A capacitor and inductor with the same reactance connected in parallel cancel out each other (open circuit), right?
A capacitor in series with an inductor does result in cancellation. This is the principle behind series capacitors. Series capacitors are primarily used in high voltage transmission applications - a capacitor in series with the transmission line introduces a capacitive reactance, -jXc, that cancels some of the inherent inductive reactance, jXl, of the transmission line. The result is that the transmission acts as though it is shorter. Series capacitors have also occasionally been used in distribution applications - in these instances, the objective has been to improve voltage regulation.
are you talking about the mains power supplies and correction capacitors? they only alter the phase relationship between current and voltage. many industrial machines have high inductance, altering the phase of the current. the correction caps put them back into phase.
