Capacitor Bank & Reactive Compensation Sizing

IEEE 18-2012 · IEC 60871-1 · IEEE C37.012 · IEEE 519-2014

IEEE 18-2012 · IEC 60871-1 · IEEE C37.012 · IEEE 519-2014 · IEEE 1036-2010
Quick Presets
System Parameters
Required for resonance check — from short-circuit study
Optional — affects IEC 60871-1 §10 overload check
Bank Configuration
Sizing Results
Fill in the parameters and click Size Capacitor Bank to size your capacitor bank.
⚡ IEEE 18-2012 §5: Q_c = P × (tan φ₁ − tan φ₂)  |  IEC 60871-1 §10: continuous I ≤ 1.30 × I_n
Sizing Results
Compliance Checks
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Methodology
FormulaStandardDescription
Q_c = P·(tan φ₁ − tan φ₂)IEEE 18-2012 §5Required reactive compensation
C = Q / (2π f V²)IEEE 18-2012 §4.3Capacitance per phase
V_rated ≥ 1.10 × V_sysIEC 60871-1 §5.2Voltage rating uplift for harmonics
I_cont ≤ 1.30 × I_nIEC 60871-1 §10.2Continuous overcurrent overload limit
h_r = √(S_sc / Q_cap)IEEE 519-2014Parallel resonance harmonic order
I_inrush = V_LN · √(C/L_sys)IEEE C37.012 §5Isolated bank inrush current peak
ΔV% ≈ Q·X_sys / V²IEEE 1036 §7.2Voltage rise at PCC
Related Tools
Short Circuit Study (IEEE C37) Harmonic Distortion (IEEE 519) BESS Grid Connection Reactive Requirements
Frequently Asked Questions
What does IEEE 18-2012 require for capacitor sizing?
IEEE 18-2012 §5 defines Q_c = P × (tan φ₁ − tan φ₂). Capacitors must be rated for continuous operation at 1.10× system voltage, 1.30× rated current, and 1.35× rated reactive power per IEC 60871-1 §10.
Why must capacitors be rated above system voltage?
System harmonics and temporary overvoltages elevate the voltage across the capacitor above nominal. IEC 60871-1 §5.2 requires rated voltage ≥ 1.10× system voltage so the capacitor withstands worst-case operating conditions without insulation failure.
How do I check for harmonic resonance?
Parallel resonance order h_r = √(S_sc / Q_cap [MVAr]). If h_r falls within ±0.5 of a characteristic harmonic (5th, 7th, 11th, 13th), amplification of harmonic voltage can damage capacitors and equipment. IEEE 519-2014 defines acceptable THD-V/TDD-I limits.
When is a detuning reactor required?
A detuned series reactor is required when harmonic resonance risk is detected (h_r near a characteristic harmonic). Typical detuning: 4.7% shifts resonance below 7th, 5.67% below 5th, 7% below 3rd. The reactor also limits inrush current.
Isolated vs back-to-back switching — what changes?
For isolated banks, inrush current is limited by the system inductance alone. Back-to-back switching (energising a second bank with the first already on the bus) produces peak inrush 2–3× higher and a high-frequency transient per IEEE C37.012. A series damping reactor is almost always required for back-to-back configurations.
What are the IEC 60871-1 §10 overload limits?
IEC 60871-1 §10 sets: (a) continuous overcurrent ≤ 1.30× I_n (due to harmonics + overvoltage combined), (b) continuous overvoltage ≤ 1.10× U_n, (c) 30 min/24h overvoltage ≤ 1.15× U_n, (d) overreactive ≤ 1.35× Q_n. Exceeding these limits causes premature dielectric failure.
Frequently Asked Questions
What does IEEE 18-2012 require for capacitor sizing?
IEEE 18-2012 §5 defines Q_c = P × (tan φ₁ − tan φ₂). Capacitors must be rated for continuous operation at 1.10× system voltage, 1.30× rated current, and 1.35× rated reactive power per IEC 60871-1 §10.
Why must capacitors be rated above system voltage?
System harmonics and temporary overvoltages elevate the voltage across the capacitor above nominal. IEC 60871-1 §5.2 requires rated voltage ≥ 1.10× system voltage so the capacitor withstands worst-case operating conditions without insulation failure.
How do I check for harmonic resonance?
Parallel resonance order h_r = √(S_sc / Q_cap [MVAr]). If h_r falls within ±0.5 of a characteristic harmonic (5th, 7th, 11th, 13th), amplification of harmonic voltage can damage capacitors and equipment. IEEE 519-2014 defines acceptable THD-V/TDD-I limits.
When is a detuning reactor required?
A detuned series reactor is required when harmonic resonance risk is detected (h_r near a characteristic harmonic). Typical detuning: 4.7% shifts resonance below 7th, 5.67% below 5th, 7% below 3rd. The reactor also limits inrush current.
Isolated vs back-to-back switching — what changes?
For isolated banks, inrush current is limited by the system inductance alone. Back-to-back switching (energising a second bank with the first already on the bus) produces peak inrush 2–3× higher and a high-frequency transient per IEEE C37.012. A series damping reactor is almost always required for back-to-back configurations.
What are the IEC 60871-1 §10 overload limits?
IEC 60871-1 §10 sets: (a) continuous overcurrent ≤ 1.30× I_n (due to harmonics + overvoltage combined), (b) continuous overvoltage ≤ 1.10× U_n, (c) 30 min/24h overvoltage ≤ 1.15× U_n, (d) overreactive ≤ 1.35× Q_n. Exceeding these limits causes premature dielectric failure.