Emerson Liebert NX Product Specification/Installation Sheet page 2

Figure 1 '1+1' System block diagram
Supplied by Others
Fuse
Battery 1
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. 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 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.
N
Input Utility
Supply A B C
UPS1
CB1
Rectifier
SW1-C
Static
Switch
Charger
Inverter
SW1-A
A B C
Q1EXT
QUPS
To Load
Input Utility
Supply A B C
UPS2
Rectifier
Fuse
Charger
Battery 2
SW1-D
Inverter
Distribution Panel QBYP
• 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 single
module 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 are 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 15 ft.,
25 ft. and 50 ft. (4.5, 7.6 and 15.2m).
2
N
CB1
SW1-C
Static
Switch
SW1-D
SW1-A
A B C
Q2EXT