Answer / marcin

Equation with power factor in is the most correct. Several
issues shall be counted before estimating no load current :

- number of the poles

- power factor - there is a curve from the manufacturer
showing how this is changed in a function of power

- size of the machine

- speed

- way of feeding machine - DOL / inverter

Example :

500kW machine 690V 750rpm In=670A, No load - 285A (~42%)

500kW machine 690V 100rpm In=520A, No load - 180A (~34%)

Answer :

KW = 1.732 * V * I * cos phi * K

where K is a factor taking all other circumstances (0,7 to 1
where 1 is ideal situation) lower K for higher number of
poles, multispeed machines, specific construction etc...

Answer / 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.

Answer / krishna

normally in KW p=vicos(phi)
if we have the value of (phi)...
then using power triangle method we can find kva and from that we can find our required answerthat is no load current

Answer / darshana sharma

At no load 30 kW, 3 phase electric motor will draw 30% to
40% of full load current.

Answer / vaibhav

There are many factors that decide no load amperes. Material characteristic of winding material, slip of motor, voltage applied, air gap between stator and rotor, motor bearing condition etc. Mostly rewinded motors show high no load ampere sometimes up to 70-80% of full load ampere. There is no thumb rule to calculate it and in case of new motor no load ampere value is generally mentioned on motor name plate.

Answer / janardan

For 2 pole motor; No load current will be the 1/3 of the Full load current.
i.e if motor takes 181.00 full load current then the no load current will
181 X 1/3 = 60.33 amp.

* for 4 pole: 1/3 to > 3/8
for 6 pole: 1/3 to <1/2
for 8 pole: 1/3 to 5/8

Answer / mathan.k

No load current of any induction motor is 21.5% of full
load current.

Answer / maheshwar das

12A

Answer / kailash vashisth

there is no such standard formulae but after a lot study i
found that for below 5 Hp motor Its 30% of full load
current and above 5 Hp its 45 to 50% of full load current

Answer / watson

i think the no load current is

Root 3 times of Full load current
i.e

I nl = 1.732 X I fl

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