46 UNINTERRUPTIBLE POWER SUPPLIES
46 UNINTERRUPTIBLE POWER SUPPLIES
" While the UPS plays its essential part in securing blackout backup appropriate to an application , its role in assuring power quality during normal utility mains supply is equally as important . Different topologies , with varying impacts on power quality " of utility supply failure . If power is restored well within the battery autonomy , the inverter is switched back to the incoming mains supply . The load has enjoyed uninterrupted operation , with complete protection from the problem .
If , however , the blackout period starts to threaten the battery autonomy , the UPS has no choice but to signal the load , allowing it to shut down gracefully in the remaining battery time . System hardware and data has been protected from damage , although the organisation suffers from lack of ICT resource . If loss of this resource is unacceptable , the only solution is a UPS in combination with a backup generator , which , with sufficient fuel , can outlast any blackout .
Such generator-UPS combinations need reliable communications between the generator , UPS and critical load , as well as a suitable control system on the generator . During short-duration blackouts , the UPS uses its battery power to avoid unnecessary generator start-ups . If a blackout becomes extended , the UPS signals the generator through an Automatic Mains Failure ( AMF ) panel to start up . The UPS battery autonomy allows the generator to come up to speed and synchronises with the UPS ’ s voltage output , while the load suffers no power interruption . Once the generator is online , the UPS takes its power to feed the load and recharge its batteries . When the UPS detects restoration of mains power , it typically waits for a few minutes before switching back to the mains . This is to ensure that the power is sustained rather than the temporary result of a utility company fault location procedure , for example .
The generator itself must be adequately prepared in several aspects to perform successfully as a power backup component . It must have an electronic governor to regulate the engine speed and therefore the alternator output frequency to ensure sufficient speed of response and accuracy . Mechanical governors are lower cost but lack the accuracy and stability needed by the UPS .
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