34 Rockwell Automation Publication 750-RM004A-EN-P - April 2018
Chapter 1 Selection Considerations
• Calculate the required external control 240V AC control circuit current
from the loading data that is shown in Table 5 on page 33
.
a. Add the current required for applicable Entry and Exit wiring bays.
b. When selecting an external control transformer power or VA rating,
multiply the total current requirement by 240V AC. Multiply this
value by 1.25 to ensure the transformer can supply inrush currents.
Inverter Output Filtering
The PowerFlex 700S drive did not offer factory-installed inverter output
filters. If filters were used, they were supplied separately or as part of an
engineered system. Typically, output reactors, dv/dt, Reflective Wave
Reduction (RWR), or possibly sine-wave filters were used if inverter output
filtering was required to reduce reflected wave voltage at the motor terminals.
The PowerFlex 755TL/TR drive or PowerFlex TM common bus inverter can
be supplied with an optional factory-installed RWR filter. The filter consists of
a low-impedance iron core reactor with damping resistors. Inverter output
filtering is specified by catalog code (-K) or (-M) in position ‘g’ of the catalog
number.
It is possible to use the existing inverter output filter, however, it may be
necessary to operate the drive in a certain mode or adjust certain parameters to
verify the drive is tuned correctly and operates with a suitable motor control
method. This is typically required if dv/dt or sine-wave filters are used.
Contact an Authorized Rockwell Automation Distributor specialist, Solution
Partner, Recognized System Integrator or Rockwell Automation account
manager to discuss these types of inverter output filters.
EXAMPLE Quantity 2 x frame 10 PowerFlex 755TM common bus inverters with
precharge, IP54 enclosure with optional entry wiring bay.
– External 240V AC control current required =
(19.2 + 0.39) x 2 = 39.2 A
– Is the total 240V AC control bus current less than 100 A? Yes.
– Calculate the VA rating of the external transformer =
39.2 A x 240V x 1.25 = 11,760VA
A standard-size control transformer rated 12…15 kVA is an
acceptable solution for this example.
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