Connection Of Converters To Grounded Systems (Tn Or Tt); Connection Of Converters To Non-Grounded Systems (It) - Siemens SINAMICS G130 Engineering Manual

Fundamental Principles and System Description
Engineering Information
In IT systems, all live parts are isolated from ground, or one point is connected to ground through a high-value
impedance. All the exposed-conductive parts (enclosures) in the electrical installation are connected to an
independent ground electrode, either separately or in a group.
Example of an IT supply system

Connection of converters to grounded systems (TN or TT)

SINAMICS converters are designed for connection to grounded TN or TT systems, i.e. three-phase supply systems
with a grounded star point. The devices are equipped with means of connecting the three phase conductors L1, L2,
L3 and the protective conductor (PE) to ground. No connection for a separate neutral conductor (N) is provided, nor
is one necessary as the converters place a symmetrical load on the three-phase system and the star point is not
therefore loaded.
If a single-phase AC voltage, e.g. 230 V, is required to supply auxiliaries or the fan, this is supplied internally via
single-phase control-power transformers that are connected between two phase conductors. Alternatively, it can be
supplied from an external source.
It is not essential to install an earth-leakage monitor at the converter input. However, suitable precautions must be
taken to ensure that the substantial ground-fault current caused by ground faults in the device is promptly interrupted.
On SINAMICS G150 and S150 cabinets and S120 Cabinet Modules, this protection can be provided by optional line
fuses or, at higher current ratings, by optional circuit breakers in the converters themselves. The type 3NE1 fuses
recommended for this purpose are dual-function fuses which provide both line protection as well as semiconductor
protection for the thyristors and diodes in the rectifiers of G150 and S120 Basic Infeeds. In systems using S120
Smart Infeeds and S120 Active Infeeds and in S150 cabinets containing IGBT rectifiers, semiconductor protection
cannot be provided by fuses of any type due to the extremely low I
however, considerably restrict the extent of damage if a rectifier has a serious fault.
Ground faults in the motor cable at the output side or in the motor itself can be detected by the electronic ground fault
monitor implemented in the inverter. The response threshold of this monitor can be parameterized to values higher
than about 10 % of the rated output current.
SINAMICS units for operation in grounded TN and TT systems are equipped as standard with RFI suppression filters
for the "second environment" (category C3 according to the EMC product standard EN 61800-3). This applies to
SINAMICS G150 and S150 cabinets, to SINAMICS G130 Chassis and to the Infeeds (Basic Infeeds, Smart Infeeds
and Active Infeeds) of the S120 modular system (Chassis and Cabinet Modules). For more information about RFI
suppression, please refer to the section "Line filters" or to the chapter "EMC Installation Guideline".

Connection of converters to non-grounded systems (IT)

SINAMICS converters can also be connected to and operated on non-grounded IT supply systems. The advantage of
IT systems as compared to grounded supply systems is that no ground-fault current can flow when a ground fault
occurs and operation can therefore be maintained. The system does not shut down on faults until a second ground
fault occurs. This advantage means that IT supply systems are widely used in areas where fault tripping needs to be
reduced to a minimum due to the processes being carried out (e.g. in the chemical, steel, and paper industry).
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t values of the IGBT chips. Type 3NE1 fuses,