G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR Department …ghrce.raisoni.net/download/EMMI_manual.pdf · G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 3 ... Switch on the supply and note

DEPARTMENT OF ELECTRICAL ENGINEERING IIIRDSEMESTER ELECTRICAL

G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 1

G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR

Department Of Electrical Engineering

IIIRD

Sem Electrical Engg.

Electrical Measurement & Measuring Instruments Lab

________________________________________________________________________

INDEX

Sr.

No.

Name of Experiment Page No.

1 Measurement of medium resistance by using

Voltmeter Ammeter method.

02

2 Measurement of medium resistance by using

Wheatstone’s bridge.

04

3 Measurement of high resistance by using loss of

charge method.

07

4 Measurement of low resistance by using Kelvin’s

double bridge.

09

5 Measurement of unknown inductance by using

Hay’s bridge.

12


Owen’s bridge.

15


Maxwell bridge.

17

8 Measurement of unknown capacitance by Desauty

bridge.

20

9 Measurement of unknown capacitance by Schering

bridge.

22

10 Measurement of 3-phase power by the one-

watt meter method.

24

11 Measurement of 3-phase power by the two-watt

meter method.

26

12 Measurement of Reactive power in 3- phase circuit

by Wattmeter method.

28


1


Experiment No-01

Aim:- Measurement of medium resistance by the Voltmeter , Ammeter method.

Apparatus:- DC ammeter(0-50mA)

DC Voltmeter (0-50V)

Dc power supply (0-30V)

Variable Resistance -100 ohm.

Connecting wires.

Circuit Diagram:-

V

A

V

A

(0-30v)

(0-50mA)

R

+ _

(0-30v)

(0-50mA)

(0-50v)R

+ --

+

-(0-50V)

100 Ohm

100Ohm

Fig.(1) Fig. (2)

Theory: -

Two types of the connections are done in this method. Ammeter voltmeter

method is shown in the figure (2) voltmeter and ammeter are connected in series, where

ammeter measures the total current flowing through the circuit and voltmeter measures

the voltage across the unknown resistance .The voltmeter should have ideally infinite

resistance and ammeter should have ideally zero resistance so that it will measure total

current flowing through the unknown resistance. But practically it is not possible and

measured value Rm of the resistance is the sum of resistance of ammeter and actual

resistance.

Rm =R1+Ra

Where

R1=Actual resistance.

Ra=Resistance of the ammeter.

It is clear from the expression that the value of measured resistance is equal to actual

resistance when ammeter has zero resistance.


1


Observation Table:-

For CASE 1 – voltmeter Ammeter Method

Voltage (volt) Current (Amp) Resistance

(calculated)

Resistance

(measured)

For CASE 2 – Ammeter voltmeter Method

Voltage (volt) Current (Amp) Resistance

(calculated)

Resistance

(measured)

Procedure:-

1) Make the connections as per circuit diagram.

2) Switch on the supply and note down the readings of ammeter and voltmeter.

3) Calculate the value of the unknown resistance by ohms low.

4) Perform the procedure for the other case similarly.

Result: - Hence the measured value of the unknown resistance is

found to be _________.

Viva Questions:-

1) What are the other methods of measurement of medium resistance?

2) What are the disadvantages of this method?


1


Experiment No.-02

Aim: - Measurement of the medium resistance by using wheatstone bridge.

Apparatus: -

Power supply (0-32V D.C)

Resistor: - R1=1KΏ, RX=1KΏ, R3=1KΏ, R4=10KΏ.

Unknown resistor=100Ώ,

Wheatstone bridge kit.

Digital multimeter-1no,

Patch chords.

Circuit Diagram:-

G

R3R1

R4Rx

0-32v

ab

c

d

I1

I2

I3

I4


1


Theory-

Wheat stones bridge is very important device used in the measurement of medium

resistances. It is an accurate and reliable instrument .The wheat stone bridge is an

instrument based on the principle of null indication and comparison measurements .

The basic circuit of a wheat stone bridge is shown in fig . it has four resistive

arms, consisting of resistances R1,RX,R3 and R4 together with a source of emf and a null

detector , usually a galvanometer G or other sensitive current meter is used. The bridge is

said to be balanced when there is no current through the galvanometer or when the

potential difference across the galvanometer is zero. This occurs when the voltage from

point ‘a’ to point ‘d’ equals the voltage from point ‘d’ to point ‘b’ or by referring to other

battery terminal, when the voltage from point ‘a’ to point ‘c’ equals the voltage from

point ‘c’ to point ‘b’.

