Reactive Power Compensation System Selection and Sizing: Fixed, Automatic or Hybrid?

Compensation system selection matters because the type and size of the system decide whether it keeps the power factor in the target band or creates new problems. When inductive or capacitive reactive energy exceeds the limits set by Türkiye's electricity market regulations, the distribution company adds a charge to the bill; the limits and how the charge is calculated are covered in our separate guide, Reactive Power Penalty in Türkiye: What It Is and How to Prevent It.

Most compensation problems come from choosing or sizing the system without data. An undersized system leaves inductive excess. An oversized system, or one with steps that are too coarse, pushes the plant into capacitive excess at night and at weekends. A system designed without a harmonic measurement can resonate with the network and damage its capacitors.

The choice depends on how the plant's reactive demand changes over time. Fixed compensation keeps a set capacitor rating permanently connected. It is simple and low-cost and suits steady loads, such as a transformer's no-load reactive demand, but on its own it causes capacitive excess whenever the load drops.

Automatic compensation divides the capacitor capacity into steps that a reactive power control relay switches in and out as demand changes. Thyristor-switched (static) steps respond faster than contactor-switched ones and suit rapidly changing loads such as welding machines, presses and elevators. Hybrid systems combine contactor-switched steps for the base load with thyristor-switched steps for fast changes, so one system can follow both.

Correct sizing starts with a load profile analysis: active and reactive power are measured over a representative period, usually at least one full week including nights and weekends, so that both the peak and the lowest reactive demand are known.

The total capacitor rating is calculated from the measured active power and the power factor before and after correction: Qc (kvar) = P (kW) × (tan φ1 − tan φ2). The smallest step has to be small enough to follow the plant's lowest demand; otherwise the system overshoots into capacitive excess at light load.

The harmonic measurement decides the capacitor technology. Where drives, UPS systems and rectifiers are significant, detuned reactors are connected in series with the capacitors so that the resonance frequency sits below the harmonics present in the plant, and harmonic filters may also be needed. Incorrectly sized systems can cause harmonic resonance and capacitor damage.

Sizing is not a one-time decision. Capacitance declines over time, fuses blow and relay settings drift out of step with the load as the plant changes, so periodic maintenance and a new measurement after major load changes keep the system matched to the plant.

Miratek Elektrik selects and sizes compensation systems from measured data and manages the entire process, from site measurements to panel manufacturing, installation and commissioning. We map the plant's active, reactive and harmonic profile, choose the system type and step structure, and manufacture the panels to IEC 61439 with detuned steps and harmonic filters where needed.

For industrial plants, organized industrial zones (OIZs) and commercial facilities across Türkiye, the goal is a correctly sized, monitored system that keeps reactive energy within the limits so penalties do not recur. Sharing your recent electricity bills and load data is enough for us to start the assessment.