CALIBRATION AND TESTING OF SINGLE PHASE
ENERGY METER
CALIBRATION AND TESTING OF SINGLE PHASE ENERGY METER
Aim: Calibration of 1-cp Energy meter (Induction Type).
APPARATUS :S.No.
1.
APPARATUS
Auto Transformer
RANGE
230v/0-230v
TYPE
Continuously
variable
Resistive
2.
Load
5kw
3.
1-Φ Energy meter
750rev/kwh
4.
Voltmeter
(0-3 00v)
M.I.
1
5.
Ammeter
(0-5A)
M.I.
1
6.
Wattmeter
300v, 5A
LPF
1
7.
Stop Watch
Digital
1
Induction
QTY
1
REMARKS
1
1
THEORY:
Induction Type Energy meter is widely used for the measurement of energy
consumed in domestic as well as in industrial installations. Induction instruments possess
lower friction and higher torque/weight ratio. And these instruments cost less and are
accurate over a wide range of loads and temperatures.
There are four main parts of the operating mechanism.
(i)
Driving System.
(ii)
Moving System.
(iii)
Braking System.
(iv)
Registering Mechanism.
Principle of Operation: The pressure and current coils of shunt and series magnets
produce two alternating fluxes, one proportional to voltage and the other proportional to load
currents. These two fluxes when cut the disc induce eddy currents in it. The interaction of
the fluxes with the eddy currents sets up a torque on the disc causing it to rotate. The speed
of the disc would then be proportional to the power being measured.
CIRCUIT DIAGRAM:
PROCEDURE:-
1. Connect the circuit as shown in figure.
2. By adjusting the autotransformer keep the voltage across the voltmeter in which current
should not exceed 2.8A in the ammeter.
3. By using stopwatch measure time for 5 rev of the disc of the energy meter and take the
corresponding readings if voltmeter, ammeter and wattmeter.
4. Repeat step-3 until the ammeter reading should not exceed 2.8A
5. Tabulate the above readings and calculate the % error of the energy meter.
TABULAR FORM:
S.NO
V (volts)
I (amp)
W, (watts)
Rev/Sec
CALCULATIONS:
%error of the energy meter=(Wi-W a)/(W*100)
Where Wi = indicating Power (watt)
Wa=Actual Power (watt)
Wa=KR/t
Where 'R' is No. of revolutions
1 Unit=1 KWH=750rev
=1000*60*60=1200rev
1 rev/sec= 1/1000 x 60 x 60 / 280
K=4800W
RESULT:- The percentage error of the energy meter is
PRECAUTIONS:
(v) Energy meter should not be over loaded.
(vi) Connect the meters with appropriate meters.
(vii)
Avoid loose connections to prevent sparks and damage to meters.
RESULT:
CROMPTON POTENTIOMETER
CROMPTION DC POTENTIOMETER
Calibration of voltmeter and ammeter
Aim: calibration of ammeter and voltmeter by using Crompton dc potentiometer
APPARATUS:
1.
2.
3.
4.
5.
6.
Dc potentiometer
Super sensitive galvanometer
Standard cell
Volt ratio box
Potentiometer shunt 0.1 Ω
Voltmeter 0-75 /150/300 V MC
7. Ammeter 0-5/10 A MC
Theory:
Working :Connect the galvanometer standard cell and 2 V supply to their appropriate terminal in
correct polarity.
Standardisation :Move the selector switch toward Std Cell position.
1.
2.
Put the combination of potential dial to the voltage of 1.0186 i.e. equal to std cell voltage
Dial is part 1-0 Volt position ani the slide wire is put at 0.0186.
Galvanometer key is prered balance the galvanometer with the help of both Rheostat
i.e. coarse & fine, his process complete the standardization process.
PROCEDURE
1. Connect the unknown voltage to the measured to the X pair of terminal with correct
polarity.
2. Move the selector switch toward x position.
3. Balance the galvanometer with the help of potential dial without disturbing Rheostat
position that-we attain in standardization process.
4. The value of unknown voltage read out directly from main dial and slide wire i.e.
unknown emp:- Main dial voltage + slide wire voltage.
5. The standardization of potentiometer is checked again by returning the switches to the
std cell.
6. By putting the voltage of main dial and slide wire equal to 1.0186 volt.
General Purpose Potentiometer Cover a maximum Range of 0-1.75 volt if higher
voltage Range have to be measured a Precision Potential divider called a volt Ratio box is
used.
There are four terminal in volt Ratio box in one Pair of Terminal Unknown Voltage to be
measured is connect and other Pair of terminal is connected to the of terminal is connected to
the X terminal of potentiometer with correct polarity. The volt Ratio box is provided with selector
switch forvoltageRange.lt has the following Ranges 0,15,30,75,150,300. Suppose the voltage
Range selected in volt ratio box is 150. The Reading of the potentiometer at balance is 0.852
the value of unknown voltage is 0.852x 150 = 85.2 volt.
1.5
Application of DC Potentiometer
1. Calibration of Voltmeter: - Fig (1) shows the Circuit Diagram for calibration of voltmeter.
Stabilized
DC
Source
Volt
Ratio
Box
V
To Potentiometer
(i) Initially keep the power supply pat fully Anticlockwise.
(ii) Arrange the circuit as shown in fig. (1)
(iii) Vary the supply in clock wise direction so that voltmeter needle coincide with major
reading i.e. IV.
(iv) Measure the voltage with the help of potentiometer using the procedure given in
working of potentiometer.
(v) The potentiometer measure the true value of voltage if the potentiometer Reading does
not agree with voltmeter. A Negative or positive error is indicated. A calibration curve
may be drawn using the voltmeter reading potentiometer Reading.
S.No.
Voltmeter Read
Vv
Potentiometer Read
Vp
Vv-Vp
Difference
2. Calibration of Ammeter:- Fig (2)
Gives the circuit for calibration of Ammeter or for measurement of current using DC
Potentiometer
Stabilized
DC
Source
A
S
To Potentiometer
Where Sis a Standard RES.
The Voltage Across Standard RES is measured with the help of potentiometer. As given in
potentiometer working.
VS : Voltage Across Std. Res.
S- : Standard RES.
1 - Vs/S
A Calibration curve indicating, the error at various. Scale Reading of Ammeter may be plated.
3. Measurement of Resistance:- The Circuit diagram for measurement of Unknown RES is
shown in Fig (3)
A
Stabilized
Power
Supply
R
To Potentiometer
S
To Potentiometer
The Unknown RES R is connected in series with standard RES. S.
The current through the circuit is controlled with the help of Rheostat. Ax the current in series
remain the same.
Vs is the voltage across Std RES.
VR voltage across unknown RES.
V = 1R
VR =I,R
Vs = I2S
Where R x S are unknown x Std RES Respectively.
I1 = VR
S
I2 = VS R
Ax I1 = I2 = I
VR = VS
R
S
R = VR X S
VS
S is Std RES then after measuring. VR x Vs we can easily measure value of unknown RES.
RESULT:
1-PHASE DYNAMOMETER POWER FACTOR METER
CALIBRATION OF 1-PHASE DYNAMOMETER POWER FACTOR METER
AIM: Calibration of 1-phase dynamometer type power factor meter.
APPARATUS:
S.NO
APPARATUS
RANGE
TYPE
QTY
1.
Auto transformer
230V/0- 23
Ov
Continuously
Variable
1
2
P.f meter
0.5 lag to
lead
Dynamometer
type
1
3.
Voltmeter
(0-300v)
M.I
1
4.
Ammeter
(0-5 A)
M.I
1
5.
Wattmeter
300v,5A
LPF
1
Choke coil
230v.5A
inductive
1
6.
REMARKS
THEORY:
The powerfactor is of a single phase electro dynamo meter type power factor meter, it
consists of a fixed coil which act as the current coil, this coil split up m to two parts and
carries the current of the circuit under test. Therefore the magnetic field produced by this
coil is proportional to main current. Two identical pressure coils A and B pivoted on a
spindle constitute the moving system. Pressure coil A has a noninductive resistance R
connected in series with it, and coil B has a highly inductive choke coil L connected in
series with it. the two coils are connected across the voltage of the circuit. The values of R
and L are so adjusted that the two coils carry the same value of current at normal
frequency .i.e. R= wL. the current through the coil A is in phase with the circuit voltage
while that through coil B lags the voltage by an angle (delta), which is nearly equals to 90
degrees. The angle between the planes of coils is also made equal to delta. There is 110
controlling device. Connections to moving coils are made through silver or gold ligaments
which are extremely flexible and thus give a minimum control effect on the moving
system.
