Detuned Capacitor Bank & Reactor Calculator
Determine series reactor inductance (p = 5.67%, 7%, 14%), series tuning frequency, capacitor terminal voltage boost, and prevent destructive harmonic resonance.
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Frequently Asked Questions
What is the purpose of a detuned harmonic reactor on a capacitor bank?
Standard power factor capacitors naturally form a parallel resonant tank circuit with the upstream transformer inductance. If this resonant frequency happens to coincide with harmonic currents produced by VFDs (such as the 5th harmonic, 300 Hz), destructive harmonic amplification occurs. A series detuned reactor forces the resonant frequency down below 250 Hz, ensuring the bank acts inductively at all harmonic frequencies.
Why do detuned reactors cause a voltage rise on the capacitors?
Because the capacitor and series reactor form a voltage divider where the reactor is inductive (+jXL) and the capacitor is capacitive (-jXC), the fundamental voltage across the capacitor terminals rises to Vc = Vbus / (1 - p). With a 7% reactor on a 480V bus, operating voltage jumps to 516V, mandating 525V or 600V rated capacitor cells.
What detuning percentage should be chosen?
A 7% reactor (tuned to 227 Hz in 60 Hz systems) is the global standard for suppressing 5th, 7th, 11th, and 13th harmonics from 6-pulse drives. A 14% reactor (tuned to 160 Hz) is specified when high 3rd harmonic currents from single-phase computer loads are present.