# Shorebook Q27



## eatsleep (Jun 27, 2019)

Does anyone understand the following question? What is the purpose of the different areas? I just do not really understand the purpose of this question. Thanks!


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## DLD PE (Jun 27, 2019)

Hmmm never heard of Shorebrook or even come across a question even remotely resembling this.  

I would choose 'D' since Area D just looks bigger than Area A.


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## fyrfytr310 (Jun 27, 2019)

MEtoEE said:


> Hmmm never heard of Shorebrook or even come across a question even remotely resembling this.
> 
> I would choose 'D' since Area D just looks bigger than Area A.


Yeah this is a "Take a swing and see what happens" question for me.  I wonder if this question is rooted in the critical angle arena which can be found in Grainger?


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## eatsleep (Jun 27, 2019)

Sorry, i should've included the answer.


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## Drewism (Jun 28, 2019)

The Shorebrook book is pretty good. The only gripe I had with it is that there is broken English in some parts and some questions didn't make sense such as missing information. But overall it was a decent book with pretty interesting questions.

This question pertains to equal area criterion and stability. If you need answer to this question then I suggest looking Power Systems Analysis and Design by Glover, Sarma and Overbye. They give a detailed explanation. I used this book to study and it's very concise with detailed examples.


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## Sthabik PE (Jul 29, 2019)

This question is for finding the condition where system stability is maintained after the fault.

From equal angle criteria, for stability of system: area C = area B.

Since network restores at 80deg and the power equations are not given we assume this as critical clearing angle.

"Critical clearing angle states that If the fault is cleared before critical clearing angle (here 80deg), stability is maintained."

So for fault clearing angle less that 80 deg; area C will  be less than area B and still stability is maintained.

Hence the condition is : area c &lt;= area B; conversely area B&gt;=area C.

If this may help you.


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