A compensated wattmeter is utilized for measuring reactive power inside a single phase circuit. The application of voltage to a pressure coil inside a wattmeter is 90°. This is in the outer phase with respect to the actual voltage. So the reading as per this will be,
Utilizing a single one wattmeter, reactive power inside a balanced 3 phase circuit can be determined. As per this, insertion of current coil is in one line, and connection of pressure coil is in the other 2 lines.
So, potential difference in a wattmeter across potential coil will be,
Now via current coil, the equation of current will be,
For power measurement, with the help of two wattmeter readings, its reactive power will be,