Theory
Three Ammeter Method
The three ammeter method are used for measurements of power.
More specifically, they are used to calculate the power
factor of a specific load
Three ammeter method for measurement of power:
The three ammeter is also used in an inductive circuit
to measure the value of the power factor, independent of
source frequency and waveforms.
In this method, as seen
on Figure , across the inductive circuit load in which the
power factor is to be determined, a non-inductive
resistance is connected parallel with the load branch. One
ammeter is used to measure total current of the circuit, the
second one measures current going through the noninductive resistance and the third ammeter measures the
current of the load branch.
This concept is illustrated in following figures.
From phasor diagram, we have:
I12 = I22+ I32 + 2 I2I3CosΦ
but,
I2 = V \ R
I12 = I22+ I32 + 2 V\R I3CosΦ
Hence the Power,
P = V I3CosΦ is given by:
⇒P = R\2( I12- I22- I32 )
also,
CosΦ = ( I12- I22- I32 ) \ 2 I2I3