Siemens SINAMICS G130 Engineering Manual page 36

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
SINAMICS units are designed for connection to three-phase AC supply systems in accordance with overvoltage
category III as defined by IEC 60664-1 / IEC 61800-5-1. They can be connected either to grounded TN or TT
systems or to non-grounded IT systems. (Exception: TN or TT systems with a line voltage > 3AC 600 V and
grounded phase conductor. In this case, the customer must take measures to limit surge voltages to overvoltage
category II according to IEC 60664-1 / IEC 61800-5-1).
Notes about grounded TN or TT systems
In grounded TN or TT systems, the supply system is directly grounded at one point. The system can be grounded at
any point, but two grounding points are normally preferred in practice:
·
Neutral of the supply system (with a star-connected system)
·
Phase conductor of the supply system
Directly grounded neutral
The neutral of the supply system (transformer, generator) is directly grounded. The voltage of the three phase
conductors relative to ground is then symmetrical and the insulation of the converter and motor to ground is evenly
stressed in all three phases on a relatively low level.
The RFI suppression filters for the second environment (Category C3 according to EMC product standard EN 61800-
3) that are integrated as standard in SINAMICS units and the optionally available RFI suppression filters for the first
environment (Category C2 according to EMC product standard EN 61800-3) are designed for use in supply systems
with directly grounded neutral and may only be used in systems of this kind.
Directly grounded phase conductor
One phase conductor of the supply system (transformer, generator) is directly grounded. The voltage of the three
phase conductors to ground is then asymmetrical and the stress on the insulation of the two non-grounded phase
conductors to ground is increased by a factor of 1.73. For this reason, the SINAMICS units described in this
engineering manual may be connected to supply systems with directly grounded phase conductor only when the
supply voltage is ≤ 600 V 3AC.
The RFI suppression filters for the second environment (Category C3 according to EMC product standard EN 61800-
3) that are integrated as standard in SINAMICS units must be disconnected from ground by removal of a metal clip
from the filter and the optionally available RFI suppression filters for the first environment (Category C2 according to
EMC product standard EN 61800-3) must not be installed. The SINAMICS units then only conform to Category C4 as
defined in EMC product standard EN 61800-3.
SINAMICS Engineering Manual – November 2015
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Ó Siemens AG