The distortion of the sinusoidal waveform of the supply network is caused by network feedback or harmonics.

Network perturbations. Copyright: Danfoss GmbH

They are caused by non-linear loads such as frequency converters, energy-saving lamps, switching power supplies in televisions, monitors and computers. All these devices load the grid with so-called harmonics, which leads to a significant distortion of the sinusoidal shape of the power grids if the load is too high.

“Grid feedback” refers to the mutual influence of consumers via the distribution grid and the influence of these same consumers on the distribution grid. This is because the interference emission of electrical loads has a negative impact on the shape, level and frequency of the supply voltage. In three-phase systems, it can also cause a change in the voltage symmetry.

This means that grid perturbations have a direct influence on the energy efficiency of the entire production plant and on the efficiency of electrical energy transport in the supply grid. Unbalanced loading of the grid, reactive power and harmonics cause additional losses, which can have a higher value in industrial low-voltage grids. Grid losses occur at all voltage levels. However, low-voltage grids have the highest losses of the entire energy supply grid, accounting for over 60 % of total losses.

The later the user takes countermeasures to eliminate grid perturbations, the more expensive the measures are. It is best to measure or estimate the load on the network during the planning stage and simulate possible solutions. Software such as MyDrive® Harmonics helps with this.

Two means are important to ensure electrical compatibility.

  1. Interference suppression of the sources by minimizing or eliminating interference.
  2. Increasing the interference immunity of the interfering device or system by preventing or significantly reducing the reception of interference.

Manufacturers use spark interference filters (also known as RFI filters, mains filters or EMC filters) to reduce such interference variables on the mains supply. This limits interference emissions to a prescribed level. It is best if the filters are installed in the appliance right from the start.

Voltage curve of an inverter with DC link choke