For bridge balance;

I1=I3= E/(R1+R3) (1)

I2=I4=E/(RX+R4) (2)

E=emf of battery.

Combining equ (1) and (2) we get

RX*R3=R1*R4

OR

RX=(R1*R4)/R3

Where RX is the unknown resistance, R1, R3 and R4 are called the ratio arms.

Observation Table: -

Ratio Arm

Resistor

Std. Arm

Resistor

Measured Rx Calculated

Rx

R1 R3 R4

Procedure: -

1) Connect the patch chords as per the circuit diagram.

2) Note the resistance of R1,R4 and R3 using multimeter.


1


3) Switch on the power supply and adjust the resistance R4 such that galvanometer

shows the zero deflection.

4) Disconnect the supply & measure the value of RX.

5) Now calculate the value of unknown Resistor R, Using formula

Rx=(R1*R4)/R3.

Result:- Unknown Resistance found to be __________Ω.

Viva Questions: -

1) What are the other methods used for measurement of medium resistance?

2) Why we use this method for measurement of medium resistance?


1


Experiment No-03

Aim:- Measurement of the high resistance by using loss of charge method.

Apparatus:-

Multimeter –1no

Voltmeter –(0-30v)-1no

Capacitor-10uf-1no

Resister-100K-1no

Power supply-(0-30v)-1no

.

Circuit Diagram:-

V

(0-30V)

S1

S2

C=10uf

R

(0-30V)

Theory:-

In this method the resistance which is measured is connected in parallel with

the capacitor C and the electronic voltmeter V. The capacitor is the charged up to some

suitable voltage by means of the battery having the voltage V and is then allowed to

discharge through the resistance.

The terminal voltage is observed over the considerable period of the time

during discharge.

Let,

V=initial voltage on the charged capacitor.

v=instantaneous discharging voltage.


1


t=the charging time of the capacitor.

V=v exp (-t/C*R)

or

V/v=exp (-t/C*R)

or

Insulation resistance

R=t/(Clog V/v)

=0.4343*t/(C log10 V/v)

R’=0.4343*t/(C log10 V/v)

Where R’ is a resistance of R1 & R in parallel

R1 represents the leakage Resistance &

R is the unknown resistor.

The test is then repeated with the unknown resistance R disconnected & the

capacitor discharging through R1

R’=(R*R1)/(R+R1)

Observation Table:-

S.

NO.

Time (sec) V

(withoutR)

V(with R) Log10(V/v)

without R

Log10(V/v)

with R

Procedure:- 1) Connections is make as per the circuit diagram.

2) Close the switch S1 and keep S2 open till the capacitor charge upto V volts.

3) Now open the switch S1 & allow the capacitor to discharge by its Owen

leakage resistance

4) Note down the reading of the voltmeter verses equal interval of the time.

5) Calculate the unknown resistance using the formula.

6) Now close the switch S1 & S2 till the capacitor charge upto V volts.

7)Now open the switch S1 & allow the capacitor to discharge through the unknown

Resistance.

Result:- Unknown value of high resistance is calculated by using loss of charge

method.

Viva Questions:- 1) Why this method is called as loss of charge method?

2)What kind of errors occurs while performing this practical?


1


Experiment No:-04

Aim: - Measurement of the low resistance by using Kelvin’s Double bridge .

Apparatus: - Regulated dc supply-1no

Standard resistance coil-1no

Kelvin’s double bridge kit.

Digital multimeter-1no,

Patch chords.

Components Used: -

Q=q=10KΩ, RX1 =5Ω, RX2=10Ω, P=p=100Ω,

RB=11KΩ,, S=Pot of 1kΩ.

Circuit Diagram: -

GP Q

pq

r

E

am n

SR

R

b

c

d

Rb


1


Theory: - Kelvin’s bridge is a modification of wheatstone bridge and always used in

measurement of low resistance. It uses two sets of ratio arms and the four terminal

resistances for the low resistance. As shown in above fig. The first set of ratio P and Q &

second set of ratio arms are p and q are used to connect to the galvanometer to a pt ‘d’ at

an Approx. potential between points ‘m’ and ‘n’ to eliminate the effects of connecting

lead of resistance ‘r’ between the known std. resistance ‘s’ and unknown resistance ‘R’.

The ratio P/Q is made equal to p/q. under balanced condition there is no current flowing

through galvanometer which means voltage drop between a and b, Eab equal to the

voltage drop between a and d, Eamd.

