Emerson 250-400kVA - Manual (Page 9)

Introduction
3
1.2.2 Bypass Mode
When the Liebert NXL is in bypass mode, the load is directly supported by utility power and is with-
out battery 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
1.2.3 Battery Mode
When utility AC power fails, the Liebert NXL 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 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 - Opera-
tion.
1.3 Options
A number of options are available from Liebert for your UPS system. (Some options are not available
for all ratings.) Described below are the most frequently provided options. The first three battery
items are required to complete the UPS system. The remaining options provide improved sys-
tem performance or convenience. Other options are available. Contact your Liebert sales representa-
tive for more information.
• Battery and Racks—The batteries provide power in the event of a power outage. The Liebert
NXL UPS can use a variety of battery types, provided the battery plant is designed for the UPS
DC voltage range and the load requirements of your application. This option is required to com-
plete the UPS system.
• Battery Cabinets—Valve-regulated, lead-acid (VRLA) sealed batteries are available in match-
ing cabinets for convenient installation and maintenance in otherwise unprotected space.
Depending on the UPS module rating, two or more cabinets may be connected in parallel to pro-
vide the additional run time. This option is required to complete the UPS system.
• Module Battery Disconnect—The UPS system utilizes a separate Module Battery Disconnect
for remotely located batteries. A sensing circuit in the UPS module, set at the battery low voltage
limit, trips the Module Battery Disconnect to safeguard the battery from excessive discharge. The
Module Battery Disconnect has an undervoltage release mechanism designed to ensure that dur-
ing any shutdown or failure mode all battery potential is removed from the UPS system. This
option is required to complete the UPS system.
• Input Current Distortion Filter—This filter reduces input current reflected harmonic distor-
tion to less than 7% reflected THD at full load. The filter is factory-installed in the UPS. This fil-
ter also improves the input power factor to better than 0.92 lagging at full load.
• Two Breaker Maintenance Bypass—This switchboard provides make-before-break mainte-
nance bypass. It includes: Maintenance Bypass Breaker (MBB) and Maintenance Isolation
Breaker (MIB).
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.