Uninterrupted Power Supply (UPS)

Uninterruptible power supply, well recognized as UPS is an electronic equipment that operate as a back-up power supply element for a prescribed period of time when the electricity supply is interrupted or when the line voltage show a discrepancy abnormally. UPS has gain value as it is badly required to offer back-up power supply to PCs. People generally do not attach much importance to power protection or backup power supply till they experience loss of expensive computer files or worse, equipment spoil at some point in electricity failure.

To acquire power supply without any interrupt, you need certain add-on things like an energy storing backup ups battery, an AC-DC charger and a DC-AC inverter. There are three major types of UPS power backup devices existing in the market. They are known as Standby or Off-Line (SBS), which is the basic model and of the lowest grade; Line Interactive (SBS), which is the intermediate model and of the middle grade; On-line which is of the highest grade. All of them use ups battery backup while the input power supply stop working, but in usual circumstances these three units handle the power differently. Of these three basic design types, each model put forward more power protection than the lower grades.

Line Interactive UPS under normal condition evens out and to a certain degree regulates the input AC voltage through a filter and a tap-changing transformer. The bi-directional inverter/charger is always connected to the output of the UPS and consumes a portion of AC power for charging the ups battery. When the input power fails, the transfer switch disconnects AC input and the battery/inverter provides output power. It is said its rate of efficiency is quite high at 90 to 96 percent.

Online UPS are chosen since it always delivers all or a considerable portion of the output power through its inverter even under normal line conditions. There are two main types of on-line UPS available in the market - Double Conversion and Delta Conversion. Double Conversion Online UPS is continuously processing the whole power through series connected AC-DC rectifier / charger and DC-AC inverter. Although this type of UPS supplies better output power quality, the double conversion results in reduced efficiency at 80 to 90 percent.

Delta Conversion Online UPS has an added "Delta Converter" that delivers a portion of the input power directly to the load and also provides power factor correction. Because of this partial bypassing of the rectifier / inverter during normal operation there is a higher efficiency up to 97%percent.

Standby UPS comprise a transfer switch and its use is to toggle the load to the battery / inverter when the AC power source fails. The transfer time is typically in between two to 10 minutes depending on the amount of time it takes to discover the vanished utility voltage and turn on DC-AC inverter. As a result of this delay, the power to the load is interrupted. The equipment's power supply should have more hold up time than UPS transfer time to stay away from the loss of data as expected. In general, a power factor corrected SMPS of a personal computer has at least 10 to 20 ms hold-up time. Since the inverter operates in standby mode and starts up only when input power fails, the SPS has the highest efficiency and reliability. This is the least costly UPS and hence the most common backup type used for PCs.

See Related Articles: Uninterrupted Power Supply (Oct 2008)