VAR Compensation

About the Technology

VAR Compensation

All loads performing useful work on a system draw active power in kW, which again accumulates in kWh on your electrical bill. Useful work is the energy that is producing a torque on the output shaft of an electrical motor or the energy dissipated in a resistive circuit. Most loads, in addition to consuming active power, also have reactive characteristics, which causes them to store energy in the magnetic or electrical field as well.

Examples of inductive loads are induction motors and transformers. They utilize the magnetic field to transfer active power; thus, they draw additional current to produce the magnetic field. The opposite is capacitive loads such as capacitors, which stores energy in the electric field. For example, an induction motor is relying on a magnetic field to be able to convert electrical energy to rotational energy. Because of this, to create the magnetic field, some amount of energy is consumed.

The increased current due to reactive power puts additional strain on the grid and also gives additional electricity costs. Capacitor banks reduce the loading on the grid. It causes the reactive power to flow between the inductive load and capacitor bank, and not between the load and the grid, thus relieving some of the reactive strain in the grid.

The amount of reactive power has been an increasing problem for the last decades, not just because of the increased electrical loads, but also because we use power electronics to perform precise control of the electrical machines. Power electronics alter the current waveform from the fundamental frequency of the grid to a waveform comprised of several frequencies above the fundamental frequency. These frequencies we call harmonic frequencies, and they do not perform any useful work in a circuit and contribute to an increased phase-lag between the voltage and current.

The use of power electronics causes fast changes in the amount of reactive power consumed by the load. Because of this fast change, conventional capacitor banks are often not fast enough to control the amount of capacitance required by the system.

EMES VAr compensating technology uses IGBT and capacitor technology to counteract the phase shift between voltage and current created by non-linear loads or linear inductive loads.

Our technology uses external current transducers that detect the load current and transmit the signal to a controller were a sophisticated reactive power algorithm extract the reactive power from the apparent power. The reactive power data obtained is used to generate a compensating reactive power signal relayed to the IGBT control, were a PWM  signal is created with a switching frequency in the kHz range. Altering the DC bus voltage in comparison with the AC line voltage generates the compensating capacitive or inductive reactive power contribution, which leads to a reactive power exchange with the network.

The technology can be used together with capacitor banks, where the capacitors carry a part of the reactive load, and the IGBT control takes care of the fast-changing peaks of reactive consumption.