Electrical Measurements Lab
Electrical Measurements Lab
Electrical Measurements Lab
I-CYCLE
II- CYCLE
LIST OF EXPERIMENTS
Aim:
To calibrate given 1- Φ energy meter using direct loading
method.
Apparatus required:
Theory:
Circuit Diagram:
Procedure:
1. Connect the circuit as per the circuit diagram.
2. Keep the autotransformer at zero voltage position and
make sure all the loads are in off position.
3. Now switch on the supply and variac is varied till to
get rated voltage.
4. Apply the load step by step and each step note the
readings of voltmeter, ammeter, wattmeter and time
taken for 25 rev of the disk of the energy meter.
5. Apply the load below rated current.
6. After note the readings switch off the all loads and
minimize the voltage and than switch off the supply.
Calculations:
The energy meter constant = 900 rev / Kwh.
For 900 rev it records 1 unit or 1 Kwh.
For 25 rev it records = 25 / 900 Kwh.
= 1 / 36 Kwh.
= (1000 X 60 X 60) /36 Wsec
Energy meter reading (E1) = 1,00,000 Wsec.
Actual energy consumed (E2) = Wattmeter reading X Time
Observation Table:
Energy
S. Voltag Wattmete Time taken Actual % Error=
Current meter
N e r reading for 25rev energy (E2-E1) /
(A) reading
o (V) (W) (T) (E2) E2
(E1)
Model Graph:
A graph is drawn between % of error and load current.
+ %
Error
I (amps)
Error
-%
Precautions:
1. Loose connections should be avoided.
2. Meter reading should not exceed beyond their rating.
3. Take readings care fully.
Result:
Hence the calibration of energy meter using direct loading is
Done.
VIVA VOICE QUESTIONS:
The second set of ratio arms , „p‟ and „q‟ are used to connect the
galvanometer to point at the appropriate potential between the points „m‟
and „n‟ to eliminate theeffect of connecting lead of resistance „r‟ between
known resistance „R‟ and standard resistance „S‟. P/Q ratio is made
equal to p/q such that the resistance of connecting led „r‟ has no effect
on the measurement.
procedure:
Calculations:
R = (P/ Q) S
Observation Table:
R=(P/Q) S
S.no. P Q s
Ω
Result:
Hence the unknown resistances of different wires are
measured.
VIVA-VOICE
1.What do you mean by low resistance?
2. What do you mean by medium resistance?
3. What do you mean by high resistance?
4. HOW does a megger differ from ohm meter?
5. Why is a megger provided with a slipping clutch?
6. What is a megger ?
7. What is the value of low resistance?
8. What is the value of high resistance?
9. What is the value of medium resistance?
PROCEDURE:
1. Connect the ckt as per the ckt diagram.
2. Keep the auto transformers at zero voltage position and first switch
on the 3 phase auto transformer supply
3. Now set the rated voltage appears across the output terminals of
phase shift transformer, which are collected to the pressure coil of
wattmeter and power factor
4. Now switch on the 1-Φ auto transformer supply and is adjusted to
a suitable value say 2A.
5. Check out the reading of power factor meter and wattmeter they
just indicating positive reading
6. First adjust the P.F reading to unity using induction regulator
,keep the voltage and current as constant vary the P.F meter
reading and corresponding wattmeter reading is noted
7. Repeat the experiment for different values of P.F
CALCULATIONS:
Actual reading of P.F =
%error = ×100
OBSERVATION TABLE:
VIVA-VOICE
1. How the power factor of a single phase circuit is measured?
2. What is principle of power factor meter?
3. What are the different types of power factor meters?
4. Why is moving iron power factor meter generally used?
5. Why is moving iron PF meters less accurate than dynamometer
type?
6. What is power factor?
7. Give expression for the PF?
8. What is synchroscope and where it is used?
9. What is crossed coil PF meter?
10. What is instrument for speed measurements?
3-Ammeter Method:
S.N P= CosΦ=
I1 I2 I3 (I1²- I2²- I3²) (I1²- I2²- I3²) SinΦ V= I2R Z=V/I3 R=ZcosΦ XL=ZsinΦ L=XL/2 Π f
o 2R 2 I2 I3
Average Inductance =
Average Resistance=
Result:
Parameters of a given choke coil by using 3 Voltmeter &
3 Ammeter methods is measured.
VIVA-VOICE
1. what is inductance ?
2. what is formula for inductive reactance ?
3. what is formula for capacitive reactance ?
4. what is capacitance?
5. what is rating of dimmer stat?
6. What is meant by choke coil ?
7. What is the difference between MC &MI instruments?
8. what is resistance?
9. what is meant by power factor?
10. what is power?
Aim:
To measure the mutual inductance of a given transformer.
