eee department electrical measurements lab manual · 2. connect the load rheostat 10 Ω/12a in...

EEE Department Electrical measurements lab manual

ELECTRICAL MEASURMENTS LAB MANUAL

Anurag college of Engineering, Aushapur


ELECTRICAL MEASUREMENTS LAB INDEX

1. Calibration of single phase energy meter.2. Calibration of single phase power factor meter.3. Power measurement by 3-Ammeter method.4. Power measurement by 3-Voltmeter method.5. Schering Bridge.6. Strain-gauge transducer.7. Measurement of Unknown Capacitance by using Desauty’s Bridge.8. Kelvin’s Double Bridge.9. Measurement of Unknown Resistance by using Wheatstone’s bridge.10. Anderson’s Bridge.11. Capacitive Pick-Up.12. Linear Variable Differential Transformer (L.V.D.T).13. Measurement of three phase reactive power with single phase watt meter.14. Crompton type DC potentiometer.15. Measurement of three phase power using single phase wattmeter and two

C.Ts.



EXPERIMENT-1CALIBRATION OF SINGLE PHASE ENERGY METER

AIM: To determine the error and percentage error at 5%, 25% and 100% of fullload current for the given single phase energy meter.

NAME PLATE DETAILS:Meter constant = 1200 rev/KWHRated Current = 10ARated Voltage = 240VRated frequency = 50Hz

APPARATUS:1. Voltmeter – (0-300V) MI2. Ammeter – (0-20A) MI3. 1-Ф variac – (230V / 0-270V) 4. Rheostats – 350Ω / 1.2A, 29Ω / 4.1A, 10Ω / 1.2A5. Stop watch6. Connecting wires

CIRCUIT DIAGRAM:

THEORY:Energy meter mainly consists of 4 parts of the operating mechanism. They

are1. Driving system2. Moving system3. Breaking system4. Registering mechanism

The driving mechanism of the meter consists of two electromagnets. The core ofthese electromagnets is made up of steel laminations. The coil of one of theelectromagnets is excited by the load current. This coil is called the current coil.The coil of second electromagnet is connected across the supply voltage andtherefore carries a current proportional to the supply voltage. This coil is called the



pressure coil. Consequently the two electromagnets are known as series and shuntmagnets respectively. Copper shading bands are provided on the central limb.

The function of these bands is to bring the flux produced by the shuntmagnet exactly in quadrature with the applied voltage. Moving system:

This consists of an aluminum disk mounted on a light alloy shaft. This discis positioned in the air gap between series and shunt magnets. The ‘Al’ disc movesin the field of this magnet and thus provides a breaking torque.Braking System:

A permanent magnet positioned near the edge of the aluminum disc forms the braking system. The aluminum disc moves in the field of the magnet and thus provides a braking torque. The position of the permanent magnet is adjustable and therefore braking can be adjusted by shifting the permanent magnet to different radial positions.Registering Mechanism: The function of a registering or counting mechanism is to record continuously a number which is proportion to the revolutions made by the moving system.

PROCEDURE:

1. Connect the circuit as shown in figure.2. Connect the load rheostat 10 Ω/12A in series with load.3. Keep the variac in minimum output voltage position.4. Keep the load in maximum position.5. Adjust the variac output equal to the rated voltage of energy meter.6. Adjust the load till rated current of energy meter passes through it. Note

down the voltmeter and ammeter readings.7. Note down the time taken for 2 revolutions of disc in the energy meter.8. Switch off the supply.9. Repeat the above steps for different currents.

TABULAR COLUMN:

S.No Voltage Current Time taken forrevolutions (S)

No. ofrevolutions

ActualEnergyWa (W)

Energyregisteredby energymeter WR

(W)

Error WR - Wa

(W)

%Error

THEORITICAL CALCULATIONS:

Actual energy consumed during ‘n’ revolutions Wa = V*I*t / 3600 watt-hourwhere V= Voltage (V)



I= Current (A)t = Time (S)

Energy registered by energy meterWR = n / meter constantError = WR - Wa

% Error = [(WR - Wa) / Wa] * 100

RESULT:The error and percentage errors are determined for single phase energy

meter at 5%, 25% and 125% of full load current.



EXPERIMENT-2CALIBRATION OF SINGLE PHASE POWER FACTOR METER

AIM: To calibrate single phase power factor meter with inductive and capacitiveloads.

APPARATUS: 1. Ammeter (0-10A) MI2. Voltmeter (0-300V) MI3. Wattmeter (300V, 10A,UPF)4. 1-Ф variac 230V / 0-270V5. 1- Ф power factor meter (300V, 10A) 6. Variable inductive / capacitive loads7. Connecting wires

CIRCUIT DIAGRAM:

THEORY:Power factor meters like wattmeter have a current circuit and a

pressure circuit. The current circuit carries the current (or definite fraction of thiscurrent) in the circuit whose power factor is to be measured. The pressure circuit isconnected across the circuit whose power factor is to be measured and is usuallysplit up into two parallel paths- one inductive and the other non-inductive. Thedeflection of the instrument depends upon the phase difference between the maincurrents in the two paths of the pressure circuit i.e. upon the phase angle or powerfactor of the circuit. The deflection is indicated by a pointer.

