Transport, installation and assembly
3.8 Connection to the converter
A5E01083943A AB
Siemens AG Operating Instructions 2.02 1FW4
47
WARNING
Dangerous voltage via the converter
As long as the feeding converter is switched on, or the DC link of the converter is not
discharged, there can be a voltage at the motor terminals even when the rotor is not
moving. Depending on the type of converter, the voltage can be up to 1,000 V. Ensure that
the five safety rules are complied with before working on the motor:
1. Isolate
2. Protect against reconnection
3. Make sure that the equipment is de-energized
4. Ground and short-circuit
5. Cover or enclose adjacent components that are still live
Preventing and reducing bearing currents
To prevent bearing currents when operating the motor with a converter, an insulated bearing
unit is used on the NDE.
CAUTION
Bearing damages
Do not bridge the bearing insulation! If the bearing insulation is bridged, damage may be
caused to the bearings due to a flow of current.
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 the
contact covers a large 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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Figure 3-2 Cable with symmetrical cable cross-section
● To ensure good discharging of high-frequency currents, provide contacting over a large
surface area. Establish a 360° contact of the cable shielding on the motor housing and on
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