Harmonic Parallel-Resonance Order
Why a bigger PF cap bank can land on the 5th harmonic, the check pf-correction never makes.
Example
You enter
- Short-circuit power at the bus (MVA) 200
- Power-factor capacitor bank (MVAR) 1.2
You get
- Resonant order 12.91th order
- Near a common harmonic? 13
Details, formula, and sources
The power-factor capacitors and the source inductance form a parallel LC circuit whose resonant order is h = sqrt(MVA_sc / MVAR_cap). If it lands on a harmonic the nonlinear loads produce (5/7/11/13th), the resonance AMPLIFIES it into destructive overvoltage and current. A 200 MVA bus with a 1.2 MVAR bank resonates at the 12.9th -- near the 13th, so the flag fires; double the bank to 2.4 MVAR and it walks DOWN to the 9.1th, because a bigger bank lowers the order toward the strong low harmonics. Ignores load damping; a detuning reactor or harmonic study is the fix. A screening aid; a harmonic study governs.
h_resonant = sqrt(MVA_sc / MVAR_cap); flag if h_resonant is within 0.5 of the 5th, 7th, 11th, or 13th harmonic.
Parallel-resonance order of a power-factor capacitor bank (IEEE 519 / IEEE 1531 harmonic filter and resonance guidance), first-principles, by name; a harmonic study governs.
The h = sqrt(MVA_sc / MVAR_cap) resonance relation is a published first-principles result; the bus short-circuit level and the bank rating come from the system data.
Estimate. AHJ and licensed professional govern.
Field names used by the API: short_circuit_mva, cap_bank_mvar, h_resonant, near_harmonic
- Resonant order h = sqrt(MVA_sc / MVAR_cap) for the parallel cap-and-source-inductance circuitIEEE 1531
- Bigger bank, lower order a larger capacitor bank lowers the resonant order toward the strong low harmonicsIEEE 519
- Idealized ignores load and resistive damping; a detuning reactor or harmonic study is the fixscope of this tile