6. Elec.measure.lab Manual 4EEE

Narasimha reddy Engineering College, Electrical Measurements Lab

Circuit diagram: CALIBRATION & TESTING OF SINGLE PHASE ENERGY METER

1 Dept. Of EEE


CALIBRATION & TESTING OF

SINGLE PHASE ENERGY METER

Aim:

To calibrate and test a single-phase energy meter.

Apparatus:

Sl.No Apparatus Range Type Quantity

1. Voltmeter 0-300V MI 1No.

2. Ammeter 0-5/10A MI 1No.

3. BoosterTransformer

0-40V/10A - 1No.

4. Energy meter 0-5/10A Induction 1No.

5. Stop clock Digital 1No.

6. 1- Auto

Transformer

230V/

0-270V,10A

1No.

7. Rheostat 50Ω/5A WoundWire 1No

8. Wattmeter 0-5/10A300V

DynamometerType UPF

1NO

9. Connecting Wires ----- ----- As

required

Theory :The energy meter is calibrated by finding error in the meter under different load

conditions. In energy meter, there are two fluxes produced by currents, flowing in the series

and shunt windings. These alternating fluxes produce emfs in the metallic disc. These emfs

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Exp-1


Observations:S.NO

V (V)

I (A)

Power(W)

Time for 10

rev(Sec)t

E2=W*t E1=meter constant

(watt-sec)

%error =

1001

Model graph: %error

0 IL(A)

3 Dept. Of EEE


inturn circulate eddy currents in the disc. Thus there are two fluxes and two eddy

currents and therefore two torques are produced. Total torque is the sum of the torques.

The speed of rotation of the disc is proportional to power.

Energy consumed=Number of pulses/Meter Constant

Procedure:

1.Connect the circuit as per the circuit diagram

2.Apply rated voltage i.e., 230V to the energy meter by varying auto transformer.

3. Current is passed through current coils with the help of booster transformer. The disc of the energy meter must rotate in the forward direction as marked on the meter..

4.For each step note down the time taken for 10 revolutions of the disc

using stop clock..

5.Note down the ammeter and voltmeter and Wattmeter readings for each step.

6.Repeat the procedure until 5A of changing the tapping of booster transformer.

7. The % error is calculated from % error = 100.

8.Plot a graph between load current and percentage error taking the load current on x-axis and percentage error on y-axis.

Precautions:

1.Initially the autotransformer should be kept in minimum position.

2. .Initially the autotransformer should be kept in minimum position.

3.Initially resistance should be kept in maximum position.

4.Time taken for 10 pulses must be determined accurately.

5. If the disc rotates in opposite directions, then reverse the (Voltage) current direction in the

(voltage ) current coils.

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Sample calculations:

Voltage = Current =Time for 10 pulses =E1 = (10/k *1000*60* Watt-secFrom meter reading = K=1200rev / kwhE1 = (10/1200)*1000*60*60=30000 Watt-sec.

Energy recorded = =

%error=

Result :

Review Questions:1. What is meant by calibration 2. What is meant by calibration curve3. What is the torque equation for an induction type energy meter4. What is meant by creeping5. What are the main parts of operating mechanism of energy meter6. What is meant by phantom loading

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Circuit diagram: CALIBRATION OF DYNAMOMETER TYPE 1-PHASE POWER FACTOR METER

6 Dept. Of EEE


CALIBRATION OF DYNAMOMETER TYPE 1-PHASE

POWER FACTOR METERAim :

To calibrate a dynamometer type power factor meter.

Apparatus :

Observations :

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S.No Apparatus Range Type Quantity

1 Ammeter 0-5/10A MI 1No.

2 Voltmeter 0-300V/ 150V MI 3No.

3 Powerfactor meter 300V/5A Dynamo 1No.

4 1- auto transformer 230V/0-270V,10A Induction 1No.

5 3 (phase shifting T/F) ---- Induction 1No.

6 Rheostat 100Ω/5A Wound

wire

1No.

7 Wattmeter 0-5/10A300V

Dynamometer

Type UPF

1NO.

8 Connecting wires ---- --- As

Required

Exp-2


S.No Voltage

applied VS

(Volts)

IL

(A)

Reading of pf

meter

Cos

(measured

value)

S1

= W/V*IS2

%error =

100

Model Gragh:

Theory:

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Single phase dynamometer type power factor meter consists of a fixed coil which is

split into two parts which carries a current of test circuit.

Two identical pressure coils are pivoted on spindle of the moving system. One

pressure coil has a resistance in series and other has an inductance in series. The two coils

are connected across the voltage of the circuit.

