If redundancy is not available to the UPS due to high load, the UPS transfers to Bypass mode
automatically and remains in that mode until the failure is corrected during maintenance and the UPS can
operate correctly again.
In an external parallel redundant system, each UPS can be isolated from the system for maintenance
while the remaining UPSs continue to supply power to the load in Online mode.
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Figure 8: Path of current through the UPS in ESS mode shows the path of electrical power through the
UPS system when the UPS is operating in Energy Saver System (ESS) mode.
Figure 8. Path of current through the UPS in ESS mode
1. Bypass input A Internal relay contact closed
2. Static switch B Internal relay contact open
3. Output C Main power flow
4. Inverter D Trickle current
5. Rectifier E Energized
6. Rectifier input F De-energized
7. Battery converter K1 Input relay
8. Battery breaker
(closed)
K3 Output relay
9. Battery K5 Backfeed relay
In ESS mode, the UPS safely provides mains current to the load when the input is within the acceptable
voltage and frequency limits. The front panel shows the UPS status ESS Mode, and the UPS is in In
Service state. In ESS mode, the surge suppression and filtering ensure pure electric energy for the load
equipment. If there are any disturbances in the input power supply, the UPS automatically transfers to
Online mode and continues to supply power to the load through the inverter. If the input AC power fails or
exceeds the system specifications, the UPS transfers automatically to Battery mode to supply
uninterrupted power to the load.
EATON 93T USER’S AND INSTALLATION GUIDE 614-40270
-
December 2023 www.eaton.eu 2233
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