Power 3 KVA
Voltage 230V
Frequency 50 Hz
Phase 1- ф
Apparatus:
Circuit Diagram:
Graph:
1. No load losses verses primary voltage.
2. Im verses no load voltage of primary.
3. Mutual induction verses voltage of primary.
Model graph:
M vs V1 W vs V1
Im vs V1
M,W,Im
V1
Result:
The Mutual inductance of a given transformer is calculated.
Precautions:
1. Loose connections should be avoided.
2. Check the connections before giving supply.
3. Note the readings carefully.
VIVA-VOICE
1. What is inductance?
2. What is mutual inductance?
3. What is the formula for voltage across inductance?
4. What is the formula for voltage across capacitance?
5. What is the difference between inductance and mutual
6. Why we are using LPF wattmeter in this experiment?
7. What is LPF wattmeter?
8. What is meant by exciting current?
9. What is meant by magnetizing current?
10. What is the formula for magnetizing current?
Apparatus:
1. DC Potentiometer.
2. Standard cell
3. Volt ratio box
4. Sensitive Galvanometer
Circuit diagram:
Circuit diagram:
Calibration of Voltmeter:
Theory:
Crompton’s DC Potentiometer
Crompton‟s DC potentiometer is a slide wire type of potentiometer. The
long slide wire is awkward, and ever for the length shown cannot be read
to a very great degree of precision. Modern laboratory type potentiometer
use calibrated dial resistors and a small circular wire of one (or) more
turns, there by reducing the size of the instrument. The circuit of a
simple laboratory type potentiometer consists of one dial switch with
filter steps ,each having a precession resistors. There is also a single turn
wire. This potentiometer consists of unknown cell. A key and a protective
resistance is used in the galvanometer circuits.
Procedure:
1. Make the connections as per the circuit diagram.
2. Calibrate the DC potentiometer by adjust coarse and fine
rheostats. When Galvanometer has null deflection and
function must be in STD mode.
Calibration of Ammeter:
Procedure:
Tabular column:
Calibration of Voltmeter:
Calibration of Ammeter:
VIVA-VOICE
AIM:
To test the given current transformer by Silsbee‟s method and to
determine the Phase Angle and Percentage Ratio error.
APPARATUS:
4 Ammeters MI (0-5A) 4
THEORY:
Silsbee‟s method is a comparison method. There are two types of
Silsbee‟s methods: deflection and null. Only deflection method is
described here. Here the ratio and phase angle of the test transformer X
are determined, in terms of that of a standard transformer S having the
same nominal ratio. The two transformers are connected with their
primaries in series. An adjustable burden is put in the secondary circuit
of the transformer under test.
An ammeter is included in the secondary circuit of the standard
transformer so that the current may be sent to the desired value .
w1 is a wattmeter whose current coil is connected to carry the
secondary current of the standard transformer. The current coil of
wattmeter w2 carries current ∆I which is the difference between the
secondary currents of the standard and test transformer s. The voltage
Circuits of the wattmeter‟s (I .e; their pressure coils) are supplied in
parallel from a phase shifting transformer at a constant voltage v.
CIRCUIT DIAGRAM:
Procedure:
1. The connections are made as per the ckt diagram.
2. With the (10x4) rheostat cutout the supply switch to the auto
transformer is closed.
Tabular column:
S.NO Ip(A) Iss(A) ID(A) Ws(A) WD1(W) WD2(W) Isx(A) RATIO Phase
ERROR angle
error
Phasor diagram:
V b
V a
ISX ISS
Φ r
IP
RESULT: Hence the phase angle and percentage ratio error are
calculated by using Silsbee’s method.
VIVA-VOICE
1. What is meant by the term “instrument transformer”?
2. What is instrument transformer?
3. How do instrument transformer is differ from power transformer?
4. What do you understand by ammeter shunt?
5. What do you understand by voltmeter multiplier?
6. Why instrument transformers are used?
7. What is meant by turn “burden “of an instrument transformer?
8. How do current transformer is differ from potential transformer?
9. What is formula for ratio error?
10. What is formula for phase angle error?
TABULAR FORM:
R1(Ω) R2(Ω) C3(µf) CX=(R1/R2)C3 Dissipation
factor
Average capacitance =
Dissipation factor=
Average Dissipation factor=
PROCEDURE:
1) The bridge is connected as shown in circuit diagram.
2) The oscilloscope is connected across the point b and d.
3) The bridge is balanced by adjusting Cy and Ry.
4) The reading are tabulated and C4 and R1 is calculated.
5) A number of reading are taken and average values are
calculated.
CALCULATIONS:
C1=Unknown capacitance
R1= Resistance representing losses in the unknown capacitance
C3=Standard capacitor
R3=Standard non-inductive resistance
R4=Variable non-inductive resistance
C4= Variable capacitor
CX=(R1/R2)C3
Dissipation factor=2∏fCxR1
RESULT:
CIRCUIT DIAGRAM:
Procedure:
1. Connect the audio oscillator and Head phones to proper
terminals.
