• Two wattmeter method can be used to measure the power in a three-phase balanced and unbalanced load system.
• In a balanced three-phase load system, the line currents are equal in magnitude and have a phase difference of 120 degrees.
• In this case, if two wattmeters are connected in the system, one between any two line wires and the other between the remaining two line wires, the sum of the readings of the two wattmeters gives the total power consumed by the load.

The formula to calculate the total power is

Ptotal = W1 + W2

where W1 and W2 are the readings of the two wattmeters.

• In an unbalanced three-phase load system, the line currents are not equal in magnitude or have a phase difference other than 120 degrees.
• In this case, the two-wattmeter method can still be used to measure the total power consumed by the load, but the power factor of the load also needs to be taken into account.
• Therefore, the two-wattmeter method is a useful and practical technique for measuring power in both balanced and unbalanced three-phase load systems.