Grounding And Pe Conductor Cross-Section; Precharging Of The Dc Link And Precharging Currents - Siemens SINAMICS G130 Engineering Manual

SINAMICS S150
Engineering Information
8.4.3

Grounding and PE conductor cross-section

The PE conductor must be dimensioned to meet the following requirements:
· In the case of a ground fault, no impermissibly high contact voltages resulting from voltage drops on the PE
conductor caused by the ground fault current may occur (< 50 V AC or < 120 V DC, IEC 61800-5-1, IEC 60 364,
IEC 60 543).
· The PE conductor should not be excessively loaded by any ground fault current it carries.
· If it is possible for continuous currents to flow through the PE conductor when a fault occurs, the PE conductor
cross-section must be dimensioned for this continuous current.
· The PE conductor cross-section should be selected according to EN 60 204-1, EN 60 439-1, IEC 60 364.
Cross-section of the phase
conductor
2
mm
Up to 16
16 to 35
35 and above
Note:
The recommendations for the North American market in AWG or MCM must be taken from the appropriate NEC
(National Electrical Code)/CEC (Canadian Electrical Code) standards.
· Switchgear and motors are usually grounded via separate local ground connections. When this grounding
arrangement is used, the current caused by a ground fault flows through the parallel ground connections and is
divided. Despite the use of the relatively small PE conductor cross-sections specified in the table above, no
impermissible contact voltages can develop with this grounding system.
Based on experience with different grounding configurations, however, we recommend that the ground wire from
the motor should be routed directly back to the converter. For EMC reasons and to prevent bearing currents,
symmetrical 3-wire three-phase cables should be used where possible instead of 4-wire cables, especially on
drives in the higher power range. The protective or PE conductor must be routed separately when 3-wire cables
are used or must be arranged symmetrically in the motor cable. The symmetry of the PE conductor is achieved
using a conductor surrounding all phase conductors or using a cable with a symmetrical arrangement of the three
phase conductors and three ground conductors. For further information, please refer to sections "Bearing currents
caused by steep voltage edges on the motor" and "Line filters" in chapter "Fundamental Principles and System
Description", as well as to chapter "EMC Installation Guideline".
· Through their controllers, the converters limit the load current (motor and ground fault currents) to an rms value
corresponding to the rated current. We therefore recommend the use of a PE conductor cross-section analogous to
the phase conductor cross-section for grounding the converter cabinet.

8.5 Precharging of the DC link and precharging currents

In the case of SINAMICS S150 converters, the DC link is precharged by precharging resistors in the Active Interface
Modules, a process which incurrs heat losses. To precharge the DC link, the converter is connected at the line side to
the line supply via a precharging contactor and precharging resistors R
contactor is closed and the precharging contactor opened again.
Precharging on SINAMICS S150 cabinet units by means of a precharging contactor and precharging resistors
The principle of precharging involves the use of ohmic resistors R
precharging resistors are dimensioned thermally to precharge the DC link of the S150 converter without themselves
becoming overloaded.
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Ó Siemens AG
Minimum cross-section of the external PE
conductor
2
mm
Minimum phase conductor cross-section
16
Minimum half the phase conductor cross-section
. Once the link is precharged, the bypass
p
and is therefore subject to losses. The
p