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A fixed capacitor bank can economically improve power factor when a facility's load stays nearly constant. But when motors cycle or production changes by shift, its compensation may be too little at peak load and too much overnight.
A full Static Var Generator (SVG) follows rapid changes, but its higher upfront cost may be hard to justify for moderately variable loads. An automatic power factor correction (APFC) panel fills the gap by switching capacitor steps as demand changes.
The question is whether APFC's speed and precision match the actual load.
An APFC panel is not separate from capacitor-bank technology. It is typically a switched capacitor bank with a controller, current transformer (CT), protection, and several stages.
This article focuses on conventional contactor-switched APFC. Thyristor-switched panels can respond faster, but they still change compensation in steps.
A fixed bank supplies approximately the same reactive power whenever connected. An APFC controller connects or disconnects stages as demand changes, avoiding unnecessary compensation at low load.
For example, APFC can remove stages when pumps stop overnight and restore them when production resumes.
An SVG uses power electronics for continuously adjustable reactive power. It follows the measured requirement rather than selecting fixed steps. It can supply capacitive compensation or absorb excess capacitive reactive power, subject to its rating.
SVG is valuable when demand changes faster than an APFC panel can switch, fine correction is needed, or both leading and lagging power factor occur.
For gradual changes, automatic capacitor steps may provide adequate correction at a lower initial cost than a comparable full SVG. Compare project-specific costs.
| Feature | Fixed Capacitor Bank | APFC Panel | Full SVG |
|---|---|---|---|
| How it adjusts | Does not adjust automatically | Switches capacitor stages | Varies reactive output continuously |
| Best load pattern | Nearly constant | Changes over shifts or operating cycles | Changes quickly or unpredictably |
| Type of correction | Capacitive, fixed amount | Capacitive, in steps | Capacitive and inductive, subject to rating |
| Low-load behavior | May overcompensate if left connected | Can disconnect unneeded stages | Can reduce output or absorb excess reactive power |
| Typical initial cost | Lowest | Between fixed bank and full SVG in many projects | Usually highest at comparable capacity |
| Main limitation | Cannot follow changing demand | Step size and switching speed limit precision | Higher initial investment |
Configuration, detuning, installation, and capacity can change actual cost and performance.
APFC suits loads that vary but do not require second-by-second correction, such as production shifts, staged HVAC, or cycling motor groups.
The controller selects the required stages, keeping power factor nearer the target while reducing light-load overcompensation. The plant need not pay for unused SVG capability.
An APFC panel is a strong candidate when:
Reactive demand changes, but not too rapidly for switched steps
The principal problem is lagging displacement power factor
The utility applies a power-factor or reactive-energy charge
A fixed bank overcompensates at low load or undercompensates at peak load
The site can be corrected with practical capacitor-step sizes
Harmonic levels and resonance risk have been assessed
The last point matters. APFC makes a capacitor bank automatic; it does not make the capacitors immune to harmonics.
APFC can only switch its available stages. An oversized minimum step may cause under- and overcorrection. A welder, crane, or lift may change demand before the panel responds.
Capacitor stages cannot absorb capacitive reactive power. More stages will not solve a persistent leading power factor.
Harmonics are another limit. Drives, rectifiers, and UPS systems can create currents that interact with capacitors and system inductance. A detuned APFC bank may be appropriate after a study, but switching does not remove harmonic current. Harmonic reduction may require an active harmonic filter, not simply SVG.
Record reactive demand during peak production, low-load shifts, and weekends. Review the utility bill for its power-factor target and penalties.
Measurements should include:
Active power, reactive power, and power factor over time
Minimum and maximum inductive reactive demand
Any periods of leading power factor
Harmonic current and voltage distortion
Existing capacitor ratings, condition, and switching arrangement
Transformer loading, system voltage, and installation space
These data show whether the bank can be converted to APFC or needs new stages, detuning, or SVG. They also inform minimum step size.
Compare installed cost, including CTs, protection, detuning, commissioning, and maintenance. A low cabinet price has little value if the system misses its target.
The price difference matters only if each option meets the same measured objective. Ask suppliers to state the target power factor, operating range, response requirements, and assumptions behind the quoted kVAr capacity. A fixed bank may have the lowest purchase price but still leave low-load overcompensation unresolved. An APFC panel costs more because it adds sensing, control, and switching, yet it can avoid buying a full SVG when changes are slow enough for capacitor steps.
For the financial case, separate the initial purchase from ongoing costs. Count capacitor and contactor replacement, maintenance access, installation work, and the expected operating life. Then compare any tariff penalties or capacity constraints that the system can actually address. APFC does not guarantee a reduction in billed kilowatt-hours; its value depends on the site's load and tariff.
An APFC panel typically contains a capacitor bank, but adds automatic control and switched stages. A fixed bank supplies a constant amount of compensation while connected; an APFC panel changes the connected amount as the load varies.
An automatically switched capacitor bank generally has a lower upfront equipment cost than a full SVG of comparable capacity, but not in every configuration. Detuning, switching equipment, maintenance, and installation affect the comparison.
No. Its primary job is reactive-power compensation. Detuned reactors can reduce resonance risk, but an active harmonic filter is used when harmonic current itself must be reduced.
Sometimes. The capacitors must be suitable for staged switching and their condition verified. The upgrade also needs a correctly located CT, controller, switching devices, protection, and an assessment of harmonics and step sizes.
For a stable load, a fixed capacitor bank may be sufficient. When demand changes across the working day, an APFC panel can be a cost-conscious upgrade: it uses capacitor steps more intelligently without requiring the full capability of an SVG. Fast, unpredictable, or leading reactive-power conditions may justify SVG instead.
The best choice begins with a load profile, not a product label. If your fixed bank no longer holds the required power factor, YT Electric can review your measurements and recommend whether APFC, SVG, or another configuration fits your facility.
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