 #1
Connorm1
 26
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 Homework Statement:

4. A fourpole, starconnected, squirrelcage induction motor operates from
a variable voltage 50 Hz threephase supply. The following results were
obtained as the supply voltage was gradually reduced with the motor
running on noload.
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 I0
(assume no load current I0 is magnetising losses) and the equivalent
circuit magnetising circuit parameters R0 and X0.
 Relevant Equations:
 P = √3 x VL x IL x CosФ
So I've attached my graph and found that the windage/friction losses occur roughly around 230Watts. I just don't know how i further explain the magnetising current I0. I know I0 = input current on no load. So do i assumed from P = √3 x VL x IL x CosФ that CosФ=230/√3*220*6.8= 0.0849 or 85.1degrees (220 and 6.8 is what i assume voltage and current are on load). I0=IL*CosФ = 6.8/0.08 = 0.577Amps. Just wish to see if I am going right so far otherwise my R0 and X0 will be wrong.