Current through one pressure coil will be in phase with the voltage and that of the

other coil lags by 90 degrees. The torques due to these two coils are in opposite to each

other.

The pointer will stop when the two torques are equal.

The deflection of the instrument depends on phase difference between the main

current and currents in the two pressure coils.

Procedure :

1. Connect the circuit as per circuit diagram.

2. Initially keep the autotransformer in minimum position

3. Initially keep Rheostat in maximum position.

4. Vary the 1-Фvariac until voltmeter connected across it reads rated voltage.

5. Vary the rheostat until ammeter shows maximum possible reading ( 4.5A)

6. Note down the readings of all the meters.

7. Through the output of three-phase induction regulator pressure coils of P.F, meter

and wattmeter are excited.

8. 3 Induction regulator is varied for different power factors.(0.5 lag to 0 .5 lead) and

all the readings are noted down every time

9. Note down the readings of all the meters at each step.

10. And by taking different load currents the readings of watt meter, voltmeter, ammeter

and P.F. meter are noted.

11. Calculate the percentage error for each step.

12. Plot a graph between IL and percentage error.

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Precautions :

1. Avoid loose connections

2. Initially keep Rheostat in maximum position.

3. Initially keep auto transformer in zero position

Result:

Review Questions:1. What is meant by power factor2. What are the types of power factor meters3. On what principle does the power factor meter work4. How many minimum current coil does a PF meter has for three phase balanced load5. How the torque is developed in PF meter6. How the current is related with the voltage in current coil

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Circuit diagram: CROMPTON POTENTIOMETER

Circuit diagram 1 : Standardizing the potentiometer

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CROMPTON POTENTIOMETER Aim:

To measure the unknown e.m.f and to calibrate the given PMMC Ammeter and

PMMC Voltmeter.

Apparatus :

Sl. No Apparatus Range Type Quantity

1 D.C.Crompton Potentiometer Kit

---- ----- 01

2 Ammeter 0-1/2A MC 01

3 Regulated power supply

Dual channel

0-30V, 2A Digital 01

4 Standard cell 01

5 Volt meter 0-30V MC 01

6 Resistance Wire <1 Ω 01

7 Multimeter 0-2V D.M.M 01

8 Connecting Wires ---- ---- As

required

9 Rheostat 300 Ω/2A Wound

Wire

01

Theory

Dc crompton’s potentiometer uses calibrated dial resistors and a small circular wire of one or

more turns in place of a long slide wire. The standardization of potentiometer is obtained by

varying the dial resistors and slide wire voltage against that of standard reference source.

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Exp-3


Block diagram of DC Crompton’s Potentiometer :

Circuit diagram 2 :

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For calibrating an ammeter, a suitable standard resistance is connected in series with ammeter

to be calibrated. Knowing the voltage across the standard resistor by the potentiometer, the

ammeter can be calibrated accurately. .

For calibrating a voltmeter, a suitable D.C supply is fed to the voltmeter. The same supply is

stepped down to a suitable value using volt-ratio box to apply to the potentiometer. Knowing this

value from potentiometer and comparing it with the voltmeter reading, it is calibrated accurately

Procedure :

standardization of potentiometer:

1. Connect the circuit diagram as per the circuit diagram (1).

2. Connect RPS of voltage ,say 2V in the circuit.

3. Press the STANDARDISE key and obtain the NULL deflection in the Galvanometer by

varying coarse rheostat & fine rheostat.

4. Galvanometer circuit to zero , obtain the null deflection using coarse & fine dials.

Thus the potentiometer is standardized.

Calibration of voltmeter:

1. Connect the circuit as per the circuit diagram (2).

2. Set the known supply voltage to ,say, 30V.(RPS2)

3. By applying the rated DC. Voltage from the potential divider circuit, the reading of the

voltmeter which is under calibration is noted (V1)

4. Press the STANDARDISE key and obtain the NULL deflection in the Galvanometer by

varying voltage &milli voltage.

5. Note down the potential dial reading

6. Calculate the total voltage and multiply with the multiplication factor to obtain the actual

value of the voltage.

7. Compare the actual value with the Voltmeter reading and calculate the % error

8. Repeat steps 2 to 6 by changing the value of unknown supply voltage. Note down the

values for 2 different voltage readings.

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TABULAR COLUMN :

FOR PMMC AMMETER

S.NO Current (I1)

Amps

Voltage (pot.

