22 Rockwell Automation Publication 750-RM003A-EN-P - April 2018
Chapter 1 Selection Considerations
Other Loads Powered from the AFE AC Power Source
Full-wave 3 phase or 6-pulse rectifiers are used by most standard AC drives that
are powered from AC power sources. If 6-pulse rectifiers are sharing the same
AC input source as the PowerFlex 755TM bus supply, follow these
recommendations:
• Apply an appropriately-sized isolation transformer to the AC input side
of the PowerFlex 755TM bus supply to help isolate unwanted
harmonics that are commonly associated with 6-pulse loads.
• If an isolation transformer cannot be used with the PowerFlex 755TM
bus supply, consider the following:
• If the 6-pulse rectifiers are equipped with 3% AC line reactors, the
combined 6-pulse rectifier load cannot exceed 150% of the bus
supply rating.
• If the 6-pulse rectifiers are equipped with integral DC link chokes,
the combined 6-pulse rectifier load cannot exceed 40% of the bus
supply rating.
If the bus supply is connected to an AC source with other drives, or devices
with AFE-type input converters that share that same AC input line source,
install an appropriately-sized isolation transformer between the power source
and the AC input of PowerFlex 755TM bus supply.
Power Source Grounding
The Safety Ground-PE must be connected to system ground. Ground
impedance must conform to the requirements of national and local industrial
safety regulations and/or electrical codes. Check the integrity of all ground
connections periodically.
The PowerFlex 700AFE bus supply can be used with various grounding
methods. The PowerFlex 755TM bus supply can be used with similar
grounding methods. There are special considerations that may require external
bus conditioning equipment, depending on the power source grounding
method. A single point (PE only) grounding scheme should be used. Some
applications with long distances between the drives or drive line-ups that could
cause large potential differences between the drive or line-up grounds may
require alternate grounding schemes. See Wiring and Grounding Guidelines
for Pulse-width Modulated (PWM) AC Drives, publication DRIVES-IN001
,
for more information. In addition, see the Drives in Common Bus
Configurations with PowerFlex 755TM bus supplies application technical
guide, publication DRIVES-AT005
, for information about how to configure
the PowerFlex 755TM bus supply depending on the power source grounding
method.
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