Induction Machine

[applepieordie]

Hello,

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

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!

 

[rg1]

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]

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. 

 

[Omer]

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.

 

[cos90]

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

 

[Stephen2awesome]

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?

 

[rg1]

rg1,  what page are you getting that equation from in Wildi?

It is Chapter 15. Not a big chapter. Page no 322 arround

 

[applepieordie]

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: