Siemens 1PH818 - Converter Operation on a Grounded Network

Measures to reduce bearing currents
To specifically reduce and prevent damage caused by bearing currents, consider the system
as a whole, which comprises the motor, converter, and driven machine. The following
precautions help to prevent bearing currents:
● Setting up a properly meshed grounding system in the system as a whole, with low
impedance for high-frequency currents
● No potential difference between the motor, converter, and working machine.
– Use symmetrical, shielded connecting cables.
– Connect the cable shield at both ends over the greatest possible surface area (360°
contact).
– Use equipotential bonding conductors between the motor and the driven machine as
well as between the motor and the converter
● Limit the voltage rate of rise by using an output filter to dampen harmonic components in
the output voltage
WARNING
Hazardous voltage at the terminals when the rotor is rotating
There is always a magnetic flux in the machine due to the permanent magnets in the rotor.
An electrical voltage is generated at the terminals each time that the rotor turns. As a result
of this, there is also a voltage at the converter output terminals via the connecting cable. When
working on the drive system, you must prevent the machine shaft from rotating.
6.4.7 Converter operation on a grounded network
NOTICE
Damage resulting from protective conductor currents
When the machine is operated on a converter with current limiter, but without ground-fault
monitoring, protective conductor currents of up to 1.7 times the external conductor current
can arise if there is a ground fault on the output side. Neither the PE conductors of normally
rated multi-core connecting cables nor the PE connecting points of normal terminal boxes
are suitable for this purpose. Material damage can result.
● Use an appropriately sized PE conductor.
● Connect the PE conductor to the grounding terminal on the motor enclosure.
Electrical connection
6.4 Auxiliary circuits
SIMOTICS M-1PH8 1PH818., 1PH822.
Operating Instructions 07/2016 81