Power distribution – Rockwell Automation 23P PowerFlex Digital DC Drive User Manual
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Rockwell Automation Publication 20P-UM001K-EN-P - July 2014
Chapter 1
Installation and Wiring
Grounding for Installations
in an Ungrounded or High-
Impedance, Neutral Ground,
or System
The PowerFlex DC drive was designed to work in distribution systems where the
isolation transformer Wye neutral is connected to earth ground. PowerFlex DC
drives are not designed to work in distribution systems that have ungrounded or
high-impedance, neutral connections, or systems that have a phase that is
referenced to earth. Symmetrical incoming power is required for correct drive
operation.
The use of a grounded Wye neutral is highly recommended to prevent common
mode rejection problems with the feedback measurement circuits in the drive.
Possible drive damage can occur because of inaccurate feedback measurements of
the incoming AC voltage, armature voltage, or field current.
If the PowerFlex DC drive is installed in a system with an ungrounded Wye
neutral or with an impedance ground connection, see
for the
necessary drive modifications that are required for proper installation.
Power Distribution
Figure 10 - Delta/Wye with Grounded Wye Neutral
Rockwell Automation strongly recommends the use of grounded neutral systems
for the following reasons:
•
Controlled path for common mode noise current
•
Consistent line to ground voltage reference, which minimizes insulation
stress
•
Accommodation for system-surge protection schemes
Figure 11 - Ungrounded Secondary
Grounding the transformer secondary is essential to the safety of personnel and
safe operation of the drive. A floating secondary can allow dangerously high
voltages occur between the chassis of the drive and the internal power structure
components.