The moving system of power factor meters is perfectly balanced atequilibrium by two opposing forces and therefore there is no need for a controllingforce. There are two types of power factor meters.

a) Electro-dynamometer type andb) Moving Iron type

PROCEDURE:



1. Connections are made as per the circuit diagram.2. Keep the variac in the minimum output voltage position.3. The inductance / capacitance is kept in maximum position.4. Vary the variac till the rated voltage 230V is obtained in voltmeter.5. The inductive load is also varied to get power factor between 0.5 lag and

near unity.6. At every power factor setting, note down the voltmeter, ammeter and watt

meter readings in addition to power factor reading.7. The above procedure for capacitance load is repeated so that power factor

varies between 0.5 lead and near unity.8. Calculate the error by using appropriate formula.

FORMULAE:

Power factor cosФt = Active Power (KW) / Apparent Power (KW)

= Wattmeter reading / (VI)Error = PF meter reading – true PF = cosФm -cosФt

%Error = [(cosФm -cosФt) / cosФt] * 100

TABULAR COLUMNS:

INDUCTIVE LOAD

S.No SupplyVoltage

(V)

Ammeterreading

(A)

Wattmeterreading

(W)

True PFcosФt=W/(VI)

MeasuredPF cosФm

ErrorcosФm-cosФt

%Error

CAPACITIVE LOAD

S.No SupplyVoltage

(V)

Ammeterreading

(A)

Wattmeterreading

(W)

True PFcosФt=W/(VI)

MeasuredPF cosФm

ErrorcosФm-cosФt

%Error

RESULT: Single phase power factor meter is calibrated with various inductiveand capacitive loads and graph was drawn.



EXPERIMENT-3MEASURMENT OF PARAMETERS OF CHOKE COIL BY THREE

AMMETER METHODAIM: To Measure the parameters of a choke coil using 3-ammeter method.

APPARATUS:1. Ammeter (0-10A) MI -12. Ammeters (0-5A) MI -23. Voltmeter (0-300V) MI -14. Resistive load5. Inductive load6. Single phase variac (230V / 0-270V)

CIRCUIT DIAGRAM:

THEORY:

The parameters of the choke coil can be measured using 3-voltmeters, 3-ammeters. Generally in the case of A.C circuits as power factor is involved, powerfactor meter must be used for the measurement of p.f. But p.f of such circuits canalso be measured by using 3-ammeters. In this experiment load comprising ofresistance and inductance i.e. choke coil is used. Parameters of the choke coil canbe measured by using three ammeters as follows. In this experiment the 3-ammeters are placed in series with resistor, inductor and supply. The phasor sum ofammeter readings (I2,I3) gives the total current I1,of the circuit. Power factor ofthe circuit is determined. Using the p.f the resistance and inductance of the chokecoil are measured as follows. PROCEDURE:

1. Connections are made as per the circuit diagram.2. Variac is kept at minimum output voltage position.3. Supply is given to the circuit and by varying the variac, adjust the voltage

across the voltmeter as 230V.4. Keep the resistance in maximum at starting.



5. For different values of inductive load note down the 3-ammeter readingsand voltmeter readings.

TABULAR COLUMN:

S.No. SupplyVoltage

(V)

Currentthrough

resistor (A)

Currentthroughinductor

(A)

TotalCurrent

I (A)

PowerFactor(cosФ)

Powerconsumedby chokecoil, PL=VI3cosФ

(W)

TotalPower

P=PR+ PL

(W)

Resistance R

(Ω)

Inductance L

(H)

Powerconsu

med byResista

nce(W)


V= Supply VoltageI1= Current in the circuitI2= Current through the resistive loadI3 = Current through the inductive load

r= resistance of the choke coilBy parallelogram law

I12= I2

2+ I32 +2 I2 I3 cosФ

cosФ= (I12- I2

2- I32) / (2 I2 I3)

Power consumed by inductive load is PL= V I3 cosФL

Power consumed by resistive load is PR= I2R (watt)

Total power consumed by load, P= PR+PL (watt)r = PL / I3

2 (ohm) ZL= V / I3 (ohm)

XL=√ (Z2 – r2) (ohms)L = XL / 2πf H

RESULT:The parameters of a choke coil are measured by 3- Ammeter method.


I2

I3

I1


EXPERIMENT-4MEASURMENT OF PARAMETERS OF CHOKE COIL BY THREE

VOLTMETER METHOD

AIM: To Measure the parameters of a choke coil using 3-voltmeter method..APPARATUS:

1. 1-Ф variac (230V/0-270V)2. Rheostat (350Ω/1.2A)3. Voltmeters (0-300V) MI – 34. Ammeter (0-10A)MI -15. Inductive load

CIRCUIT DIAGRAM:

THEORY:

Generally in the case of A.C circuits as power factor is involved in theexpression for power, power factor meter must be used for the measurement of p.f.But p.f of such circuits can also be measured by using 3- voltmeter method. In thisexperiment load comprising of resistance and inductance i.e. choke coil is used.Parameters of the choke coil can be measured by using three voltmeters as follows.One voltmeter is connected across resistance and other is connected acrossinductance. The phasor sum of these two voltmeter readings fives the total voltageapplied to the circuit. From the above calculations power factor of the circuit isdetermined. Using the p.f the resistance and inductance of the choke coil aremeasured as follows.

PROCEDURE:

1. Connect the circuit as per the circuit diagram.



2. Keep the variac in minimum output voltage position.3. Keep the rheostat in maximum position.4. Switch on the supply.5. Note down the readings of all meters for different values of inductive loads.

TABULAR COLUMN:

S.No. SupplyVoltage

(V)

Voltageacrossresistor

(V)

Voltageacross

inductor(V)

Current I(A)

PowerFactorcosФL

Powerconsumed

byresistancePR= V2I

(W)

Powerconsumed

by thechoke coil,

PL=V3IcosФL

(W)

TotalPower

P=PR+ PL

(W)

Resistance

RL (Ω)

Induct-anceL (H)

Resist-ance ofthe choke coil, r (Ω)


V1= Supply VoltageV2= Voltage across resistive loadV3= Voltage across inductive loadI = Current in the circuit

By parallelogram lawV1

2= V22+ V3

2 +2 V2 V3 cosФω

Cos Фω= (V12- V2

2- V32)/(2 V2 V3)

Power consumed by choke coil is PL= V2 I cosФL

Power consumed by resistive load is PR= V2 I (watt)

Total power, P= PR+PL(watt)Impedance in the circuit, Z= V3 / I (ohms)Resistance = V2 /I (ohms)PL/ I2 = rReactance, XL = √ (Z2 – r2) (ohms)Inductance in the circuit L= XL / (2πf) H

RESULT:The parameters of a choke coil are measured by 3- voltmeter method.


V

2

V3

V1


EXPERIMENT-5SCHERING BRIDGE

AIM: To determine the capacitance of a capacitor and its dissipation factor.

APPARATUS: Schering BridgeHead PhonesProbes

CIRCUIT DIAGRAM:

PROCEDURE:

1. Make the connections as shown in the figure, using AC supply of 1KHZ andhead phones.

2. Connect one unknown capacitor.3. Set the capacitor dial C2 and resistance dial R at zero positions.4. Adjust R1 to some value.5. Vary R2 to minimize the sound in the head phone.6. Note the values of R1, R2 & C1.7. Calculate the value of unknown capacitor using the formula.

C = C1R2/R1

EXAMPLE: C1 =0.01µF R1=2100 OHMS R2=2100OHMS

C = C1R2/R1

=0.01µF

To find the dissipation factor of a capacitor:

1. Without disturbing the setting of the bridge inductance some resistance ‘R’say 500Ω.



2. Now adjust the capacitor C2 to minimize the sound in the head phone.3. Calculate the dissipation factor using the formula

Dissipation factor D = ωCRWhere ω = 2Πf f = frequency of the oscillator R = series resistance of a capacitor representing the loss in

the capacitorC = Capacitance of the capacitor

4. Repeat the experiment with different values of resistance ‘R’.

EXAMPLE: Dissipation factor D = ω*C*R

=2Π*E+3*0.01*E-6*R=2Π*E+3*0.01*E-6*600=0.077

RESULT:Thus unknown capacitance and its dissipation factor are found using

Schering Bridge.



EXPERIMENT-6STRAIN-GAUGE TRANSDUCER

AIM: To measure strain due to applied loads, using resistance strain-gauge

transducer.

APPARATUS: 1. Strain gauge module 2. Weights3. Multimeter

CIRCUIT DIAGRAM:

THEORY:

Resistance strain-gauge transducers are used to sense the elongation/strainunder applied loads. It depends upon the fact that the resistance (R = ρ.L/A)changes under elongation. But the change in resistance is small. For this reason,strain-gauges are connected in the arms of a bridge. The detector used in the bridgewill show null deflection under no load. But under loads, the resistance changeswhich result in deflection in the detector. Deflection in the meter is a measure ofchange in resistance.

In this equipment, on a mild steel flat, two single element bakelite basestrain-gauges with nominal value of resistance 120Ω are mounted with the help of



adhesive cement. One of the gauges is on the top surface of mild steel and theother is on the bottom surface.

PROCEDURE:

1. Ensure that the instrument is switched off.2. Connect the transducer to panel by cable provided.3. Potentiometer marked Ex. Adjustment may be any where.4. Switch on the main supply of the instrument.5. Adjust the excitation voltage using Multimeter and Ex. Adj. trimpot to 5

volts. Measure this voltage between Red and Black terminals on panel.6. Select 2 arm/4 arm configuration using switch provided.7. Now with the help of Coarse and Fine potentiometer adjust meter reading to

zero.8. Now apply gentle pressure by hand on the cantilever beam. The meter will

show some reading. If you apply force in upward direction, the meter willshow negative reading.

9. Now the setup is ready for experiment.10. Put weight of 500gm. in weight pan. Note down the reading. Add weights in

the weight pan in steps of 500gm. and note down corresponding readings.

OBSERVATION:

S.No.

Weight(load)

Eout

AscendingEout

Descending

AverageEout

Stress Strain*E-5

Eout

(Calcu.)Error

CALCULATIONS:

1. Length of the cantilever from center of Gauge to the loading hook center =L =19cms.

2. Thickness of the cantilever = t =0.4cms3. Width of the cantilever = b =3cms.4. Modulus of Elasticity for Mild steel = 2*106 Kg / Cm2

5. Gauge factor = 2

Now Stress = M/Z, where M= Length of cantilever (L) * Applied load (Kg)

Z= 1/6 bt2

Strain = Stress / Modulus of Elasticity= Stress / 2*106

ΔR / R = Gauge factor * Strain



EOutput = EExc.* (ΔR / R) Volts

Note that, this calculations is for 4 Arm Bridge and when we are using 2 armbridge configurations, whatever theoretical answer, is to be divided by 2.

PRECAUTIONS:

1. Ensure cantilever assembly is properly fixed on the table.2. Disconnect the transducer from the panel after completing experiment.3. Do not tamper strain gauge on cantilever.

