46 Rockwell Automation Publication DRIVES-AT005D-EN-P - May 2022
Chapter 4 Non-regenerative Bus Supply Configuration
Appendix A show the maximum external DC bus capacitance values and corresponding precharge delay times for PowerFlex 755TM non-
regenerative bus supply. If bus supply modules are paralleled, sum the maximum external bus capacitance values for each module to
determine the total maximum DC bus capacitance. Set the PowerFlex 755TM non-regenerative supply precharge delay times such that the
total DC bus capacitance can be precharged by the non-regenerative supply.
10. Verify that the system AC and DC bus bars and cables are sized to support the expected current. The total rated DC bus current is the sum of
all inverter/drive rated DC input currents as described in PowerFlex 755TM System DC Bus Ratings on page 99
. Alternatively, the rated DC bus
current can be calculated by dividing the total rated AC output current in step 8 by 0.9.
The PowerFlex 755TM system standard bus bars are rated for 3000 A DC and optional (-P46) 4700 A DC. All DC bus bars in the common DC
bus lineup must have the same amp rating. See PowerFlex 755TM System DC Bus Ratings on page 99
for more information about the DC bus
bar ratings and options. If the calculated total DC rated amps exceed these ratings, special design considerations are required to ensure the
AC and DC bus bar systems are sized to handle the expected AC and DC currents. Back-to-back or center-fed enclosure lineups may be used
to satisfy these requirements. See the associated PowerFlex 755T technical data and installation manuals for more information. Third-party
enclosures with suitably rated AC and DC bus bars may also be employed to meet the AC and DC current requirements of this example
system.
Ensure that you have adequate AC and DC overload and overcurrent devices capable of protecting the PowerFlex 755TM non-regenerative
bus supply and associated AC and DC circuit conductors and bus bars.
Example Advanced Sizing PowerFlex 755TM Non-regenerative Bus Supply Calculation
This example represents a 480V AC input system with five motors and mixed product family drives. The acceleration and deceleration times are
assumed to be less than one minute so we can take advantage of the overload duty of the inverter drives and the bus supply. Bold text in the table
represents calculated values based on the calculation methods described earlier.
Steps 1…5 are summarized in the following table.
• All drive products are rated for 480V AC system power voltage.
• Pmaccel, Pmrun and Pmdecel are the motor shaft power requirements of the application.
• Paccel, Prun, and PDecel are the calculated DC input power requirements of the inverter drives.
6. The highest output absolute value power total is 1483.2 kW heavy duty (HD). Use this value to select the minimum DC output power for the
PowerFlex 755TM non-regenerative bus supply.
7. Use Table 13 on page 72
, to select the DC bus output power rating 480V AC PowerFlex 755TM non-regenerative bus supply that supports the
value in step 6.
Because the DC bus power exceeds the rating of a single (1X) or a dual-density (2X) non-regenerative module, it’s necessary to parallel non-
regenerative dual-density (2X) power modules. See Paralleling PowerFlex 755TM Non-regenerative Modules on page 41
for more information
about paralleling modules.
For this example, two dual-density (2X) modules are paralleled.
The PowerFlex 755TM non-regenerative supply total heavy duty (HD) continuous DC output power rating for this example is 1633 kW DC.
IMPORTANT The PowerFlex 755TM non-regenerative bus supply does not contain
overload protective devices. Ensure that you provide AC overload
protective devices that protect the non-regenerative supply and
associated AC and DC conductors and bus bars.
Section
Name
Motor Nameplate Accel DC Bus Power (kW) Run DC Bus Power (kW) Decel DC Bus Power (kW)
Power (kW) Efficiency Pmaccel Paccel
(1)
(1) Drive output power calculations include factors for polarity of power, motor efficiency, and inverter efficiency
Pmrun Prun
(1)
Pmdecel PDecel
(1)
Drive 1 933 0.95 1120.0 1215.41 900.0 976.67 -40.0 -36.86
Drive 2 45 0.9 56.0 64.15 -50.0 -43.65 -10.0 -8.73
Drive 3 522 0.94 705.0 773.20 480.0 526.43 70.0 76.77
Drive 4 7.5 0.87 11.0 13.03 6.5 7.70 -10.0 -8.44
Drive 5 22 0.9 20.0 22.91 14.0 16.04 -15.0 -13.10
Bus Supply OL
Duty
None=1.0
ND=1.1
HD=1.5
1.5
DC Bus Power Totals
(2)
(2) Output power total calculations include overload duty of the bus supply
1392.5 1483.2 19.9
Bus Supply DC Bus Output Power 1483.2 kW HD
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