Wattmeter
CIRCUIT DIAGRAM:
PH
(0 – 5A)
M.1 A
L
M
V
M
V
C
1–Φ
Variac
P. F. Meter
L
C
R – Load
Resistance
V
(0 – 300)
M.1
Inductive
Load
N
PROCEDURE:
∑
Connect the circuit diagram as shown in figure.
∑
To adjust the auto transformer voltage and observe the voltage across voltmeter.
(viii)
Keep the rheostat, in maximum position and change the tapings of the
inductor from minimum to maximum position and observe the powerfactor.
(ix) After the inductance reaches the maximum position, the vary the rheostat checking
would not exceed 5A then the power factor will going to decrease less than 0.5.
(x) Then make the rheostat to maximum position and short the inductor and observe
the power factor reading which shows unity (or)nearly to unity i.e. 0.99.
(xi) Note down the wattmeter volt meter, arid power factor meter readings.
TABULAR FORM-
S.NO
V(Volts)
I(amps)
CALCULATIONS:
V = Volt meter reading
I = Ammeter reading
W = Wattmeter reading.
W (watts)
Power
POWER (P) - VICOSΦ
COSΦ = P/VI
Power factor
MODEL GRAPH:
V
ϕ
IA
˄ ~
IB
900
I
PRECAUTIONS:
(xii)
(xiii)
(xiv)
RESULT :
Pf meter should not be over loaded
Connect the meters with appropriate rating.
Avoid loose connections to prevent sparks and damage to meters
The % error of power factor meter is ______________
SCHERING BRIDGE
SCHERING BRIDGE
AIM: To measure the unknown value of capacitor using schering bridge
APPARATUS:
CIRCUIT DIAGRAM:
PHYSITECH's Schering Bridge trainer.
Multimeter.
CRO
BNC probes and connecting wires
IMBALANCE
AMPLIFIER
THEORY:
Alternating current bridge methods are of outstanding importance for measurement of
electrical quantities. Measurement of inductance, capacitance, storage factor, loss factor may
be made conveniently and accurately by employing a.c. bridge networks.
Schering bridge is widely used for capacitance and dissipation factor measurements.
Although the Schering bridge is used for capacitance measurements in a general sense, it is
particularly useful for measuring insulating properties, i.e., for phase angles very nearly 90°. In
fact schering bridge is one of the most important of the a.c. bridges It is extensively used in the
measurement of capacitance in general, and in particular in the measurement of the properties
of insulators, capacitor bushings, insulating oil and other insulating materials.
The connections of the bridge under balance conditions are shown in figure below.
C1= capacitor whose capacitance is to be determined
r1 = a series resistance representing the loss in the capacitor
C2 = a standard capacitor. This capacitor is either an air or a gas capacitor and hence is loss
free. However, if necessary, a correction may be made for the loss angle of this capacitor.
R1= a non-inductive resistance.
C3= a capacitor.
R2= a variable non-inductive resistance in parallel with capacitor C3.
The inspection of the circuit shows a strong resemblance to the comparison bridge.
Arm2 now contains a parallel combination of a resistor and a capacitor, and the standard arm
contains only a capacitor. The standard capacitor is usually a high-quality mica capacitor for
general measurement work or an air capacitor for insulation measurements. A good'quality
mica capacitor has very low losses (no resistance) and therefore a phase angle of
approximately 90°. An air capacitor, when designed carefully, has a very stable value and a
very small electric field; the insulating material to be tested can easily be kept out of any strong
fields.
At balance condition:
(r1 + 1/jωC1) (R2/1+jcωC3R2) = R1*1/jωC2
(r1 + 1/jωCi) R2 = R1/jωC2 (1+jωC3R2)
R1R2 - jR2/ωC1 = -jR1/ωC2 + R1R2C3/C2
By equating real and imaginary terms, we obtain:
r1 = R1C3/C2
and C1= C2(R2/R1)
Dissipation factor
D1= tanδ= ωC1r1=ω (C2R2/R1)(R1C3/C2)= ωR2C3.
Therefore values of capacitance C1, and its dissipation factor are obtained from the
values of bridge elements at balance.
Permanently setup schering bridges are sometimes arranged so that balancing is done
by adjustment of R2, with C2 remaining fixed. Since R1 appears in both the balance equations
and therefore there is some difficulty in obtaining balance but it has certain advantages as
explained below:
The equation for capacitance is C1= C2 (R2/R1) and since R2 and C2 dial of capacitor
C3can be calibrated to read the dissipation factor directly.
It should, however, be understood that the calibration for dissipation factor holds good
for one particular frequency, but may be used at another frequency if correction is made by
multiplying by the ratio of frequencies.
PROCEDURE:
1)
2)
3)
4)
5)
6)
Connect AF Oscillator 0/P to the AF l/P of isolation transformer.
Connect AF O/P to the AB terminals of the bridge.
Connect CD terminals of bridge to the l/P of imbalance amplifier.
Connect the capacitor to the C1 terminals.
Switch ON PHYSITECH's Schering Bridge trainer.
Observe the sine wave at the secondary of the isolation transformer on an
oscilloscope.
7) Now connect the oscilloscope to the O/P of imbalance amplifier.
8) Vary R2 for fine balance adjustment, i.e., output waveform should be minimum.
9) The balance of the bridge can also be observed by using loudspeaker. Connect
the O/P of balance amplifier to the speaker terminals instead of oscilloscope.
10) By adjusting n and R2, observe the minimum sound in the loudspeaker
11) By disconnecting the circuit measure R2 value using multimeter.
12) Calculate the capacitance value by substituting C2, R2 and R1values in the
formula C1=C2 (R2/R1).
RESULT:
ANDERSON BRIDGE
ANDERSON BRIDGE
AIM:
To determine the inductance value in terms of a standard capacitor.
APPARATUS:
(xv) PHYSITECH's Anderson Bridge trainer.
(xvi) Inductances.
(xvii) CRO.
(xviii) Multimeter
(xix) BNC probes and connecting wires.
Lx = C (R3/R4) [R (R4+R3) + R2R4]
THEORY:
Alternating current bridge methods are of outstanding importance for measurement of
inductance, capacitance, storage factor, loss factor may be made conveniently and accurately
by employing a.c. bridge networks.
The Anderson's bridge is a modification of the Maxwell's inductance-capacitance bridge
In this method, the self-inductance is measured in terms of a standard capacitor.
Anderson's Bridge
Be measured.
R1 =Resistance of self- inductor.
r1 = Resistance connected in series with self-inductor.
r, R2,R3,R4 = Known non-inductive resistances.
C = Fixed standard capacitor.
At balance, I1 = I3 and l2 = lc + I4.
Now I1R3 = lC'1/jωc, Therefore lc = I1jωCR3.
And other balance equations are,
I1 (r1+R1+jωL1) = l2R2+lC r
And I c(r+1/jωC) = (l2-lc)R4.
Substituting the value of IC in these equations, we have
I1 (r1+R1+jωL1) = l2R2+l1jωCR3r (or) l1 (r1+R1+jωL1-jωCR3r)=l2R2.
And jωCR3l1 (r+1/jωC)=(l2-l1JωCR3) R4
From these two equations, we obtain,
I1 (r1+R1+jωL1-jωCR3r)=l1 (R2R3/R4+JωCR2R3r/R4+jωCR3R2)
By equating real and imaginary parts, R1=(R2R3/R4)-r1.
And L1=C (R3/R4)[r (R4+R2)+R2R4]
An examination of balance equations reveals that to obtain easy convergence of
balance, alternate of r1 and r should be done as they appear in only one of the two balance
equations.
ADVANTAGES:
1.
In case, adjustments are carried out by manipulating control over r1 and r, they
become independent of each other. This is a marked superiority over sliding balance
conditions met with low Q coils when measuring with Maxwell's bridge.
2.
A study of convergence conditions would reveal that it is much easier to obtain
balance in the case of Anderson's bridge than in Maxwell's bridge for low Q- coils.
3.
A fixed capacitor can be used instead of a variable capacitor as in the case of
Maxwell's bridge.
4.
This bridge may be used for accurate determination of capacitance in terms of
inductance.
DISADVANTAGES:
(a)
The Anderson's bridge is more complex than its prototype Maxwell's bridge. The
Anderson's bridge has more parts and is more complicated to setup and manipulate.
The balance equations are not simple and in fact are much more tedious.
(b)
An additional junction point increases the difficulty of shielding the bridge.
1.
