Emerson Liebert NX 10-30kVA - Manual (Page 67)

Operation
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Normal Mode
Operating in normal mode, the NX’s rectifier derives power from a utility AC source and supplies reg-
ulated DC power to the inverter, which regenerates precise AC power to supply the connected equip-
ment. The rectifier also uses the utility source power to charge the batteries.
Battery Mode
When utility AC power fails, the 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 NX automatically shifts back to Normal mode, with
the rectifier powering the critical load.
Bypass Mode
When the NX is in bypass mode, the load is directly supported by utility power and is without battery
backup protection.
The NX’s static transfer switch will shift the load from the inverter to bypass mode without an inter-
ruption 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 user
Maintenance Mode
For maintenance or repair, the NX may be operated in maintenance mode. To place the NX in mainte-
nance mode, the load must be transferred to bypass and the inverter must be turned off. When those
conditions are met, the rotary switch may be turned to MAINT and the UPS may be shut down, per-
mitting disconnecting the batteries for maintenance.
Parallel Redundancy Mode (System Expansion)
For higher capacity, higher reliability or both, the outputs of up to four UPS modules can be pro-
grammed for directly paralleling while a built-in parallel controller in each UPS ensures automatic
load sharing.
Frequency Converter Mode
The Liebert NX can be programmed into frequency converter mode for either 50Hz or 60Hz stable
output frequency. The input frequency may vary from 40Hz to 70Hz. In this mode, the static bypass
operation is disabled and the battery becomes optional, depending on any requirement to operate in
battery mode (stored energy mode).
NOTE
If the inverter is asynchronous with the bypass, the static switch will transfer the load from the
inverter to the bypass WITH interruption in AC power to the critical load. This interruption
will be less than 15ms (in 50Hz), or less than 13.33ms (in 60Hz). This interruption time may be
altered by modifying the Output transfer interrupt time setting.
!
CAUTION
The internal maintenance bypass must not be used when the UPS system is in 1+N parallel.
!
WARNING
The UPS input and output must be protected with external overcurrent protection devices. In
maintenance mode, the input and output busbars remain energized.