Modes Of Operation; Normal Mode; Bypass Mode; Battery Mode - Emerson Liebert NXL 250 kVA Operation And Maintenance Manual

1.2

Modes of Operation

1.2.1

Normal Mode

Operating in normal mode, the Liebert NXL'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 DC sources.
1.2.2

Bypass Mode

When the Liebert NXL is in bypass mode, the load is directly supported by utility power and is
without DC source backup protection.
The Liebert NXL's inverter 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
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 10ms. This interruption time may be altered by modifying the Output transfer
interrupt time setting.
1.2.3

Battery Mode

When utility AC power fails, the Liebert NXL protects the critical load by instantaneously channeling
DC source power to the inverter, which continues supporting the critical load without interruption.
When utility power returns and is within acceptable limits, the Liebert NXL automatically shifts back
to Normal mode, with the rectifier powering the critical load.
1.2.4

Maintenance Bypass

The installation of a Maintenance Bypass Cabinet or Assembly is recommended to allow you to totally
isolate the UPS from all power sources. Use of the Maintenance Bypass is described in 2.0 -
Operation.
1.2.5

ECO Mode

The ECO Mode feature improves the overall efficiency by powering the critical bus from the bypass
static switch instead of the inverter.
The user has the ability to start/stop ECO Mode manually via HMI or automatically based on time
and day of week schedule entries.
When the critical bus goes out of tolerance (voltage, frequency or slew rate), the BPSS is turned off
and the inverter powers the critical bus.
The inverter is always ready to take the load in the event that the bypass source fails.
1.2.6

Intelligent Paralleling

Intelligent Paralleling is intended to increase system efficiency and to reduce the operating hours on
the modules. Intelligent Paralleling will put one or more paralleled modules into standby operation
when the number of redundant modules is above the user-specified threshold, plus some hysteresis.
3
Introduction
® ™
Liebert NXL