Compensation of reactive power

SOF ELEKTRO d.o.o. deals with energy efficiency, i.e. the production of complete reactive energy compensation systems both low and medium voltage, peak load limit, project and installation of new energy saving lighting fixtures, revision of power substations, production of all types of electrical installations, maintenance, automation of the manufacturing processes, etc.

Compensation of reactive power

Reactive power is a part of completely consumed energy for creating and maintenance of the magnetic field in electrical machines. The largest consumers of reactive power are electric motors and transformers, but also fluorescent tubes, rectifiers, computers, etc.
In addition to the fact that reactive power occupies transmission and production capacities, there are also significant losses in conductors and transformers that occur during its transmission.
Voltage drops in the electric power system are partly due to excessive consumption of reactive power.
The size describing the percentage of reactive power which is spent is called the power factor.
The system of tariffs is currently being introduced by Elektroprivreda Srbije in which every consumption of reactive power below the optimum limits, i.e. below power factor 0.95 is described as an overconsumption.
Compensation of reactive power implies the installation of equipment that generates reactive energy thus compensates for its consumption in the plant which leads to a significant reduction in the amount of reactive power taken from the grid.
In this way the consumption of the primary power isn’t significantly reduced but the company’s expenditure for electricity is.
Reactive power costs are typically about 15% of the total electricity bill. By compensation of reactive power this complete item should be eliminated almost completely.

Reactive power compensation is one of the most attractive energy saving measures with instant effects and a short period of investment repayment. The prices of compensation equipment are such that this investment is payable within 6 months to 2 years.

The basic principle of reactive power compensation

While operating, inductive loads (single-phase and three-phase asynchronous motors, transformers, chokes, fluorescent lighting …) pull out of the grid not only the active power which turns into useful operation (rotation of the motor shaft, brightness) but also reactive power which is used to create the magnetic field. Unlike active power which is permanently “consumed” in the loads, reactive power “oscillates” between the sources and them. The presence of reactive power in the system has negative consequences – although it does not perform useful work, it burdens the transfer lines. The total power of a system is a vector sum of the active and reactive power of the system.

The presence of reactive energy in the system is measured by the power factor (cos ρ).
The power factor is defined as the ratio of the active and total power of a load:

Electric power utility charges the consumption of reactive energy. Monthly cost for the reactive energy can be significant depending on the number and size of reactive energy loads in the plant, that is, the number and power of the asynchronous motors since they are the most common ones. In order to reduce reactive power costs, capacitor boxes are installed. From the diagram below we see that the active power that turns into useful work remains the same.

After installing the capacitor batteries, electricity meter which measures the reactive power registers far smaller amount of it as loads demanding reactive power are now supplied locally from them (from the batteries). The process is oscillatory, i.e. in the first semi-period loads take the energy from the capacitor and during the second period they return this energy to the capacitor.

Many other results are achieved by installing the capacitor batteries aside from reducing power consumption such as:

  • • Increase of available power;
  • • Reduction of losses in transfer lines;
  • • Reduction of voltage drops;
  • • Long durability of equipment.


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