6. POWER MEASUREMENT BY TWO WATTMETER METHOD

```FR. CONCEICAO RODRIGUES COLLEGE OF ENGINEERING
Department of Electronics Engineering
6. POWER MEASUREMENT BY TWO WATTMETER METHOD
1.
Course, Subject & Experiment Details
LC RESONANCEEstimated Time
2014 – 2015
Course & Semester
Chapter No.
Experiment Type
F.E. (ALL) – Sem. I
3
Hardware Performance
2.
.
Subject Name
Chapter Title
Subject Code
Experiment No.6 – 02 Hours
Basic Electrical and Electronics
Engineering Laboratory
Three phase circuits
FE 105
Aim & Objective of Experiment
To measure the power in 3 -phase balanced star and delta connected load and to determine the
power factor.
3.
Expected Outcome of Experiment
This experiment helps students to understand power measurement in 3-phase circuits and to
determine the power factor of the given load.
4.Brief Theoretical Description
Two wattmeter method is the most suitable method for the power measurement in 3Φ circuits. It is
applicable for balanced as well as unbalanced 3Φ load . Power factor can also be determined by this
method.
IN STAR CONNECTION
iR + iY + iB = 0
Where iR, iY, iB are instantaneous currents.
iB = -(iR + iY).
Instantaneous power
P = iRvR + iYvY + iBvB
= iRvR + iYvY - (iR + iY)vB.
= iR(vR – vB) + iY(vY – vB).
= iRvRB + iYvYB.
= W1 + W2.
Basic Electrical and Electronics Laboratory- Experiment 6
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FR. CONCEICAO RODRIGUES COLLEGE OF ENGINEERING
Department of Electronics Engineering
IN DELTA CONNECTION
vRY + vYB + vBR = 0
Where vRY, vYB, vBR are instantaneous voltages.
VRY = -( vYB + vBR).
The instantaneous power
P = iRvBR + iYvRY + iBvYB
= iRvBR - iY( vYB + vBR) + iBvYB
= (iR – iB)vBR + (iB – iY)vYB.
= W1 + W2.
Thus in both star and delta circuits, the sum of the two wattmeter readings w1 and w2 is equal to
the total power consumed in the circuit.
Power factor angle is given by formula Φ = tan-1 [√3(w2 – w1)]
(w2 + w1)
FORMULA:
P = √3VLILcos Φ
Φ=tan-1[√3(w2 – w1)]
(w2 + w1)
Basic Electrical and Electronics Laboratory- Experiment 6
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FR. CONCEICAO RODRIGUES COLLEGE OF ENGINEERING
Department of Electronics Engineering
5.r
Circuit Diagram & Experimental Setup
Figure No.1
Figure No.2
Basic Electrical and Electronics Laboratory- Experiment 6
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FR. CONCEICAO RODRIGUES COLLEGE OF ENGINEERING
Department of Electronics Engineering
6.
Apparatus Required
1.Wattmeter
2.
3.
4.
5.
7.
250 V, 5A
Ammeter
0 – 2.5 A
Voltmeter
0 – 500 V
Connecting wires.
M/I Type
M/I type
2 Nos
1Nos
Experimental Procedure
1. Connect the circuit as shown in the Figure No1 to measure the power in star
2. Check the circuit and switch on 3Φ supply switch.
3. Take the readings of the ammeters, voltmeters and wattmeters connected in
the circuit.
4. Total power measured is given by (w1 + w2) watts.
5. Calculate the power by formula P = √3VLILcosΦ
6. Compare the two results.
7. Repeat the experiment for different loads.
8. Connect the delta as shown in the Figure No 2. Repeat the procedure for
Basic Electrical and Electronics Laboratory- Experiment 6
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FR. CONCEICAO RODRIGUES COLLEGE OF ENGINEERING
Department of Electronics Engineering
8
Observation Table
OBSERVATION TABLE:
Lamp
phase
IL
VL
W1
W2
AMP
(V)
(WATT)
(WATT)
P=W1+W2
P=√3VLILc
osф
STAR
CKT
DELTA
CKT
9
Conclusions & Inferences
100
Post Lab Questions
1.What are the advantages of power measurement by two wattmeter method ?
2.Draw the phasor diagram and prove that sum of two wattmeter reading is equal to 3phase power
3.How to calculate power factor from wattmeter readings?
4.How reactive power can be measured using this method?
Basic Electrical and Electronics Laboratory- Experiment 6
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