Vacon NX Active Front End, User Manual

Page: 42 / 110

4
vacon • 40 Active Front End (AFE)
Tel. +358 (0) 201 2121 • Fax +358 (0)201 212 205
4.14 Pre-Charging circuit
The Active Front End unit requires an external pre-charging circuit. The purpose of the pre-
charging unit is to charge the voltage in the intermediate circuit to a level sufficient for connecting
the Active Front End unit to the mains. The charging time depends on the capacitance of the
intermediate circuit and the resistance of the charging resistors. The technical specifications of
Vacon's standard pre-charging circuits are shown in Table 20. Pre-charging circuits are suitable
for 380-500 Vac and 525-690 Vac.
The Active Front End unit must not be connected to mains without pre-charging. In order to ensure
the correct operation of the pre-charging circuit, the input circuit-breaker or contactor, as well as
the pre-charging circuit contactor, must be controlled by the Active Front End unit. The input
circuit-breaker or contactor as well as the pre-charging circuit contactor must be connected as
shown in Appendix 70.
If the capacitance of the intermediate circuit in the system exceeds the values shown, please
contact the nearest Vacon office.
The example shown in Appendix 70 uses a spring-return switch. The switch has positions 0-1-
START. The spring returns the switch from position START to position 1. To start the pre-charging,
the switch is turned from position 0 via 1 to START. When pre-charging starts, the switch can be
released and it returns to position 1. No other control measures are required. The Active Front End
application controls the main contactor of the system with Relay Output RO2, see Appendix 72.
When pre-charging of the intermediate circuit is ready the main contactor will be closed. The status
of the main contactor is monitored via digital input (Default is DIN4). As a default the main contactor
monitoring is ON but it can be set OFF with parameter. The main contactor should not be possible
close without pre-charging.
To open the main contactor, simply turn the switch to 0. The contactor should not be opened under
load. Opening the contactor under load will shorten its service life.
NOTE! Wirings what are used for connecting the pre-charging circuit to the intermediate circuit has
to be double insulated.
NOTE! Enough space must be reserved around the resistors to ensure sufficient cooling. Don’t
place any heat sensitive components near the resistors.
Table 20. Capacitance Min and Max value for Pre-charging circuit
Frame size Resistance
Capacitance
Min Max
FI9
2x47R 4950 μF 30000 μF
FI10
2x20R 9900 μF 70000 μF
FI13
2x11R 29700 μF 128000 μF