Hi,

I have been given the following information for the question the motor is a 50Hz, 8 pole induction motor with 4% full load slip. Rotor resistance is .001Ω per phase and a stand still reactance of .005Ω per phase.

I need to find the ratio of max to full load torque

I have been able to work out a few things for the problem but I have been looking at it now and not sure what the next step is.

I want to find the torque but the formulas need either a voltage, EMF or a current. I think that I am heading in the right direction just need a push.

The working so far are in the attachment.

Thanks for your time

 

The slip at maximum torque will be

\(s_{T_{max}}=\frac{R_{2}}{\sqrt{R_{2}^{2}+X^{2}}}\)

and

\(\frac{T_{max}}{T}=\frac{\frac{s_{T_{max}}}{s} + \frac{s}{s_{T_{max}}}}{2}\)

You have the full load slip as 4% at torque T. R2 & X are also given.

 

I will have to try and find these formulas in my study books and do some more questions. The answers that i obtained in this question are close to the TB answers.


Thanks for the help again

 

Actually I notice the formula I gave for sTmax is wrong

It should be

\(s_{T_{max}}=\frac{R_{2}}{\sqrt{R_{1}^{2}+X^{2}}}\)

where R1 & R2 are the values for the standard induction motor equivalent circuit at steady state conditions. It seems in your question R1 is assumed to be either zero or a value you have to determine from other information ......?