RESULT:Thus the measurement of strain due to applied loads, is found using

resistance strain-gauge transducer.

EXPERIMENT-7



MEASUREMENT OF UNKNOWN CAPACITANCE BY USINGDESAUTY’S BRIDGE

AIM: To measure the unknown capacitance by using Desauty’s bridge.

APPARATUS:1. Head phones2. Desauty’s bridge circuit3. Patch cards

CICUIT DIAGRAM:

PHASOR DIAGRAM:

THEORY:



The bridge is the simplest method of comparing two capacitances. Thebalance can be obtained by varying either R3 or R4 in this bridge. The advantage ofthis bridge is its simplicity. But this advantage is nullified by the fact that it isimpossible to obtain balance if both the capacitors are not free from dielectriclosses. Thus with this method on loss less capacitor like air capacitors can becompared. In order to make measurements on imperfect capacitors i.e. capacitorshaving dielectric losses, modified Desauty’s bridge is used. By using this modifiedbridge if the dissipation factor of one of the capacitors is known, the value for theother can be determined.

PROCEDURE:

1. Connections are made as per the circuit diagram.2. Supply is given across ‘a’ and ‘c’.3. Set capacitance of C1 to a particular value.4. Vary the resistances such that no sound is heard in detector.5. Repeat the same for different settings of C1.


Z1Z4 = Z2Z3

E1 = E2

E3 = E4

[1/ (-jωC1)] * R4 = [1/ (-jωC2)] * R3

C2 = (R3 / R4)

TABULAR COLUMN:

S.NO. C1 (µF) R3 (Ω) R4 (Ω) Unknown capacitanceC2 = (R3 / R4)* C1 (µF)

AverageCapacitance

(µF)

RESULT:

The unknown capacitance has been measured by using Desauty’s bridge.

EXPERIMENT-8KELVIN’S DOUBLE BRIDGE



AIM: To determine the unknown resistance of a resistor (low resistance) usingKelvin Double Bridge.

APPARATUS:1. Kelvin’s Double Bridge2. Sensitive Galvanometer3. Battery (or) DC source4. Four terminal resistors, Two terminal resistor, cable

CIRCUIT DIAGRAM:

THEORY: The Kelvin’s double bridge incorporates the idea of a second set ofratio arms- hence the name double bridge-and the use of four terminal resistors forthe low resistance arms. The first set of ratio arms is M, Q. the second set of ratioarms m,q is used to connect the galvanometer to a point ‘d’ at the appropriatepotential between the known resistance X and the standard resistance S.

The ratio q/m is made equal to M/Q.Unde4r balance conditions thereis no current through the galvanometer , which means that the voltage dropbetween n and D is equal to the voltage drop between n,t.

PROCEDURE:

1. Give supply to the terminals marked by ‘Battery’ from the D.C source (or)battery.

2. Connect the galvanometer to the terminal marked “Galvanometer”. 3. Connect the unknown resistor to the standard arm.4. Press the galvanometer key marked ‘INITIAL’ and notes the deflection. If

the deflection is high adjust the variable arm. If the deflection is small,release ‘INITIAL’ key and press FINAL key adjust slide wise dial until thedeflection is zero.

5. The unknown resistance can be calculated using the formula,



X = (milliohm decade value + slide wire milliohm value) * RangeMultiplier

RESULT: Thus the resistance of an unknown resistor by using Kelvin’s DoubleBridge was found.

EXPERIMENT-9



MEASUREMENT OF UNKNOWN RESISTANCE BY USINGWHEATSTONE’S BRIDGE

AIM: To determine the resistance by using the Wheatstone’s bridge.

APPARATUS:1. Resistors (200 Ω / 1.5A) – 1

(350 Ω / 1.2A) – 1 (29 Ω / 4.1A) – 2

2. Voltmeter (0-300V) MC – 13. Ammeter (0-10A) MC – 1

CIRCUIT DIAGRAM:

THEORY:Wheatstone bridge is used for measuring medium resistance (1 Ω - 0.1M

Ω). It has four sensitive arms, consisting of resistances together with a source ofEMF and a null detector usually a galvanometer or other sensitive current meter. Itcontains two fixed arms called ratio arms. One is known resistance and other isstandard resistance which can be varied.

The current through the galvanometer depends on the potential differencebetween points ‘B’ and ‘D’. The bridge is said to be balanced when there is nocurrent through the galvanometer or when the potential difference across thegalvanometer is zero.

PROCEDURE:

1. Make the connections as per the circuit diagram.2. Keep the resistance in maximum position.3. Switch on the supply.4. Vary the resistance ‘S’ till zero current flows in the ammeter.5. Measure the effective resistance ‘S’ with multimeter.




When bridge is balanced, I1 P = I2 R --------------→ (1)I1 = I3 = E / (P+Q) -----→ (2)I2 = I4 = E / (R+S) -----→ (3)

From (1), (2) & (3)I1P = EP / (P+Q)I2R= ER / (R+S)EP / (P+Q) = ER / (R+S)R= PS / Q

RESULT:The unknown resistance has been determined by using the Wheatstone’s

bridge.

