An uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically the utility mains, fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide instantaneous or near-instantaneous protection from input power interruptions by means of one or more attached batteries and associated electronic circuitry for low power users, and or by means of diesel generators and flywheels for high power users. The on-battery runtime of most uninterruptible power sources is relatively short—5–15 minutes being typical for smaller units—but sufficient to allow time to bring an auxiliary power source on line, or to properly shut down the protected equipment.

Why a UPS?

The quality of power is not perfect. In an increasingly hi-tech, automated world, a growing number of loads are sensitive to momentary power interruptions, voltage sags and blackouts. They are also affected by over-voltage conditions such as swells and surges.

Hurricanes, tornadoes, and earthquakes aren’t the only disasters that damage PCs, servers, and other computers. The abrupt loss of electricity prevents systems from closing open applications, completing replication actions, finishing disk activities, and shutting down properly. Lost data and corrupted databases and applications often result.

Powerful electrical spikes also cause trouble. A computer’s sensitive electronics can easily be destroyed by electrical surges spawned by lightning strikes or power grid fluctuations.

Uninterruptible Power supplies (UPSes) help prevent the damage that occurs from both power loss and common electrical fluctuations. However, just plugging in a UPS and connecting computer equipment doesn’t guarantee systems are properly protected.

The losses and costly down-time associated with such disturbance are the drivers behind the need for protection.

UPS Capacity

The power rating of electrical equipment may be stated in Watt (W) or volt Ampere (VA) 1KVA = 1000VA.

UPS manufacturers generally use VA or KVA to describe the UPS output ratings, and it is this rating which determines the maximum load that can continuously be supported by the UPS when the mains supply fails.

UTypes of UPS

UPS are in different ranges vis-à-vis

Micro Systems – up to 250VA
Mini Systems – 500 to 2000VA
Medium Systems – 3 to 20KVA
High power systems – 30 and above

Generally, UPS can be group into two ranges:

Low range – below 30KVA
High range – above 30KVA

There are a number of categories of UPS systems; however they can be classified in three main groups:

Off-line systems
Line-interactive systems
On-line systems

Of all the categories of UPS, the online system is the best because guaranteed continuous and total power conditioning with failsafe / overload protection, no break on mains failure and wide input voltage tolerance.