capacitive reactance

[TNPE]

That is true, but most commonly, you're given power and voltage when doing pu analysis.  And Vline is the "base" that you use... That's my question for the board, why?  I'm askinng this since it sort of relates to the original post.

 

[TNPE]

PU analysis can look like a sleight of hand, voodoo black magic show... But...

Z=Vline^2/Sbase is correct

But why?  It's pretty intuitive once you see it.  

 

[rg1]

The question asks total capacitance. They seem to be attempting for that. I have check it. But that is not the way. There is nothing like total capacitance. The capacitance in star connection will have less Voltage rating and more current rating( less Xc more C); capacitance in delta will have more voltage rating and less current rating (more Xc less C).  And we say 3 capacitors of this particular ratings are required. Generally we measure total capacity in VARs and not in Farads. Because total of anything (R,L,C) will depend on how you connect them(series parallel combination). Your confusion is justified. 

Yes , I studied it again,  the solution of the book is wrong, without any doubt. He too is assuming it to be star connected system and his answer that is 5 microfarad multiplied by error (sqrt3) he is making in the beginning in the formula gives your answer 8.66==9 microfarad. So there is nothing like total capacitance he is asking in the question. He should have formulated and formatted the question in a better way.

 

[rg1]

PU analysis can look like a sleight of hand, voodoo black magic show... But...

Z=Vline^2/Sbase is correct

But why?  It's pretty intuitive once you see it.  

Zbase=Zb; Vphase base=Vpb, Vline base=Vlb, same for I ( Voltage in Volts, current in Amps)

Zb=Vpb/Ipb

=Vlb/(sqrt3*Ilb)

=Vlb**2/(sqrt3*Vlb*Ilb)

=(1000*Vlb)*(1000*Vlb)/(1000000*sqrt3*Vlb*Ilb)

=Vlb**2/Sb ( Voltage in kV and S in MVA)

Now we take can whatever is easily available to us in the question. 

 

[Omer]

Thanks @rg1 and @TNPE for elaborating on the subject.

As you mentioned rg1, the formulation of the question could have been better.