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.
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 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.
Common examples include electric motors (especially at start-up), transformers, refrigeration compressors and fluorescent lighting ballasts.
Capacitive loads store and release energy. In a commercial or industrial system, their main job is to improve power factor.
Examples include capacitor banks used for power factor correction, certain filtering components within variable speed drives, and specific electronic power supplies.
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.
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.
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.
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.
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.
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.
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.