Range
Type
Qty
1
Voltmeter
(0-600V)
MI
1 no.
2
Wattmeter
1,600V,10A,
D.M.T
1 no.
MI
1 no.
LPF
3
Ammeter
0-10A,
4
3 autotransformer
415/0-470V,
1no.
10A, 8.14KVA
5
10A, 415V
3 loading inductor
1 no.
Theory:
Reactive power measurement in 3- circuits using 1- wattmeter can be done only for
balanced 3- loads. By connecting the current coil of the wattmeter in one line and the pressure
coil across the other two lines of 3- circuit, current through the current coil and voltage across
the pressure coil are determined. Now as the current in the current coil lags the voltage by an
angle of 90, the wattmeter reads a value proportional to the reactive power of the circuit.
15
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Circuit diagram :
Model graph (Indaicative Only) :
16
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Procedure :
1. Connect the circuit as per the circuit diagram.
2. Keep the variac of the auto-transformer in minimum position.
3. Close supply TPST switch and vary the auto-transformer slowly and apply rated voltage
i.e.230V.
4. Vary the load gradually and at different loads, note down readings of ammeter, Voltmeter
and Wattmeter.
5. Draw the phasor diagram.
Phasor Diagram :
Observations :
For ideal inductive load  = 900 --> Sin= 1
Reactive power
S.
N
o
Voltage
Current
VL volts
IL amp
Wattmeter
reading
Reactive power (actualvalue)
(measured
Qa=
value)Qm=
(W)
3W (VAR)
3VL I L sin 
%error =
{(Qm-Qa)/
Qa}×100
( VAR )
1
2
3
4
5
17
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Sample calculations :
Load voltage VL =
Load current IL =
Watt meter reading W =
3W =
Reactive power (actual value in W) = 3VL I L sin  =
Reactive power (measured value) =
% error =
measured value - actual value
x100
actual value
=
Result:
18
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Exp-6
MEASUREMENT OF PARAMETERS OF A CHOKE COIL
USING 3-VOLTMETER AND 3-AMMETER METHOD
Aim :
To measure parameters of a choke coil by 3 voltmeter method and 3 ammeter method.
Apparatus :
S.No
Apparatus
Range
1
Choke coil
230 V, 0.39A
Copper wound
1 No
2
Ammeter
0-1/2 A
MI
1 No
0-5 A
MI
2 No
3
Voltmeter
0-300V
MI
2 No
0-75V
MI
1 No
1
4
Phase
auto
transformer
Type
230V/0-270V,10A
Quantity
1 No
5
Rheostat
145 /2.8A
Wire wound
1No
6
Rheostat
25 /5A
Wire wound
1No
Theory & Formulae:
Inductances of about 50 to 500mH can be measured using this method. It is suitable for iron
cored coils, since the full normal current can be passed through it during measurement. From
the phasor diagram,
VS
2
2
2
VS = VR + VL + 2 VR VL cos
VL
VS  VR  VL
r
, Also cos =
2VRVL
r 2  (L) 2
2
cos =
2
2

where r is the resistance and L is the inductance of the coil.
VS  VR  VL
1
r
=
 L=
2VRVL
2f
r 2  (L) 2
2
2
2
19
2
VR
2
4r 2VR VL
 r2
2
2
2
VS  VL  VR
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Circuit diagrams :
(i) 3 voltmeter method :
figure-1
(ii) 3 Ammeter method :
figure-2
Procedure :
1. Make the connections as per the circuit shown in figure (1)
2. Initially keep the autotransformer in minimum position.
3. Close supply DPST switch.
4. Vary the applied voltage by varying the auto-transformer until rated current flows
through the choke coil.
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Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
5. Note down the readings of all the meters.
6. Make connections as per the circuit shown in figure(2).
7. Repeat steps 2,3,4 and 5.
8. Draw the phasor diagram for both the methods.
Observations :
3-Ammeter method:
S.
Is
Ir
IL
V
Pf Cos = Resistance R Inductive
Inducta
N
(A)
(A)
(A)
(V)
Is  IR  IL
2I R I L
reactance
V cos 

IL
XL=
nce (H)
V sin 

IL
XL/2L
o
2
2
2
=
L
=
1
2
3-Voltmeter method :
S.
Vs
Vr
VL
N
(V) (V) (V)
o
I
Pf Cos = Resistance R Inductive
(A)
Vs  VR  VL
2VRVL
2
2
2
=
reactance
VL cos 

