Rockwell Automation Publication 750-RM003A-EN-P - April 2018 21
Selection Considerations Chapter 1
Power Source Considerations
The PowerFlex 700AFE bus supply is typically powered from a dedicated
isolation transformer with a solid ground X0 connection. This is the
recommended power source and grounding method. See the existing power
source wiring diagrams to confirm the following power source electrical
information:
•kVA
•primary voltage
•secondary voltage
•% impedance
• secondary winding configuration
• grounding method, solid ground X0, resistance grounded, ungrounded
• other electrical equipment powered from the secondary of the
transformer
To verify that the PowerFlex 755TM bus supply operates reliably with the
existing power source, consider the following factors.
Sizing
The PowerFlex 755TM bus supply is suitable for use on a power source that is
capable of delivering 100,000 A rms symmetrical amperes at 400/480/600V
and 65,000 A rms symmetrical amperes at 690V.
The PowerFlex 755TM bus supply must not be used on undersized or high-
impedance supply systems. The supply system kVA must be equal to or greater
than the drive-related kW. The system impedance must be less than 10%.
Operation outside of these limits can cause instability, which results in
shutdown.
You must take into account the kVA of all PowerFlex 755TM bus supplies on
the distribution system and the system impedance of upstream transformers.
System Impedance
Bus Supply kVA
Transformer kVA
-------------------------------------------
Transformer % Impedance=
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