Reading) V

Resistance

(ohms)

I2 = V/R

(Amp)

% Error =

*100

FOR PMMC VOLTMETER:-

S.No Volt meter reading (V1) (volts)

Pot. reading V0(volts)

V2= n*V0

(Volts) % Error=

*100

Model Gragh:

FOR PMMC AMMETER

FOR PMMC VOLTMETER:-

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Calibration of ammeter :

1. Select a suitable potentiometer shunt depending on the range of current to be measured.

2. Connect the circuit diagram as per the circuit diagram (2).

3. Set the known supply voltage to ,say, 30V.(RPS2)

4. The current (I1) in the ammeter is note down

5. The voltage drop across the load ® is note down using potentiometer.

6. The standard value of current in the circuit is calculated form the formula V/R =I2

7. Then the % error is calculated from the formula % Error = *100

8. This process is repeated for different values of current.

Sample Calculations :

For Calibration of voltmeter

Total voltage =

True value of voltage =

Measured value of voltage =

% error = [ Measured value – True value ] / True value * 100

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Precautions:

1.Fine and course dials in the potentiometer kit should not be disturbed ,

once the potentiometer is standardized.

2.RPS-1 should be of 2V. if the voltage is more than 2 volts,a suitable

external highly stable resistance should be connected in series with the

RPS-1.

3..Connections should always be made with due care of polarity.

5.Voltage higher than < 2 volts should not be connected across the TEST

terminals.

6.Standardize the potentiometer at intervals during prolonged tests to compensate for

any slight drift in the RPS-1 voltage.

Result:

Review Questions:1. What is the principle of basic potentiometer2. What is meant by standardization of potentiometer? Why it is necessary 3. What are the applications of D.C potentiometer4. What is meant duo-range potentiometer5. What is the principle of vernier potentiometer

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Circuit diagram : KELVIN’S DOUBLE BRIDGE – MEASUREMENT OF RESISTANCE

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KELVIN’S DOUBLE BRIDGE – MEASUREMENT OF RESISTANCE

Aim:

To determine the resistance of given unknown resistor..

Apparatus:

Sl.No Apparatus Range Type Quantity

1. Kelvin’s double bridge

trainer kit

--- ---- 01No

2. Unknown resistance <1 Ω ---- 1 No

3. Galvanometer ---- Analog 1 No.

4. Standard cell 1.0185V --- 1 No.

Theory:

Kelvin’s double bridge is used for the measurement of low resistances(of the order less than

1).Wheatstone bridge is used for the measurement of medium resistances ranging from a few

ohms to several megaohms.

The lower limit for the measurement is set by the resistance of the connecting leads and

by contact resistance of the binding posts. The error caused by leads may be corrected fairly

well, but contact resistance presents a source of uncertainty that is difficult to overcome.

This is eliminated in the Kelvin’s double bridge by connecting the galvanometer to any

intermediate point of the known resistance(r) .Due to this, the resistance(r) is divided into two

parts i.e., second set of ratio arms(P,Q)

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Exp-4


Procedure:

1. Initially set the galvanometer to zero position by adjusting the knob provided on it

2. Connect the battery to the terminals provided on the kit

3. The wire whose resistance has to be measured is connected between the terminals C1 and C2

and short circuit the terminals P1 and C1, P2 and C2.

4. Initially keep the slide wire at zero ohm position and vary the ‘variable standard resistance’

and multiplier until the ‘G’ deflection is minimized.

5. By varying the slide wire slowly, adjust the ‘G’ position to zero in initial and final positions

of ‘G’ switch for a particular value of sensitivity. Note down the values of variable

resistance and slide wire resistance.

6. To eliminate errors, due to thermal e.m.f reverse the direction of the current using reversing

switch and take another reading as above. The mean of these two values will give the

correct value of unknown resistance

7. Calculate the unknown resistance at each step.

8. Repeat the process for different values of sensitivity.

Precautions:

1.The galvanometer should not be operated in short circuit position.

2.While changing the sensitivity of the galvanometer, it should be set in

lock position.

3. Slide wire is varied slowly by observing galvanometer reading.

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Observations:

s.no Multiplier Range

Maindial Reading

Slidewire Reading*0.001Ω

Resistance(Ω)

1.2.3.4.5.

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For the given wire

Rx= (Main dial reading +slide wire reading)*Multiplier range

Where Rx is the unknown resistance.

Result :

Review Questions:1. What is meant by bridge balance2. What is the basic difference between Wheatstone bridge and Kelvin Bridge3. What is the range of resistance is to be measure by using Kelvin’s Double Bridge4. Why Kelvin Bridge is proffered for measurement of low resistance compared with other

bridges

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Circuit diagram : CT TESTING BY SILSBEE’S METHOD

23 Dept. Of EEE

Exp-5


CT TESTING BY SILSBEE’S METHODAim:

To determine the ratio and phase angle errors of a current transformer by silsbee’s

method.

