Eaton 93E Series - 5.2.4 Bypass Mode

Eaton 93E UPS (20–30 kVA, 208/220V) Installation and Operation Manual 164000301—Rev 04 57
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 Normal mode.
Figure 32. Path of Current Through the UPS in standard Normal Mode
Battery
Battery
Switchgear
Inverter
Switchgear
Rectifier
Switchgear
Rectifier
Input
Bypass Input
Output
Static
Switch
Battery
Converter
Bypass
Switchgear
Rectifier
Inverter
Input
Breaker
Breakers Switchgear
Closed
Open
Main Power Flow
Trickle Current
Energized
De-Energized
If the UPS becomes overloaded or unavailable, the UPS switches to Bypass mode. The UPS automatically
returns to Normal 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.
55..22..44 BByyppaassss MMooddee
CAUTION
The critical load is not protected from voltage or frequency fluctuations or power outages while the UPS is in
Bypass mode.
The UPS automatically switches to Bypass mode if it detects an overload, load fault, or internal failure. The UPS
can also be transferred from Normal mode to Bypass mode manually. The bypass source supplies the
commercial AC power to the load directly. Figure 33 shows the path of electrical power through the UPS
system when operating in Bypass mode.
In Bypass mode, the output of the system is provided with three-phase AC power directly from the system
input. While in this mode, the output of the system is not protected from voltage or frequency fluctuations or
power outages from the source. Some power line filtering and spike protection is provided to the load but no
active power conditioning or battery support is available to the output of the system in the Bypass mode of
operation.
Understanding UPS Operation