Now

Eab = Eamd

Eab=(P*Eac/P+Q); Eac=I[R+S+[(p+q)r/p+q+r]] ---------(1)

Eamd= I[R+ p/p+q[ (p+q)r/p+q+r]]

=I[R+p*r/(p+q+r)] ----------------------- (2)

For zero deflection->

Eab=Eamd

[ P/P+Q]I[R+S+(p+q)r/p+q+r]=I[R+pr/p+q+r] --3)

Now, if

P/Q=p/q

Then equa… (3) becomes

R=P/Q=S -(4)

Equation (4) is the usual working equation. For the Kelvin’s Double Bridge .It indicates

the resistance of connecting lead r. It has no effect on measurement provided that the two

sets of ratio arms have equal ratios. Equation (3) is useful however as it shows the error

that is introduced in case the ratios are not exactly equal. It indicates that it is desirable to

keep r as small as possible in order to minimize the error in case there is a diff. between

the ratio P/Q and p/q.

R=(P*S)/Q

Observation Table: -

P (ratio arm

resistor)

Q (ratio arm

resistor)

Standard resistor

S

R measured

value

Calculated

R


1


Procedure: -

1) The circuit configuration on the panel is studied.

2) The unknown resistance is connected as shown.

3) The value of P,Q was selected such that

P/Q=p/q

4) S was adjusted for proper balance i.e., galvanometer to shows zero deflection.

5) The value of Unknown Resistance R=(P*S/Q) was calculated.

Precautions-

1) Check all the connections before turning ON the power supply.

2) Note the readings accurately.

Result- The observed value of unknown resistance is __________.

Viva Questions:

1) Why this method is called as double bridge method?

2) Can this method be beneficial for measurement of low value of

Resistance or not?


1


Experiment No :-5

Aim: - Measurement of the unknown Inductance by using Hay’s bridge.

Apparatus:- Multimeter

LCR meter

Hay’s bridge kit,

Patch cords.

Components Used: -

R2=100Ω, R3= 4.7KΩ, R4= 100Ω, C4= 1uf

Circuit Diagram:-

G

R3

A

D

B

C

L1

R1

R4

R2

C4

I1

I2

I1

I2

E

E1 E3

E2E4


1


Observation:-

R2 = __________.

C4 = __________. For Unknown Inductance Lx1:-

Calculated - Lx1 = (R2R3C4) /(1+ω2R4

2C4

2).

Lx1 =________mH.

Measured - Lx1 = ________mH.

Quality factor (Q)=1/ωR4C4.

For Unknown Inductance Lx2:

Calculated - Lx2 = (R2R3C4) /(1+ω2R4

2C4

2).

Lx2 =________mH.


Quality factor (Q)=ωR4C4.

Theory:-

The hays bridge is the modification of the Maxwell Bridge. This bridge uses a

resistance in series with the standard capacitor. The bridge has four resistive arms in

which the arms one is consists of the resister R1, Lx .The arm 2 is consists of the variable

resistance R3.The low value of the resistance is obtain by the low resistive arms of the

bridge. The value of R4 and C4 is the standard value of the capacitor and resistance.

By using the unknown inductance having a resistanceR1. R2, R3,R4-is the known

non-inductive resistance and C4 is standard value of the capacitor. The unknown value of

inductance and Quality factor of the Bridge is obtained by formula.

Lx = (R2R3C4) /(1+ω2R4

2C4

2)

Quality factor (Q)=(1/ωR4C4)

For value of Q greater 10, the term (1/Q)2

will be smaller & hence neglected. Therefore Lx= R2*R3*C4

Basic AC bridges consist of four arms, source excitation and a balanced detector.

Commonly used detectors for AC bridges are:

(1) Head phones

(2) Vibration galvanometers

(3) Tunable amplifier detectors

Vibration galvanometer is extremely useful at power and low audio

frequency ranges. Vibration galvanometers are manufactured to work at various

frequency ranging from 5 KHZ to 1 KHZ. But one most commonly used between


1


200HZ.

Advantage-1) This Bridge gives very simple expression for unknown for High Q coil.

2) This bridge also gives a simple expression for Q factor.

Disadvantage- 1) The hays bridge is suited for the measurement of the High Q inductor.

2) It is used to find the inductor having the q value of the smaller then 10.

Procedure:-

1) Study the circuit provided on the front panel of the kit.

2) Connect unknown inductance LX1 in the circuit. Make all connections to

complete the bridge.

