A line reactor is needed for high short-circuit power levels, partly to protect the actual inverter against excessive harmonic currents, and thus against overload, and partly to limit line harmonics to the permitted values. The harmonic currents are limited by the total inductance comprising the line reactor and mains supply cable inductance. Line reactors can be omitted if the mains supply cable inductance is increased sufficiently, i.e., the value of RSC must be sufficiently small.
RSC = Relative Short-Circuit power: Ratio of short-circuit power Sk Line at the supply connection point to the fundamental apparent power Sinv of the connected inverters (to IEC 60146‑1‑1).
PM330 Power Module requirements:
Line reactor can be omitted
Line reactor required
200 ... 500
It is recommended that a line reactor is always connected on the line side of the inverter, as in practice, it is often not known on which supply configuration individual inverters are to be operated, i.e. which supply short-circuit power is present at the inverter connection point.
A line reactor can only be dispensed with when the value for RSC is less than that in the above table. This is the case, when the inverter, as shown in the following figure, is connected to the line through a transformer with the appropriate rating.
A line reactor is always needed if a line filter is used.
In this case, the line short-circuit power Sk1 at the connection point of the inverter is approximately:
Sk1 = Stransf/(uk transf + Stransf / Sk2 line)
Stransf = Transformer rated power
SK2 line = Short-circuit power of the higher-level voltage level
uk transf = Relative short-circuit voltage