2 Assembly and installation
BU 0600 en-2319 31
2.3 Chokes
Due to their operating principle, frequency inverters also generate effects on the motor side (e.g.
harmonics, steep flanks, EMC interference) which may cause faults in the operation of the system or
in the device itself. Input or link circuit chokes are primarily used for mains protection; in contrast,
output chokes reduce effects caused by the motor.
2.3.1.1 Input choke SK CI1-…
By using a mains input choke the charging current from the mains and the harmonics are reduced.
For this, chokes fulfil several functions:
1. Reduction of the harmonics in the mains voltage upstream of the choke
2. Increase of efficiency due to lower input currents
3. Extension of the service life of the link circuit capacitors
The use of chokes is recommended if e.g. the component of the installed inverter power exceeds
20 % of the transformer power. In addition, the use of chokes is advisable for very hard networks or
capacitative compensation systems. Chokes also reduce the negative effects of asymmetrical mains
voltages.
If large voltage fluctuations occur in the supply network due to switching actions, e.g. frequent
switching of large consumers connected in parallel, supply via power rails, or if other devices cause
harmonics, the use of chokes is also recommended.
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