Vacon NX Active Front End User Manual

Contents

4vacon • 40 Active Front End (AFE)Tel. +358 (0) 201 2121 • Fax +358 (0)201 212 2054.14 Pre-Charging circuitThe 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 connectingthe Active Front End unit to the mains. The charging time depends on the capacitance of theintermediate circuit and the resistance of the charging resistors. The technical specifications ofVacon's standard pre-charging circuits are shown in Table 20. Pre-charging circuits are suitablefor 380-500 Vac and 525-690 Vac.The Active Front End unit must not be connected to mains without pre-charging. In order to ensurethe correct operation of the pre-charging circuit, the input circuit-breaker or contactor, as well asthe pre-charging circuit contactor, must be controlled by the Active Front End unit. The inputcircuit-breaker or contactor as well as the pre-charging circuit contactor must be connected asshown in Appendix 70.If the capacitance of the intermediate circuit in the system exceeds the values shown, pleasecontact 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 bereleased and it returns to position 1. No other control measures are required. The Active Front Endapplication 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 statusof the main contactor is monitored via digital input (Default is DIN4). As a default the main contactormonitoring is ON but it can be set OFF with parameter. The main contactor should not be possibleclose without pre-charging.To open the main contactor, simply turn the switch to 0. The contactor should not be opened underload. 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 hasto be double insulated.NOTE! Enough space must be reserved around the resistors to ensure sufficient cooling. Don’tplace any heat sensitive components near the resistors.Table 20. Capacitance Min and Max value for Pre-charging circuitFrame size Resistance CapacitanceMin MaxFI9 2x47R 4950 μF 30000 μFFI10 2x20R 9900 μF 70000 μFFI13 2x11R 29700 μF 128000 μF