Resistance Theoretical Values (Ω) Practical Values (Ω)PQRS



EXPERIMENT-10ANDERSON’S BRIDGE

AIM: To determine the self inductance of a coil by Anderson bridge

APPRATUS: Anderson Bridge Head Phones Galvanometer

ProbesCIRCUIT DIAGRAM:

THEORY:

This bridge infact is a modification of the Maxwell’s Inductance-Capacitance Bridge. In this method the self inductance is measured in terms of astandard capacitor. This method is applicable for a precise measurement of selfinductance over a wide range of values. Fig shows the connection of the bridge forbalanced condition.

L = Self inductance to be measuredr = Resistance connected in series with the self inductor.R,P = Known non-inductive resistancesC = fixed standard capacitor.

At balanced condition L = CR (Q+2r)

PROCEDURE: D.C balance

1. Make the connections as shown in the figure, with DC supply,Galvanometer and one unknown inductance.

2. Adjust ‘r’ dial to 0Ω.3. Now, adjust ‘R’ to same value and press the galvanometer.


C

E


4. Use resistance dial S only for fine balance in the galvanometer and note thevalue of R.

AC balance with head phones:

1. Replace the DC supply with AC supply of 1KHZ.2. Replace galvanometer with head phones.3. Set the standard capacitor ‘C’ at position 0.1μFand adjusts the resistance

dial ‘r’ to minimize the sound in the head phone.4. Note the value of r, R and C.5. Now calculate the value of unknown inductance using the formula

L = CR (Q+2r) 6. Repeat the experiment with another value of unknown inductance and Capacitor C.EXAMPLE: R=46 OHMS

S=0.2 OHMSP=Q=1000 OHMSC=0.1µFR=4400 OHMSL=C*R(Q+2r) =0.1E-6*46*9800 =45mH

RESULT:Thus the self inductance of a coil was determined by using Anderson’s

Bridge.



EXPERIMENT-11CAPACITIVE PICK-UP

AIM: To calibrate capacitive pick-up.

APPARATUS: Capacitive Transducer

CIRCUIT DIAGRAM:

PROCEDURE:

1. Connect the capacitive pick-up to the input socket on front panel.2. Keep the input angular displacement to zero position.3. Check for zero reading on meter. Otherwise by operating potentiometer

marked MIN, obtain zero reading for zero angular position of the shaft.4. Now turn the shaft of the capacitive pick-up full clockwise position in a

gentle manner corresponding to 170º by operating knob MAX, if requiredagain check zero reading.

5. Note down the readings corresponding to input angular displacement, andindicated angular displacement on the meter. Enter the readings in the table.

6. Plot the input and output readings on X-axis and Y-axis on graph. Thefollowing points should be noted.

(a) There is a lot of non-linearity of the indicated Vs actual reading. Thereason is the non-linearity of 0 and C of the ganged condenser.

(b) This method of angular displacement is free from mechanicalfriction (neglecting the friction in the ball bearings of the shaft). Thisis a advantage over potentiometer method.

(c) The effect of the cable capacitance can be observed by playing withthe wires leading to the capacitive transducer. When wires are taken



away from each other‘t’ meter reading increases indicating thateffective ‘C’ has decreased.

PRECAUTIONS:

1. If you touch the metallic plate on which the capacitor is mounted theoscillations will stop and meter reading will negative.

2. Keep the pick-up free from dust particles etc. 3. If in any way the stator and rotor plates are shorted together, the oscillations

will not start. Under this condition check for a short between stator & rotorplate by means of multimeter. Remove the short and then circuit will beready for use.

OBSERVATIONS OF WAVEFORMS:

1. Connect terminal TP-1 to live terminal of C.R.O and ground of theinstrument to ground of C.R.O. Then at terminal TP1 you can observe asquare waveform variable in frequency as the shaft rotates.

2. At terminal TP-2, output of the amplifier is observed. Again square waveform is observed.

3. At terminal TP-3, constant pulse width, constant height pulses variable infrequency are observed. This output is fed to meter finally.

TABULAR COLUMN:

S.No. Input AngularDisplacements

(deg)

MeterReading(deg)

% Error

RESULT: Capacitive Transducer is calibrated and waveforms at differentterminals were observed.



EXPERIMENT-12LINEAR VARIABLE DIFFERENTIAL TRANSFORMER

AIM: 1. To determine the characteristics of LVDT.2. To calibrate LVDT.

APPARATUS:

1. Excitation power source.2. LVDT kit.

CIRCUIT DIAGRAM:

PROCEDURE:

1. Connect the transducer to the input socket on front panel.2. The magnetic core may be displaced using thumb wheel, so that the pointer

on the brass rod coincides to zero, using potentiometer marked MIN onpanel.

3. Now if the core is displaced by a known amount and the meter readings canbe entered in the table.

4. Plot the graph of input displacement (X-axis) Vs output indication (Y-axis).



TABULAR COLUMN:

S.No. InputDisplacement X-

axis (mm)

Meter Reading %Error

PRECAUTIONS:

1. Initial zero linearity of the output variations Vs input variations.2. Move the core gently.

RESULT: LVDT was calibrated and the waveforms at different terminals areobserved.



EXPERIMENT-13MEASUREMENT OF 3-Φ REACTIVE POWER WITH 1-Φ WATTMETER

AIM: To measure three phase reactive power with single phase wattmeter.

APPARATUS:1. Three phase supply2. Three phase variac3. Three phase Inductive load (415V, 10A)4. Single phase wattmeter (300V, 10A,LPF)5. Voltmeter (0-300V)6. Ammeter (0-10A)

CIRCUIT DIAGRAM:

PROCEDURE:

1. Make the connections as per the circuit diagram.2. See that the variac is in the minimum output voltage position.3. Switch on the supply with the help of TPST.4. Vary the variac such that the voltmeter shows some reading (say 120V).5. Note down the reading of wattmeter.

