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Figure 1 '1+1' System block diagram
Operating Principles
Redundancy Paralleling
The redundancy parallel system can noticeably
improve system reliability. In normal condition, nei-
ther 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 redun-
dancy 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 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 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.
Supplied by Others
NN
Input Utility
Supply A B C
Input Utility
Supply A B C
Distribution Panel
UPS1 UPS2
CB1 CB1
RectifierRectifier
SW1-C SW1-C
Static
Switch
Static
Switch
Charger Charger
Battery 2Battery 1
FuseFuse
Inverter Inverter
SW1-D SW1-D
SW1-A SW1-A
A B CA B C
Q1EXT Q2EXT
QBYPQUPS
To Load