Rockwell Automation Publication 750-RM004A-EN-P - April 2018 23
Selection Considerations Chapter 1
Power Source Sizing
PowerFlex 755TL/TR drives are suitable for use on a power source having a
short circuit current rating of 100,000 Arms symmetrical amperes at 400/480/
600V and 65,000A rms symmetrical amperes at 690V. The actual short circuit
rating may be further limited by an interrupting capacity rating of user-
supplied branch circuit fuses and circuit breaker.
The PowerFlex 755TL/TR drives must not be used on undersized or high-
impedance supply systems. The supply system kVA must be equal to or greater
than the drive kW, and the system impedance must be less than 10%.
Operation outside these limits can cause instability resulting in PowerFlex
755TL/TR drive shutdown.
You must take into account the kVA of all PowerFlex 755TL/TR drives on the
distribution system and the system impedance of upstream transformers. See
publication DRIVES-IN001
for more information.
Other Loads Powered from the AC Power Source
Full-wave, three-phase, 6-pulse rectifiers are used by most standard AC drives
that are powered from AC power sources. If 6-pulse rectifiers share the AC
input source with PowerFlex 755TL/TR drives, follow these
recommendations.
• Apply an appropriately-sized isolation transformer to the AC input side
of the PowerFlex 755TL/TR to help isolate any unwanted harmonics
that are commonly associated with 6-pulse loads.
• If an isolation transformer cannot be used, consider the following
recommendations:
– If the 6-pulse rectifiers are equipped with 3% AC line reactors, the
combined 6-pulse rectifier load cannot exceed 150% of the
PowerFlex 755TL/TR drive rating.
– If the 6-pulse rectifiers are equipped with integral DC link chokes,
the combined 6-pulse rectifier load cannot exceed 40% of the
PowerFlex 755TL/TR drive rating.
If the PowerFlex 755TL/TR product is connected to an AC source with
additional drives or devices that are equipped with active front end converters
sharing that same AC input line source, it is recommended to install an
appropriately sized isolation transformer between the power source and the
AC input of each PowerFlex 755TL/TR drive.
System Impedance
PowerFlex 755TL/TR kVA
Transformer kVA
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Transformer % Impedance=
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