# Homework Help: Determine the total of windage and friction losses

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1. Jun 10, 2017

### rob1985

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Hi I was wondering if someone could tell me the equation for finding out what the windage and friction losses are based on the information below. Ive drawn the graph and I can work out the I/0, R0 and X0

A four-pole, star-connected, squirrel-cage induction motor operates from

a variable voltage 50 Hz three-phase supply. The following results were

obtained as the supply voltage was gradually reduced with the motor

Stator line voltage 220 164 112 88 42

Stator line current (amperes) 6.8 5.4 3.9 3.8 3.7

Stator power (watts) 470 360 278 244 232

(a) By plotting a suitable graph from these results, determine the total of

windage and friction losses, the no load magnetising current II0

(assume no load current II0 is magnetising losses) and the equivalent

circuit magnetising circuit parameters R0 and X0.

2. Jun 10, 2017

### jim hardy

You don't really have enough information for a precise calculation
but you can estimate .

It's magnetizing plus friction and windage losses.

At constant speed Friction / windage is independent of voltage but magnetizing loss is not.
Try a search on terms "Steinmetz magnetizing loss" , here was my first hit: http://web.eecs.utk.edu/~dcostine/ECE482/Spring2015/materials/magnetics/CoreLossTechniques.pdf

Hmmm. i see you have watts.
Was that measured with a wattmeter ?
If so, you might plot watts versus voltage but backward - start with high voltage of left and decreasing as you move right. . It'll be roughly asymptotic to friction and windage. That's because magnetizing loss is proportional to flux raised to some power, typically cited as 1.4 or 2.
So as you decrease voltage your magnetizing losses drop off quickly leaving the lion's share to friction and windage.

Another estimate would be from RPM at no load and published speed-torque curve. Torque at observed slip is friction and windage.

Best way is to put it on a dynamometer and spin it, measure torque.

3. Jun 11, 2017

### rob1985

So how do I estimate what the losses are, is there a formula I can use

4. Jun 11, 2017

### Staff: Mentor

Read again carefully what @jim hardy told you.