Considering the above complications of the Anderson's bridge, in all the cases where a
variable capacitor is permissible the more simple Maxwell's bridge is used instead of
Anderson's bridge.
PROCEDURE:
1.
2.
3.
4.
5.
Connect AF oscillator O/P to the AF l/P terminals of isolation transformer.
Connect an inductance across Lx terminals.
Switch ON PHYSITECH's Anderson Bridge trainer.
Connect the DET terminals of the bridge to the Detector l/P terminals.
Adjust the value of R, by moving it in clockwise direction to obtain balance condition.
Observe the balance condition in CRO by connecting it to the O/P of detector.
6. For further fine balance, vary Ri, which will compensate for the resistive component of
the inductor because every inductor has some resistance.
7. The balance of the bridge can also observed by using loudspeakers.
8. Connect the O/P of detector to the speaker terminals. By varying R1 and R observe the
minimum sound in the loudspeaker.
9. At the condition, by disconnecting all connections, measure R and R1 values.
10. Calculate the inductance value by substitution the measured values.
Result:
KELVIN DOUBLE BRIDGE
KELVIN DOUBLE BRIDGE
AIM:
To calculate the unknown resistance using Kelvin Double Bridge trainer
APPARATUS:
1.
2.
3.
PHYSITECH's Kelvin Double Bridge trainer.
Galvanometer.
Connecting wires.
CIRCUIT DIAGRAM
The Kelvin double bridge incorporates the idea of a second set of ratio arms-hence the
name double bridge-and the use of four terminal resistors for the low resistance arms. Figure
above shows the schematic diagram of the Kelvin bridge. The first set of ratio arms is P and
Q. The second set of ratio arms, p and q is used to connect the galvanometer to a point d at
the appropriate potential between points m and n to eliminate the effect of connecting lead of
resistance r between the known resistance, R, and the standard resistance, S.
The ratio p/q is made equal to P/Q. Under balance conditions there is no current
through the galvanometer, which means that the voltage drop between a and b, Eab is equal to
the voltage drop Eamd between a and c.
Now Eab = [P/(P+Q)j Eac and Eac = I [R+S+(p+q) r/(p+q+r)]
and Eamd = I [R+p/(p+q){(p+q)r/(p+q+r)}] = I [R+pr/(p+q+r)]
For zero galvanometer deflection, Eab = Eamd.
Therefore [P/(P+Q)] I [R+S+(p+q) r/(p+q+r)] = I (R+pr/(p+q+r)]
Or R = (P/Q) S + qr/(p+q+r)[(P/Q)-(p/q)]. --------------(a)
Now, if P/Q=p/q, the above equation becomes, R = (P/Q)*S. ------------ (b)
This equation is the usual working equation for the Kelvin bridge. It indicates that the
resistance of connecting lead, r, has no effect on the measurement, provided that the two sets
of ratio arms have equal ratios. Equation (a) is useful, however, as it shows the error that is
introduced in case the ratios are not exactly equal, it indicates that it is desirable to keep r as
small as possible in order to minimize the errors in case there is a difference between ratios
P/Q arid p/q.
In a typical Kelvin bridge, the range of resistance covered is 0.1µΩ to 1.0Ω. The
accuracies are as under:
From 1000 µΩ to 1.0 Ω : 0.05%
From 100 µΩ to 1000 µΩ : 0.2% to 0.05%
From 10 µΩ to 100 µΩ : 0.5% to 0.2% limited by thermoelectric emfs.
THEORY:
Precision measurements of component values have been made for many years using
various forms of bridges. The simplest form of bridge is for the purpose of measuring
resistance and is called the Wheatstone bridge. There are variations of the wheatstone bridge
for measuring very high and very low resistance's. There is an entire group of ac bridges for
measuring inductance, capacitance, admittance, conductance, and any of the impedance
parameters.
The classification of resistance, from the point of view of measurement, is as follows:
(xx) Low Resistances: All resistances of the order of 1Q and under may be classified as
low resistances.
(xxi) Medium Resistances: This class includes resistances from 1Q upwards to about 0.1
MQ
(xxii) High Resistances: Resistances of the order of 0.1 Mn and upwards are classified as
high resistances
The methods used for measurement of medium resistances are unsuitable for
measurement of low resistances i.e., resistance having a value under 1Q. The reason is that
the resistance of leads and contacts, though small, are appreciable in comparison in the case
of low resistances. For example a contact resistance of 0.002£2 causes a negligible error
when a resistance of 100Q is being measured, but the same contact resistance would cause
an error of 10% if a low resistance of the value of 0.020 is measured. Hence special type of
construction and techniques have to be used for the measurement of low resistances in order
to avoid serious errors occurring on account of the factors mentioned above.
Low resistance's are constructed with four terminals as shown in figure below. One
pair of terminals CC1 (called the current terminals) is used to lead current to and from the
resistor. The voltage drop is measured between the other two terminals PP1, called the
potential terminals.
The methods for measurement of low resistances are:
1) Ammeter Voltmeter method.
2) Kelvin's double bridge method.
3) Potentiometer method.
The Kelvin Bridge is a modification of the Wheatstone bridge and provides greatly
increased accuracy in the measurement of low-value resistances, generally below 1Ω.
Consider the bridge circuit shown in figure below, where r represents the resistance of
the lead that connects the unknown resistance R to standard resistance S. Two galvanometer
connections indicated by dotted lines, are possible. The connection may be either to point 'm'
or to point 'n'. When the galvanometer is connected to point m, the resistance, r, of the
connecting leads is added to the standard resistances, S, resulting in indication of too low an
indication for unknown resistance R. When the connection is made to point n, the resistance, r,
is added to the unknown resistance resulting in indication of too high a value for R.
Suppose that instead of using point m, which gives a low result, or n, which makes the
full line in figure below.
If at point 'd’ the resistance r is divided into two parts, r1 and r2, such that
If at point 'd’ the resistance r is divided into two parts, r1 and r2, such that r1/r2=P/Q
Then in the presence of n, the resistance of connecting leads, causes no error in the
result. We have,
R+ r1=P/Q (S+r2), but r1/r2=P/Q---------- (1)
or
r1/( r1+r2) = P/(P+Q) or r1 = [P/(P+Q)]r, where as
r1+r2 =r.
and r2 = [Q/(P+Q)] r.
Therefore we can write equation (1) as
(R+[P/(P+Q)]*r) = (P/Q) (S+[Q/(P+Q)]*r)
Or
R=(P/Q) S. ---------------(2)
Therefore, we conclude that making the galvanometer connection as at C, the
resistance of leads does not affect the result.
This process is obviously not a practical way of achieving the desired result, as there
would certainly be a trouble in determining the correct point for galvanometer connections. It
does, however, suggest the simple modification, that two actual resistance units of correct
ratio be connected between points m and n, the galvanometer be connected to the junction of
the resistors. This is the actual Kelvin bridge arrangement, which is shown in figure below
The voltage 'V', indicated in figure, is thus IR times the resistance R between terminals
PP1 and does not include any contact resistance drop that may be present at the current
terminals CC1.
Resistors of low values are thus measured in terms of resistance, between potential
terminals, which becomes perfectly and precisely definite in value and is independent of the
contact resistance drop at the current terminals. Contact resistance drop at the potential
terminals need not be source of error, as current crossing at these terminals is usually
extremely small or even zero for null methods. Also this contact resistance now becomes a
part of the potential circuit and is, therefore, a negligible part of the total resistance of the
potential circuit since potential circuits have a high value of resistance.
PROCEDURE:
1.
2.
3.
4.
5.
6.
7.
Short the 5000Ω terminal to 47Ω terminal and short other terminal of 47Ω to terminal a.
Select any particular resistance for P and Q, such that P/Q = p/q.
Connect Galvanometer across G terminals.
Connect any one resistor provided on the trainer to the Rx terminals.
Short p and m, q and n, and m and n terminals.
Switch ON PHYSITECH's Kelvin Double Bridge trainer.
Adjust S for proper balance, and at that balancing condition remove all the connections and
measure the S value using multimeter.
8. Calculate the value of unknown resistance, using the formula, Rx = (P/Q)*S.
RESULT:
Calibration of L.P.F Watt Meter by Phantom testing
Aim: - Calibration of 1-Ф Power factor Meter by (L.P.F) phantom loading.
