Inductive vs capacitive loads
Electrical efficiency is a balance between two forces: inductive loads, such as motors and transformers, that make current lag voltage and create inefficiency; and capacitive loads, such as PFC capacitor banks, that make current lead. Power factor correction adds capacitive load to counteract the inductive lag, bringing the system to near-unity efficiency and avoiding demand penalties.
- Inductive loads (motors, transformers) make current lag voltage, which lowers power factor.
- That lag raises apparent power (kVA) without doing more useful work, inflating demand charges.
- Capacitive loads (PFC capacitor banks) make current lead, cancelling the lag.
- Power factor correction adds just enough capacitance to bring the system back to near-unity.
Every piece of equipment can be classified by the type of load it places on the supply. Understanding the difference between inductive and capacitive loads is the key to mastering system efficiency, which is measured by the power factor.
Capacitive and inductive load examples, side by side:
| Capacitive load | Inductive load | |
|---|---|---|
| What the current does | Leads the voltage | Lags behind the voltage |
| Examples | Capacitor banks used for power factor correction, filtering components within variable speed drives, some electronic power supplies | Electric motors (especially at start-up), transformers, refrigeration compressors, fluorescent lighting ballasts |
| Effect on power factor | Raises it by cancelling inductive lag. Too much makes it lead | Lowers it: kVA rises while useful kW stays the same |
| Effect on your bill | Sized right, it brings billed kVA demand back down | Inflates maximum demand (kVA) charges |
Inductive loads: the heavy lifters that cause lag
Inductive loads are the heavy lifters. They use magnetic fields to operate, and include electric motors and transformers. They are critical for driving mechanical processes, but they demand reactive power to sustain those magnetic fields.
- Current lag: inductive loads make the current waveform lag behind the voltage waveform.
- Power-factor challenge: that misalignment raises the apparent power (kVA) drawn from the utility, even though the useful power (kW) is unchanged, which inflates maximum demand charges.
Common examples include electric motors (especially at start-up), transformers, refrigeration compressors and fluorescent lighting ballasts.
Capacitive loads: the energy savers that correct power factor
Capacitive loads store and release energy. In a commercial or industrial system, their main job is to improve power factor.
- Current lead: capacitive loads make the current waveform lead the voltage waveform.
- Power-factor improvement: they counteract the lagging current from inductive loads, bringing current and voltage back into alignment and raising the power factor toward the ideal value of 1 (unity).
Examples include capacitor banks used for power factor correction, certain filtering components within variable speed drives, and specific electronic power supplies.
Achieving balance for optimal efficiency
The art of power factor correction is balance: adding just enough capacitance to cancel the inductive lag, without overcorrecting. Get it right and the system draws close to only the real power it needs, cutting kVA demand and the charges that come with it.
What this means for your electricity bill
On a demand-based tariff, you pay for maximum demand in kVA: the highest 30-minute average of the month. Inductive loads raise kVA without adding useful work, so every motor and compressor inflates that charge. Some tariffs also bill reactive energy (kVArh). What counts is your power factor at the moment of peak demand, not on an average day.
Correction adds capacitance sized to your load. That is what power factor correction is. Get the size wrong and the problem flips. A bank left switched in at low load makes power factor lead, and utilities penalise a leading power factor too. Leading power factor at low load can mean a capacitor stage whose contactor has stuck closed. Variable speed drives and LED lighting add a third risk: harmonics, and what they do to correction equipment.
See power factor correction, and what Augos charges for it, or read how the survey works.
What is an inductive load?
Equipment that uses magnetic fields to operate, such as electric motors, transformers, refrigeration compressors and fluorescent lighting ballasts. They draw reactive power to sustain their magnetic fields, which makes current lag voltage.
Why do inductive loads lower power factor?
The lag between current and voltage increases the apparent power (kVA) drawn from the utility, even though the useful power (kW) is unchanged. That artificially inflates maximum demand charges.
What is a capacitive load?
A load that stores and releases electrical energy and makes current lead voltage. Examples include capacitor banks used for power factor correction, filtering components within variable speed drives and some electronic power supplies. In a commercial or industrial system, capacitor banks are added specifically to improve power factor by counteracting inductive lag.
How does correction achieve balance?
By adding just enough capacitive reactive power to cancel the inductive reactive power, bringing current and voltage back into alignment and raising the power factor toward unity.
How can you tell whether a load is inductive or capacitive?
Compare the current with the voltage. If the current lags, the load is inductive and the power factor is lagging. If it leads, the load is capacitive and the power factor is leading. In Augos, lagging and leading power factor are charted in different colours, so over-correction stands out.