Precharging the afe, Introduction, Important guidelines – Rockwell Automation 20Y PowerFlex Active Front End User Manual

Page 78: Introduction important guidelines

Rockwell Automation Publication 20Y-UM001E-EN-P - July 2014

Chapter 2

AFE in IP21 Rittal Enclosure—Installation/Wiring

Precharging the AFE

This section contains important information about AFE precharging.

Introduction

An AFE in the IP21 Rittal enclosure contains an internal precharging circuit.
The precharging unit is used to charge the DC bus capacitors. The charging time
depends on the capacitance of the intermediate circuit and the resistance of the
charging resistors.

Table 20

shows the technical specifications for the precharge

in the AFE enclosure. For correct operation of the precharging circuit, the input
circuit breaker and the precharging circuit contactor must be controlled by the
AFE.

Table 20 - Total DC Bus Capacitance Limits for Precharging Circuit of AFE in IP21 Rittal Enclosure

Important Guidelines

The following guidelines must be read and understood.

If drives without internal precharge are used and a disconnect is installed
between the input of the drive and the DC bus, you must use an external
precharge circuit between the disconnect and the DC input of the drive.

If drives with internal precharge are used with a disconnect switch to the
common bus, you must connect an auxiliary contact on the disconnect to a
digital input of the drive. The corresponding input must be set to the
‘Precharge Enable’ option. This provides the proper precharge interlock,
guarding against possible damage to the drive when connected to a
common DC bus.

The precharge status of the AFE must be interlocked with the connected
drives, such that the drives are disabled (not running) when the AFE is in a
precharge state.

Frame Size

Resistance

Capacitance, min

(1)

(1) The minimum capacitance is built into the AFE.

Capacitance, max

(2)

(2) The maximum capacitance is the capacitance of the AFE plus the external capacitance.

2 x 20 ohms

9900 μF

70,000 μF

2 x 11 ohms

29,700 μF

128,000 μF

ATTENTION: If the maximum capacitance is exceeded, component damage in
AFE occurs.