What should the target power factor be?

To avoid a reactive energy penalty, the power factor must be kept above a defined limit in the inductive direction. In practice a target around 0.98 both prevents the penalty and reduces the risk of over-compensation.

Is over-compensation harmful?

Yes. If more capacitors than needed stay in circuit, reactive power is fed back to the grid, which can cause a capacitive reactive penalty and a voltage rise. An automatic stepped system prevents this risk.

How does harmonics affect compensation?

In a high-harmonic environment, bare capacitors can resonate and draw excessive current. In that case detuned (reactor-equipped) compensation must be used. Argus EMS makes this risk visible by monitoring the harmonic level.

Reactive Power Compensation: How It Works

What Is Reactive Power Compensation?

Reactive power compensation is the process of correcting the power factor by locally producing the reactive power that inductive loads (motors, transformers, ballasts) draw from the grid. The goal is to bring apparent power (kVA) closer to active power (kW), thereby both avoiding reactive energy penalties and using the facility's electrical capacity efficiently. Argus EMS continuously monitors power factor and reactive consumption, making both the need for and the adequacy of compensation visible.

How Is Compensation Done Step by Step?

A sound compensation project follows these steps:

Measurement: The current power factor and the active/reactive load profile are recorded over a defined period.
Calculation: The capacitor power (kVAr) required to reach the target power factor is calculated.
Stage design: The total kVAr is split into stages to follow changes in load.
Reactive controller selection: A control relay that switches stages in and out automatically is selected.
Harmonic check: If harmonic distortion is high, a detuned (filter) reactor is added.

Argus EMS provides field data for the measurement and verification steps, ensuring the design fits the real load profile.

How Is Capacitor Power Calculated?

The required reactive power is found from the active power and the difference of the tangents of the current and target power factor angles: Qc = P × (tanφ1 − tanφ2), where P is active power, φ1 the current and φ2 the target power factor angle. The table below summarizes an example scenario.

Quantity	Value
Active power (P)	400 kW
Current power factor	0.80
Target power factor	0.98
Required capacitor power (Qc)	≈ 219 kVAr

Fixed or Automatic Stepped?

Fixed compensation may suffice for facilities with a constant load; but if the load varies, an automatic stepped system is essential. Over-compensation leads to a capacitive penalty, under-compensation to an inductive penalty. Argus EMS monitors deviations in both the inductive and capacitive direction, revealing whether the number of stages and the controller settings are working correctly.

The Continuity of Compensation

Capacitors lose capacitance over time and contactors wear out; therefore compensation is not a system to install once and forget. Continuous power factor monitoring catches a failing stage early. Argus EMS raises an alarm when the power factor drops below target, preventing a reactive penalty before it occurs.