APC BK600EI - Manual (Page 18)

Page 16
4.6 Transformer
The UPS’s transformer is an electrical component which “steps up” the output voltage of
the inverter to the normal utility line voltage. In addition, it serves to isolate the UPS from
equipment failures.
4.7 Monitoring and control electronics
This block is the “brain” of the UPS. The monitoring and control circuitry detects utility
failures such as blackouts, sags and brownouts; synchronizes the inverter’s output
frequency and phase to that of the utility; detects low battery voltage conditions; directs
the load transfer switch; and governs all user controls, indicators and computer interface
functions.
4.8 Operation during a utility failure
In anticipation of a utility failure such as a blackout, sag or brownout, the UPS continu-
ously monitors the utility voltage and readies the inverter for “synchronous” transfer.
This means the inverter’s phase and frequency is adjusted to match the phase and
frequency of the utility. If the utility voltage falls outside acceptable limits, the UPS rapidly
transfers your equipment to power derived from the UPS’s battery via the inverter and
transformer described earlier. This transfer typically takes place within 8 milliseconds.
Once operating in this mode, the UPS will beep once every 5 seconds to alert the user that
there is limited time available to save files and shut down the computer. If the utility power
is not restored to normal, the UPS will eventually sound continuous beeps to alert you that
less than two minutes remain before the UPS shuts down and ceases to power your
equipment. This is called a low battery condition which means that the UPS’s usable
battery capacity is nearly spent. The UPS will automatically shut down if the UPS is not
turned off during the low battery alarm.
If the UPS detects the return of normal utility voltages at any time during operation using
its alternate power source, the inverter voltage will be smoothly re-synchronized to match
the phase and frequency of the utility. Once synchronized, the load transfer switch will re-
transfer your equipment to power supplied by the utility. After an extended utility outage,
the battery charger resupplies the battery with energy at a pace which is consistent with
maximizing the service life of the battery (the battery
could be charged faster, but wouldn’t
last as long).