Determine the sum of the windage and friction losses for this motor

[rob1985]

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. I've drawn the graph and I can work out the I/0, R0 and X0A four-pole, star-connected, squirrel-cage induction motor operates froma variable voltage 50 Hz three-phase supply. The following results were

obtained as the supply voltage was gradually reduced with the motor

running on no-load.

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.

 

[jim hardy]

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

(assume no load current II0 is magnetising losses)

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.pdfHmmm. 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.

 

[rob1985]

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

 

[anorlunda]

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

Read again carefully what @jim hardy told you.

 

[Thunderchild]

i am another victim of this poorly explained HNC module. I'd be lost without John Birds book Electrical Circuit theory and technology but it is not an in depth discussion of electri motors.

From the little I have gleaned from the module the main losses are windage and friction with magnetics being ignored. Therefore surely the windage and friction losses are infact the V x I given as they are the sum total of the main losses.

Surely the magnetising current is the current supplied to he stator easily calculated with the line voltage and the stator power.

 

[ajskelly]

Did anyone get anywhere with this? I am looking into it now,

I've plotted my points on the graph and extrapolated to get windage and friction losses.

However struggling to find the no load magnetising power loss.

Aware that the power taken from the supply is virtually equal to the core losses in the motor but where to begin?