Apparatus:


1. Ammeter 0-1A

0-5A

MI

MI

01No

02 No

2. Wattmeter 300V,5A UPF 02No

3. C.T. testing kit ---- ---- 01No

5. Phase shifting

transformer

3-,440V,50Hz,500VA - 1No

6. Current transformer 50VA,660v,50Hz Standard 1 No

7. Connecting Wires ----- ----- As

required

Theory and formulae:

It is a comparison method. The ratio and phase angle error of test transformer X are determined

in terms of ratio and phase angle errors of a standard current transformer having same nominal

ratio. This is a deflection method.

W1 = 0 , W1q = VqISS cos 90=0

W2q = Vq . component of I in phase with Vq = Vq . Iq = Vq Isx sin(x - s)

W1p = Vp Iss cos 00 = Vp Iss

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Exp-5


W2P = VpIp = Vp [ Iss – Isx cos(x - s) ]

W2P = VP ISS - VP ISX

V = VP = Vq

W1 P = V ISS ; W2P = V. ISS - V. ISX

W2P = W1 P - V. ISX ( or ) V. ISX = W1 P - W2P

RX = (IP/ISX ) , RS = (IP/ISS ) ;

RX / RS = [ (V. ISS ) / (V. ISX ) ]

= W1 P / (W1 P - W2P)

(or) RX = [W1 P / (W1 P - W2P) ] * RS

RX = [1 + (W2P / W1 P ) ] * RS

tan (X - S ) = W2q / (W1 P - W2q) => X = [ W2q / (W1 P - W2q) ] + S

X = [ W2q / W1 P ] + S

Procedure:

1. Connect the circuit as per the circuit diagram.

2. The CT Testing kit secondary circuit is set to minimum value position.

3. Switch on the 1- mains supply and Also switch on 3- supply by using 3- auto

transformer and apply rated voltage.

4. Increase Ist (5A) by varying CT Testing kit in the primary circuit.

5. Adjust the phase shifting transformer such that WS is zero. Note down the readings of all the

meters. The readings of wattcmeters are noted down as W1p and W2p

6. Vary the phase shifting transformer such that WS is maximum. Note down the readings of all the

meters. The readings of wattmeter are noted down as W1q and W2q

7. calculate the ratio and phase angle errors.

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Tabular column:

S.No

IP

(A)ISS

(A)ISX

(A) WSWD1

(W)WD2

(W)ID

(A)

%Ratio error=

[(Kn - RX)/ RX

] * 100

%Phase angle error=

s+(WD2 /

V. ISS ) * (180 / )


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Standard CT values: Ratio error = 1% , Nominal ratio, Kn =

Phase angle error = , Voltage V =

Readings:

IP =

ID =

ISS =

ISX =

WS =

WD1 =

WD2 =

RS = (IP/ISS ) =

RX = RS [ 1 + (WD 1 / WS) ] =

% Ratio error = [(Kn - RX) / RX ] * 100 =

Phase angle error X = s+ [ (WD2 / V. ISS ) * (180 / ) ] =

Precautions :

1. Initially the Phase shifting transformer should be kept in ZPF position.

2. Initially 1- & 3- Autotransformers should be in minimum position.

3. Switch off the supply while reversing secondary terminals of current transformer.

4. Wattmeters WD1 and WD2 must be sensitive

Result:

The ratio and phase angle errors of the given current transformer are determined by using

Silsbee’s method.

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Circuit diagram: ANDERSON’S BRIDGE

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29 Dept. Of EEE


ANDERSON’S BRIDGE Aim :

To measure inductance and calculate Q-factor of an inductor using Anderson’s bridge.

Apparatus :

1. Andersons bridge kit - 1No.

2. Connecting wires

Theory:

Anderson’s bridge is a modification of Maxwell’s inductance-capacitance bridge. It is used for

measurement of self-inductance of coils with a very low value of Q. This cannot be done using

Maxwell’s bridge because balance has to be obtained using a fixed capacitor and varying the

resistances alternately. Alternate variation of the resistances leads to the disturbance of resistive

balance, and it moves to a new value giving slow convergence to balance.

By using an Anderson’s bridge, balance can be obtained easily with alternate

adjustments of the two variable resistances which are independent of each other.

Circuit diagram :

30 Dept. Of EEE

Exp-6


P=Non-inductive resistance

Q=Non-inductive resistance

R=Non-inductive resistance

S=Resistance connected in series with the self-inductor

r=Non-inductive resistance

C=Standard capacitor

Procedure :

For DC balance:

1. Connect from ‘DC supply’ terminals on the kit to ‘supply terminals’ on the kit.

2. Connect terminals marked “galvo” to the terminals marked “detector” and unknown

inductance to the terminals marked “unknown”.

