Eaton® 9390 (100–160 kVA) UPS Installation and Operation Manual 164201604—Rev F 40
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Static
Switch
K5
retrevnIreifitceR
K1 K3
Battery
Converter
Battery
Battery
Breaker
Main Power Flow
Trickle Current
Energized
De-Energized
Closed
Open
Breakers Contactors
To ensure the load remains energized, the UPS automatically transfers the output to the internal bypass when
one of these abnormal conditions occur; the output of the system exceeds acceptable voltage and frequency
tolerances, the system is overloaded, or the inverter fails. The transfer is initiated by turning on the static
switch and opening the output contactor K3, also called a Make-Before-Break transfer. The transfer occurs in
less than 4 mS (quarter cycle) to ensure that the output load is not interrupted. The static switch remains on
until either the inverter is able to support the system output or the unit is placed into a maintenance position
where repairs can be made.
If the UPS initiates its own transfer to bypass for any reason other than operator intervention, the UPS
attempts to restart the inverter (if not running already) and attempts a transfer back online to support the output
of the system. Three attempts are made within ten minutes to return the inverter online automatically before
the UPS locks out any further attempts. After three attempts, the UPS remains in bypass and an alarm
condition is enunciated. The UPS can also be transferred to bypass using the front panel controls.
Bypass mode is a normal operating mode, not an alarm condition. However, if the UPS is unable to return to
Normal mode following an automatic transfer to Bypass mode, an alarm condition is recorded.
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When the UPS is operating in Energy Saver mode, the bypass source supplies the commercial AC power to the
load directly through the static switch. Some power line filtering and spike protection is provided to the load but
no active power conditioning or battery support is available. All power converters are off and are in the ready
state (in case a forward transfer is needed). During this mode, the output contactor is closed and the link is
maintained through the diode bridge. Figure 7-4 shows the path of electrical power through the UPS system
when operating in Energy Saver mode.
Understanding UPS Operation
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