The problems to the grid that harmonics cause:

- reduction of the torque of the shaft of induction motors;

- increased losses due to engine overheating and possible damage to insulation materials;

- additional vibrations in AC motors, reducing their service life;

- increasing the losses in the windings and the magnetic core of the transformers, leading to damage to the latter;

- reduction of the service life of the electrical equipment due to the strengthening of the thermal and electrical ageing of the insulation;

- the appearance of a constant component of current or voltage, which can cause saturation of the magnetic circuit and lead to an increase in the magnetizing current;

- failure of reactive power compensators, overheating of cosine capacitors and increase of current through them, which reduces their service life;

One of the most promising ways to reduce the currents and voltages of high harmonics in industrial grids is the use of power filters for high harmonics, which are a series connection of inductive and capacitive resistors tuned to resonate with the filtered harmonic. Fixed filter kits are widely used for the 5th, 7th, 11th and 13th harmonics, which complement the capacitor banks used to compensate for reactive power.

In this case, the most promising is the use of filter compensating devices, which are passive LC filters tuned to the frequencies of the respective harmonics. The parameters of the filter are chosen in such a way that the connections are tuned to resonate with the frequencies of the filtered harmonics, and their capacity allows to generate the required reactive power at the industrial frequency. The advantages are:
- the ability to compensate for selected harmonics (identified in the results of a survey of the undertaking's network);
- the possibility (limited) for reactive power compensation, including dynamic (for automatic devices);

However, these devices have a number of disadvantages:
- impossibility to adapt the filters to the time-varying frequency spectrum of harmonics in the enterprise grid, due to the fixed tuning frequency;

- low quality of reactive power compensation (partially due to the small number of control steps), due to the fact that the main task of these devices is to compensate the harmonics;

- high sensitivity to setting accuracy. If the connections are not set up correctly, the efficiency of these devices decreases sharply, and there may even be an increase in the level of harmonics in the network;

- large size and high price. For example, a device tuned to the 5th harmonic at a nominal main current of 240 A weighs 3240 kg and measures 1450x1545x2980;

- lack of function to eliminate phase imbalance;