3. Switch on mains supply provided on the kit board.

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4. Adjust the resistance dial R until galvanometer shows null deflection, to get fine balance

adjust resistance ‘S’.

5. Switch off mains supply on the kit board.

6. DC balance should not be disturbed, i.e R and S should not be varied.

For AC balance :

1. Connect the terminals marked “AC supply” to the terminals marked “supply” on the kit

board & head phones across the terminals marked “detector”.

2. Keep standard capacitor at 0.1f or at 0.2f.

3. Adjust r till sound in head phones becomes minimum.

4. This gives ac balance point.

5. Note down values of P, Q, R, S, r & C

6. Calculate inductance using L = RC (Q+2r)

7. Calculate the Q factor of the circuit using Q = L/(R-S)

8. Repeat the experiment for different unknown inductance values.

Observations :

Frequency of supply f = 1KHZ, = 2f = 6283.18 rad/s

S. no P() Q() R() S() r() C(F) L( mH)Q=

L/(R-S)

1


Non inductive resistance P=

Non inductive resistance Q=

Non inductive resistance R=

32 Dept. Of EEE


Resistance connected in series with self inductances S=

Non inductive resistance r=

Fixed standard capacitor C=

Self inductance L=RC(Q+2r)=

Quality factor Q=L(R-S)=

Result:

Self inductance and Q-factor are determined using Anderson’s bridge.

33 Dept. Of EEE

S.NO L (mH) Q

1


SCHERING BRIDGE Aim:

To measure capacitance of an unknown capacitor and to determine its dissipating factor using

Schering bridge.

Apparatus:

1.Schering bridge kit -1 no.

2. Head phones

3.Connecting wires

Theory:

Schering bridge is used for the measurements of capacitance and dissipating factor. From

the balance, the equation to obtain the value of capacitance is

C1=C2(R2/R1)

Since R1and C3 are fixed values, capacitance value can be obtained directly by varying R2.The

dissipation factor can be obtained directly from the equation

D1=C1r1

34 Dept. Of EEE


Circuit diagram:-

C1 = unknown capacitance

C2 = standard capacitance

C3= variable capacitance

R1 = non inductive resistance

R2 = variable non inductive resistance in parallel with C3

Procedure:-

1. Connect “AC supply” of 1k Hertz to the “supply” terminals and one unknown

capacitor on the kit to the “unknown” terminals.

2. Connect head phones to the “detector” terminals.

3. Set the standard capacitor switch to 0.01 mf position.

4. Set the decode capacitor dial c3 to any value (say at 500 pf)

5. Set decade resistance dials R1 at any value( say 153 )

35 Dept. Of EEE


6. Adjust R2 until the sound in headphones is minimized. If it is not minimized

appreciably, readjust R1 with alternative adjustment, then adjust R2 until no sound in

head phones is observed.

7. Note down the Values of R1, R2, C2, C3 and tabulate.

8. Repeat the above process for different values of unknown capacitance.

9. At each step find out the value of C1 .

Where C1 = C2.R2 / R1

And dissipation factor D = 2 fC1r1

where r1 = R1 x C3 / C2 and r1 is the resistance representing loss in C1

10. Repeat the same for another unknown value of capacitor.

Observations

S.no R1() R2() C2 (mF) C3(pF) C1 =

C2.R2 / R1

r1 =

R1.C3 / C2

D=

2fC1r1


Non-inductive resistance R1=

Variable non-inductive resistance R2=

Standard capacitance C2=

Variable capacitance C3=

Unknown capacitance C1= C2.(R2 / R1)=

Internal resistance of C1 = r1= R1.(C3 / C2)=

Dissipation factor=2fC1r1=

Result:-

Capacitance of given capacitor is

S.no C1 D r1

1.

36 Dept. Of EEE


MEASUREMENT OF 3-PHASE REACTIVE POWER USING SINGLE PHASE WATTMETER

Aim : To measure reactive power in a three-phase circuit using single phase wattmeter.

Apparatus :

Sl.No Apparatus Range Type Qty1 Voltmeter (0-600V) M I 1 no.2 Wattmeter 1,600V,10A,

LPFD.M.T 1 no.

3 Ammeter 0-10A, M I 1 no.4 3 autotransformer 415/0-470V,

10A, 8.14KVA1no.

5 3 loading inductor 10A, 415V 1 no.

Theory:

Reactive power measurement in 3- circuits using 1- wattmeter can be done only for balanced

3- loads. By connecting the current coil of the wattmeter in one line and the pressure coil across

the other two lines of 3- circuit, current through the current coil and voltage across the pressure

coil are determined. Now as the current in the current coil lags the voltage by an angle of 90,the

wattmeter reads a value proportional to the reactive power of the circuit.

