No Load current of Induction Motor

(1) friction losses can increase with rpm so that efficiency will be different

(2) You haven't mentioned voltage rating of both motor. If it is different, your full oad current will be different.

(3) Even with same voltage rating, rpm, KW and enclosure type, always there is minor difference in efficiency for different make motors depending on design difference.

Voltage rating of both motors is same, 415 volts (delta ).Enclosure of 45 KW motor is D225M and of 55 KW is AMW250M2H1.

ONe possible answer is in the conductors

Yes i agree the quality of copper used is an impartent factor.

crm

it may due to their manufacturing aspects like length of overhang in stator winding, rotor impedance, core material used

You are measuring current, not power.

The phase angle on the motors is different as are the speeds.

You are 'comparing apples & oranges`.

if the size of the voltage are equivalent then the size of the wire use in the windings and therefore the size of the current may be different different.

also, the conductors govern the phase, and therefore can affect the response of the rotor thus varying the speed. and the arrangement of the magnets in the rotor have a baring on the torque, and I guess therefore quite possibly the power output.

also, the response of the governing phase can have a minute effect.

so, it could be a number of things, and without seeing the circuit diagrams and wiring diagrams, it is comparing apples and oranges.

Dear Friend

No load current of motor and transformer is due to the iron loss in the machine. Thus if one machine is drawing greater current compared to other, then it is (a) due to the characteristics of iron used in the machine (b) due to higher operating flux density. Copper does not play any significant role in the no load current drawn. It has a major impact on the full load efficiency.

Ashok Toshniwal, Bangalore, India

Best answer. This is why no two motors are going to be exactly the same unless they are the same make and model. Even then, they need to be of the same production run in order to be close to exact because different batches of steel (for the laminations) will have slightly different characteristics.

While it would be true that Copper (I²r) losses can represent the majority of loss percentage, they are based on a percentage of load. So if the load is gone, the I²r losses are minimal and in fact are just the copper losses based upon the fixed losses. What remains then are those fixed losses such as the iron losses, friction, windage and stray losses.