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Line Interactive UPS

A range of line interactive uninterruptible power supplies including desktop, tower and rack mount uninterruptible power supplies suitable for a wide variety of applications including CCTV, security panels, EPOS terminals, IT servers and networks accessories. Line interactive UPS tend to be single phase output systems and can provide longer runtimes by oversizing the UPS or adding external battery cabinets where the UPS design provides this option.

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What Is A Line Interactive Uninterruptible Power Supply?

A line interactive UPS is an uninterruptible power supply which is classed under IEC EN62040-3 as Voltage Independent (VI). The inverter section of the UPS system is energised but only supports the load when the mains power supply fluctuates or fails completely.

This type of UPS technology is best suited to uninterruptible power supplies up to 3kVA and allows for a compact UPS design with an internal battery and a relatively low cost. Some UPS manufacturers supply larger line interactive models up to 10kVA but all are limited to a single phase input and output supply.

The UPS tends to have a built-in automatic voltage stabiliser (AVS) which under normal conditions (when the mains power supply is present) protects the connected load from mains power problems including sags, surges and brownouts.

The AVS can be transformer based and sometimes referred to as a buck/boost transformer. When the input voltage is high, the transformer ‘bucks’ to reduce the output voltage and when it is high the transformer ‘boosts’ the output supply voltage. The ‘buck/boost’ transformer uses a series of transformer taps to adjust the output voltage. An AVS can also be referred to as an automatic voltage regulator (AVR). A small battery charger is built into the UPS and charges the battery set. The UPS also has a built-in EMC/filtering circuit to provide protection from mains borne interference in the form of electrical noise, spikes and transients.

If the mains supply voltage falls outside the input voltage window or the input frequency window of the AVS or AVR, the inverter section connects to the load supply line and powers the connected load. The inverter section draws on the DC (direct current) of the built-in battery set and inverts this into an AC waveform to power the load.

When the inverter section picks up the load or disconnects there is typically a 2-4mS break in electrical supply. This is well within the capacitance level of the switch mode power supply (SMPS) within a computer or server which can hold capacitance up to 15-20mS or longer.

The output waveform from inverter can be a pure sinewave or square wave. A square wave output is sometimes referred to as a Pseudo sinewave. The inverter section may also be rated for long running periods at 80-100% load allowing additional battery extension packs to be connected to a rear panel connector (if available). The loads are generally connected using IEC320 sockets.

For more information on line interactive UPS please contact our projects team.