Wattmeter reading W = Vbc Ia cos (90-Φ) = VL IL sinΦ

Reactive Power = √3 W= √3 VL IL sinΦ



PHASOR DIAGRAM:

VERIFICATION:

1. Switch of the supply.2. Disconnect the wattmeter pressure coil from Y,B phases and connect to phase R

and neutral of the load.3. Now switch on the supply.4. Vary the variac such that the voltage is again 120v.5. Note down the wattmeter (W2), voltmeter (V), ammeter (A) readings.6. The wattmeter now gives the per phase value of the power consumed by the

load.7. Reactive power can be verified using the formula,

Q = √[3(VI)2-P2

RESULT:

Multiplying the wattmeter reading with √3 gives you the reactive powerconsumed by the load.

EXPERIMENT-14


Vab

Va

Vb

Vc

Φ

90-Φ

Ia


CROMPTON TYPE DC POTENTIOMETER

AIM: To calibrate PMMC ammeter & PMMC Voltmeter using Crompton type DC Potentiometer.

APPARATUS: DC Potentiometer PMMC Ammeter PMMC Voltmeter

Volt Ratio Box Standard cell Battery

CIRCUIT DIAGRAM:

STANDARDISING THE POTENTIOMETER

PROCEDURE:

1. Connect the Galvanometer, standard Cell and Battery to their appropriateterminals on the Standard Cell and Battery.

2. Set the potential dials to the exact voltage of the standard cell.3. Press the STANDARDISE key and obtain a balance on the galvanometer by

rotating the battery rheostats (Coarse and Fine).4. Galvanometer should no deflection with STANDARDISE key pressed.

Then the potentiometer has been standardized for use.



CALIBRATION OF PMMC VOLTMETER

1. Connect the RPS, voltmeter to the primary of the Volt Ratio Box, withproper polarity.

2. Connect the secondary terminals (marked 1.5V) to the ‘TEST’ terminals ofthe potentiometer. Other connections need not be disturbed.

3. Adjust the RPS to a position such that voltmeter reads say 4V.4. Press the TEST key and obtain the balance on the galvanometer by

changing the setting of the potential dials.5. Note the readings of the potential dials.

Ex. Input terminals used for volt ratio box E & 150VPotentiometer reading = 0.042VInput voltage = (150/1.5)0.042 = 4.2v

TABULAR COLUMN:

S.NO Measuredvalue

Actual value=measuredvalue/actual value

Error %error

CALIBRATION OF PMMC AMMETER

CIRCUIT DIAGRAM:

PROCEDURE:

1. Connect the circuit as per the circuit diagram.2. Make other connections as usual.3. Vary the RPS such that ammeter shows some readings say (7.5A).4. Standardize the potentiometer and measure the unknown potential across

the shunt potential terminals as usual.5. The value of current flowing is then found by dividing the measured

potential in volts by the resistance of shunt in ohms.Ex. By using potentiometer shunt of 0.1Ω



Potentiometer reading = 0.7545VCurrent flowing = 0.7545/0.1 = 7.545A

%Error = 6.66

RESULT: PMMC Ammeter and PMMC Voltmeter were calibrated using DC Potentiometer.

EXPERIMENT-15



MEASUREMTNT OF 3-Ø POWER WITH 1- Ø WATTMETER & 2 C.Ts

AIM: To measure 3-Ø power with 1-Ø wattmeter & 2 CT’s.

APPARATUS:

2 CT’s - (0-100)/5A

Ammeter - (0-10) A

Ammeter - (0-2) A

3 Rheostats -10Ω/9A

Wattmeter - (150V, 10A, UPF)

Voltmeter - (0-200) V

CIRCUIT DIAGRAM:

PROCEDURE:

1. Make the connections as per the circuit diagram.2. By varying the variac, apply voltage (say 100V).

Power consumed by the load = C.T ratio * wattmeter reading (watts)



PHASOR DIAGRAM:VE

RIFICATION:

Power consumed by the 3-Ø load = √3 * VL * IL = 288 wattsReading on the wattmeter, W =150 wattsPower as per the wattmeter reading = W * C.T.R

=150*2= 300 watts

RESULT: Thus the measurement of 3-phase power with single phase wattmeterand 2 C.Ts.


Va

Vb

Vc

Ia

I

b

Ia-I

b

Vab

-Vb

Φ


GLOSSARYCALIBRATION OF EMERGY METER

1. CALIBRATON: Comparing with the reference meter, so that we can try toreduce the losses.

2. CREEPING: It is a error, in some meters a slow but continuous rotation isobtained even when there is no current flowing through the current coil &only pressure coil is energized. This is called creeping.

3. CAUSES FOR CREEPING:a. Over compensationb. Over Voltagec. Vibrations

4. PHANTOM LOADING: When the current rating of a meter under test ishigh, a test with actual loading arrangements would involve a considerablewaste of power. In order to avoid this, phantom loading (or) fictitiousloading is done. Phantom loading consists of supplying the pressure circuitfrom a circuit required normal voltage & current from a separate lowvoltage supply. Phantom loading is to test meters having a large currentratings for which loads may not be available in laboratory. This also reducedpower losses during testing.