Apparatus:S.NO
01
02
03
04
05
06
07
08
Equipment
Range
Type
Phase shifting T/F
1
Voltmeter
(0-300)v
MI
Ammeter
(0-5)A
MI
P.F Meter
5/10A,300v,1500W
I-Ф Variac
230V/(0-270)V
Rheostat
100Ω/5A
Wattmeter
5/10A,300V,300W
Connecting wires
Quantity
1
1
1
1
1
1
Theory:The connections of a single phase electro dynamic type. Power factor meter is show in figure. It
consists of fixed coil which acts as the current coil. This is split up in two parts and carries the current of
the circuit under test. Therefore the main current two identical pressure coils. A and B Provided on a
spindle constitute the moving system. Pressure coil A has a non inductive resistance R connected in
series with it. The two coils are connected across the voltage of the circuit the value of R&L are so
adjusted that the two coils carry the same value of current at normal frequency that is RL
Procedure:7) Connect the circuit as per the circuit diagram.
8) By adjusting the variac the rated voltage is applied across the pressure coil of wattmeter &
power factor meter.
9) Rated current is made to pass through the coils.
10) Now adjust rotor position of phase shifting transformer for different values of power factor
meter.
11) Tabulate the readings.
12) From wattmeter readings find values of power factor &compare from with value of power
factor meter.
Precautions:3) Avoid loose connections.
4) Avoid parallax errors.
Result:-
The L.P.F wattmeter has been calibrated by phantom loading. An average error of ±5% is
found.
Observation table:
- S.No
Voltmete
r(V)
I (Amps)
P.F
Meter
Cos Ѳ
Wattmet
er (W)
Theoretic % Error
al
Cos Ѳ
Circuit Diagram: -
Calibration of L.P.F Watt Meter by Phantom testing
RESISTANCE STRAIN GUAGE –
STRAIN MEASURMENT AND CALIBRTATION
RESISTANCE STRAIN GUAGE –
STRAIN MEASURMENT AND CALIBRTATION
Aim: to determine the strain due to corresponding change in weight of resistance strain guage
Apparatus required:
1. Strain measurement trainer
2. Strain gauge cantilever beam
3. Weights
THEORY:
The primary object of the INSTRUMENTATION TRAINER is to introduce and to educate electronic
instrumentation systems in a manner sufficiently complete that the students will acquire proper
knowledge and the idea about the transducers and their applications to measure mechanical and terminal
quantities. The mechanical quantities include strain, force, pressure, torque, displacement, acceleration,
frequency, etc. The terminal quantities include temperature and heat flux.
It is understood that the students will have a conceptual understanding of these quantities through
exposure of mechanics or physics courses, such as static's, dynamics, and strength of materials or
thermodynamics. The student's experience in actually measuring these quantities by conducting
experiments, however, will usually be quit limited. It is an objective of this tutor to introduce methods
commonly employed in such measurements and the usage of such electrical components such as
capacitance, resistance, inductance, intensity, etc.
Emphasis in the instrumentation trainer will be directed toward electronic instrumentation systems rather
than mechanical systems. In most cases electronic systems provide better data more accurately and
completely characterize the design or process being experimentally evaluated. Also, the electronic system
provides an electrical out put signal that can be used for automatic data reduction or for the control of the
process. These advantage of the electronic measurement system over the mechanical measurement
system have initiated and sustained trend in instrumentation toward electronic methods.
An attempt is made through these "Instrumentation trainer" to make as easy as possible for the students to
learn about the electronic instrumentation system and various transducers used for the measurement of
mechanical component. The instrumentation tutor panels are design in such a way that the block
diagrams of the stages of electronic instrumentation system are clearly pictured on them. This makes the
instrumentation tutor self-explanatory and also the best teaching aid for Engineering students.
Since the instrumentation tutors are not instruments as a whole the accuracy of the measurement cannot
be claimed. It is very clear that the instrumentation tutor are only for demonstration purpose and cannot
be used for any external measurement other than conducting experiments.
THE ELECTRONIC INSTRUMENTATION SYSTEM.
The complete electronic instrumentation system usually contains six sub systems or elements.
The TRANSDUCER is a devise that convert a change in the mechanical or thermal quantity being
measured into a change of an electrical quantity. Example strain gauges bonded in to an specimen, gives
out electrical out put by changing its resistance when material is strained.
TRANSDUCER
SIGNAL
CONDITIONER
AMPLIFIER
POWER
SUPPLY
RECORDER
DATA
PROCESSOR
The POWER SUPPLY provides the energy to drive the Transducers, example differential transformer,
which is a transducer used to measure displacement requires an AC voltage supply to excite the coil.
SIGNAL CONDITIONERS are electronic circuits that convert, compensate, or manipulate the out put
from in to a more usable electronic quantity. Example the whetstone bridge used in the strain transducer
converts the change in resistance AR to a change in the resistance AE
AMPLIFIERS are required in the system when the voltage out put from the transducer signal
conditioner combination is small. Amplifiers with gains of 10 to 1000 are used to increase their signals to
levels where they are compatible with the voltage - measuring devices.
RECORDERS are voltage measuring devices that are used to display the measurement in a form that
can be read and interpreted. Digital/Analog voltmeters are often used to measure static voltages.
DATA PROCESSORS are used to convert the out put signals from the instrument system into data that
can be easily interpreted by the Engineer . Data processors are usually employed where large amount of
data are being collected and manual reduction of these data would be too time consuming and costly.
THE INSTRUMENT
UNIQUE Digital Strain measuring setup comprises of Strain Indicator and Cantilever Beam setup. Strain
Indicator is a strain gauge signal conditioner and amplifier used to measure strain due to load applied on
the cantilever beam. The strain gauge are bonded on the cantilever beam and are connected in the form of
whetstones bridge. A pan and weights upto lKg is provided to load the cantilever beam. Uniques Strain
measuring setup is a complete system which can be used to conduct measurement on strain using strain
gauges. The strain indicator is provided with zero balancing facility through adjustable potentiometer.
Digital display will enable to take error free readings.
The digital indicator comprises of four parts.
1. Power Supply 2. Signal conditioning 3. Amplifier
4. Analog and digital converter.
The inbuilt regulated power supply used will provide sufficient power to electronic parts and also
excitation voltage to the strain gauge bridge transducers. The signal conditioners Buffers the output
signals of the transducers. Amplifier will amplifies the buffered output signal to the required level where
it is calibrated to required unit. Analog to digital converter will convert the calibrated analog out put to
digital signals and display through LED's.
THEORY BEHIND IT
When a material is subjected to any external load, there will be small change in the mechanical
properties of the material. The mechanical property may be, change in the thickness of the material or
change in the length depending on the nature of load applied to the material. This change in mechanical
properties will remain till the load is released. The change in the property is called strain in the material
or the material get strained. So the material is mechanically strained, this strain is defined as ' The ratio
between change in the mechanical property to the original property'. Suppose a beam of length L is
subjected to a tensile load of P Kg the material gets elongated by a length of □l So according to the
definition strain S is given by
S = □l/L
.....Eq1
Since the change in the length of the material is very small it is difficult to measure □l. So the strain is
always read in terms of microstrain. Since it is difficult to measure the length Resistance strain gauges
are used to measure strain in the material directly. Strain gauges are bonded directly on the material
using special adhesives. As the material get strained due to load applied, the resistance of the strain
gauge changes proportional to the load applied. This change in resistance is used to convert mechanical
property in to electrical signal which can be easily measured and stored for analysis.
The change in the resistance of the strain gauge depends on the sensitivity of the strain gauge. The
sensitivity of strain gauges is usually expressed in terms of a gauge factor Sg where Sg is given as
∆R / R = Sg
........Eq 2
Where □ is Strain in the direction of the gauge length.
The output □R / R of a strain gauge is usually converter in to voltage signal with a Whetstones bridge, If
a single gauge is used in one arm of whetstones bridge and equal but fixed resistors is used in the other
arms, the output voltage is
Eo = Ei / 4 (□Rg/Rg )
.... Eq3
Substituting Eq 2 into Eq 3 gives
Eo = 1/4 (Ei Sg □ )
....Eq 4
The input voltage is controlled by the gauge size ( the power it can dissipate) and the initial resistance of
the gauge. As a result, the output voltage Eo usually ranges between 1 to 10 □V / microunits of strain.
6
SPECIFICATION
DISPLAY RANGE
: 31/2 digit RED LED display of 200 mV FSD to read up to +/-1999 microstrain
GAUGE FACTOR SETTING :
2.1
BALANCE
:
Potentiometer to set zero on the panel.
BRIDGE EXCITATION
:
10VDC
BRIDGE CONFIGURATIONS :
Full bridge.
MAX. LOAD
:
lKg.
