Low voltage capacitor banks and filter banks

Both capacitor banks and filter banks are used in low voltage (LV) power systems for reactive power compensation and power quality improvement, but they serve different primary purposes.

1. Low Voltage Capacitor Banks

Purpose:

  • Reactive power compensation (power factor correction)
  • Voltage support (reduces line losses and improves efficiency)

Components:

  • Capacitors (fixed or switched)
  • Contactors/thyristor switches (for step control)
  • Protective devices (fuses, overload relays)
  • Controller (measures PF and switches steps)

Applications:

  • Industrial plants with inductive loads (motors, transformers)
  • Commercial buildings to avoid utility power factor penalties
  • Solar/Wind farms for grid compliance

Limitations:

  • Can amplify harmonics if system has existing distortion (risk of resonance).
  • Not designed for harmonic filtering (unless detuned).

2. Low Voltage Filter Banks

Purpose:

  • Harmonic filtering (reduces THD—Total Harmonic Distortion)
  • Reactive power compensation (secondary benefit)

Types:

  • Passive Filters:  LC circuits tuned to specific harmonics (e.g., 5th, 7th, 11th), mainly used for factories with VFDs, arc furnaces
  • Detuned Reactors + Capacitors Series reactors prevent resonance (e.g., 7% or 14% impedance), mainly used for systems with moderate harmonics
  • Active Power Filters (APF) Electronic compensation (injects opposite harmonics), mainly used for dynamic loads with varying harmonics

Applications:

  • Data centers (prevent harmonic overheating)
  • Hospitals (clean power for sensitive equipment)
  • Industrial facilities with VFDs, UPS systems, etc.
  • Advantages Over Plain Capacitor Banks:
  • Prevents harmonic resonance issues.
  • Reduces voltage distortion and equipment overheating.

3. When to Use Which?

  • Use a Capacitor Bank if:

Your main issue is low power factor (not harmonics).

Your system has low harmonic distortion (THD < 5%).

  • Use a Filter Bank (Passive/Active) if:

You have high harmonics (e.g., from VFDs, rectifiers).

You need both power factor correction and harmonic mitigation.

  • Hybrid Solution: Some installations use detuned capacitor banks (with reactors) to avoid resonance while still improving PF.


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