Power Factor Correction Explained
A practical engineering guide to power factor correction (PFC) for buildings and facilities. It explains real, reactive and apparent power, the power triangle, why inductive loads drag power factor down, how capacitor banks and APFC panels supply reactive power locally, why detuned reactors are needed where harmonics are present, and the cost benefits of higher PF in the UAE.
Power factor is one of the most misunderstood numbers on an electrical bill, yet it directly affects how much current a facility draws, how hot its cables and transformers run, and what a utility charges for capacity. In simple terms, power factor is the ratio of the useful power that does real work to the total power the system has to supply. A low power factor means the network is moving more current than the actual workload requires.
Power factor correction is the engineering practice of bringing that ratio back up, usually toward a target of around 0.9 to 0.95, by adding equipment that supplies reactive power locally instead of importing it from the grid. For MEP-heavy buildings in the UAE — full of motors, chillers, pumps and HVAC — correcting power factor is often one of the fastest, lowest-risk ways to cut demand charges and free up spare capacity.
How it works
Every AC electrical system deals with three kinds of power. Real power (kW) is the power that actually does work — turning a motor, producing cooling, generating light or heat. Reactive power (kVAr) does no net work; it sustains the magnetic fields that inductive equipment needs. Apparent power (kVA) is the total power the supply must physically deliver, combining the two. Power factor is simply kW divided by kVA.
These three quantities form the power triangle: real power along the base, reactive power along the vertical, and apparent power as the hypotenuse. Power factor equals the cosine of the angle between real and apparent power. When reactive power grows, the angle widens, apparent power and current rise, and power factor falls — even though the useful work has not changed.
The main culprits are inductive loads. Motors, transformers, fluorescent and discharge ballasts, lifts, pumps and air-conditioning compressors all draw magnetizing current that lags the voltage. The more lightly loaded a motor runs, the worse its power factor tends to be. In a typical UAE building dominated by HVAC and pumping, the uncorrected power factor can sit well below the level utilities prefer.
Capacitor banks fix this because capacitors are the electrical opposite of inductors: they supply leading reactive power that cancels the lagging reactive power of motors. Installed near the load or at the main switchboard, a capacitor bank generates the reactive power locally, so the grid no longer has to push that component through cables and the transformer. The result is lower current for the same real work.
Because loads vary, fixed capacitors alone can over- or under-correct. An automatic power factor correction (APFC) panel solves this: a controller continuously measures power factor and switches capacitor steps in and out via contactors or thyristors to hold the target. Where the building contains VFDs, UPS or LED drivers, those loads inject harmonics that can resonate with plain capacitors and damage them — so the bank is built with detuned reactors in series with each step. The payoff is consistent: lower apparent power and demand charges, reduced losses, less voltage drop, and reclaimed capacity in the existing infrastructure.
Main types
In the UAE
- UAE distribution utilities (such as ADDC and AADC in Abu Dhabi, and DEWA in Dubai) expect customers to maintain a healthy power factor and can apply low-power-factor surcharges or capacity-based demand charges, so correction directly reduces the bill and supply-size requirements.
- Sustainability frameworks such as Abu Dhabi's Estidama Pearl Rating System reward reduced electrical losses; a higher power factor lowers losses in cables and transformers and helps a building's efficiency case.
- The growth of VFDs, LED lighting, UPS systems and other power electronics raises harmonic levels, which is why detuned capacitor banks and, where needed, active harmonic filters are now standard rather than optional.
How GPR applies this
As an Abu Dhabi MEP contractor, GPR sizes and installs power factor correction as part of the electrical design for commercial, industrial and residential projects, from individual compensation at large chillers and pumps to central APFC panels at the main board. We carry out load and harmonic assessments before specifying detuned reactors or active filters, so corrected systems stay reliable under real UAE conditions — lowering demand charges, reducing losses and reclaiming supply capacity without upsizing the connection.
Frequently asked questions
What power factor should a building target?
Most utilities and designs aim for roughly 0.9 to 0.95 or higher. Correcting all the way to unity (1.0) is usually avoided because it risks over-correction and leading power factor at light load.
Does power factor correction reduce my electricity (kWh) bill?
It does not reduce the real energy (kWh) your equipment consumes, but it lowers apparent power (kVA) and current, which cuts capacity or demand charges and reduces losses — so the total bill typically falls.
Will capacitors fix harmonics?
No. Plain capacitors only correct reactive power and can worsen harmonic problems by resonating. Harmonics need detuned reactors or active harmonic filters.
Where should the capacitor bank be installed?
Individual compensation at a large motor unloads more of the network, while central compensation at the main board is simpler and cheaper. Many UAE installations use a mix of both.
How is the capacitor bank size determined?
It is calculated from the existing power factor, the target power factor and the load's real power (kW), then verified against a harmonic study to decide whether detuning is required.