Understanding UPS Operation
Eaton
®
Power Xpert
®
9395P-900 UPS Installation and Operation Manual P-164000501—Rev 09
www.eaton.com/powerquality
6-23
6.4
Multiple UPS Distributed Bypass System
Distributed bypass parallel operation extends the normal operation of 9395P-900 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-900 UPS parallel system supports a critical load in five different
modes of operation. The standard operation modes are:
l
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.
l
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).
l
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).
l
In Bypass mode, the critical load is directly supported by utility power through the bypass circuit in each
UPS.
l
In Battery mode, the battery provides DC power, which maintains UPM operation. The UPM batteries
support the critical load.
The UPSs continually monitor themselves and the incoming utility power and automatically switch between
these modes as required, without operator intervention, except when manually switching to Bypass mode. The
sophisticated detection and switching logic inside the UPSs ensures that operating mode changes are
automatic and transparent to the critical load, while internal monitoring systems indicate the current mode of
operation. The UPSs switch operating modes in response to these system events:
Summary of Contents for Power Xpert 9395P-900 Series
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