POWER
:
230 V +/- 10% at 50Hz. with perfect grounding.
:
All specifications nominal or typical at 23° C unless noted.
CANTILEVER BEAM SPECIFICATION
MATERIAL
: Stainless Steel
BEAM THICKNESS (t)
: 0.25 Cm.
BEAM WIDTH ( b)
: 2.8 Cms.
BEAM LENGTH (Actual)
: 22 Cms.
YOUNGS MODULUS (s )
: 2 X 106 Kg / cm2
STRAIN GAUGE
: Foil type gauge
GAUGE LENGTH (1)
: 5 mm
GAUGE RESISTANCE (R)
: 300 Ohms.
GAUGE FACTOR ( g)
: 2.01
CANTILEVER BEAM SETUP
PHYSICAL DIMENSION OF THE CANTILEVER BEAM
PHYSICAL DIMENSIONS
Over all BEAM Length (X) : 300 mm
Actual Length ( L )
Width of the Beam (b)
Thickness of the Beam (t)
CONNECTION DETAILS
: 220.0 mm ( Middle of the Strain Gauge Grid to
loading point)
: 28.0 mm
: 2.5 mm
PROCEDURE
v Check connection made and Switch ON the instrument by toggle switch at the back of the box. The
v
v
v
v
v
v
display glows to indicate the instrument is ON.
Allow the instrument in ON Position for 10 minuets for initial warm-up.
Adjust the ZERO Potentiometer on the panel till the display reads '000'.
Apply 1 Kg load on the cantilever beam and adjust the CAL potentiometer till the display reads 377
micro strain, (as per calculations given below) Remove the weights the display should come to
ZERO incase of any variation adjust the ZERO pot again and repeat the procedure again. Now the
Instrument is calibrated to read micro-strain.
Apply load on the sensor using the loading arrangement provided in steps of l00g upto lKg.
The instrument displays exact microstrain strained by the cantilever beam
Note down the readings in the tabular column. Percentage error in the readings, Hysteresis and
Accuracy of the instrument can be calculated by comparing with the theoretical values.
Specimen calculation for cantilever beam
S = (6 P L) / BT2E
P = Load applied in Kg. (1 Kg)
L = Effective length of the beam in Cms. ( 22 Cms)
B = Width of the beam (2.8 Cms)
T = Thickness of the beam ( 0.25Cm)
E = Youngs modulus ( 2 X 106)
S = Microstrain
hen the microstrain for the above can be calculated as fallows
S=
S=
S=
Sample Readings:
6 X 1X22
2.8 X 0.252 X ( 2 X 106)
3.77 X 10"4
377 microstrain.
A
B
SL. No. Weight (in Grams)
% ERROR
=
c
Actual readings (using
formulae) S = (6 P L) /
BT2E(in micro strains)
D
Indicator readings (in
micro strains)
[(Actual Reading ( C) - Indicator Readings f (D)] x 100
Max. Weight in gms
12
Graph : Graph Plotted Actual Readings (X-axis) Vs Indicator Readings (Y-axis)
Y-axis
Indicator
Reading
in
Micro
strain
X-axis
38 75
113 150 187 224 260 297 336
Actual reading in Micro
strain
E
ERROR in
0/ /o
Load Vs Strain
Y-axis
Strain
in
Micro
strain
X-axis
Load in gms
RESULT:
MEASUREMENT OF PARAMETERS OF CHOKE COIL BY
USING 3 – AMMETER METHOD
MEASUREMENT OF PARAMETERS OF CHOKE COIL BY USING
3 – AMMETER METHOD
AIM: -To measure the parameters of a choke coil using 3-ammeter method.
APPARATUS:S. No.
APPARATUS
RANGE
TYPE
QTY
1.
Dimmeterstat
230/0-230V
1-PH
1
2.
Rheostat
360/1,2A
Wire
1
1
3
3.
Voltmeter
(0-300v)
wound
M.I
4.
Ammeter
(0-2.5A)
M.I
5.
Load: choke coil.
-
1
REMARKS
j
I
THEORY;
Choke coil is highly inductive circuit which is used in the applications where
high voltage surge is needed for a short duration of time. It is generally used in the tube
light circuit to give high voltage surge during starting and to maintain steady voltage
during its operation.
I3
MODEL GRAPH:
I1
I2
PHASOR DIAGRAM
RESULT:- Thus the choke coil parameters are:
Resistance R = _______________Ohms
Impedance Z= _______________Ohm s
Power factor, Cos θ =___________
Inductance, L = ________________Henry
Reactance XL = _______________Ohms
PRECAUTIONS:
(i) Avoid loose Connections to Prevent Sparking at terminals and damaging the
meters.
(ii) Connect appropriate range of meters,
(iii) Readings should be taken with out parallax error
PROCEDURE:Connect the circuit as shown in figure.
Switch On the supply,
Take die readings of 3- ammeters at different supply voltage Which should cot
exceed 250V.
Tabulate the readings sad calculate the parameters of die Choke coil.
TABULATOR FORM:
S.No.
V (VOLTS)
(AMP)
CALCULATIONS
I12 = I22 + I32 +2 I2 I3 Cos Φ
Cos Φ = (I12 – I22 – I32) / (2 I2 I3)
RL = Z CosΦ
XL = Z SinΦ
ZL = RL + j x L
POWER = V I3 Cos Φ ; Z Sin Φ
Result:
(AMP)
(AMP)
MEASURMENT OF PARAMETERS OF CHOKE COIL USLNG:
3-VOLTMETER METHOD
MEASURMENT OF PARAMETERS OF CHOKE COIL USLNG:
3-VOLTMETER METHOD
AIM:- To Measure the parameters of a choke coi! using 3-voltmeter method
APPARATUS:S. No.
APPARATUS
1.
1-ph Variac
2.
3.
Rheostat
Load: Choke coil
4.
Voltmeter
5.
6.
RANGE
230v/0- 230v
500Q/1.2A
—
TYPE
Continuously
Variable
Wire wound
QTY
REMARKS
11
—
1
(0-300v)
M.I.
1
Ammeter
(0-1 A)
M.I.
i
Connecting
wires
—
—
THEORY:
Choke coil is highly inductive circuit, which is used in the applications
where high voltage surge is needed for a short duration of time. It is generally
used in the tube light circuit to give high voltage surge during starting and to
maintain steady voltage during its operation.
CIRCUIT DIAGRAM;
PROCEDURE:(xxiii)
(xxiv)
(xxv)
(xxvi)
Connect the circuit as shown in figure.
Switch ON the supply.
Take the readings of 3-voltmeters at different supply voltages.
Tabulate the readings and calculate the parameters of the choke coil.
TABULATOR FORM:
S.No
I (amp)
V, (volts)
V2 (volts)
V3 (volts)
CALCULATIONS:- from thePliasor diagram
V12 = V22 + V32 + V2+ V3 Cos Φ
Cos Φ = (V12 – V22 – V32) / (2 V2 V3)
RL = ZL CosΦ
XL = ZL SinΦ
ZL = V3 / I Ω
L = X / 2 πƒ H
MODEL GRAPH:
V1
V3
θ
V2
PHASOR DIAGRAM
RESULT:- Thus die following choke parameters are measured by 3- voltmeter Method:
I.
II.
The self indue tance of die choke coil = ________Henry
The internal resistance of the choke coil =_______ohms
Power factor of the choke coil = _________
PRECAUTIONS:
1. Avoid loose Connections to prevent sparking 3t terminals And damaging
the meters.
2. Connect appropriate range of meters.
3. Readings should be taken widi out parallax error.
RESULT:
MEASUREMENT OF 3-PHASE REACTIVE
POWER
MEASUREMENT OF 3-PHASE REACTIVE POWER
OBJECTIVE
To measure 3-phase reactive power by single wattmeter.
RESOURCES
Sl.
No.
Equipment
Range
Type
Quantity
1.
Voltmeter
0-600V
M.I.
1
2.
Ammeter
0-10A
M.I.
1
3.
Wattmeter
600V, 10A, UPF
Dynamo Meter
1
4.
3-Phase Variac
415V/(0-450)V
-
1
CIRCUIT DIAGRAM
Measurement of 3-phase Power Factor
PROCEDURE
1. Make connection as per the circuit diagram
2. Switch ON the supply under no load conduction.
3. Note down the voltmeter, ammeter and wattmeter reading.
4. Now, gradually apply the load the corresponding variation on the meter can be noted.
5. The reactive the 3-phase reactive power using single wattmeter is found.
TABULAR COLUMN
Sl.
