One wattmeter method is used to measure power in a three-circuit when
Right Answer is:
The load is balanced in all three phases
One wattmeter method is used to measure power in a three-circuit when the load is balanced in all three phases.
In this method, only one single-phase wattmeter can be used to measure the total three-phase power. In this method, the current coil (CC) of the wattmeter is connected in series with any phase and the pressure coil (PC) is connected between that phase and the neutral as shown in Fig.
The one-wattmeter method has a demerit that even a slight degree of unbalance in the load produces a large error in the measurement. ln, this method one wattmeter will measure only the power of one phase. Hence, the total power is taken is three times the wattmeter reading.
Total Power = 3 × Vph. Iph. cosφ
Note:- The two and three-wattmeter methods can be used for balanced as well as unbalanced load.