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applepieordie

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Hello,

What equation is being used in the solution? (question from Kaplan sample exam)

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Is max torque synonymous to max power? 

In Graffeo's book I see the formula: Slip at which Pmax occurs at = Sp = Rrotor/(Rrotor + Zeq), where Zeq = Zmotor + Zstator. But this equation seems slightly different than the one used int he solution.

Also, if you have good machine references (such as a formula sheet) to share it would be greatly appreciated.

Thanks!

 
From the equivalent circuit of Induction motor, we see that Pmax or Tmax occurs when (Rexternal+r2)/slip= IZeqI. where Zeq is (r1+j(x1+x2)) . IMHO this is the basic equation. This also available in Wildi. From this equation the answer at slip 1 comes Rexternal+.333=IZeqI= sqrt((.645)**2+(1.11+.978)**2)=1.37 on primary side. 

 
From the equivalent circuit of Induction motor, we see that Pmax or Tmax occurs when (Rexternal+r2)/slip= IZeqI. where Zeq is (r1+j(x1+x2)) . IMHO this is the basic equation. This also available in Wildi. From this equation the answer at slip 1 comes Rexternal+.333=IZeqI= sqrt((.645)**2+(1.11+.978)**2), gives Rexternal=1.37 ohms on primary side. 

 
From the equivalent circuit of Induction motor, we see that Pmax or Tmax occurs when (Rexternal+r2)/slip= IZeqI. where Zeq is (r1+j(x1+x2)) . IMHO this is the basic equation. This also available in Wildi. From this equation the answer at slip 1 comes Rexternal+.333=IZeqI= sqrt((.645)**2+(1.11+.978)**2)=1.37 on primary side. 
Yes, you are right.

I think book answer is wrong including r2 in the calculation of Zeq.

Wildi is the best.

 
Where did you get this Kaplan? Kaplan changed their name to Brightwood and the book I purchased from them looks nothing like this.

 
From the equivalent circuit of Induction motor, we see that Pmax or Tmax occurs when (Rexternal+r2)/slip= IZeqI. where Zeq is (r1+j(x1+x2)) . IMHO this is the basic equation. This also available in Wildi. From this equation the answer at slip 1 comes Rexternal+.333=IZeqI= sqrt((.645)**2+(1.11+.978)**2)=1.37 on primary side. 
rg1,  what page are you getting that equation from in Wildi?

 
Where did you get this Kaplan? Kaplan changed their name to Brightwood and the book I purchased from them looks nothing like this.
I didn't purchase if from Brightwood. I got this exam (in pdf format) from a colleague and was told it is the Kaplan exam. 

My guess is it is probably an older sample exam as it has many errors. I found this thread dated 2010 in the forum where a poster called cableguy made an errata list and it matches the errors I see in the pdf I have: 






 
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