Permissible Total Cable Length For S120 Infeed Modules Feeding Multi-Motor Drives - Siemens SINAMICS G130 Engineering Manual

Fundamental Principles and System Description
Engineering Information
1.6.7

Permissible total cable length for S120 Infeed Modules feeding multi-motor drives

General
In the case of SINAMICS S120 multi-motor drives where an S120 Infeed Module supplies a DC busbar with more
than one S120 Motor Module, not only the length of the cable between each individual Motor Module and its
associated motor is limited, but also the total cable length (i.e. the sum of the motor cable lengths for all the Motor
Modules that are fed from a common Infeed Module via a common DC busbar). Strictly speaking, the length of the
DC busbar should also be taken into account when calculating the permissible total cable length. In practice,
however, the length of the DC busbar is negligible in comparison to the total lengths of motor cables in multi-motor
drives and the DC busbar length can consequently be ignored for the purposes of this particular calculation.
The total cable length must be restricted to ensure that the resulting total capacitive leakage current Σ I (sum of
Leak
the capacitive leakage currents I generated from the individual Motor Modules 1 ... n), which depends on the
Leak
overall motor cable length, does not overload the Infeed Module. This current is flowing back to the DC busbar via
either the line filter of the Infeed Module or the supply system and via the Infeed Module itself.
Route of the resulting total leakage current Σ I for a multi-motor drive with SINAMICS S120
Leak
If the total cable length and, in turn, the total leakage current Σ I are not sufficiently restricted, the integrated line
Leak
filters according to category C3 of EN 61800-3, the power components of the Infeed Module, and the snubber circuits
for the power components in the Infeed Module may be overloaded due to an excessive current or dv/dt load.
The permissible total cable lengths are device specific and are, therefore, specified in the relevant catalogs or in the
section "Checking the total cable length with multi-motor drives" of the chapter "General Information about Built-in
and Cabinet Units SINAMICS S120".
For more information about the cause of capacitive leakage currents and their magnitude, see section "Line filters".
EMC information
SINAMICS S120 multi-motor drives with a total cable length of several hundred meters or more generally only meet
the criteria of category C4 according to the EMC product standard EN 61800-3. This standard, however, clearly
states that this is permissible for complex systems of this type with rated currents of ³400 A used in an industrial
environment, as well as for IT supply systems. In such cases, system integrators and plant operators must define an
EMC plan, which means customized, system-specific measures to ensure compliance with the EMC requirements.
This applies regardless of whether the SINAMICS S120 multi-motor drive is operated on a grounded TN supply
system with line filters integrated in the SINAMICS Infeed Module as standard, or on a non-grounded IT supply
system with a deactivated line filter.
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