Power distribution – Rockwell Automation 20P PowerFlex Digital DC Drive User Manual
Page 35
Rockwell Automation Publication 20P-UM001I-EN-P - February 2013
35
Installation and Wiring
Chapter 1
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 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 may 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
on page
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. Leaving the secondary floating allows dangerously
high voltages between the chassis of the drive and the internal power structure
components.