UNDERSTANDING UPS OPERATION
Eaton
Power Xpert 9395P-600 (380V-600V) UPS Installation and Operation Manual
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P-164000710 Rev 1
www.eaton.com/powerquality
6-23
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In Bypass mode, the critical load is directly supported by utility power through the
bypass circuit in each UPS.
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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:
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A
command
is an intervention that is externally initiated by an operator or by some
site action. A command causes the UPSs to switch operating modes; it usually
does not require any further action.
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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.
The following paragraphs describe the differences in the parallel system operating
modes, using block diagrams to show the power flow during each mode of operation.
6.4.2
Online Mode – Distributed Bypass
In Online mode, utility AC power is supplied to the UPSs. Each UPS then conditions
the incoming AC power and provides clean, regulated AC power to tie cabinet or
distribution panel for parallel systems up to four modules. The applied load is shared
equally among the available UPMs in the system.
Figure 6‐17 shows the path of electrical power through the parallel system when
operating in Online
mode.
If the utility AC power is interrupted or is out of specification, the UPSs automatically
switch to Battery mode to support the critical load without interruption. When utility
power returns, the UPSs return to Normal mode.
If the UPSs become overloaded or unavailable, the distributed bypass system
switches to Bypass mode. The distributed bypass system automatically returns to
Normal mode when the overload condition is cleared and system operation is
restored within specified limits.
