Page 455 - Basic Electrical Engineering

= V I 2 sin φ sin 30°
ph ph
or, (W − W ) = 3 V I sin φ
2
1
ph ph
or, (W − W ) = V I sin φ (4.17)
L L
1
2
Dividing eq. (4.17) by eq. (4.16)

or,

Power factor,

Thus, from the two wattmeter readings, we can calculate the total active and
reactive powers and the power factor of the circuit.

Effect of change of power factor on wattmeter readings

We will now study the effect of change of load power factor on the wattmeter

readings. Let us rewrite the wattmeter readings as

We will consider a power factor of unity, 0.5, less than 0.5, and 0 and study
the effect on the wattmeter readings.

i. At unity power factor i.e., when cos ϕ = 1 i.e., ϕ = 0