APC BK600EI User Manual download pdf (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).

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APC BK600EI User Manual Page 18