How to Measure 3-Phase Reactive Power of a Induction Motor Using Single Wattmeter

Here we aim to measure the three phase reactive power ‘Q’ absorbed by the given 3Φ induction motor by using single wattmeter. The formula for the reactive power ‘Q’ absorbed by “Balanced Load” is given by
formula for reactive power absorbed by balanced loadwhere,

  • Q = Total reactive power absorbed
  • VL = Line voltage of supply
  • Vph = Voltage per phase of supply
  • IL = Line current of supply
  • Iph = Phase current of supply
  • Φ = power factor angle

The break load on the induction motor can be taken as a balanced load on the I.M. The measurement can be done using the conventional ‘Dynamometer type of wattmeter’. Here the current coil of the wattmeter is connected in the R-phase, the pressure coil is connected between Y-phase and B-phases.

Assuming that, Q = total reactive power.

total-three-phase-reactive-power

for delta connection, delta-connection
The phase angle between IR and VYB is (90 – Φ)

reading of wattmeter and formula for reactive power Q



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