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An uninterruptible power supply (UPS), uninterruptible power source or sometimes called a battery backup is a device which maintains a continuous supply of electric power to connected equipment by supplying power from a separate source when utility power is not available.
A UPS is inserted between the source of power (typically commercial utility power) and the load it is protecting. When a power failure or abnormality occurs, the UPS will effectively switch from utility power to its own power source almost instantaneously.
While not limited to any particular type of equipment, a UPS is typically used to protect computers, telecommunication equipment or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption or data loss. UPS units come in sizes ranging from units which will back up a single computer without monitor (around 200 VA) to units which will power entire data centers or buildings (several megawatts). Larger UPS units typically work in conjunction with generators.
Historically, UPS units were very expensive and were most likely to be used on expensive computer systems and in areas where the power supply is interrupted frequently. However, UPS units are now more affordable, and have become an essential piece of equipment for data centers and business computers, but are also used for personal computers, entertainment systems and more.
In North America in particular, the electrical grid is under increasing strain particularly during heavy demand periods such as summer when air conditioning use is at its highest. In order to prevent blackouts, electrical utilities will sometimes use a process called load shedding, which involves cutting the power to large groups of customers for short periods of time. The single biggest event that brought attention to the need for UPS power backup units was the 2003 North America blackout in the north-eastern US and eastern Canada.
A UPS is not to be confused with a standby generator, which does not provide protection from a momentary power interruption and may result in an interruption when it is switched into service, whether manually or automatically. However, such generators are typically placed before the UPS to provide cover for lengthy outages.
Common power problems
There are nine common power problems that UPS units are used to correct. They are as follows:
Power failure - Total loss of utility power;
Power sag - Short term under-voltage;
Power surge (spike) - Quick burst of over-voltage;
Under-voltage (brownout) - Low line voltages for an extended period of time;
Over-voltage - Increased voltages for an extended period of time;
Line noise - distortions superimposed on the power waveform.;
Frequency - variation of the power waveform.;
Switching transient – under-voltage or over-voltage for up to a few nanoseconds.;
Harmonic Distortion - multiples of power frequency superimposed on the power waveform.;
UPS units are divided into categories based on which of the above problems their UPS units address.
Read more at Wikipedia.org
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