If the utility AC power is interrupted or is out of specification, the UPS
automatically switches to the battery mode to support the critical load without
interruption. When utility power returns, the UPS returns automatically to the
double conversion mode.
If the UPS becomes overloaded or unavailable, the UPS seamlessly switches to
the bypass mode and continues supplying the load through the static bypass.
The UPS automatically returns to the double conversion mode when the
abnormal condition, such as an extended time overload, is cleared and the
system operation is restored within the specified limits.
If a UPM within the UPS suffers an internal failure, the remaining UPMs continue
to support the load in the double conversion mode. The UPS is automatically
internally redundant when the UPS is not operating at full load. However, if
internal redundancy between the UPMs is not possible due to high load, the UPS
switches automatically to the bypass mode and remains in that mode until the
failure is corrected and the UPS is back in operation.
In an external parallel redundant system, each UPS can be isolated from the
system for service while the remaining UPSs support the load in the double
conversion mode.
3.3.1.2
Variable Module Management System mode
When Variable Module Management System (VMMS) mode is enabled, the load
is powered by UPMs in double conversion mode. The UPS status indicated on
the display is
Unit Online VMMS
and the UPM status is
Active
.
UPS efficiency varies according to the load level at which the UPS operates.
VMMS technology enables achieving optimised system efficiency by
automatically optimising the UPM load level. As an example, when the load is
very low, a minimum of one UPM is online. This enhances the UPS system
efficiency by several percentage points.
The remaining UPMs are ready to switch to double conversion mode
instantaneously, if the load increases. The load will remain protected by double
conversion UPS the entire time, even during and after a load step.
It is possible to configure VMMS mode to include power module redundancy at all
times, so that a number of additional redundant UPMs are always online.
When the UPMs are in ready state, the IGBT converters are constantly powered,
since the rectifier input and inverter output relays are closed. The DC link is also
powered. Only the IGBT gate signals are suspended. The only step needed to
come out of ready state is to gate the IGBT switches. Since DC voltage is
constantly present, the inverter is able to start instantaneously: the 2 ms transfer
to double conversion is practically seamless.
3.3.1.3
Energy Saver System mode
Figure 5: Path of current through the UPS in the Energy Saver System mode
shows the path of electrical power through the UPS system when the UPS is
operating in the Energy Saver System (ESS) mode.
© Eaton Corporation plc 2020. All rights reserved.
Revision: 006
Document ID: P-164000493
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Eaton 91PS/93PS UPS 8–40 kW
User’s and Installation Guide
