For the same kVAR, a delta-connected bank needs one third the capacitance of a star one — because reactive power scales with the square of the voltage each capacitor sees.
Q = 2πfCV². In delta each capacitor sits across the full line voltage; in star it sits at line/√3, so its V² is three times smaller and it takes three times the capacitance to deliver the same correction. That is why delta is the default. The trade is voltage rating: every delta capacitor must withstand full line voltage. Quoting a kVAR figure without saying which connection it assumes is how the wrong part gets ordered.
The trade is not free: each delta capacitor sees the full line voltage rather than the phase voltage, so it needs a proportionally higher voltage rating. You buy a third of the capacitance and pay for it in insulation — and on an unbalanced supply the two connections behave differently.
Estimate with the rule, then check it against the calculator that models it properly.
Open Power Factor Calculator →For the same kVAR, a delta-connected bank needs one third the capacitance of a star one — because reactive power scales with the square of the voltage each capacitor sees. Q = 2πfCV².