No.
Voltmeter
reading
(V)
Ammeter
reading
(A)
Wattmeter
reading (W)
sinØ=
W/VI
CosØ=
cos(sin-1(W/VI)
Q=
1.
2.
3.
4.
Sl.
No.
KVA =
V
KW =
VIcosθ
KVAR =
VIsinθ
1.
2.
3.
4.
MODEL CALCULATIONS
3-Ø reactive power by one wattmeter =
W (VARS)
RESULT
Hence the 3-Ø reactive power by one wattmeter was measured experimentally.
PRE-LAB QUESTIONS
1. How do you define reactive power?
2. What are the different types of powers available?
3. Explain the significance of reactive power in a power system.
4. What is the advantage of measuring 3-phase reactive power using single watt meter.
5. whether this method is applicable to unbalanced loads?
6. what are the disadvantage of reactive power
7. what are the advantages of 3-phase power systems over single phase system
8. What are the differences among apperent ,real and reactive powers
9. what is the formula for apperent ,real and reactive powers
LAB ASSIGNMENT
1. Conduct an experiment to find the 3-phase reactive power using two watt meters
POST-LAB QUESTIONS
1. What did you find any observations while finding the reactive power
2.
How do current transformer is differ from potential transformer?
3. why you have chosen variable 3-phase y-connected load
4. Did you find any differences among the values of apparent ,real and reactive powers
W
MEASUREMENT OF 3-PHASE POWER ONE 1-PHASE
WATTMETER AND TWO CURRENT TRANSFORMERS
MEASUREMENT OF 3-PHASE POWER ONE 1-PHASE WATTMETER AND TWO CURRENT
TRANSFORMERS
OBJECTIVE
To measurement of 3-phase power one 1-phase wattmeter and two Current Transformers (CTs).
RESOURCES
S. No.
Equipment
Range
Type
Quantity
UPF
600V,10A,1500W
1
-
5/5A
2
1.
Wattmeter
2.
Current Transformers (CTs)
3.
Voltmeter
0-600V
MC
1
4.
Ammeter
0-10A
MC
1
5.
Resistive Load
-
3-Ph, 415V, 10A, 5kW
1
6.
Connecting wires
-
-
Sufficient
CIRCUIT DIAGRAM
PROCEDURE
Standardization
6. Connections are given as per the circuit diagram.
7. Supply is switched on.
8. Apply the different resistive loads
9. The meter readings are noted as per table given.
TABULAR COLUMN
Sl.
No.
Load
(A)
Wattmeter
Reading
(WL)
Ammeter
Reading
(IL)
Voltmeter
Reading
(VL)
Power
Consumed
by Load (PL)
% Error
1.
2.
3.
4.
5.
MODEL CALCULATION
PL = VL * IL* CosØ
P L = VL * IL
(CosØ = 1 since the load is resistive)
% Error = (WL – PL)*100/ WL
RESULT
Hence the power in 3-phase circuit is measured by using 1-phase wattmeter and two CTs and error
in meter is found.
PRE-LAB QUESTIONS
1. What is electrodynamometer type wattmeter?
2. What is meant by balanced load?
3. What is meant by unbalanced load?
4. What is instrument transformer?
5. Why instrument transformers are used?
6. What is meant by term “burden “of an instrument transformer?
7. What is meant by testing of instrument transformers?
8. What are the different testing methods for a current transformer?
9. Why the secondary of a CT should not be kept open?
10. Where a current transformer is standardized?
LAB ASSIGNMENT
1. How to extend the range of given wattmeter with the help of instrument transformers?
2. Can you perform the same experiment with the help of potential transformers?
POST-LAB QUESTIONS
1. What is the difference between current and potential transformers?
2. How to reduce the losses occur in the instrumental transformers?
3. What are the conditions are to be followed while doing the experiment?
CALIBRATION OF LPF WATTMETER BY
PHANTOM TESTING
CALIBRATION OF LPF WATTMETER BY PHANTOM TESTING
OBJECTIVE
To calibrate of LPF wattmeter by phantom loading method and compare the energy consumed with
direct loading.
RESOURCES
S.
No.
1.
Equipment
Type
Range
Quantity
Auto Transformer
1-phase
230/0-270V AC
1
2.
Voltmeter
0-300V
MI
1
3.
Ammeter
0-10A
1
4.
LPF Wattmeter
Dynamometer
MI
150/300/600V, 2.5/5A,
1500W
5.
Inductive Load
1-phase
0-150mH, 5A
1
6.
Connecting wires
-
-
Sufficient
1
CIRCUIT DIAGRAM
PROCEDURE
10. Connections are given as per the circuit diagram and switch on the supply.
11. Kept the autotransformer (1&2) in minimum position
12. The Auto Transformer 2 is varied in pressure at the voltmeter reading is adjusting to
rated value is 150V
13. Slowly the Auto Transformer 1 is varied in current coil at the ammeter reading is
adjusted at different valued in steps from 0-5amps.
14. The experiment is repeated for different values of current at constant voltage.
15. After noting the values slowly decrease the auto transformer till ammeter and
voltmeter comes to zero position and switch off the supply
TABULAR COLUMN
SL. No
Voltage
(V)
Ammeter
(A)
Wattmeter
(W)
CosØ
% Error
1.
2.
3.
4.
MODEL CALCULATIONS
Wm = V * I CosØ
= VP * IC
(CosØ = 0.2 since Short circuited)
WC = W
% Error = (WM - WC) * 100/ WM
RESULT
Hence the LPF wattmeter is calibrated by phantom loading method and power consumed by meter
is compared with that of direct loading.
PRE-LAB QUESTIONS
1. What is meant by phantom loading
2. What is meant by low power factor?
3. How is electrostatic wattmeter superior to other types of wattmeter?
4. How does LPF Wattmeter are differ from ordinary wattmeter?
5. What is formula for low power factor?
6. What are the errors in wattmeter7.What is meant by fictitious load?
7. What are the special features of a wattmeter suitable for working on LPF circuits?
8. Define %error used in LPF wattmeter
9. What is the condition of load to select the low power factor meter?
LAB ASSIGNMENT
1. Conduct experiment to calibrate LPF meter by phantom loading by taking the capacitive loading
.if not give reasons.
POST-LAB QUESTIONS
1. Why the error in the LPF meter increases with loading.
2. What coil is used to reduce the %error in LPF meter calibration.
3. What are the precautions are to be followed while doing the experiment.
PERCENTAGE RATIO ERROR AND THE
PHASE ANGLE ERROR OF THE GIVEN
CURRENT TRANSFORMER BY
COMPARISON
SILSBEE’S METHOD OF TESTING CURRENT TRANSFORMERS
AIM:
To determine the percentage ratio error and the phase angle error of the given current
transformer by comparison with another current transformer whose error are known.
APPARATUS:
S. No
1
2
3
4
5
6
7
Equipment
Standard CT
Testing CT
Wattmeter
Ammeter
Rheostat
Phase shifting
transformer
Range
0-5A
0-300V
MI type
Type
AC
AC
LPF
AC
AC
Quantity
2
2
THEORY:
This is a comparison type of test employing deflect ional methods. Here the ratio and
phase angle of the test transformer x are determined in terms of that of a standard
transformer s having same nominal ratio.
The errors are as follows say:
Error
Ratio Error
Phase Angle Error
S
RS =
θs =
X
RX =
θX =
CT
The primaries of the two CTs are connected in series and the
current through them is say IP. The pressure
coils
of
two
wattmeters are supplied with constant voltage V from a phase shifting transformer.
The current coil of wattmeter W1 is connected to S through an
ammeter. The current coil of wattmeter
W2 is
connected as shown in fig and carriers a current SI.
SI = Iss - Isx (Victorian difference)
Where in is the current in the current coil of W1 and Isx is the current flowing through
the burden. The
phase shifting transformer is
adjusted so that the wattmeter W1 reads zero.
W 1q = VpcqIss cos 90 = θ
W2q = Vpcq SI cos (θX – θs )
= V Isx sin (θX – θs )
Where Vpcq is the voltage from the phase shifting transformer, which is in quadrature
with the Iss in is
current coil of W1.
Then the phase of the voltage from to phase shifting transformer is shifted through 90º.
Therefore, now
V is in phase with the current Iss.
