58 Eaton 93E UPS (20–30 kVA, 208/220V) Installation and Operation Manual 164000301—Rev 04
The internal bypass is comprised of a solid-state, silicon-controlled rectifier (SCR) continuous static switch, and
the bypass switchgear. The static switch is used instantaneously anytime the inverter is unable to support the
applied load. The continuous static switch is wired in series with the bypass switchgear, and together they are
wired in parallel with the rectifier and inverter.
The static switch, being an electronically-controlled device, can be turned on immediately to pick up the load
from the inverter while inverter switchgear opens to isolate the inverter. The bypass switchgear is normally
closed, ready to support the static switch unless the bypass input source becomes unavailable.
If the UPS transfers to Bypass mode from Normal mode due to any reason other than operator intervention,
the UPS automatically attempts to transfer back to Normal mode (up to three times within a ten minute period).
The fourth transfer locks the critical load to the bypass source and requires operator intervention to transfer.
Figure 33. Path of Current Through the UPS in Bypass 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
55..22..55 BBaatttteerryy MMooddee
The UPS automatically transfers to Battery mode if a utility power outage occurs, or if the utility power does not
conform to specified parameters. In Battery mode, the battery provides emergency DC power that the inverter
converts to AC power.
Figure 34 shows the path of electrical power through the UPS system when operating in Battery mode.
Understanding UPS Operation
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