5. METER CONSTANT: The number of revolutions made per KWH.6. EMF GENERATED IN THE DISC:

e=K*Ф*nФ=flux of the permanent magnetK=constant n=speed of the rotation

7. In induction type energy meter, compensation for static friction is providedby shading bands which are actuated by to provide a constant torqueirrespective of load.

8. In induction type wattmeter, the meter can be reversed by reversing thepotential coil terminals or current coil terminals.

9. If an induction type energy meter runs fast, it can be slowed by adjusting theposition of braking magnet and making it more away from the centre of thedisc.



CALIBRATION OF SINGLE PHASE POWER FACTOR METER

1. Power factor cosФ=P/(VI)2. Power factor meters also having current coil and potential coil like

wattmeter.3. The current circuit carries the current in the circuit in the power factor is to

be measured.4. Pressure circuit is connected across the circuit whose power factor is to be

measured and is split into two parallel paths. One is inductive and other isnon-inductive.

5. The direction of the instrument depends upon the phase difference betweenmain current and currents in the two paths of potential coils. i.e. phaseangle.

6. There are two types of power factor metersa. Electrodynamometer type PF meterb. MI type PF meter

ELECTRODYNAMOMETER TYPE PF METER:There are two identical pressure coils (A, B), A is a pure resistance coil and

B is high inductive coil. This is high accurate.

MI Type PF meter:There are two categories depending on whether the operation of instrument

upon a rotating magnetic field or number of alternating fields.ADVANTAGES:

a. Working forces are large as compared to electrodynamometersb. Scale can extended over 360°c. Simple & robust in construction and is cheap

DISADVANTAGES:a. Errors are introduced in these meters owing to losses in iron parts. The

losses are depends upon the load, frequency.b. Less accurate than electrodynamometer type meter.c. Calibration of these instruments is appreciably affected by variations in

supply frequency and voltage waveform.



MEASUREMENT OF 3-Ф REACTIVE POWER WITH 1-Ф WATTMETER

1. Reactive power Q = VI sinФ2. Reactive power serves as a check on power factor measurements. Since

ratio of reactive power to active power is tanФ= Q/P3. Varmeter is volt ampere reactive meter. (Electrodynamometer type).4. Varmeters don’t read correctly if harmonics are present or if the frequency is

different from that used when calibrating the instrument.5. In measurement of 3-Ф reactive power with 1-Ф wattmeter, the current coil

of the wattmeter is connected in one line and pressure coil the other twolines. Current through the current coil is I2 and voltage across the pressurecoil is V13.

6. Reading of the wattmeter is V13 I2 cos(90+Ф) = √3 * VI cos (90+ Ф)= - √3VI sin Ф.

7. Total reactive volt amperes of the circuit Q= 3VI sin Ф8. Phase angle = Ф=tan-1(Q/P).



CROMPTON TYPE D.C POTENTIOMETER

1. The Crompton type potentiometer is also called laboratory typepotentiometer.

2. Basically a potentiometer is a null type instrument and it is aninstrument designed to measure an unknown voltage by corresponding itwith a known voltage. (Supplied by a standard cell or reference source).

3. Since a potentiometer measures voltages, it can also be used todetermine current simply by measuring the voltage drop produced by theunknown current passing through a known standard resistance.

4. STANDARDISATION: This is a process of adjusting the workingcurrent so as to match the voltage drop across a portion of sliding wireagainst a standard reference source is known as standardization.

5. Standardization of potentiometers is done in order that, they becomeaccurate and direct reading.

6. Potentiometer is extensively used for a calibration of voltmeters,ammeters and wattmeters. Also used for measurement of current, power andresistance. Since it is a D.C device, the instruments to be calibrated must beD.C MI or electrodynamometer type.

7. The potentiometer method of measurement of resistance is suitablefor measurement of low resistances.

CALIBRATION OF VOLTMETER:1. The fore most requirements in this calibration process is that a

suitable stable D.C voltage supply is available since any changes in thesupply voltage will cause a corresponding change in the voltmetercalibration.

2. For accuracy measurements, it is necessary to measure voltages nearthe maximum range of the potentiometers, as far as possible.

3. Two rheostats are used one for coarse adjustments and another forfine adjustments.CALIBRATION OF AMMETER:

1. A standard resistance of suitable value and sufficient current carryingcapacity is placed in series with the ammeter under calibration.

2. The voltage across the standard resistor is measured with the help ofpotentiometers and the current through the standard resistance can becomputed.I = V/R

LINEAR VARIABLE DIFFERENTIAL TRANSFORMER (LVDT)



1. Mostly widely used inductive transducer to translate the linear motion intoelectrical signals in LVDT.

2. This transformer consists of one primary and two secondary (having equalno. of turns) winding.

3. The two secondary windings are identically placed on either side of theprimary winding.

4. The primary winding is supplied from A.C source and the output voltage ofsecondary-1 is ES1 and the output voltage of secondary winding-2 is ES2.

5. The output voltage of the transducer =E0 = ES1~ES2, at null position ES1=ES2.

ADVANTAGES:1. High range for measurement of displacement (1.25mm to 250mm)2. Friction less (between coil and core), having infinite mechanical life.3. Electrical isolation 4. For outputs no need of amplification and high sensitivity.5. Rugged construction, low hysterisis, low power consumption.

DISADVANTAGES:1. Sensitive to stray magnetic fields.2. Performance affected by vibrations.3. Dynamic response is limited mechanically by the mass of the core &

electrically by frequency of applied voltage.4. Temperature affects the performance.

