In two wattmeter method, we have two types of connections:

In star connection of load, the reading of wattmeter one is product phase current and voltage difference (V2-V3) and the reading of wattmeter two is the product of phase current and the voltage difference (V2-V3). Thus, the total power of the circuit is sum of the reading of both the wattmeters.

Mathematically we can write P=P1+P2=I1(V1+V2) + I2(V2-V3).
But  I1+I2+I3=0, hence putting the value of I1+I2=-I3.
We get total power as P=V1I1+V2I2+V3I3.

The reading of wattmeter one can be written as P1 = -V3(I1 – I3) and reading of wattmeter two is
P2= -V2(I2 – I1).
But V1+V2+V3=0, hence expression for total power is P=V1I1+V2I2+V3I3.

## Watch this Video to know about 2 Wattmeter method

Also Check Out – Working of Single Phase Energy Meter

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Measurement of Power Factor in 3 Phase Load by 2 Wattmeter Method – Electrical Practical