Why need reactive energy management?
Jan 07,2020

Part 1:Principle of reactive energy management

All AC electrical networks consume two types of power: active power (kW) and reactive power (kVAr):

  1. The active power P (in kW) is the real power transmitted to loads such as motors,lamps, heaters, computers, etc. The electrical active power is transformed into mechanical power, heat or light.

  2. The reactive power Q (in kVAr) is used only to power the magnetic circuits of machines, motors and transformers.

  3. The apparent power S (in kVA) is the vector combination of active and reactive power.

The circulation of reactive power in the electrical network has major technical and economic consequences. For the same active power P, a higher reactive power means a higher apparent power, and thus a higher current must be supplied.

The circulation of active power over time results in active energy (in kWh).

The circulation of reactive power over time results in reactive energy (kvarh).

In an electrical circuit, the reactive energy is supplied in addition to the active energy.

Due to this higher supplied current, the circulation of reactive energy in distribution networks results in:

  1. Overload of transformers
  2. Higher temperature rise in power cables
  3. Additional losses
  4. Large voltage drops
  5. Higher energy consumption and cost
  6. Less distributed active power

Reactive energy supplied and billed by the energy provider

Reactive energy supplied and billed by the energy provider

For these reasons, there is a great advantage in generating reactive energy at the load level in order to prevent the unnecessary circulation of current in the network.

This is what is known as "power factor correction". This is obtained by the connection of capacitors, which produce reactive energy in opposition to the energy absorbed by loads such as motors.

The result is a reduced apparent power, and an improved power factor P/S’ as illustrated in the diagram opposite.

The power generation and transmission networks are partially relieved, reducing power losses and making additional transmission capacity available.

The reactive power is supplied by capacitors.No billing of reactive power by the energy supplier

The reactive power is supplied by capacitors.No billing of reactive power by the energy supplier

Part 2:Benefits of reactive energy management

Optimized reactive energy management brings economic and technical advantages as follows:

Savings on utility bill

Eliminating penalties on reactive energy and decreasing kW / kVA.

Reducing power losses generated in the transformers and conductors of the installation.


Loss reduction in a 630 kVA transformer PW = 6,500 W with an initial Power Factor = 0.7.

With power factor correction, we obtain a final Power Factor = 0.98.

The losses become: 3,316 W, i.e. a reduction of 49%.

Increasing service capacity

A high power factor optimizes an electricalinstallation by allowing better use of the components.

The power available at the secondary of a MV/LV transformer can therefore be increased by fitting power factor correction equipment on the low voltage side.

The table opposite shows the increased available power at the transformer output through improvement of the Power Factor from 0.7 to 1.

Increasing service capacity Savings on utility bill

Reducing installation cost

Installing power factor correction equipment allows conductor cross-section to be reduced, since less current is absorbed by the compensated installation for the same active power.

The opposite table shows the multiplying factor for the conductor cross-section with different power factor values.

Improved voltage regulation

Installing capacitors allows voltage drops to be reduced upstream of the point where the power factor correction device is connected.

This prevents overloading of the network and reduces harmonics, so that you will not have to overrate your installation.

Part 3 Method for determining compensation
The selection of Power Factor Correction equipment should follow the following 3-step process and must be done by any people having the relevant skills:

Before the 3 steps, should calculate the required reactive power.

Step 1: Selection of the compensation mode:

  1. Central, for the complete installation
  2. By sector
  3. For individual loads, such as large motors.

Step 2: Selection of the compensation type:

  1. Fixed, by connection of a fixed-value capacitor bank;
  2. Automatic, by connection of a different number of steps, allowing adjustment of the reactive energy to the required value;
  3. Dynamic, for compensation of highly fluctuating loads.

Step 3: Allowance for operating conditions and harmonics

single line diagram of mv capacitor banks

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