how we calculate the 30 KW 3phase electric motor current on
noload

Answer Posted / r. n. sharma

Torque of a rotor depends on its diameter and weight along
with winding as well as material and methodology of
construction and also on applied bearings and lubrication. A
bulky, heavier rotor will draw more no load current than
small, light weight rotor. Formula : Torque (T) = qr (Where
q=Tangential force acting at PCD of winding due to effect of
current flowing through it, and r= distance of winding from
centre of the shaft). This torque only tries to rotate the
dead weight(W) of the rotor on no load. It can be said
T=qr=(W + rolling friction in bearings + wind resistance).
These all factors can be calculated easily and then finally
to arrive the result i.e. no load current, however bearing
frictional force and wind force can be ignored.

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