Three Phase Power Measurement By Two Wattmeter Method

It is always better to have a clear idea about you need. Wheather it is your life or your power system. So measure properly your power demand!!!!!!

In this article we shall learn how to measure three phase power. All the power system runs in three phase system. And we shall focus on measurement of three phase power.

The most famous method used is two watt meter method.

So in this article we shall see how using two wattmeter we can measure three phase power.

Let us see the circuit diagram.

Fig 1:Circuit diagram of three phase power measurement/
https://electricaltechnologyrishi.blogspot.com

Where,

A,B, C are the power supply terminals.

W1, W2 are the two wattmeters. CC having less no of turns is current coil which creates deflecting torque due to current, VC is the voltage coils having higher no of turns, it creates deflection due to voltage. So together they creates deflecting torque for power.

Ia, Ib, Ic are the line current.
Vab, Vac, Vbc are the line to line voltage.

Now three phase power

P=Va.Ia+Vb.Ib+Vc.Ic

As the system is balanced so

Ia+Ib+Ic=0

Since from the circuit we can see that Ic is not getting measured as no wattmeter current coil is connected, so we shall rewrite Ic in terms of Ia, and Ib

From the equation written above we can say,

Ic=-(Ia+Ib)

P=Va.Ia+Vb.Ib+Vc.-(Ia+Ib)

  =Va.Ia+Vb.Ib-VcIa-VcIb

  =(Va-Vc).Ia+(Vb-Vc).Ib

  =Vac.Ia+Vbc.Ib

Now see wattmeter W1 measures Ia and voltage between terminal A & C i.e. Vac.

So, W1 measures Vac.Ia

Let's check W2!!!!!

W2 measures current Ib & voltage between B & C so Vbc.

Hence W2 measures Vbc.Ib

So summing up W1 &W2 we will get the value of total power.

Hence power P=W1+W2

So from the abive explanation and circuit diagram we can measure three phase power.

However in modern days three phase wattmeters are used for three phase power measurement. In this type of wattmeter the deflection torque is created by both the element of Vac.Ia and Vbc.Ib. So principly it also follows the method of two watt meter.

There is another difference. The wattmeter current coil doesn't connect with the power circuit directly but through a current transformer, and the voltage coil is connected by a voltage transformer.

Now a days far more modern technology is available. Digital Multi Function Meters takes inputs from CT and PT, then it is coverted to digital signals, and calculated internally to display the watt reading by its own algorithm.

Hope you have enjoyed this article. Please share your opinion in the comment box. And for all of our other posts please visit the page "Site Map"

Thank you.......