Uninterruptible Power Supplies (UPS)

Description

Uninterruptible power supplies (UPS) are electronic devices used to provide uninterrupted supply of electric power to the load for a specific time during utility power loss or under abnormal power conditions such as voltage fluctuations, line noise, brownouts, power surges, etc. Usually UPS consists of a backup battery, an AC to DC rectifier and a DC to AC inverter. The rectifier stores the incoming line power in the battery after converting AC power into DC power; when there is an electrical power loss, the inverter converts the battery DC power into AC power to provide uninterrupted supply of power to the load. The performance of UPS is measured in terms of VA.

Types

Uninterruptible power supplies are classified as follows:

• Offline or standby uninterruptible power supplies - operate whenever there is a disruption in the electrical power supply
• Online or double conversion uninterruptible power supplies - maintain stable connection from the UPS battery to the electrical equipment
• Ferro-Resonant uninterruptible power supplies - work similar to offline UPS except that they use ferro-resonant transformer to filter the output
• Line Interactive uninterruptible power supplies – use multi-tap variable voltage autotransformer to tolerate under-voltage brownouts and over-voltage surges

Specifications

The specifications to be considered for uninterruptible power supplies are listed below:

• Capacity (Watts / VA)
• Input / Output voltage specifications (Volts)
• Interface options (for communication)
• Mounting options
• Surge suppression
• Phase output specifications (single or three phase)
• Operating temperature range

Applications

The applications of uninterruptible power supplies are:

• Provides highly reliable power protection for network and server rooms
• Provides protection to personal computer from power fluctuations
• Provides risk-free operation of electronic equipments during sudden power surges in industrial applications
• Provides reliable power protection in hospitals for medical or life-support systems