We have gathered the concepts most often encountered in electrical installations under short, clear topic headings.
1
What is reactive power?
Part of the current we draw from the grid is converted into work (heat, light, motion), while another part is used to build the magnetic field of loads such as motors, transformers and ballasts. The part converted into work is called active power (kW); the part that shuttles back and forth for the magnetic field is called reactive power (kVAr).
Reactive power does no work, but it still makes current flow through cables and transformers. Both act together on the total current; this combination is called apparent power (kVA).
S² = P² + Q²
P active power (kW)
Q reactive power (kVAr)
S apparent power (kVA)
2
What is the power factor (cos φ)?
The power factor is the ratio showing how much of the apparent power drawn is actually converted into active power. The closer it is to 1, the more efficiently the installation uses the grid.
cos φ = P / S
When the power factor is low, a higher current is needed to draw the same active power. This leads to the following consequences:
Cables and transformers are loaded more than necessary.
Line losses and voltage drop increase.
The installation wastes part of its capacity on reactive current.
If the limits set by the distribution company are exceeded, a reactive energy charge appears on the bill.
3
Inductive and capacitive loads
Loads reflect reactive power to the grid in two different ways:
Inductive loads: Asynchronous motors, transformers, welding machines, fluorescent ballasts. They draw inductive reactive power from the grid. This is the most common type in industry.
Capacitive loads: Capacitors and some electronic devices. They supply capacitive reactive power to the grid.
The purpose of compensation is to supply the inductive reactive power locally with capacitors. However, if capacitors stay connected when the load drops, the installation can move into the capacitive region. Going capacitive is also subject to limits, so the amount of capacitance connected must be adjusted to the load.
Inductive load drivers help protect against capacitive loading by switching shunt reactors in at the desired value.
4
Reactive penalty limits
Under the regulations of Türkiye's Energy Market Regulatory Authority (EPDK), a certain amount of reactive energy relative to the active energy drawn is allowed free of charge. If these ratios are exceeded, a charge applies to the excess. Inductive and capacitive are monitored separately.
Installation
Inductive limit
Capacitive limit
Connection power below 50 kVA
%33
%20
Connection power 50 kVA and above
%20
%15
These ratios correspond approximately to the following power factor values:
Reactive / Active ratio
Approx. cos φ
%33
0.95
%20
0.98
%15
0.99
Ratios and conditions of application may be updated when regulations change. For current values, refer to the EPDK regulation and to your electricity bill.
5
What does a compensation system consist of?
An automatic compensation panel basically combines the following parts:
Current transformer: Transmits the current drawn by the installation to the relay.
Reactive power control relay: Calculates the power factor from current and voltage and decides which steps to switch in or out to reach the target value.
Switching elements: Contactors or thyristor modules switch the steps in and out.
Capacitors: Supply the reactive power.
Shunt reactors: Used to balance capacitive excess when needed.
Protection elements: Fuses, switches and alarm equipment.
The relay continuously monitors changes in the load and adds or removes steps accordingly. In this way the power factor is kept around the target value.
6
Contactor and thyristor switching
Two methods are used to switch capacitor steps in:
If the load changes very fast, a contactor-based system cannot keep up. In that case the reactive power may not be supplied at the required moment. Thyristor switching is preferred for such loads.
7
Harmonics
Non-linear loads such as drives, rectifiers, UPS units and LED lighting distort the current waveform. The components that appear at multiples of the fundamental frequency (50 Hz) are called harmonics.
In a network with harmonics, capacitors can go into resonance, draw excessive current, overheat and have a shorter life. Therefore, in installations with high harmonics:
The harmonic level should be measured first,
If necessary, a series detuning reactor (filtered compensation) should be used with the capacitors,
The capacitor voltage rating must suit the network voltage and the harmonic level.
The harmonic level can be determined by measuring with an energy analyzer.
8
What does an energy analyzer measure?
An energy analyzer lets you monitor the electrical condition of an installation in a single device. The following quantities are usually measured:
Phase voltages and currents
Active, reactive and apparent power
Power factor (cos φ) and frequency
Active and reactive energy consumption
Harmonic components
These values help you understand whether the compensation system is working correctly, whether the penalty limits are being exceeded and how the load changes during the day.