CAPACITIVE PICK-UP



1. Pick-up is also called transducer. Transducer is a device which converts thenon electrical quantity into electrical quantity.

2. Principle in the capacitive pick-up is the change of capacitance which maycause by

a. Change in overlapping area (A).b. Change in distance between plates (d).c. Change in dielectric constant.

C = ЄA/d = (Єr*Є0*A)/dЄ = Єr*Є0 = permittivity of mediumЄr= relative permittivity of mediumЄ0= permittivity of free space = 8.85 * 10-12

3. These changes caused by physical variables like displacement, force &pressure, dielectrical constant (in liquids and gases).

4. Capacitive transducer used for measurement of linear displacement.5. Output impedance of a capacitor transducer is high, so a careful design of

the output circuitary.XC = 1/(2ΠfC)

ADVANTAGES:1. Require extremely small forces to operate.2. Extremely sensitive.3. Having good frequency response.4. Having high input impedance & therefore loading effects are minimum

resolution of order 2.5*10-3 mm.5. Applications where stray magnetic fields render the inductive transducers

useless.6. Force requirement is very small & hence small power to operate them.

DISADVANTAGES:1. Metallic parts must be insulated from each other in order to reduce the

effects of stray capacitances, the frames must be earthed.2. Non-linear behaviour, therefore guard rings must be used to eliminate this

effect. The guard rings are also must in order to eliminate the effect of strayelectric fields, especially when the transducers have a low value ofcapacitance of the order power factor.

3. The output impedance of capacitive transducers tends to be high on accountto their small capacitance value.

4. The capacitance of a C.T. may changed on account of presence ofextraneous matter like dust particles & moisture.

5. It is a temperature sensitive.6. Instrumentation circuitary used with these transducers is very complex.

STRAIN GAUGE TRANSDUCER



1. If a metal conductor is stressed or compressed, its resistance changes. Onaccount of this fact that both length and diameter of conductor change. Alsothere is a change in the value of resistivity of the conductor when it isstrained & its properity is called piezoresistive effect.

2. The change in the value of the resistance due to change in resistivity.Therefore resistance strain gauges are also called piezoresistive gauges.

3. Strain gauges are used for measurement of strain and associated stress inexperimental stress analysis.

Resistance of Unstrained gauge R = ρ*L/A4. Gauge factor Gf = (ΔR/R)/(ΔL/L) , where ΔL/L is strain (Є)

Types of strain gauges:a. Unbounded metal strain gauges.b. Bonded metal wire strain gauges.c. Bonded metal foil strain gauges.d. Vaccum deposited thin metal film strain gauges.e. Sputter deposited thin metal strain gauges.f. Bonded semiconductor strain gauges.g. Diffused metal strain gauges.

5. Strain gauges are broadly used for two major types of applications:a. Experimental stress analysis of machine & structures.b. Construction of force, torque, pressure, flow & acceleration

transducers.

ANDERSON’S BRIDGE



1. This is a method is used to measure self inductance of a coil in terms ofstandard capacitor.

2. The other bridges used for finding self inductances are a. Maxwell’s Inductance Bridge-Measures inductances by comparison

with a variable standard self-inductance.b. Maxwell’s Inductance Capacitance Bridge-Measures inductance by

comparing with a standard variable capacitance.c. Hay’s Bridged. Anderson’s Bridge-Self inductance in terms of standard capacitor.e. Owen’s Bridge-Measures inductance in terms of capacitance.

3. Balance condition for the Anderson’s Bridge is I1 = I2 and I3 = IC + I4.



DESAUTY’S BRIDGE1. Desauty’s Bridge is used to measure the unknown capacitance by

comparing two capacitors (loss less capacitors like air capacitor).2. The other bridges used for measuring the capacitance are

a. Schering Bridge-Measuring Capacitance & its dissipation factor. Thisis used for measuring relative permittivity of dielectric material.

b. High Voltage Schering Bridge-the supply is obtained fromtransformer at supply frequency, here we are using vibrationgalvanometer as detector.

3. The balance condition for Desauty’s Bridge is I1 R1 = I2 R2

4. Relation between capacitors C1, C2 is C1 = C2 * (R2/R1)



WHEATSTONE BRIDGE

1. Wheatstone Bridge is used for measuring the change in resistance byprecise measurement of low resistance.

2. By using Wheatstone Bridge we can measure the resistances in the mediumrange.

3. The change in the resistance gives the direct measurement of strain (if mealconductor is stressed or compressed, then change in resistivity of conductordue to strains).

4. We are going to measure the medium resistance by using these methods,a. Ammeter-Voltmeter Method.b. Substitution Methodc. Wheatstone Bridge Methodd. Carry Forster Bridge method

5. In Wheatstone Bridge these is no deflection meters.



KELVIN’S DOUBLE BRIDGE

1. Kelvin’s Double Bridge method is used for measurements of lowresistances.

2. In the Kelvin’s Double Bridge we are using the deflecting meter.3. There are some methods used for measuring low resistance.

a) Ammeter Voltmeter method.b) Kelvin’s double bridge method.c) Potentio meter method.



SCHERING BRIDGE

1. Schering Bridge is used for finding the capacitance of a capacitor and itsdissipation factor.

2. The balanced condition for Schering Bridge is Z1Z4 = Z2Z3

3. Schering Bridge is also used for measuring the leakage resistance.


eee department electrical measurements lab manual · 2. connect the load rheostat 10 Ω/12a in...

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