I
XL
Inducta
nce (H)
= L
=
XL/2L
VL sin 

I
1
2
Sample calculations:
(i) 3-Ammeter method:
cos = Is2 – IR2 – IL2 / 2IRIL =
Resistance = (V / IL) cos =
Inductive reactance of the coil = XL= [V/IL] sin =
21
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Inductance = [ XL/2f ] =
Where w is the frequency of supply in hertz = 50Hz
(i) 3-Voltmeter method:
Power Factor
cos = Vs2 – VR2 – VL2 / 2VRVL
=
Resistance = (VL / I) Cos =
Inductive reactance of the coil = XL= [VL/I] sin =
Inductance = [ XL/2f ] =
Where f is the frequency of supply in hertz = 50Hz
Phasor diagrams :
3-voltmeter method:
V1
V3

3-Ammeter method :
V2

I2
I3
I1
Precautions :
1. Avoid loose connections
2. Keep autotransformer in minimum position before closing supply DPST.
3. Readings are to be taken without parallax error.
Results: The parameters of the given choke coil by 3 voltmeter method and 3 ammeter
methods are measured as
3-Ammeter method
3-Voltmeter Method
Resistance of the coil R
Inductance of the coil L
Power factor
22
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Exp-7
CALIBRATION OF LPF WATTMETER
BY PHANTOM LOAD TESTING
Aim :
To calibrate the given LPF wattmeter using phantom load testing.
Apparatus :
S.No
1
2
3
4
5
6
Apparatus
1- Auto transformer
Ammeter
Voltmeter
Voltmeter
Wattmeter
Inductive load
Range
230V/0-270V, 10A
0-10A
0-300V
0-150V
300V, 10A
250V/1-15 A
Type
MI
MI
MI
LPF
Quantity
2 nos.
1 no.
1 no.
1 no.
1no.
1no.
Theory:
When the current rating of a meter is high, a test with ordinary loading arrangement would
involve a considerable wastage of power.
In order to avoid this, phantom or fictitious loading is done.
In phantom loading , pressure coil is connected across the supply voltage and current coil is
connected in series with low voltage source, but it can supply the rated current because
impedance will be low. Due to the above arrangement, the total power consumed for testing the
meter is low when compared with actual loading of wattmeter.
23
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Circuit diagram:
Model graph (Indaicative only):
% error
IL(A)
Procedure :
1) Connect the circuit as per the circuit diagram.
2) Initially keep the two autotransformers and inductive load in minimum position.
3) By varying the autotransformer2 in the pressure circuit, the voltmeter reading is adjusted to
rated value i.e 230V.
4) By slowly varying the autotransformer1 in current coil circuit, the voltmeter reading is
adjusted to 150V.
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Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
5) Apply inductive load in steps and tabulate the readings of all meters and calculate % error
at each step.
6) Plot the graph between IL and % error.
Observations:
cos  = 0.2
S.No
Voltmeter
Reading(V)
Ammeter
Reading(A)
% Error =
Wattmeter
Reading(Wr)
(W)
True Power
WT=VI cos (W)
Wr  WT
x100
WT
1
2
3
4
5
Sample Calculations:
Voltage V =
Current IL=
Wattmeter reading (Wr) =
True power (WT) =
% Error =
Wr  WT
x100 =
WT
Precautions:
1) Loose connections must be avoided.
2) Meter readings should not be exceeded beyond their ratings.
3) Apply the voltage slowly so that the current is within the limited range of ammeter.
Result:
25
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Exp-8(a)
LINEAR VOLTAGE DIFFERENTIAL TRANSFORMER
Aim:
To study the operational characteristics of LVDT
Apparatus:
LVDT TRAINER KIT
Theory:
Differential Transformer, based on a variable inductance principle, are also used to measure
displacement. The most popular variable-inductance transducer for linear displacement
measurement is the linear variable differential transformer (LVDT). The LVDT illustrated in the
fig. Consists of three symmetrically spaced coils wound on to an insulated bobbin. A magnetic
core, which moves through the bobbin without contact, provides a path for magnetic flux
linkages between coils. The position of the magnetic core controls the mutual between the center
or primary coil and with the two outside or secondary coils.
When an AC carrier excitation is applied to the primary coil, voltages are
induced in the two secondary coils that are wires in a series-opposing circuit. When the core is
centered between the secondary coils, the voltage induces between secondary coils are equal but
out of phase by 1800. The voltage in the two coil cancels and the output voltage will be zero.
When the core is moves from the center position, an inductance imbalance occurs between the
primary coils and the secondary coil and an output voltage develops. The output voltage is a
linear function of the core position as long as the motion of the core is with in the operating
range of the LVDT.
26
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Circuit diagram :
Procedure :
1. Connect the terminals marked “PRIMARY” on the front panel of the instrument to the
terminals marked “PRIMARY” on the transducer itself, with the help of the flexible
wires provided along with. Observe the colour code for the wires provided and the colour
of the binding posts.
2. Identically establish connections from terminals marked “SECONDARY”. Observe the
colour code for wires provided and the colour of the binding posts.
