Page 451 - Basic Electrical Engineering

I Ph = 32 A

I Ph = I = 32 A
L
V L = 400 V

V Ph = 231 V

Total Power = V I cos ϕ
L L
= 3 V I cos ϕ
Ph Ph
= 3 × 231 × 32 × 0.56

= 12418 W
= 12.418 kW

Total reactive power = V I sin ϕ
L L
= 3 V I sin ϕ
Ph Ph
= 3 × 231 × 32 × 0.83

= 18406 VAR

= 18.406 kVAR

4.8 MEASUREMENT OF POWER IN THREE-PHASE CIRCUITS

We have known that in dc circuits power is measured as the product of
voltage and current, i.e., power, P = VI. DC power can be measured using a

voltmeter and an ammeter. In ac circuits power, P = VI cos ϕ. In three-phase
ac circuits, total power is three times the power per phase. Wattmeter is an

instrument used for measurement of power in ac circuits. Wattmeters are
available as single-phase wattmeters and three-phase wattmeters. Single-
phase wattmeters can be used to measure three-phase power. In case of star-

connected balanced load with neutral connection, only one single-phase
wattmeter can be used to measure the three-phase power. The three-phase

power is three times the single-phase power. For unbalanced three-phase
loads, i.e., if the currents in the three phases are not the same, two wattmeters