UNDERSTANDING UPS OPERATION
Eaton 9395 UPS (450–825 kVA) Installation and Operation Manual
S
164201725 Rev 4
www.eaton.com/powerquality
6-4
If the utility AC power is interrupted or is out of specification, the UPS automatically
switches to Battery mode to support the critical load without interruption. When utility
power returns, the UPS returns to Online mode.
NOTE
Bypass mode is not available on a UPS configured as an IOM.
If the UPS becomes overloaded or unavailable, the UPS switches to Bypass mode.
The UPS automatically returns to Online mode when the overload condition is cleared
and system operation is restored within specified limits.
If the UPS suffers an internal failure, it switches automatically to Bypass mode and
remains in that mode until the failure is corrected and the UPS is back in service.
6.2.3
Energy Saver System Mode
NOTE
VMMS and ESS modes are mutually exclusive. If ESS mode is enabled, VMMS mode is disabled.
NOTE
ESS mode requires the UPS to be factory built with a Continuous Static Switch (CSS).
When the UPS is operating in ESS mode, commercial AC power is supplied directly to
the critical load through the continuous static switch. Power line filtering and spike
protection for the load are provided by the input and output filter networks, and the
UPS actively monitors the critical bus for power disturbances. When in this mode, the
input and output contactors are closed and the link is maintained through the diode
bridge.
If commercial power voltage or frequency disturbances are detected, the system
forward transfers to Battery mode for minor disturbances and then to double
conversion mode for more severe disturbances. During a complete power outage, the
transfer takes place within 2 ms to ensure loads being fed by the system output are
not interrupted. All forward transfers transfer to Battery mode before returning to
double conversion mode.
In High Alert mode the unit transfers from ESS mode to double conversion mode or if
in double conversion mode remains in double conversion mode for a default time
period of one hour (customer configurable). At the completion of the time period, the
unit defaults back to ESS mode. If the High Alert command is received during the
time period, the timer will be restarted.
ESS mode is a normal operating mode, and not an alarm condition. While the UPS is
in this mode, the Online light on the front display will illuminate.
6.2.4
Variable Module Management System
NOTE
VMMS and ESS modes are mutually exclusive. If VMMS mode is enabled, ESS mode is disabled.
In VMMS mode, the UPS operates as a traditional double conversion UPS. However,
the UPS will selectively shift the load to fewer UPMs based on the required load in
order to force the remaining UPMs to carry a higher load. The efficiency rating for
each UPM is highest when loads are greater than 50% of the system rating.
Therefore, with multiple UPMs, a UPS can achieve higher efficiencies for lighter
loads.
