Rockwell Automation PowerFlex 755TM Original Instructions Manual Download

Page: 46 / 120

Rockwell Automation Publication DRIVES-AT005D-EN-P - May 2022

Chapter 4 Non-regenerative Bus Supply Configuration

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