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ELECTRICAL MEASUREMENT LAB
Department of Electrical Engineering
Supervisor
Submitted by
Dr. Girish Parmar
Control & Instrumentation
(Associate Professor)
Department of Electronics Engineering
University College of Engineering,
Rajasthan Technical University, Kota
February, 2015
Experiment No.: 3
OBJECT: To measure the power in 3-φ load by (i) two wattmeter method at different value of load (ii)
One watt meter method.
APPARATUS REQUIRED:
Wattmeter, ammeter, connecting loads, 3- φ star connection load, voltmeter.
THEORY:
Two wattmeter method is the most commonly used method for measurement of power as this can be
used for balanced & unbalanced of the used is balanced.
The reading of W1 wattmeter is given by is a balanced
W1 = E12 i1 cos (30+ φ)
While reading of W2 wattmeter is given by
W2 = E32 i3 cos (30- φ)
Since if it is a balanced circuit
|E12 | = |E32| = √3 |EPN|
|i1 | = |i3| = |i| (say)
Therefore W = W1 + W2
W = √3 EPH i cos (30+ φ) + √3 EPH i cos (30- φ)
= 2 √3 EPH i cos 30 cos φ
= 3 EPH i cos φ
W = √3 EL i cos φ
This is nothing but the 3- φ power in the balanced load.
CIRCUIT DIAGRAM:
Fig. 3.1 Circuit Diagram Of Power factor Meter Using watt meter
CALCULATION:
Power Factor = cos φ
φ = tan-1 [√3 (W1-W2) / (W1+W2)]
φ = tan-1 [√3(-160 / 400)]
φ = tan-1 [-√3 × 0.4]
φ = -34.71
P.F. = cos φ = 0.82
OBSERVATION TABLE:
S.NO.
E
I
W1
(VOLTS)
(AMP)
(WATT)
W2
(WATT)
W1 + W2
W1 – W2
(WATT)
(WATT)
% ERROR
Calculation of power factor:
Φ = tan-1 [√3 (W1 – W2) / (W1 + W2)]
P.F. = cos Φ
RESULT:
We have performed the experiment of power factor measurement by 2- Wattmeter method. And the
results are……………….
Power (active) = W1 + W2
Power factor = ……………