Determine phase - voltage and power:
A balanced star connected load is supplied from a symmetrical 3-phase 440 Volt system. The current in each of the phase is 40 Amp and lags 30^{o} behind the phase voltage. Determine
1. phase voltage,
2. power,
3. reactive power drawn by a the load, and
4. phase impedance.
Solution
For three phase star connected load voltage applied V_{L }= 440 Volt
(a) V _{ph} = 440/ √3 = 254.03 Volt
Power current = I ph = 40 ∠ - 30^{o} Amp = I _{L}
(b) Power P_{3φ} =3 V_{L} I _{L} cos φ = 3 × 440 × 40 cos 30^{o}
= 26400 Watt = 26.4 kW
(c) Reactive power drawn by the load:
Q_{3φ }= √3 VL I L sin φ
= √3 × 440 × 40 sin 30^{o}
= 15242.047 V_{ar} = 15.24 kVA_{r}
(e) Phase impedance Z _{ph} = V _{ph }I _{ph}
=254.03 ∠ 0^{o} / 40 ∠- 30^{o }= 6.35 ∠ 30^{o }Ω