Multiple Ups Distributed Bypass System; Multiple Ups Parallel System Modes - Eaton Power Xpert 9395 Series Installation And Operation Manual

Understanding UPS Operation
6.4

Multiple UPS Distributed Bypass System

Distributed bypass parallel operation extends the normal operation of Power Xpert 9395 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 and/or for redundancy. 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 Power Xpert 9395 UPS parallel system supports a critical load in five
different modes of operation. The standard operation modes are:
NOTE
In Normal mode, the paralleled UPMs supply the critical load with clean, filtered power. Each UPM battery
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charger also provides charging current for the battery if needed.
In Bypass mode, the critical load is directly supported by utility power through the bypass circuit in each
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UPS.
In Battery mode, the battery provides DC power, which maintains UPM operation. The UPM batteries
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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:
A command is an intervention that is externally initiated by an operator or by some site action. A command
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causes the UPSs to switch operating modes; it usually does not require any further action.
A notice is a minor system event that may or may not require attention.
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An alarm is a system event that requires immediate intervention.
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TM
6-14 Power Xpert
The Variable Module Management System and Energy Saver System modes are
mutually exclusive.
9395 UPS (300 kVA) Installation and Operation Manual 164201728—Rev 10