Reactive Power Measurement – AMPERES
For reactive power measurement in a single-phase circuit, we used compensated wattmeter. In compensated wattmeter the voltage applied to the pressure coil is 90° out of phase with the actual voltage and the wattmeter will read the reactive power VI cos(90° – Φ) i.e VI sinΦ.
In single-phase measurement the field of pressure coil lag behind by 90° when it measures actual power.
The single-wattmeter method is used for power measurement in the balanced three-phase circuit. The current coil of the wattmeter is inserted in one line and the pressure coil of it is connected across the other two lines.
The current flowing through the current coil of the wattmeter is
The potential difference (pd) across the potential coil of Wattmeter
Reactive power can also be determined from two wattmeter readings connected for measurement of power
Reactive power of load circuit, Q