Rockwell Automation 8720MC 8720MC Regenerative Power Supply User Manual User Manual

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4-8

Wiring

• Rating of regenerative power of the 8720MC-RPS is less than

rated power both in the instantaneous rating and continuous
rating.

• When rectifier portion of inverter is composed of thyristor, CR

snubber circuit between anode and cathode of thyristor may
become overloaded. Therefore, treating time for regenerative
power must be within 5 seconds for 3 minutes. Because the
current "I

" flowing through CR snubber circuit in the power

regeneration mode is represented by the following formula,
verify the specifications of CR snubber circuit.

• Do not fail to connect ACL unit of 3% impedance toward

inverter rating with the AC input line of inverter. Without ACL
unit, excessive circulating current will flow between the
8720MC-RPS units.

• Even during the power running, current will be supplied from

the 8720MC-RPS unit to DC bus proportionally to the impedance
ratio of both reactors at the 8720MC-RPS unit and inverter. This
current must not exceed the rating of the 8720MC-RPS unit.

• Set the parameter of the FWD Current Limit (U.001) to zero (0).

• Set the parameter of the Discharging Function Enable (F.017) to

zero (OFF).

• Set the DC bus voltage to start power regeneration to the

parameter of the DC Bus Voltage Reference (U.000).

• Open all the terminals PR1, PR2 and PR3 for connecting

precharge/discharge resistor. Because these terminals are open,
the unit does not perform precharge/discharge operations.
Precharge/discharge must be performed on inverter side.

• Do not fail to enter the READY signal of inverter to (PWR).

[A]

= (8 0.03 x R

[

Ω

]) x C [