4.11.2
Reducing bearing currents
If you want to prevent damage due to bearing currents, you must take the entire system into
account, i.e., the motor, converter and driven machine. The following measures help to prevent
bearing currents:
● In addition to grounding the motors via the grounding conductor, supplement the RF
grounding with braided flat copper cables or RF stranded conductors. Ensure that contact
is established across the largest possible surface area. Solid copper cables are not suitable
for RF grounding because of the skin effect.
● Use symmetrically constructed, shielded connection cables to connect the motor to a
converter. The cable shielding, made up of as many strands as possible, must have good
electrical conductivity. Braided shields made of copper or aluminum are well suited.
Connect the shielding at both ends on the motor and on the converter. Keep unshielded
cable ends as short as possible.
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Concentric copper or aluminum shield
Steel armor
● To ensure that high-frequency currents are appropriately discharged, establish a contact
through the largest possible surface area at both ends. Establish a 360° contact of the cable
shielding on the motor housing and on the protective grounding bar of the converter. On
the motor end for example, this can be done using EMC screw joints at the cable entry
ports. On the converter end, you can use EMC-shielded clips, for example.
● In the overall system, set up a properly meshed grounding system with low impedance for
high-frequency currents.
● No potential difference between the motor, converter, and working machine.
– Use equipotential bonding cables between the terminal box and the‑ high-frequency
grounding point on the motor enclosure.
– Use a separate high-frequency equipotential bonding cable between the motor
enclosure and the protective grounding bar of the converter.
– Use a separate high-frequency equipotential bonding cable between the motor
enclosure and the driven machine.
● Use the common-mode filter (damping cores) at the converter output. The Siemens sales
representative is responsible for selection and dimensioning.
● Limit the rise in voltage by using output filters. Output filters dampen the harmonic content
in the output voltage.
Preparations for use
4.11 Converter operation
SIMOTICS T-1FW4 Heavy Duty 1FW4407-1KM81-1BC0-Z
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Operating Instructions 11/2018