W1p = V Iss
W2p = VSI sin (θX – θs )
=V [Iss – isx cos (θX – θs )
= W1p – VISX Cos (θX – θs ) As (θX – θs ) ~ 0
Therefore VIsx = W1p – W2p
Ip
RX = ----------ISX
Ip
RS = ----------ISS
RX
IS
V Iss
W1p
----- = ---- = ---------- = ------------RS
ISX
V Isx
W1p -W2p
RX = RS (1 + W2p / W1p)
Now to obtain the Phase Angle Errors
Sin (θX – θs ) = W2q / V Isx
Cos(θX – θs ) = W1p - W2p
-------------V Isx
Tan (θX – θs ) = W2Q
--------------------W1p - W2p
OR
θX =
W2θ
------------- +θs radius
W1p - W2
CIRCUIT DIAGRAM
Fig – 10.0 Silsbee’s Method of Testing Current Transformers
TABULAR COLUMN
S. No
1
2
I ss
W iq
W2q
W1p
W2p
Rx
PROCEDURE
1. The connections are made as per the circuit diagram. The burden is adjusted to
have a suitable current In. the phase angle is adjusted using the phase shifting
transformer will wattmeter W1 reads zero. Reading of the other wattmeter
(W2q) is noted.
2. A phase shift of 90 is obtained by the phase sulfating transformer. The two
wattmeter readings W Ip and W 2p are then observed
3. The ratio error is calculated using the formula Rx = Rs
4. The phase angle error is calculated using the formula
5. The experiment is repeated by varying the burden and setting different values
for Iss.
6. The average values of Rs and are then obtained.
Θx
PRECAUTIONS
1. W2 is sensitive instrument. Its current coil may be defined for small values. It is
normally designed to carry about 0.25 A for testing CTs having a secondary
current of 5 Amps
RESULT:
The percentage ratio error and the phase angle error of the given current transformer by
comparison with another current transformer whose error is known are measured
PRE LAB VIVA QUESTIONS
1.What is instrument transformer?
2.Why instrument transformers are used?
3.What is meant by term “burden“ of an instrument transformer?
4.What is meant by testing of instrument transformers?
5.What are the different testing methods for a current transformer?
6.Why the secondary of a CT should not be kept open?
7.What is Capacitive Voltage transformer?
8.What are the applications of CVT?
9.What is formula for ratio error?
10. What is formula for phase angle error
POST LAB VIVA QUESTIONS
1.How to reduce ratio error in a current transformer?
2.How to reduce phase angle error in a current transformer?
3.What are the various other methods of testing CT’s?
4.What are the advantages and disadvantages of this method?
5.Define burden in the case of CT.
6.What are the most important design criteria to reduce the errors in a C.T.
7.What is the turn’s compensation and why it is use?
L V D T TRAINER
L V D T TRAINER
AIM: LVDT are robust, absolute linear position/displacement transducers; inherently
frictionless, they have a virtually infinite cycle life when properly used. As AC operated LVDTs
do not contain any electronics, they can be designed to operate at cryogenic temperatures or up
to 1200 °F
APPARATUS:
S. No
1.
Equipment
LVDT
CIRCUIT DIAGRAM:
LVDT trainer kit:
Type
Trainer Kit
Quantity
1
Figure : Circuit Diagram Of LVDT And Capacitance Pickup-Characteristics And Calibration
PROCEDURE:
1. Connections are made as per the circuit diagram
2. Switch on the supply keep the instrument in ON position for 10 minutes for initial warm
up
3. Rotate the micrometer core till it reads 20.0 mm and adjust the CAL potentiometer to
display 10.0 mm on the LVDT trainer kit.
4.
Rotate the micrometer core till it reads 10.0 mm and adjust the zero potentiometer to
display 20.0 mm on the LVDT trainer kit.
5.
Rotate back the micrometer core to read 20.0 mm and adjust once again the CAL
potentiometer till the LVDT trainer kit display reads 10.0 mm. Now the instrument is
calibrated for 10mm range.
6.
Rotate the core of micrometer in steps of 2 mm and tabulate the readings of micrometer,
LVDT trainer kit display and multimeter reading.
TABULAR COLUMN:
S. No
Micro meter
Reading in MM
Output Voltage
1.
2.
3.
4.
5.
6.
GRAPH:
RESULT:
PRE LAB VIVA QUESTION
1. What is LVDT
2. What is transducer?
3. How many transducers are there?
POST LAB VIVA QUESTIONS
1. How many windings the transformer in LVDT have in its construction?
2. How the secondary’s are connected in the transformer of LVDT?
EXPERIMENT-16
AIM: To determine the percentage ration error and the phase angle of the given current
transformer by comparison with another current transformer whose error are known
APPARATUS:
SNO
NAME OF COMPONENT
RANGE
TYPE
QUANTITY
1.
Standard CT
10/5A
2 winding
1
transformer
2.
Testing CT
10/5A
2 winding
1
transformer
3.
Wattmeter
300V/10A
LPF
2
4.
Ammeter
0-10A
MI
2
5.
Rheostat
360Ω/1.6A
Wire wound
1
6.
Phase shifting Transformer
5KVA, 0-1 p.f.
1
7.
Single phase Autotransformer
0-250V,2KVA
1
CIRCUIT DIAGRAM:
Fig: circuit diagram
PROCEDURE:
1. The connections are made as per the circuit diagrm. The burden is adjusted to have a
suitable current in the phase angle is adjusted using the phase shifting transformer will
wattmeter W1 reads Zero.
2. Reading of the other wattmeter (w2q) is noted.
3. A phase shift of 90 is obtained by the phase shifting transformer. The two wattmeter
readings W 1p and W2p are then observed.
4. The ratio error is calculate ding the formula Rx = Rs
5. The phase angle error is calculated using the formula
6. The experiment is repeated by varying the curden and setting different values for Iss.
7. The average values of Rs and are then obtained
TABULAR COLUMN:
S. No. ISS
W1q
W2q
MODEL CALCULATIONS:
W1p = V Iss
W 2p = VSI sin (θx – θs)
= V (Iss – Isx cos (θx – θs)
= Wip = Visx cos (θx – θs)
As (θx – θs)~0
Therefore Visx = W 10 W2p
Rx = Ip/Isx
Rs = Ip / Isx
Rx
Rs
I SS
I SX
VI SS
VI SX
W1p
W 1 pW 2 p
È W2p˘
Ratio error Rx = Rs Í1 +
˙
Î W1 p ˚
Now to obtain the phase Angle Errors
Sin (θx – θs) = W2q / VIsx
W1p
W2p
Rx
θx
Cos (θx – θs) = (Wp – W2p) / V Isx
Tan (θx – θs) = W2q / (W1p – W2p)
OR
Phase angle error θx = W2q / (W1p – W2p)
Phase angle error θx = W2q / (W1p – W2p) + θs
RESULT
PRE LAB VIVA QUESTION
1) How types of Silsbee’s methods ? And what are those ?
2) Silsbee’s methods----------- method
3) What is Burden of transformer?
POST LAB VIVA QUESTION
1)Define (C.T&P.T)
A. Transformation ratio
B.. Turns ratio
C .Nominal ratio
D .RCF
2) Comparison between C.T & P.T
DIELECTRIC OIL TESTING
DIELECTRIC OIL TESTING
OBJECTIVES
1) To test the dielectric strength or breakdown potential of the insulating oil.
2) To test the acidity of the transformer oil.
THEORY
The insulating oil used for insulation and cooling purpose must be free from moisture to
improve the insulation strength. Sludge is an oxidized product. It is formed due to the presence
of acids and alcohols in the oil. The insulating property of transformer oil is reduced due to the
formation of the sludge. Sludge reduces the rate of heat transfer, blocks the ducts and increases
the operating temperature.
The dielectric strength of insulating oils is 40KV per mm when applied for one minute. Its flash
point is 106 ˚c and sludge is 1% to 2%. Its specific gravity is 0.88 and dielectric constant is 22.
Its pour point is -40˚c . The following laboratory tests has to be carried on the transformer oil to
determine its usability.
1) Dielectric strength test.
2) Acidity test.
To supervisor in charge of operation
1) If the operator does not read the language in this manual, translate the manual into appropriate
language.
2) Help the operator in understanding this manual before operation.
3) Keep the manual near the tester for easy access by the operator.
4) While the tester is delivering its Test voltage, never touch H.V. area or else one will be
electrified and run the risk of death by electric shock.
5) The electric shock or accident may occur due to absence of grounding.
Power supply:
1) Voltage
: 240V AC single phase 50 Hz.
2) Line fuse : 10 Amp.
3) AC plug : 3 core mains with 3 pin plug.
