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Four decades ago, a business milestone took place that gives meaning to what Salicru is  today: the manufacture and commercialisation of its first uninterruptible power supply  (UPS) system. Today, these devices are part of our homes, offices, industries and  infrastructures. But, do you know how many types of UPS system there are and what they  are used for?

There are three basic types of UPS using different technology: Off-line, Line- interactive and On-line double conversion. Each type provides different levels of  protection and there are several factors that determine which one best suits the needs  of the system that requires protection: level of reliability and availability required,  type of protected equipment and the application or environment concerned.

Although all three types meet the minimum requirements for the protection of IT  environments, the fundamental differences are important in relation to the level of  performance and quality of the output voltage provided. The main parameter that  differentiates them is essentially whether or not the battery allows the sensitive load  to receive power directly from the mains: Off-line and Line-interactive UPS systems  only operate in the event of a power supply failure, whereas, in On-line systems, the  load is permanently powered by energy generated by the UPS itself, regardless of  whether a power supply exists.

Below is a description of each of them in more detail:

• Off-line or Standby (according to standard IEC 62040-3, classification VFD,  output voltage and frequency dependent on input), in which the mains input passes  directly to the output until a failure occurs, which is when the inverter becomes  responsible for providing energy. This type of UPS is low cost and offers sufficient  protection for office environments. It is not appropriate for cases in which mains  power is low quality (e.g. industrial estates) or subject to frequent interruptions.

• Line-interactive (according to standard IEC 62040-3, classification VI, output  voltage independent of input), in which a transformer/stabiliser is added, through  which the load is powered in the presence of mains power. This is used to protect  corporate networks and IT applications from power failures, overvoltages and  undervoltages. The device is controlled by a microprocessor that monitors the quality  of the power and reacts to fluctuations. The main advantage of a Line-interactive UPS  is that it compensates for voltage fluctuations without the use of batteries.

• On-line double conversion (according to standard IEC 62040-3, classification  VFI, voltage and frequency independent of input), in which the output voltage is  completely generated by a sequence of converting alternating current to direct current  (AC/DC), followed by converting direct current to alternating current (DC/AC),  producing a power supply without any electrical interference. This type of system is  the most reliable way of protecting critical loads from all kinds of mains power  disturbances.

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