Most modern industrial electrical grids are characterized by a significant content of nonlinear loads, creating many operation problems. Power harmonic filters are one of the most effective ways of reducing voltage distortion in electrical grids. The use of power filters solves two main concerns - to reduce the input current harmonic distortion of the power supply system and compensate for the reactive power of loads. As a rule, the sizing nominal parameters of filter circuits is carried out by the power supply system characteristics in stationary (steady) operating condition. However, field experience has shown that this approach does not always ensure a trouble-free operation of filters, and the main reason is no consideration of transient overvoltages and overcurrents in the sizing of the parameters of filter capacitors and reactors. The article is devoted to the problem of sizing the nominal parameters of filter reactors, as one of the two main components of the filter, for industrial electrical grids with a significant intensity of switching events. It is shown that for such electrical grids it is necessary to include transient overvoltages and overcurrents to the correct sizing parameters of filter reactors.

The main parameters of filter reactors are analysed, and their calculation’s peculiarities are considered. The characteristics of transients in filter reactor circuits, which are caused by the main technological and emergency switching events in industrial power supply systems with nonlinear loads, are given. It is shown that different types of switching events have different repetitiveness that should also be considered when sizing the parameters of filter reactors.

The method for determining the critical transient overcurrents and overvoltages in the filter circuit in calculating the design values of rated currents and overvoltages of the filter reactors is developed. The use of this method in the design of power filters will avoid possible damage to filter reactors due to overheating of the windings and accelerated insulation ageing during operation, caused by intense transients in the filter circuit.

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