2. 230 V supply is given to the Bridge oscillator.
3. In the Bridge the value of P, Q, R is equal to 1000 Ω.
Minimum sound can be obtained by varying „S‟ and „M‟
alternatively.
4. The best way to get balance is to vary „S‟ first to dicers the
sound in the headphones. The final minimum sound can be
obtained by varying „M‟.
L= C [RQ + (R+S) M]
Where
„L‟ is in henries
„C‟ is in farads
Other resistances are in Ohms.
„S‟ includes the resistance of self-inductance also for all
calculations.
7. The experiment for the same inductance can be reputed
By selecting of deferent value of „C‟ and gating balance by
varying „S‟ and „M‟. The mean vale of „L‟ can be calculated.
Bridge arms:
VIVA VOICE
1. Maxwell bridge is used for measurement of
_________________________
2. Maxwell‟s bridge is very convenient and useful bridge for
determination of
Inductance of a coil having ________________________
3. why there are two conditions of balance in ac bridges ?
4.why is high grade insulation employed in high impedance bridges?
5. why are highly sensitive detectors undesirable for the operation
of ac bridges ?
6. In an Anderson bridge , the unknown inductance is measured in
terms of________________
7.Anderson bridge is used for the measurement of ______________________
8Anderson bridge is a modification of _________________________________
9.Anderson bridge is used to measure______________________
9.CALIBRATION OF LPF WATTMETER BY PHANTOM LOAD TEST
Theory:
Calibration of LPF watt meter by phantom loading :
When the current rating of a meter under test is high as test with
actual loading arrangements‟ would involve considerable wastage of
power. In order to avoid this”phantom” or “frictions” loading is done.
Phantom loading consist of supply the pressure circuit from a
circuit of a required normal voltage and a current circuit from a low
voltage supply. It is possible to circulate the rated current throw the
current circuit with a low voltage supply as the impedance of the circuit
is very low with this arrangement the total power supplied for the test is
that due to the small pressure coil current at normal voltage, pulse that
due to the circuit current supplied at low voltage. The total power ,
required for testing the meter is comparatively very small.
Procedure:
1. Connect the circuit as per the circuit diagram.
2. Initially keep the two autotransformers at minimum output
voltage.
3. By varying the autotransformer in pressure circuit the voltmeter
reading is adjusted to a rated value.
4. By slowly varying the autotransformer reading is adjusted at
different values in steps.
5. The same procedure is repeated by connecting ammeter and
wattmeter 10A range.
Calculations:
True power=VI COSΦ
%Error=(W-Wt/Wt) X 100
Observation table:
For Current 5A:
Voltmeter Ammeter Wattmeter True %Error
(V) (A) (W) power (W-Wt/Wt) X
VICOSØ 100
Observation table:
For Current 2.5A:
Voltmeter Ammeter Wattmeter True %Error
(V) (A) (W) power (W-Wt/Wt) X
VICOSØ 100
Model Graph:
-%Error
VIVA-VOICE
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 wattmeter?
7.What is meant by fictitious load?
8.What are the special features of a wattmeter suitable for working on
LPF circuits?
9.What is the rating of dimmer stat?
Theory:This method can be used only when the load is balanced. The
connections are shown in the figure. The current coil is connected in one
of the lines and one end of the pressure coil to the same line, other end
being connections alternatively to the other two lines. Power
measurements are made in high voltage circuit connecting the wattmeter
to circuit through current and potential transformers. Voltmeters and
Ammeters are affected by only ratio errors while watt meters are
influenced in additional by phase angle errors.
CIRCUITDIAGRAM:
Procedure:
1. Connect the ckt as per the ckt diagram.
2.The motor is started with the help of starter.
3.Varying the load on the motor by tighten the spring balance over the
pully of the motor.
4. Take the corresponding reading of the voltmeter, ammeter and
wattmeter.
5.Repeat the process for different values up to rated current
6.Calculate the reactive power.
Calculations:
Power factor, cosΦ = W/VI
Reactive power, Q = VI sinΦ
KVAR = Q/1000
Model graph:
P .F KVAR
F KVAR
P.F
IL(A)
Precautions:
1. loose connections should be avoided.
2. operate the starter care fully.
3. loads should not exceeding beyond their rating.
4. proper rating meters should be used.
5. check the connections before giving supply.
Result:
Hence the 3- phase reactive power is measured by 1-phase wattmeter
method and characteristics curve between KVAR and P.F with load
currents are plotted.
VIVA-VOICE
1. What is electrodynamometer type wattmeter ?
2. What is meant by KVAR ?
3. What is formula for reactive power?
4. What is meant by UPF wattmeter?
5. What is rating of three phase induction motor?
6. What is meant by TPST switch?
7. What is meant by DOL starter?
8. What is meant by balanced load?
9. What is meant by unbalanced load?
10. What is model graph of reactive power measurement?