Emerson 40-200KVA Mode D'Emploi

The Liebert

®

 NX

™

 contains an electronically controlled switching circuit that enables the critical load 

to be connected to either the inverter output or to a bypass power source via the static bypass line. 

During normal system operation the load is connected to the inverter and the inverter contactor is 

closed; but in the event of a UPS overload or an inverter failure, the load is automatically transferred 

to the static bypass line.
To provide a clean (no-break) load transfer between the inverter output and static bypass line, the 

bypass static switch activates, connecting the load to bypass. To achieve this, the inverter output and 

bypass supply must be fully synchronized during normal operating conditions. This is achieved 

through the inverter control electronics, which make the inverter frequency track that of the static 

bypass supply, provided that the bypass remains within an acceptable frequency window.
A manually controlled, maintenance bypass supply is incorporated into the UPS design. It enables the 

critical load to be powered from the utility (bypass) supply while the UPS is shut down for routine 

maintenance.

The UPS is designed to operate as an on-line, double-conversion, reverse-transfer system in the 

following modes:

Operating in normal mode, the Liebert NX’s rectifier derives power from a utility AC source and 

supplies regulated DC power to the inverter, which regenerates precise AC power to supply the 

connected equipment. The rectifier also uses the utility source power to charge the batteries.

When utility AC power fails, the Liebert NX protects the critical load by instantaneously channeling 

battery power to the inverter, which continues supporting the critical load without interruption. 

When utility power returns and is within acceptable limits, the Liebert NX automatically shifts back 

to Normal mode, with the rectifier powering the critical load.

When the Liebert NX is in bypass mode, the load is directly supported by utility power and is without 

battery backup protection.
The Liebert NX’s inverter static switch and bypass static switch will shift the load from the inverter 

to bypass mode without an interruption in AC power if the inverter is synchronous with the bypass 

and any of the following occurs:

• inverter fails
• inverter overload capacity is exceeded
• inverter is manually turned off by the user