Measuring Capacitance Across A-B Terminals

Question: While testing a 100KVAR 480V 3 phase wye connected capacitor, what would the expected uF be across A-B terminals?

I keep coming up with 1152, but the testguy quiz says its 576. Why??


So you accurately got the equivalent capacitance of 1152 for a single capacitor. Since this is wye connected however, if you measure across A+B, you are not measuring one capacitor, but 2. You’re measuring the cap installed from A to neutral and the Cap installed from neutral to B. The other phase is open so it is two series capacitors across A & B. Capacitors add as if they are parallel resistors when they are in series, so the measured value between terminal A and B is the total capacitance of the series circuit of of cap A and B. Or Ca*Cb/(Ca+Cb) = C^2/2C = C/2 or 1152/2 = 576. If they were delta connected, 1152 would be accurate. Hope that clears it up.