At no load operation, the power absorbed by the asynchronous motor covers the Joule looses in the stator winding, the looses in the equivalent resistance of the magnetizing circuit (named as iron looses) and the mechanical looses.

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The sum of the last two components

,

can be determined experimentally, for supplying voltage more and more small (Figure 6).

Figure 6

As only the iron looses depends on the supplying voltage, the intersection point of the extrapolation of the graphic dependence

,

will represent the mechanical looses P_mec.