Page 462 - Basic Electrical Engineering

Inductance per phase,

Example 4.16 The power input to a three-phase motor is measured by two

single-phase wattmeters. The total input power has been measured as equal to
15 kW and the power factor calculated as 0.5. What have been the readings

of the two wattmeters?

Solution:

Total power = W + W = 15 kW
2
1
We have to calculate W and W 2
1

When we measure three-phase power by the two-wattmeter method, the

readings of the two wattmeters are

W 1 = V I cos (30 − ϕ)
L L
and W 2 = V I cos (30 + ϕ)
L L
cos ϕ = 0.5, ϕ = 60°