Electrical and electronics sample problem 110

sample problem 110, how to analyze this problem? I don't get the solution. Shouldn't this be similar to Y - delta transform?

For some reason I cannot find my book, but from my notes, it seems like it's asking you for the capacitance between a and b. If you re-draw the circuit so that a and b are the points that you are looking into the circuit at, point c will just hang off the circuit and not have any influence on the capacitance.

Think of it as putting a voltage source between points a and b. Point c doesn't have a return (or ground) path so it has no effect on the capacitance, so it's just 2 capacitors (a and b) in series.

So it has nothing to do with Wye to Delta transform? Is three phase circuit in the study range?

I think this one of those problems that trys to make you over think it. But as the poster above said point c is floating so that cap becomes meaning less. In the end its caps in series, which if you treat like parrell resisters its the product/sum of the values. So Cab = (30*30)/(30+30)=15