The test is performed at poly-phase voltages and rated frequency applied to the stator terminals. When motor runs for some times and bearings get lubricated fully, at that time readings of applied voltage, input current and input power are taken. To calculate the rotational loss, subtract the stator I²R losses from the input power.

Calculation of No Load Test of Induction Motor

Let the total input power supplied to induction motor be W₀ watts.

Where,
V₁ = line voltage
I₀ = No load input current

Rotational loss = W₀ – S₁
Where,
S₁ = stator winding loss = N_ph I² R₁
N_ph = Number phase
The various losses like windage loss, core loss, and rotational loss are fixed losses which can be calculated by

Stator winding loss = 3I_o²R₁
Where,
I₀ = No load input current
R₁ = Resistance of the motor

Core loss = 3G_oV²