Eaton 93PM Series - Page 87

Eaton 93PM UPS 480V Three-Wire – 100 kW Frame Installation and Operation Manual 164000227—Rev 07 75
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When the UPS is operating in ESS mode, commercial AC power is supplied directly to the critical load through
the internal bypass with the power module in a standby state. Surge protection and some filtering is also
provided, ensuring that clean power is delivered to the load equipment. If a commercial power brownout,
blackout, overvoltage, undervoltage, out-of-tolerance frequency condition occurs, or any other disturbance is
detected in the incoming power, the system forward transfers to normal mode (double-conversion on
demand). In case of a complete utility outage or if input power is outside the tolerances of the system, the UPS
transfers to battery mode and continues to supply conditioned, clean power to the critical load. When the input
line returns to normal operating range, the UPS returns to ESS operation. For charging batteries, the UPS will
not enter ESS mode until charger output is 25% or less of maximum charger current.
When operating in ESS, the UPS detection and control algorithms continuously monitor incoming power quality
and allow the fast engagement of power converters. Typical transition time to double conversion is less than
two milliseconds, which is practically seamless. If the UPS detects a fault condition while operating in ESS, it is
also able to detect and determine whether the fault is caused by the load or if it is upstream from the UPS. A
fault at the bypass source results in an immediate switch over to the inverter. A fault in the utility switches the
UPS out of Energy Saver System (ESS) mode while a fault in the load keeps the UPS in ESS mode.
When power conditions are within acceptable limits, the UPS operates as a high-efficiency, energy-saving
system — providing surge protection for IT equipment and ensuring clean power is delivered to the critical load.
Energy saver system increases system efficiency to 99% at 100% linear load and nominal Vin.
Figure 39 shows the path of electrical power through the UPS system when the UPS is operating in Normal
mode.
ESS mode is a normal operating mode, and not an alarm condition. While the UPS is in this mode, the
NORMAL light on the front display will illuminate.
Figure 39. Path of Current Through the UPS in Energy Saver System Mode
Static
Switch
Bypass Input
Rectifier Input Output
Bypass Switchgear
Rectifier
Switchgear
Inverter
Switchgear
Battery
Switchgear
Closed
Open
Main Power Flow
Trickle Current
Energized
De-Energized
Switchgear
Rectifier Inverter
Static
Switch
Battery Converter
Battery
Understanding UPS Operation