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Eaton 93PM-L 20–200kW (208V) UPS Installation and Operation Manual 164000724—Rev 01
The internal bypass is comprised of a solid-state, silicon-controlled rectifier (SCR) continuous static switch. The
static switch is used instantaneously anytime the inverter is unable to support the applied load. The continuous
static switch is 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 the inverter switchgear opens to isolate the inverter.
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 38. Path of Current Through the UPS in Bypass Mode
Bypass Input
Rectifier Input
Rectifier
Switchgear
Main Power Flow
Trickle Current
Energized
De-Energized
Rectifier
Battery
Converter
Battery
Switchgear
Battery
Inverter
Inverter
Switchgear
Output
Static
Switch
Closed
Open
Switchgear
55..22..55
B
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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.
shows the path of electrical power through the UPS system when operating in Battery mode.
During a utility power failure, the rectifier no longer has an AC utility source from which to supply the DC output
voltage required to support the inverter. The rectifier switchgear opens and the battery instantaneously
supplies energy to the battery converter. The converter boosts the voltage so that the inverter can support the
customer's load without interruption. The opening of the rectifier switchgear prevents system voltages from
bleeding backwards through the static switch and rectifier snubber components to the utility source.
If the input power fails to return or is not within the acceptance windows required for normal operation, the
battery continues discharging until a DC voltage level is reached where the inverter output can no longer
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