Environmental conditions:
Do not operate the tester in adverse environments, such as
a) Flammable atmosphere = To avoid fire and explosion hazard.
b) Un-stable position = Slant position or where the tester may be subjected to the vibrations.
c) Heat = Nearby source of heat, operating temperature of the tester is up to 50˚c.
d) High humidity = Operating humidity range of tester is 20 to 80% RH.
e) Ventilated place.
f) Dusty atmosphere.
g) Near high sensitive devices: such as communication receivers, lest the noise generated by the
tester should interfere with such devices.
General:
i) Purpose:
Insulating oil testers has been designed and produced to test electrical strength of liquid
insulating materials such as transformer oils, capacitor oils etc. The test set carries out test on
these materials as per the Bureau of Indian Standard specifications no: I S 6792 and
International IEC 156.
ii) Features:
1) Test cell type 'TC2' is supplied with the set and is per I S 6792, having two 36mm
mushroom electrodes which are also recommended by IEC and various other international
standards.
2) The test voltage should be increased gradually and in smooth manner from zero to maximum
output at an approximate spped of 2KV per second(+/- 20%)
3) The high voltage transformer operates at low flux density ensuring distortion free output
voltage right upto maximum voltage.
4) The step less voltage regulator is (toroidal) auto transformer type. It's own magnetizing
current is negligible and thus it delivers harmonic free output.
5) The principal of voltage breakdown voltage indication is that at an instant of break-down an
overload relay trips and disconnects the H V. The overload relay is adjusted at the factory so that
transient sparks do not trip.
6) The control panel is printed with the legend. The controls are ergonomically placed that when
the unit is use on a table or bench all controls and the meter can be observed and operated easily.
7) The oil cell is placed on the transformer by opening a clear plastic lid through which oil cell
can be observed.
8) Heavy feet are provided on the test set so that it can withstand transport shocks and at the
same time it does not mar the surface on which it is used.
9) Safety
i)Maximum operator and equipment safely have been built in. When plastic lid is opened, it
activates a micro switch shutting off the supply to the unit. A zero return interlock arrangement
makes it obligatory to bring the H.V. to zero after every breakdown test. The circuit logic is such
that H.V. cannot be switched 'ON' under any circumstances unless the H.V. is brought to zero.
10) Lamps indicate the various conditions i.e. 'MAINS ON', 'H V OFF' and 'H V ON'.
11) The unit is given a fine industrial finish and is provided with carrying handles.
12) KV meter is calibrated in Kilo volts but is connected to the voltage appearing on the primary
of the H V transformer . Although the combination forms at P T and meter circuit, the meter is
calibrated by actually comparing the high voltage delivered by the transformer as shown on a
standard electrostatic voltmeter.
SPECIFICATION:
1) Input Voltage
2) Test cell
3) Electrodes
4) Spacing gauge
: 240V, 50Hz, single phase, AC mains.
: Fig 2 of IS 6792.
: 36mm diameter, mushroom.
: 2.5mm
Precautions while testing un-filtered oil:
Testing of oil without being filtered:
The poor oil is reclaimed oil without being filtered and this oil contains plenty of water and
impurity, whose dielectric strength is mostly under 10KV. If such poor oil with water is tested,
the tester which tests the high dielectric strength. The high voltage testing system of the
instruments is damaged. The clause of damage is (See figure 1) During testing, there is
insulating oil filled between the two hemispheres of the high voltage poles. When testing, the
voltage increases and the difference becomes bigger as voltage is increased, as different coils
can endure different voltages, so the oil under test will be broken-down by the ascending voltage
when its higher than the breaking voltage, then there will be heavy current transient caused by
breakdown. Depending on the current , the instruments will turn off the switch to cut off the
high voltage and turn to the state of "HV OFF". When the poor oil contains more water, the
water particulate will be shaped into a vaporous line under the high voltage. As the voltage
between the two hemispheres (electrodes) continues to ascend, the line becomes thicker, the
resistance of the water becomes smaller. But the process doesn’t have a sudden breakdown
discharge, so the instrument will be damaged, for example , the current limiting resistor or the
safety will be burned out.
Test of the low withstand voltage oil:
The dielectric strength of the kind of oil is usually between 15 KV to 35KV. The instrument can
test normally even if the oil contains a small amount of water and impurity. Because during the
process of the voltage pressure ascending , several air bubbles or impurity will be absorbed
between the two hemispheres to cause the discharge, then the bubbles will be pile out to the air
and the space left will be supplied by the nearby oil. Therefore the voltage can continue to
ascend to breakdown the oil on the maximum endure point.
Test of the poor oil:
The user should be sure that how poor the oil is. The dielectric strength of this kind of oil is
mostly a little more than 10 KV and the oil contains water drops or impurity which can be seen
by our eyes, so don’t use the instrument to test. Generally, in the poor oil kept stayed for more
than 24 hours, the bigger water drops sink at the bottom of oil and the tiny air bubbles float on
the surface of the oil. The user has to draw out the samples in the middle with the vessel
unpolluted by water. During the period of the experiment, user should spy on the oil to see if
there are vaporous lines between the two hemispheres as in the figure1. Once the user sees the
vaporous lines, user should switch off HT right away, or there is several durative
discharging when the voltage is rising and the tester’s circuit cannot turn off the HT
automatically, the user should turn off HT and the power at once and stop testing that
kind of oil.
OPERATING INSTRUCTIONS:
For electric strength
1) Earth the unit. This is an extra safety requirement for operator.
2) Connect the unit to a properly earthed single phase mains supply.
3) Adjust the distance between the electrodes in the test cell using the correct clearance.
Adjust the electrode gap as follows:
Loosen the knurled thumb screws by turning them anti clock wise move spindles by
turning and set the gap between the electrodes according to the GO gauge.
Tighten the knurled knobs by turning them clockwise. This will fix the electrode spacing
and
eliminate frequent checking of the gap size.
4) Open the lid. Cradle the test cell on the holders of the H V transformer and ensure proper
placement of test cell. Close the lid.
5) Operation: Breakdown test
Put the main rocker switch in the ON position. The MAINS ON lamp lights up and the
HV OFF lamp also lights up.
Press the HV ON button and move output control knob in full anti clockwise direction till
the HV OFF lamp goes off and the HV ON lamp lights up. This action is simultaneously.
HV is now switched.
Advance the output control knob in the clock wise direction.
The pointer of KV meter reads the voltage applied to the test cell.
Advance the output control till breakdown occurs and the overload trips cutting off the
supply of HV transformer.
The HV ON lamp goes off and HV OFF lamp lights up. Do not advance the voltage
control any further. Breakdown voltage can be read from the meter.
The user is requested to refer to I S 6792 specifications and carry out six tests on the same
filling . After the tests are made up the unit should be switched off and the oil cells should
be removed and cleaned as per the notes.
Withstand test:
Put the mains rocker switch in the ON position. The MAINS ON lamp lights up and the
HV OFF lamp also lights up.
Press the HV ON button and move output control knob in full anti clock wise direction
till the HV OFF lamp goes off and the HV ON lamp lights up.
Advance the output control knob in the clock wise direction.
The pointer of KV meter reads the voltage applied to the oil test cell.
When the meter indicates the voltage at which the withstand test is to be carried out, stop
moving the voltage regulator. Now watch the time and after the desired time, shut off HV
by pressing HV OFF switch.
If there is a breakdown in the small oil, the overload relay will be tripped. The high
voltage supply will be cutoff and the HV ON lamp will go off. The voltmeter will
continue to indicate the voltage applied when the oil sample failed, thus recording its
breakdown voltage.
The voltage regulator can be returned to zero by manually turning the regulator knob fully
anti clock wise. Switch the mains supply to the OFF position before lifting the hood to
gain access to the test cell.
GENERAL MAINTENANCE TIPS:
Problems
Causes
Remedies
Mains not switching Faulty means lead
on
HT not
ON
Check continuity of leads
Fuse
Check fuse
Rocker switch
Check switch
HT door inter lock
Check micro switch(S2). When switch
pressed NO should show continuity
switching Zero
interlock
operated
not Bring voltage control knob fully anti
clock wise and simultaneously press
HT ON press switch.
Breakdown in oil not
taking place
a) Faulty trip circuit
b) HT Transformer
Variable voltage not Variable regulator
appearing at HT
primary
a) Check PCB/ U-93-2M.
b) Check continuity of HT coils,
check whether primary voltage
appearing at primary terminal
strip.
Check regulator. Check carbon from
track. Replace carbon brush, if it is not
making proper contact.
Electrode Adjusting:
Vaporous lines due to water and impurities in oil: