Uninterruptible power supply(UPS)

UPS (Uninterruptible power supply)

An uninterruptible power supply (UPS), also known as a continuous power supply (CPS) or 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. It differs from an auxiliary power supply or standby generator, which does not provide instant protection from a momentary power interruption, however could be used to provide uninterrupted power to equipment for 1 - 20 minutes until a generator can be turned on. Integrated systems that have UPS and standby generator components are often referred to as emergency power systems.

Types of UPS
There are three distinct UPS types:
Off-line: remains idle until a power failure occurs, and then switches from utility power to its own power source, almost instantaneously.
Line Interactive: A line-interactive UPS maintains the inverter in line and redirecting the battery's DC current path from the normal charging mode to supplying current when power is lost
On-line: continuously powers the protected load from its energy reserves stored in a lead-acid battery or flywheel, while simultaneously replenishing the reserves from the AC power. It also provides protection against all common power problems, and for this reason it is also known as a power conditioner and a line conditioner.

Applications
The basic technology of UPS hardware can have many forms when applied for different purposes. Any of the technologies may be recombined as redundant systems or designed for special needs.
There are various common power problems that UPS units are used to correct. They are as follows (with a typical example of damage that might be caused):
1. Power failure — Total loss of utility power, with possibility of severe transient conditions upon failure and/or restoration: Causes electrical equipment to stop working (transients may cause permanent damage).
2. Voltage sag — Transient (short term) under-voltage: Causes flickering of lights.
3. Voltage spike — Transient (short term) over-voltage i.e. spike or peak: Causes wear or acute damage to electronic equipment.
4. Under-voltage (brownout) — Low line voltage for an extended period of time: Causes overheating in motors.
5. Over-voltage — Increased voltage for an extended period of time: Causes light bulbs to fail.
6. Line noise — Distortions superimposed on the power waveform: Causes electro magnetic interference.
7. Frequency variation — Deviation from the nominal frequency (50 or 60 Hz): Causes motors to increase or decrease speed and line-driven clocks and timing devices to gain or lose time.
8. Switching transient — Instantaneous under voltage (notch) in the range of milliseconds to seconds: May cause erratic behavior in some equipment, memory loss, data error, data loss and component stress.
9. Harmonic distortion — Multiples of power frequency superimposed on the power waveform: Causes excess heating in wiring and fuses.
UPS units are divided into categories based on which of the above problems they address. Manufacturers categorize their products in accordance with the number of power related problems they address.

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