2 Assembly and installation
BU 0505 EN-3021 45
2.7 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.
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2.7.1 Mains chokes
In principle, there are two types of chokes which are used to provide mains protection. Input chokes
are connected into the supply cables directly upstream of the inverter; on the other hand, link circuit
chokes are installed in the direct current link circuit of the frequency inverter. The functions of both
chokes are comparable.
With the input choke / link circuit 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.
Above an inverter power of 45kW (Size 8) use of a link circuit choke is always recommended.
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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2.7.1.1 Link circuit choke SK DCL-
The link circuit choke is installed in the immediate vicinity of the frequency inverter and is connected
directly to the direct current link circuit of the inverter. All chokes have a protection class corresponding
to IP00. The choke used must therefore be installed in a control cabinet.
Inverter ID Filter type Part No. Data sheet
SK 5xxE-452-340-A … -552-340-A
SK 5xxE-752-340-A … -902-340-A
Table 11: Link circuit choke SK DCL-...
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