Powerware (4080 KVA) 9390 User Manual download pdf (Page 61)

Understanding UPS Operation

7-7

Powerware

9390 UPS (40–80 kVA) Installation and Operation Manual S 164201535 Rev C

During an outage, the UPS prohibits transfers to bypass and provides upstream protection.

The backfeed protection contactor is opened, preventing system output voltage from

bleeding across the static switch snubber components to the bypass input source.

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 n o rmal 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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Powerware (4080 KVA) 9390 User Manual Page 61