Liebert NX 1+1 User Manual
LIEBERT NX 1+1 SYSTEM
PRODUCT SPECIFICATION AND INSTALLATION SHEET
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General
The Liebert NX UPS uses intelligent and reliable
decentralized technology to achieve parallel operation of two modules of the same rating.
The 1+1 system is used to:
• Increase the reliability of the system to ensure
adequate power supply to the critical load connected.
• Increase serviceability and allow the execution of
maintenance operations and reparations without
affecting the ordinary operating conditions of the
system (depending on the redundancy level).
CAUTION
!
An external maintenance cabinet is strongly
recommended to maintain the power supply to
load in case of complete maintenance.
Conditions for Parallel System
1. Each UPS module should have the same rating,
the same firmware and hardware version.
2. Each UPS module must have the same bypass
source.
3. The outputs of all UPS modules are connected
altogether.
4. The main inputs can be from different sources, but
the phase rotation sequence of main inputs,
bypass inputs and outputs must be correct and the
same.
5. The parallel logic cable and load sharing cable
must be connected in a ring correctly (See
Figure 2)
Features of Parallel System
1. The hardware and firmware for parallel UPS
module operation is standard in the Liebert NX,
and the configuration can be set up by changing
the settings in configuration software.
2. 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, shutting
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.
3. The total load of the parallel system can be
queried from each module’s liquid crystal display
screen.
4. Optional monitoring background software can
treat the entire parallel system as a big
single-module UPS, and provide corresponding
management. It can also get the information for all
modules by connecting to just one of the modules.
1
Figure 1 '1+1' System block diagram
Supplied by Others
Input Utility
Supply A B C
UPS1 UPS2
Charger Charger
Inverter Inverter
NN
CB1 CB1
SW1-C SW1-C
Static
Switch
Battery 2Battery 1
SW1-D SW1-D
SW1-A SW1-A
Q1EXT Q2EXT
Distribution Panel
Input Utility
Supply A B C
FuseFuse
RectifierRectifier
Static
Switch
A B CA B C
QBYPQUPS
To L o ad
Operating Principles
Redundancy Paralleling
The redundancy parallel system can noticeably
improve system reliability. In normal condition, neither UPS module works at full load. That means
that even if the load is increased, the system will not
transfer to bypass. And when a UPS module shuts
down due to any failure, the remaining UPS module
can still power and protect the load. When redundancy is lost due to module failure or load increase,
the parallel system will trigger an alarm.
Operation Modes Summary
The parallel system also has operation modes such
as normal, battery, bypass and maintenance bypass.
All UPS modules in the 1+1 parallel system operate
in coordination.
• Normal Mode Operation
The load is powered by the inverters of all the
UPS modules in the system. If the frequency of
bypass is within the synchronous range, the
inverter will be synchronized with the bypass.
Otherwise, the system will operate at nominal
frequency.
• Battery Mode Operation
The batteries of all UPS modules power the load
through their inverters. The system operates at
nominal frequency.
• Bypass Mode Operation
The condition to transfer to bypass mode is the
same as that for a single module system. The
bypass of all the UPS modules powers the load.
• Maintenance Bypass Mode Operation
The sequence to transfer to maintenance bypass
mode is the same as for transferring a singlemodule system. The maintenance bypass
switches should be switched on as synchronously
as possible. Thus the system can be repaired
without interrupting the power supply to critical
load.
Intermodule Control
Two kinds of signals are used for the parallel cables:
• Analog signals—UPS output unbalanced current
• Digital signals—control logic signals, parallel
cable status
Parallel control cables should be connected to the
parallel board (M3) of all modules and form a ring to
provide redundancy as shown in Figure 2.
Two types of Parallel control cables needed:
• DB9 for analog signals with one end DB9/F and
one end DB9/M
• DB25 for digital signals with one end DB25/F and
one end DB25/M
These come in lengths of 5m, 10m, &15m.
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