3. Keep pot marked “MAX” in most anticlockwise position.
4. The magnetic core may be displaced and the pointer may be brought to zero position. If
the DPM is not indicating zero, use potentiometer marked “MIN” to get zero on DPM at
zero mechanical position. If the core is displaced in both directions, the meter must show
indications with appropriate polarity. Now displace the core to 19 mm positions in one of
the directions. Adjust the “MAX” pot to get an indication of 19.00 on the DPM under
these conditions. We may again check for zero position also.
5. Now the core can be displaced by a known amount in the range of +19 and -19 mm and
the meter readings can be note down. It may noted that by inter changing the secondary
27
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
terminals or the primary, the polarity of the meter indication can be reversed for a given
direction of input displacement.
6. For LVDT provided with dial gage, adjust the magnetic core carefully by rotating the
control knob in the clockwise direction. Note that for these type arrangement,
displacement in only one direction i.e. positive direction is possible.
7. Plot the graph of input displacement and the output indication on the X and Y axes
respectively.
Observations :
Input displacement Output
(mm)
Indication
S.No.
Precautions:
1. While connecting lead wire from panel to transducer, make proper connections following
colour code.
2. Move the core with a gentle fashion by operating the knob for core movement very
carefully. Do not try to effect the core movement beyond the given range.
Result :
28
Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Exp-8(b)
STRAIN GUAGE
Aim:
To measure the strain by using the strain guage.
Apparatus:
Strain measurement trainer
-
1
Strain guage cantilever beam
-
1
Weights
-
10gm,100gm,etc.
Theory :
Strain guage is a transducer which converts the applied load strain in to the change
in resistance of the materials. It is connected as one of the arms of the wheat stone
bridge. According to change in resistance of material used in strain guage breidge
unbalanced voltage will be appeared and this voltage is calibrated in to the values
of strain.
In tail type strain guage, nichrome, which has low temperature
coefficient, is used. This wire is designed in such a way that its thickness will be
0.005mm. It is connected on paper bakelite sheet of thickness 0.05mm and there it
is attached to the cantilever beam with adhesive material. Here cantilever beam is
tee material whose strain is to be found. The nichrome is designed in such a way
that its natural strain should be zero.
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Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Circuit diagram :
supply
Procedure:
1. Connect the flexible wires provided with the strain gage cantilever beam
between terminals 1-1, 2-2 and 3-3 and 4-4.
2. Amp. Gain pot may be kept in the position of 100.
3. Keep the switch SW2 in the downward position (4 arm configuration).
4. Turn on the mains supply. By gently moving the balance pot P1 and P2,
Obtain initial balance on the meter and wait for 5 minutes to allow the strain
gage temperature to stabilize.
5. Now apply a weight of 1kg on the cantilever and adjust the gain pot so that
reading of 1.00 is obtained on the DPM. Now remove the weight and check
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Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
for the bridge balance. After one or two such adjustments we will be able get
a reading of 1.00 on the DPM.
6. Apply the load on the sensor using loading arrangement provided in steps up
to 5kg.
7. Note down the readings in the tabular form. The % error is calculated by
comparing the theoretical values.
8. Plot graph of applied load versus the indicated meter reading.
Observations :
S.No.
Weight on the DPM
cantilever (kg)
readings(kg)
Practical
Theoretical % Error
value strain value strain
(V)
(V)
Sample Calculations:
Theoretical :
L  Efficient length of beam (15.5cm)
b  Width of bean (2.0 cm)
t  thickness of beam (0.59 cm)
G  Gauge factor (2.0)
Eout  strain, in V.
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Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
R  strain gage resistance.
Exc strain gage excitation (5V)
E  Modulus of Elasticity (2*106 kg/cm2)
S  Sensitivity of strain gauge (100mV/Kg)
By definition
stress = f = (W*L)/(0.166*bt2) =
strain = stress / E = f/E =
ΔR/R = strain * Gauge factor =
We can consider
Eout = Exc * (ΔR/R) =
Practical:
Eout = S*W =
% Error = {(Practical Eout – Theoretical Eout )/ Theoretical } x 100
Precautions:
Avoid loose connections
Result:
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Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Exp-9
DIELECTRIC OIL TESTING USING H.T.TESTING KIT
Aim:
To determine break over voltage of given dielectric oil, using H.T testing kit.
Apparatus:
1. Dielectric oil testing kit – 1No.
2. Dielectric oil.
Theory:
The dielectric strength of an oil is the potential at which it starts behaving as a conducting
medium. In the HT testing kit, the oil to be tested is placed in an acrylic box consisting of two