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Exp-7


Circuit diagram :

Model graph:

38 Dept. Of EEE

IR

VY

BVY

VB

N

VR


Procedure :

1. Connect the circuit as per the circuit diagram.

2. Keep the variac of the auto-transformer in minimum position.

3. Close supply TPST switch and vary the auto-transformer slowly and apply rated voltage

i.e.230V.

4. Vary the load gradually and at different loads, note down readings of ammeter, Voltmeter

and Wattmeter.

5. Draw the phasor diagram.

Phasor Diagram :

Observations :

For ideal inductive load = 900 --> Sin= 1

39 Dept. Of EEE


S.

N

o

Voltage

VL volts

Current

IL amp

Wattmeter

reading

(W)

Reactive power

(measured

value)Qm=

Reactive power

(actualvalue)

Qa=

%erro

r =

(Qm-

Qa)/

Qa*1

00

1

2

Sample calculations :

Load voltage VL =415V Load current IL =1.0AWatt meter reading W =480W Reactive power (measured value) = = *480=831.38 VArReactive power (actual value) = = *415*1*1=718.8W

% error =

=[(831.38-718.8)/718.8]*100

=15.66%

Result:

Three phase reactive power is measured using single phase wattmeter

40 Dept. Of EEE


MEASUREMENT OF PARAMETERS OF A CHOKE COILUSING 3-VOLTMETER AND 3-AMMETER METHOD

Aim :

To measure parameters of a choke coil by 3 voltmeter method and 3 ammeter method.

Apparatus :


1 Choke coil 230 V, 0.39A Copper wound 1 No

2 Ammeter0-1/2 A M I 1 No

0-5 A M I 2 No

3 Voltmeter0-300V M I 2 No

0-75V M I 1 No

41 Phase auto

transformer230V/0-270V,10A 1 No

5 Rheostat 145 /2.8A Wire wound 1No

6 Rheostat 25 /5A Wire wound 1No

Theory & Formulae:

Inductances of about 50 to 500mH can be measured using this method. It is suitable for iron cored coils, since the full normal current can be passed through it during measurement. From the phasor diagram, VL

VS

2 = VR2 + VL

2 + 2 VR VL cos VS

cos = , Also cos =

where r is the resistance and L is the inductance of the coil. VR

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Exp-8


= L=

Circuit diagrams :

(i) 3 voltmeter method :

figure-1

(ii) 3 Ammeter method :

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figure-2

Procedure :

1. Make the connections as per the circuit shown in figure (1)

2. Initially keep the autotransformer in minimum position.

3. Close supply DPST switch.

4. Vary the applied voltage by varying the auto-transformer until rated current flows

through the choke coil.

5. Note down the readings of all the meters.

6. Make connections as per the circuit shown in figure(2).

7. Repeat steps 2,3,4 and 5.

8. Draw the phasor diagram for both the methods.

Observations :

3-Ammeter method:

S

.

N

o

Is

(A)

Ir

(A)

IL

(A)

V

(V)

Pf Cos = Resistance R

=

Inductive

reactance

XL=

Inducta

nce (H)

L =

XL/2L

3-Voltmeter method :

Sl

N

o

Vs

(V)

Vr

(V)

VL

(V)

I

(A)

Pf Cos = Resistance R

=

Inductive

reactance

XL =

Inducta

nce (H)

L =

XL/2L

43 Dept. Of EEE



(i) 3-Ammeter method:

cos = Is2 – IR

2 – IL2 / 2IRIL=

Resistance = (V / IL) cos=

Inductive reactance of the coil = XL= [V/IL] sin =

Inductance = [ XL/2f ] =

Where w is the frequency of supply in hertz = 50Hz

(i) 3-Voltmeter method:

Power Factor cos = Vs2 – VR

2 – VL2 / 2VRVL =

Resistance = (VL / I) Cos =

Inductive reactance of the coil = XL= [VL/I] sin =

Inductance = [ XL/2f ] =

Where f is the frequency of supply in hertz = 50Hz

Phasor diagrams :

3-voltmeter method: V1

V3

V2

3-Ammeter method :

I2

I3 I1

Precautions :

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1. Avoid loose connections

2. Keep autotransformer in minimum position before closing supply DPST.

3. Readings are to be taken without parallax error.

Results :

3-Ammeter method 3-Voltmeter Method

Resistance of the coil R

Inductance of the coil L

Power factor

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CALIBRATION OF LPF WATTMETERBY PHANTOM LOAD TESTING

Aim :

To calibrate the given LPF wattmeter using phantom load testing.

