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UNDERSTANDING UPS OPERATION
6.4
Multiple UPS Distributed Bypass System
6-22
Eaton Power Xpert 9395P-600 (380V-600V) UPS Installation and Operation Manual
Distributed bypass parallel operation extends the normal operation of 9395P-600
UPSs by offering increased capacity and/or redundant capability. The parallel system
continues to maintain power to the critical loads during commercial electrical power
brownout, blackout, overvoltage, undervoltage, and out‐of‐tolerance frequency
conditions.
The output of the system is normally supplied by Uninterruptible Power Modules
(UPMs) contained in each UPS. Multiple UPMs are connected with their outputs in
parallel (tied together) to provide a load level greater than the rating of one UPM, for
redundancy, or both. The paralleled UPMs supply the output load with protected
power as long as the load does not exceed the combined rating of the paralleled
UPMs.
The power system is redundant as long as one of the UPMs can be disconnected
from the output bus and the remaining UPMs can continue to supply power to the
load without exceeding their ratings.
When the load is being supplied by the UPMs, the system output bus is continuously
monitored for an overvoltage or undervoltage condition. If an out of limits condition is
detected, the paralleled UPMs transfer the load to bypass using the UPS static
switches.
Communication is required between the UPSs for system metering and mode
control. System level communication and control are accomplished using a Controller
Area Network (CAN). A single building alarm in each UPS, connected to the other
UPSs in parallel and tied to the bypass contactor auxiliary contacts in each UPS, are
used for a secondary communication path. This arrangement ensures bypass control
even if the CAN bus is lost.
The system is paralleled for redundancy (1+1) in a system where two UPMs are
paralleled together and the load is less than the supporting capability of one of the
UPMs. The system is paralleled for capacity (2+0) if both UPMs in a system are
required to support the load.
A parallel capacity system can also be redundant (2+1), as long as there is always one
or more UPMs online than required to support the load.
6.4.1
Multiple UPS Parallel System Modes
Similar to the single UPS system, the 9395P-600 UPS parallel system supports a
critical load in five different modes of operation. The standard operation modes are:
S
In Normal mode, the paralleled UPMs supply the critical load with clean, filtered
power. Each UPM battery charger also provides charging current for the battery if
needed.
S
In Energy Saver mode, commercial AC power is supplied directly to the critical load
through the continuous static switch and transfers automatically to Online mode if
an abnormal condition is detected. The Energy Saver mode requires a UPS with a
continuous static switch. Energy Saver mode in a parallel system operates the
same as it does in a single UPS system (see paragraph 6.2.3).
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In Variable Module Management mode, the UPS operates as a traditional
double-conversion UPS, but selectively shifts the load to fewer UPMs to increase
the efficiency of the UPS. In a parallel system each UPS will require at least one
UPM to be in double-conversion mode at all times; otherwise, Variable Module
Management mode operates the same as it does in a single UPS system (see
paragraph 6.2.4).
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