Page 461 - Basic Electrical Engineering

Example 4.15 Three equal impedances, each consisting of R and L in series
are connected in star and are supplied from a 400 V, 50 Hz, three-phase,
three-wire balanced supply system. The power input to the load is measured

by the two-wattmeter method and the two wattmeters read 3 kW and 1 kW,
respectively. Determine the values of R and L connected in each phase.

Solution:

Reading of wattmeter 1, W = 3 kW
1
Reading of wattmeter 2, W = 1 kW
2
Total power P = W + W = 3 + 1 = 4 kW
2
1

Power factor of the circuit,

Line current,

Impedance of the circuit per phase

= 30.237 Ω
∴ R = Z cos ϕ = 30.237 × 0.7559 = 22.856 Ω

Reactance per phase,