A line reactor is needed for high short-circuit power levels, partly to protect the actual converter against excessive harmonic currents, and thus against overload, and partly to limit the line harmonics to the permissible values. The harmonic currents are limited by the complete inductance comprising the line reactor and line supply cable inductance. Line reactors can be omitted if the line supply cable inductance is increased sufficiently, i.e. the RSC value must be sufficiently small.

RSC = Relative Short-Circuit power: Ratio of short-circuit power S_{K line} at the supply connection point to fundamental apparent output S_conv of the connected converters (according to IEC 60146‑1‑1).

The following applies for SINAMICS G130 converter built-in units:

It is recommended that a line reactor is always connected on the line side of the converter, as in practice, it is often not known on which supply configuration individual converters are to be operated, i.e. which supply short-circuit power is present at the converter connection point.

A line reactor can only be omitted when the value for RSC is less than the values listed in the above table. This is the case, when the converter, as shown in the following figure, is connected to the line supply via a transformer with the appropriate rating.

Notice:

However, a line reactor is always required when a line filter is used.

In this case, the line short-circuit power S_k1 at the connection point of the converter is approximately:
S_k1 = S_transf / (u_k transf + S_transf / S_k2 line)