metal electrodes. By varying the distance between electrodes and by applying high voltage
across the electrodes, the break over voltage of the oil is determined.
Dielectric strength of oil =
break over volta ge
(kV/cm)
distance
Dielectric strength of oil decreases with moisture.
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Vignan’s University, Vadlamudi
Electrical Measurements Lab
Circuit Diagram:
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Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Procedure:
1. Take the oil cup and adjust the gap between the electrodes with the help of gauge.
2. Fill up oil test cup with oil to be tested, close it with the lid and place it on the HT horns
under the hinged acrylic cover and close the acrylic cover properly.
3. Keep the variac in minimum position.
4. Connect the mains lead to the 220V, single phase AC 50Hz supply.
5. Switch ON the power supply by operating the toggle switch, then yellow neon bulb glows
indicating that the HT kit is switched off.
6. Press the HT ‘ON push’ switch.
The red Neon lamp will start glowing and the HT
transformer circuit will be energized, the green neon bulb start glowing.
7. In case the red indication does not glow, check up the hinged acrylic cover is properly closed
and the variac knob is fully rotated in the anticlockwise direction for ‘0’ start.
8. Now start rotating the variac knob slowly in the clockwise direction till the flash over occurs
across electrodes in the oil test cup. The speed of ratio should be such that the voltage rises
at the rate of 2 kv/sec.
9. As soon as flash over occurs, the supply of the high voltage transformers, will be cut off and
the voltage pointer will also stop indications the flash over level.
Note down the reading of voltmeter and distance between the electrodes.
10. To repeat test on the sample, switch OFF the mains supply and stir the test pot with the help
of a clean rod and let it cool for sometime and close the acrylic cover properly.
11. Repeat the steps 2 to 10.
12. Switch OFF the mains supply after the tests are over.
Observations:
S.NO
Distance between
electrodes (Cm)
the Break over voltage Dielectric strength of
of oil (KV)
oil =
break over volta ge
distance
(kV/cm)
1
2
3
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Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Precautions:
1. The lid of the HT testing kit should be closed properly.
2. The variac should be kept in minimum position initially.
3. Oil cup must be kept on the HT testing horns properly.
Result :
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Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Exp-10
Measurement of 3-Phase Power Using 2 CTs and 1 Wattmeter
Aim:
To measure the 3-φ power in a balanced circuit using 2 CTs and 1
Wattmeter.
Apparatus:
Sl.No
Apparatus
Range
Type
Quantity
7.
Voltmeter
0-600V
MI
1No.
8.
Ammeter
0-10A
MI
1No.
9.
Current Transformer
5/5 A
-
2 No.
3KW
-
1No.
10. Loading rheostat
Theory :
In this method the power absorbed in a 3-φ balanced circuit is measured using a single
wattmeter in conjunction with 2 CT's. Usually 2-Wattmeter method is used measure the 3-φ
power for both balanced and unbalanced load, but method like this requires only one wattmeter.
The CT's used for this method should be of 1:1 ratio.
The primaries are connected in series with the 2 phases. The secondaries are connected to
the current coil of wattmeter such that the difference in the two phase currents will flow through
the current coil. The wattmeter pressure coil is connected between the same two phases.
Any wattmeter measures the product of
Voltage across pressure coil
VRY = VR - VY
Current through the current coil
IRY = IR - IY
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Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Cosine of phase angle between voltage and current is φ.
ω = VRY. IRY.cos φ
VR = VY = VB = V
IR = IY = IB = I
VRY = VR - VY = √3 V
IRY = IR - IY = √3 I
ω = 3V.I.cos φ = 3× phase active power
The circuit is assumed to be connected in star, for delta connection also the procedure is valid
and the wattmeter reads directly total power absorbed.
Circuit diagram:
Phasor diagram
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Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
Procedure
1. Give the connections as per the circuit diagram.
2. Apply 415 V, 3-φ, 50Hz supply closing the TPST switch.
3. Vary the load in suitable steps.
4. At each load note down the wattmeter readings.
5. Tabulate the results. Expected example tabulated results are as follows:
S.No
VL (Volts)
IL (Amps)
Wattmeter
ω Calculated
Reading
(1.732VLIL
(Watts)
Cosφ)
1.
2
3
4
5
Sample calculations:
Line Voltage VL=
Line Current VR =
3- Phase Power = 1.732VLIL Cosφ =
Precautions :
1. Avoid loose connections
2. Readings are to be taken without parallax error.
Result:
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Department of Electrical & Engineering
Vignan’s University, Vadlamudi
Electrical Measurements Lab
ELECTRICAL
MEASUREMENTS
LAB MANUAL
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Department of Electrical & Engineering