Apparatus :

S.No Apparatus Range Type Quantity1 1- Auto transformer 230V/0-270V, 10A 2 nos.2 Ammeter 0-10A MI 1 no.3 Voltmeter 0-300V MI 1 no.4 Voltmeter 0-150V MI 1 no.5 Wattmeter 300V, 10A LPF 1no.6 Inductive load 250V/1-15 A 1no.

Theory:

When the current rating of a meter is high, a test with ordinary loading arrangement would

involve a considerable wastage of power.

In order to avoid this, phantom or fictitious loading is done.

In phantom loading , pressure coil is connected across the supply voltage and current coil is

connected in series with low voltage source, but it can supply the rated current because

impedance will be low. Due to the above arrangement, the total power consumed for testing the

meter is low when compared with actual loading of wattmeter.

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Exp-9


Circuit diagram:

Model graph:

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IL(A)

% error


Procedure :

1) Connect the circuit as per the circuit diagram.

2) Initially keep the two autotransformers and inductive load in minimum position.

3) By varying the autotransformer2 in the pressure circuit, the voltmeter reading is adjusted to

rated value i.e 230V.

4) By slowly varying the autotransformer1 in current coil circuit, the voltmeter reading is

adjusted to 150V.

5) Apply inductive load in steps and tabulate the readings of all meters and calculate % error

at each step.

6) Plot the graph between IL and % error.

Observations:

cos = 0.2

S.NoVoltmeter

Reading(V)

Ammeter

Reading(A)

Wattmeter

Reading(Wr)

(W)

True Power

WT=VI cos

(W)

% Error =

Sample Calculations:

Voltage V =

Current IL=

Wattmeter reading (Wr) =

True power (WT) =

% Error = =

Precautions:

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1) Loose connections must be avoided.

2) Meter readings should not be exceeded beyond their ratings.

3) Apply the voltage slowly so that the current is within the limited range of ammeter.

Result:

The given LPF wattmeter is calibrated by phantom loading and a graph is drawn between IL

and %error.

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LINEAR VOLTAGE DIFFERENTIAL TRANSFORMER

Aim:

To study the operational characteristics of LVDT.

Apparatus:

LVDT TRAINER KIT

Theory:

Differential Transformer, based on a variable inductance principle, are also used to measure

displacement. The most popular variable-inductance transducer for linear displacement

measurement is the linear variable differential transformer (LVDT). The LVDT illustrated in the

fig. Consists of three symmetrically spaced coils wound on to an insulated bobbin. A magnetic

core, which moves through the bobbin without contact, provides a path for magnetic flux

linkages between coils. The position of the magnetic core controls the mutual between the center

or primary coil and with the two outside or secondary coils.

When an AC carrier excitation is applied to the primary coil, voltages are

induced in the two secondary coils that are wires in a series-opposing circuit. When the core is

centered between the secondary coils, the voltage induces between secondary coils are equal but

out of phase by 1800. The voltage in the two coil cancels and the output voltage will be zero.

When the core is moves from the center position, an inductance imbalance occurs between the

primary coils and the secondary coil and an output voltage develops. The output voltage is a

linear function of the core position as long as the motion of the core is with in the operating

range of the LVDT.

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Exp-10


Circuit diagram :

Model graph: out put voltage

Total linear voltage Core position IL(A)

Procedure :

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1. Connect the power supply chord at the real panel to the 230v 50Hz supply. Switch on the instrument by pressing down the toggle switch. The display glows to indicate the instrument is ON.

2. Allow the instrument is ON position for 10 minutes for initial warm up.

3. Rotate the micrometer till it reads “20.0”.

4. Adjust the CAL potentiometer at the front panel so that the display reads “10.00”.

5. Rotate the core of micrometer till the micrometer reads ’10.00’ and adjust the zero pot till the display reads “00.0”.

6. Rotate back the micrometer core up to 20.0 and adjust once again CAL pot till the display reads 10.0, Now the instrument is calibrated for 1 m10 mm range. As the core of LVDT moves the display reads the displacement in mm.

7. Rotate the core of the micrometer in steps of 1 or 2mm and tabulate the readings. The micrometer will show the exact displacement given to the LVDT core, the display will read the displacement sensed by the LVDT. Tabulate the readings.

Observations :

Micro meter reading (mm) Display (mm) Error Voltage

(mv)

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Graph:

Plot the graph between output voltage Vs Core position

Result :

The operation of LVDT is observed and graph between output voltage and core position is

plotted and the curve is linear.

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STRAIN GUAGE

Aim:

To measure the strain by using the strain guage.