3) Put the supply ON

4) Set the null point of galvanometer by adjusting variable resistance R3.

5) Note value of R2, R3, and C4 by removing connection by patch cords.

6) Calculate theoretical value of LX1 using L=R2R3C4

7) Measure value of LX2 by LCR meter and compare it.

8) Repeat process for LX2.

Result:- The unknown inductance is measured using Hay’s bridge and is found to

be___

Viva Questions:-

1) What is the Q factor of the coil?

2) Which bridges are used for measurement of inductances?


1


Experiment No :-6

Aim:- Measurement of the unknown inductance by using OWEN’S bridge method

Apparatus:-

Digital multimeter, Patch chords.

Components used:

R3=1K(pot), C4=1uF, R2=1K(pot),

L1= L2= ------

Galvanometer, 12VAC source.

Circuit Diagram:-

GA

D

B

C

R1L1 R3

C4R2

C2

Theory:-

Bridge are used for the accurate measurement of electrical quantities viz;

esistance, Capacitance, Inductance, Storage Factor, Loss factor etc. Depending upon the

excitations used , the bridge are classified as AC bridges & DC bridges.


1


Owen’s – Inductance Capacitance Bridge comes under category of AC bridges and it is

used for measurement of an Inductance in terms of capacitance. General form of AC

bridges consists of four arms of impedances & AC excitation.

Let

L1= unknown self inductance of resistance

R2=variable non- inductive resistance

R3= fixed non- inductive resistance

C2=variable standard capacitor

C4=fixed standard capacitor

And

At balance condition,

(R1+jwL1) (1/jwC4)=(R2+1/jwC2)*R3

Separating the real & imaginary terms, we obtain:

L1=R2R3C4

&

R1=R3*C4/C2

Procedure:-

1. Study the circuit provided on the front panel of the kit.

2. Connect unknown inductance LX1 OR LX2 by patch chords

3. Switch ON power supply

4. By varying the pot R2 & R9 make bridge balance

5. Switch off the power supply, disconnect the patch chords & measure the value of

R3& R2

6. Find the value of unknown inductance by using formula

7. L1=R2R3C4

Observations: Measured value of L Calculated value of L

Result:- Using Owen’s Bridge we can calculate the value of unknown inductance &

we found there is short difference between theoretical and practical value of L.

VIVA QUESTIONS:-

1) Draw the Phaser diagram of OWE’N Bridge?

2) What are the balancing conditions of any a.c. bridge?


1


Experiment no 7

Aim:- Measurement of the unknown inductance by using Maxwell’s bridge.

Apparatus:- Digital multimeter,

Patch chords.

R2=100Ω, R4=1KΩ, R3=4.7KΩ,

C4=1µf, LX2=318mH, LX1=73 mH

Circuit Diagram:-

G

R3

A

D

B

C

L1

R1

R2 C4

R4

E

I1

I3

I2

I4

Theory:-

The Maxwell

’s bridge is used to measured inductance by comparison

with a standard variable capacitance. One of the ratio arms has a résistance and

the capacitance in the parallel.

In this bridge at the balance condition there is no current flow in the


1


galvanometer.

At balanced condition,

(R1+jwL1) (R4/1+jwC4R4) = R2*R3

By separating the real and imaginary term, the unknown value of the

resistor (R1) and the unknown value of the capacitor (C1) has given below.

R1= R2*R3/R4

L1= (R2*R3*C4)

Observation:-

R2 = __________.

C4 = __________. For Unknown Inductance Lx1:-

Calculated - Lx1 = (R2R3C4)

Lx1 =________mH.


Quality factor (Q)=ωR4C4

For Unknown Inductance Lx2:

Calculated - Lx2 = (R2R3C4)

Lx2 =________mH.


Advantage-

1) This bridge is very useful for measurement of a wide range of a

inductance at the power and audio frequencies.

2) The frequency does not appear in any of the two equations.

Disadvantage-

1) This bridge requires a variable standard capacitor, which may be

Vary expensive if the calibration to a high degree of the accuracy.

2) The bridge is limited the measure the low Q value.


1


Procedure:-

1) Study circuit on kit from panel.

2) Connect unknown inductance LX1 in circuit. Make all possible connections to

complete the network. Switch the supply on.

3) Set null point of galvanometer by adjusting variable resistance R3

4) Note values of R2, R3, C4 by removing their connections. Calculate theoretical

values of LX using L1=R2R3C4.

