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5.2 Configuring Parallel Sbasystem Operation
5.2.1 General
The Liebert
®
NX
™
uses intelligent and reliable decentralized technology to achieve parallel operation
of two or more modules.
The parallel system is used to:
• Increase the reliability of the system to ensure adequate power supply to the critical load con-
nected.
• Increase serviceability and allow the execution of maintenance operations and repairs without
affecting the ordinary operating conditions of the system (depending on the redundancy level).
5.2.2 Features of Parallel System
• The controls for parallel UPS module operation are standard in the Liebert NX, and the configu-
ration can be set up by changing the settings in configuration software.
• It is easy to install the parallel cables in a ring, providing high reliability and redundancy. And
the intelligent paralleling logic provides the user with maximum flexibility. For example, shut-
ting down or starting up the UPS modules in the parallel system can be done in any sequence. If
an overload transfer occurs, the whole system can recover automatically from bypass mode after
the overload is cleared.
• The total load of the parallel system can be queried from each module’s liquid crystal display
screen.
Figure 14 Parallel system block diagram
UPS Module 2
UPS Module 3
UPS Module 4
480V, 3W
Output
IOB1
IOB2
IOB3
IOB4
UOB
480V DC
Battery Input
480V, 3W
Input
(Field Removable
Jumper for Dual
Input)
Bypass
Static
Switch
DC
DC
Liebert NX UPS (40-200kVA) Liebert NX Basic Paralleling Cabinet
AC
DC
DC
AC
RIB = Rectifier Input
Breaker
IOB = Inverter Output
Breaker
MBB = Maintenance
Bypass Breaker
MIB = Maintenance
Isolation Breaker
LDB = Load Distribution
Breaker