Apparatus:

Strain measurement trainer - 1

Strain guage cantilever beam - 1

Weights - 1000g

Theory :

Strain guage is a transducer which converts the applied load strain in to the change

in resistance of the materials. It is connected as one of the arms of the wheat stone

bridge. According to change in resistance of material used in strain guage breidge

unbalanced voltage will be appeared and this voltage is calibrated in to the values

of strain.

In tail type strain guage, nichrome, which has low temperature

coefficient, is used. This wire is designed in such a way that its thickness will be

0.005mm. It is connected on paper bakelite sheet of thickness 0.05mm and there it

is attached to the cantilever beam with adhesive material. Here cantilever beam is

tee material whose strain is to be found. The nichrome is designed in such a way

that its natural strain should be zero.

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Exp-11


Circuit diagram :

supply

Procedure:

1. Check the connections made and switch ON the instrument by toggle.

2. Allow the instrument in one position for 10 min for initial warmup.

3. Select full or (short) half period configuration from the selection switch on

the panel.

4. Adjust the zero position potentio meter on the panel till the display reads

“Zero”.

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5. Apply 1 kg load on the cantilever beam and adjust the CAL pot till the

display reads 377 Micro strain.

6. Remove the weights the display should come to “Zero”. In case of any

variations adjust zero again and repeat the procedure again. Now the

instrument is calibrated to read s.

7. Apply the load on the sensor using loading arrangement provided in steps of

100g up to 1kg.

8. Instrumental displays exact micro strain by the cantilever beam.

9. Note down the readings in the tabular form. The % error is calculated by

comparing the theoretical values.

Observations :

Weight (Kg)Actual value micro strain

(/m)

Theoretical % Error

SPECIMEN CALCULATIONS:

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P Load applied in kg

L Efficient length of beam in com (22 cm)

B Width of bean (1.8 cm)

T thickness of beam (0.25 cm)

micro strain

young’s modulus (2x106)

% error = (practical – theoretical ) / Theoretical x 100

Precautions:

Avoid loose connections

Result:

Strain is measured by using strain guage by applying different loads.

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DIELECTRIC OIL TESTING USING H.T.TESTING KIT

Aim:

To determine break over voltage of given dielectric oil, using H.T testing kit.

Apparatus: 1. Dielectric oil testing kit – 1No.

2. Dielectric oil.

Theory:

The dielectric strength of an oil is the potential at which it starts behaving as a conducting

medium. In the HT testing kit, the oil to be tested is placed in an acrylic box consisting of two

metal electrodes. By varying the distance between electrodes and by applying high voltage

across the electrodes, the break over voltage of the oil is determined.

Dielectric strength of oil = (kV/cm)

Dielectric strength of oil decreases with moisture.

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Exp-12


Circuit Diagram:

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Procedure:

1. Take the oil cup and adjust the gap between the electrodes with the help of gauge.

2. Fill up oil test cup with oil to be tested, close it with the lid and place it on the HT horns

under the hinged acrylic cover and close the acrylic cover properly.

3. Keep the variac in minimum position.

4. Connect the mains lead to the 220V, single phase AC 50Hz supply.

5. Switch ON the power supply by operating the toggle switch, then yellow neon bulb glows

indicating that the HT kit is switched off.

6. Press the HT ‘ON push’ switch. The red Neon lamp will start glowing and the HT

transformer circuit will be energized, the green neon bulb start glowing.

7. In case the red indication does not glow, check up the hinged acrylic cover is properly closed

and the variac knob is fully rotated in the anticlockwise direction for ‘0’ start.

8. Now start rotating the variac knob slowly in the clockwise direction till the flash over occurs

across electrodes in the oil test cup. The speed of ratio should be such that the voltage rises

at the rate of 2 kv/sec.

9. As soon as flash over occurs, the supply of the high voltage transformers, will be cut off and

the voltage pointer will also stop indications the flash over level.

Note down the reading of voltmeter and distance between the electrodes.

10. To repeat test on the sample, switch OFF the mains supply and stir the test pot with the help

of a clean rod and let it cool for sometime and close the acrylic cover properly.

11. Repeat the steps 2 to 10.

12. Switch OFF the mains supply after the tests are over.

Observations:

S.NO Distance between the electrodes (Cm)

Break over voltage of oil (KV)

Dielectric strength of oil =

(kV/cm)1

Precautions:

1.The lid of the HT testing kit should be closed properly.

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2. The variac should be kept in minimum position initially.

3. Oil cup must be kept on the HT testing horns properly.

Result :

The break over voltage of the dielectric oil is determined by using HT testing kit

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6. Elec.measure.lab Manual 4EEE

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Transcript of 6. Elec.measure.lab Manual 4EEE