5) Measure actual value of LX1 using LCR meter. Compare this value with

calculated. also calculate Q factor by using above equation.

Result:- Unknown inductance measured using Maxwell’s bridge is found to be

LX1=____ , & LX2 =__---------.

___________

Viva Questions:-

1) What are the limitations of this bridge?

2) What is the difference between this method and Hays bridge method?


1


Experiment no-08

Aim:- Measurement of the unknown capacitance by using De Sauty’s bridge.

Apparatus:-

De Sauty’s bridge kit

Digital multimeter,

Patch chords,

R2=100Ω, R4=10KΩ, R3=10KΩ,

C2=1µf, CX1= 1µf, CX2=4.7µf

Circuit Diagram:-

G

R3

A

D

B

C

R4

C1

C2

E

I1

I3

I2

I4

Theory:- Bridge are used for the accurate measurement of electrical quantities viz;

Resistance, Capacitance, Inductance, Storage Factor, Loss factor etc. Depending upon the

excitations used , the bridge are classified as AC bridges & DC bridges.

De-sauty Bridge comes under category of AC bridges and it is used for measurement of

capacitance. General form of AC bridges consists of four arms of impedances & AC


1


excitation.

At balanced condition,

(1/jwC1) * R4 = (1/jwC2)*R3

Separating real & imaginary part,

C1= C2*(R4/R3)

Resistance

R3

Calculated

C1=C2*R4/R3

Measured

C1

Procedure: -

1) Study the circuit provided on the front panel on the kit.

2) Connect the unknown capacitance of the position given.

3) Set the null point of galvanometer by adjusting the variable resistor R3.

4) Calculate the value of unknown capacitance by formula given

Result: -The values of unknown capacitance is measured using De Sauty’s bridge is

found to be C1= ______uF.

VIVA questions:

i) What are the limitation of this bridge?

ii) Can Dissipation factor be measured by this

bridge?


1


Experiment No-09

Aim:- Measurement of the unknown capacitance using schering bridge.

Apparatus:- Schearing bridge kit

digital multimeter,

patch chords,

Circuit Diagram:-

G

R3

A

D

B

C

R1

C1

C2

E

I1

I2

I3

IC4

IR4

C4

R4

Theory:- The schering bridge is one of the most important ac bridge used extensively for the

measurement of capacitance.

In schering bridge the arm 1 contains a series combination of the resistor and the

capacitor and standard arm contain only one capacitor. The standard capacitor is usually a

standard high quality mica capacitor.

In the balance condition of the bridge the sum of the phase angles of the arms 1


1


and 4 is equal the sum of the phase angle of arms 2 and 3.At the balance condition there

is no current flow in the galvanometer.

At balance condition,

[R1+(1/jωC1)] * [R4/(1+jωC4R4)] =R3/( jωC2)

After solving & equating real & imaginary parts, we get

R1= C4*R3/C2.

C1= R4*C2/R3

Observation:-

R4 = __________.

C2 = __________. For Unknown Capacitor C1:-

Calculated - C1 = (R4*C2/R3)

C1 =________.

Measured - C1 = ________.

Dissipation factor (D.f)=ωR4C4

Procedure: - 5) Study the circuit provided on the front panel on the kit.

6) Connect the unknown capacitance of the position given.

7) Set the null point of galvanometer by adjusting the variable resistor R4

8) Calculate the value of unknown capacitance by formula given

Result: -The values of unknown capacitance is found to be C1= ______uF.

Viva Questions-

1) What is the Q factor of the coil?

2) Which bridges are used for measurement of inductance


1


Experiment no-10

Aim-. Measurement of the 3phase power by the one watt meter method.

Apparatus:-

Three phase variable load.

Wattmeter (0-5A)-, 300v-1no

Ammeter (0-10A)-1no

Voltmeter (0-600v) , (0-300v)-2no

Three phase variac.

Circuit Diagram:-

M L

C V

R

Y

B

N

V

A

R

RR

(0-5A)

(0-300v)

(0-5A,300V)

(100 Ohm,5A)

(100 Ohm,5A)

(100 Ohm,5A)

3-

Phase,440V,Supply

Theory:- In this method the total power consumed is calculated by using one wattmeter .

This method is used only if the load is balanced. Current coil is connected in series with

one phase ‘R’ & pressure coil of the wattmeter is connected between ‘R’ phase & Neutral

of the 3- phase load.

