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Why an Uninterruptible Power Supply?

Data centres, servers, LAN nodes and telecommunication systems must always be protected against possible problems with power supply. Sudden blackouts and variations in the mains supply may lead to system malfunctions and severe data losses. But even other types of electrical equipment can be damaged or In turn cause damage or Inconvenience if there is a fault in the mains supply.

You only need to think about the checkouts in supermarkets, lighting systems and Industrial production units, not to mention safety systems, medical equipment, pumping Installations and automatic devices in general.

The simplest and most effective way of coping with these disturbances in the electricity network is to Install a UPS unit (UPS stands for Uninterruptible Power Supply). Acting as an interface between the mains and the loads, a UPS guarantees the continuity and the quality of the electricity supplied to the loads, regardless of the condition of the mains.

In fact these machines stabilise the voltage perfectly, eliminating all disturbances and when the mains supply fails, they even supply voltage via a series of batteries which provide power long enough to guarantee the safety of persons and the system. In order to select the type of appliance that is best suited to ensure the required level of protection, you need to be aware of the types of problems with the mains supply that may disturb your appliances.

Reference technical standards


EN 62040-1-1 is the reference standard regulating the basic safety requirements for UPSs used in areas accessible to operators. EN 62040-1-2 1s the reference standard regulating UPS used in restricted access locations (control panels, electricity cabinets etc.).

Electromagnetic compatibility

UPSs are designed to operate in situations where disturbances can occur but, at the same time, to emit the lowest possible number of disturbances so as not to cause Inconvenience with other appliances in the system. The Immunity and emission limits as well as the test methods are defined in the IEC EN 62040-2 standard.


The reference document is “Method of specifying the performance and test requirements” EN 62040-3; this standard is a guide to achieving better understanding between manufacturers and users, as it defines the performance levels that must be declared and the test methods for this.

All UPS Riello UPS are designed and constructed in compliance with the above standards and thus they bear the CE marking.

Types of UPS

Off-line (VFD)

In normal operating mode, the load is powered directly from the mains through the UPS static switch. When the mains voltage is not within the UPS preset tolerances, the  load is transferred to the inverter in about 2-4 ms using battery power. The voltage generated by the inverter is typically step-wave or square-wave.

Line Interactive (VI)

In normal operating mode, the load is powered from the mains through an AVR (Auto Voltage Regulator) circuit. This device corrects voltage variations within its capacity for regulation, returning the voltage to its default values. When the variations in the power supply are not within the capacity for AVR circuit, the inverter intervenes and through the stored energy in its batteries it ensures the continuity and quality of the power supply. The transition from stabilized mains to inverter supply takes place in about 2-4 ms and the voltage generated by the inverter can be of a sinusoidal type or step-wave (square-wave) type depending on the UPS model.

Double Conversion (VFI)

In normal operating mode, the load is powered by the combination of rectifier/inverter. When the AC input supply is not within the voltage and frequency tolerances, the unit enters into battery mode operation where the battery/inverter combination continues to power the load for as long as its power lasts, or until the AC input power returns within the required tolerances. The intervention time for battery operation is instantaneous (0 ms). If the rectifier/inverter fails or in the event of an overload, either in the permanent or transition mode, the unit goes into bypass mode (0 ms), where the load is temporarily supplied via the reserve line.