Here-V1=V2=V3=V (line voltage)

& I1=I2=I3=Line


1


&V13-V12=V23

3- phase power = √3* V1*I1*cos θ (The load is resistive so cos θ=1)

= 3* Wattmeter Reading

Observation Table:-

Sr no Voltage Current Power 3 phase watt

Procedure:- 1) Make the arrangement as per the circuit diagram.

2) Increase the dimmerstat reading

3) Note the corresponding values of voltmeter ,ammeter and wattmeter.

4) Take consequent 3 readings.

Result:- The 3phase Power by one watt meter method is ________Watts.

Viva Questions:- 1) Explain in short how the wattmeter is connected in the circuit to .

Measure the power delivered to the Load and the Line.

2) Explain How the Resistive Power is measured by the Wattmeter

Method.


1


Experiment no- 11

Aim:- Measurement of the 3phase power by the two watt meter method.

Apparatus:- Ammeter (0-5A)- 1no.

Voltmeter (0-600v) –1no

Rheostat (100 ohm-5A)-3no

Wattmeter (300V-5A) -2no.

3-PHASE dimmerstat

connecting wires.

Circuit Diagram-

M L

C V

R

Y

B

N

V

A

RR

(0-5A)

(0-300v)100ohm

5A

100ohm

5A

100ohm

5A

R

300v,5A

300V,5A

3-phase,440V,Supply

C V

ML


1


Theory:- Here two wattmeter are connected to measure power in 3 phase circuit.

Let V1,V2,V3 be rms values of phase voltage and

i1,i2,i3 be rms values of line current

Phase voltage=V1=V2=V3=V

Line voltage=V13=V23=V12=√3V

Power factor=cos φ

Reading of P1 wattmeter =V13*I1cos(30-φ)

= √3VIcos(30-φ)

Reading of P2 wattmeter= V23*I2cos(30+φ)

= √3VI(30+φ)

Sum of two wattmeter readings=P=P1+P2

= √3VI[cos( 30-φ)- cos(30+φ)]

=3VIcosφ

Total Power consumed by the load P= W1+W2.

Observation Table:-

Sr no Voltage Current Power 3 phase watt

W1 W2 W1+W2

Procedure:- 1) Make the arrangement as per the circuit diagram.

2) Adjust supply voltage to 100v. Take the reading when the wattmeter is connected

between the R and Y phase.

3) Repeat previous for the different reading of the voltage.

4) Also note the corresponding current.

5) Now connect wattmeter between R and B phase .

6) Repeat the previous procedure which will give by the total power consumed by

the load.

Result:- Hence it is found that the calculated power and the measured power by the two

wattmeter method is nearly same.

Viva Questions:- 1) Explain the working of 3phase wattmeter?

2) Explain in short how the wattmeter is connected in the circuit to measure

the power delivered to the Load?


1


Experiment no- 12

Aim:- Measurement of the 3phase Reactive power by the one watt meter method.

Apparatus:- Ammeter (0-5A)- 1no.

Voltmeter (0-600v) –1no

Rheostat (100-5A)-3no

3- phase variable reactive load.

3-PHASE dimmerstat

connecting wires.

Circuit Diagram-

M L

C V

R

Y

B

N

V

A

(0-5A)

(0-300v)

(0-5A,300V)

3-phase,

440V,Supply

3-Phase,5A

Inductive

Load

THEORY:- The reactive power in the ckt. Is Q = Visinθ. It is often convenient &

essential that reactive power be measured in the given ckt. for load connections & it also

serves the check on power factor measerement.

Tanθ = REACTIVE POWER / ACTIVE POWER

Reactive power in a 3-phase balance ckt. is measured by connecting current coil of

wattmeter in one line. & pressure coil across other two lines as shown in above fig.


1


Reading of wattmeter = V23* I1 Cos(Φ +90)

= -√3V I sin Φ

Therefore = V23*I1*Sin Φ.

Total reactive power of 3- phase ckt.

Q= 3VISin Φ = √3 * wattmeter Reading

Observation Table:-

Sr. no VL IL Power

(W)

3-phase Q

=√3*Wattmeter

Reading

Procedure:- 2. Make the arrangement as per the circuit diagram

3. Adjust the variac to obtain line voltage.

4. Vary the load in such a way that current through phase is equal.

5. Note down the readings.

Result:- The reactive power found to be =______.

VIVA QUESTION:-

1) What are the other methods for measurement of Reactive Power?

2) What is the Difference between Active & Reactive Power?

Documents

G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR Department …ghrce.raisoni.net/download/EMMI_manual.pdf · G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 3 ... Switch on the supply and note