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Appendix A. Specifications
Line interactive UPS units
Line interactive UPS units are also referred to as VI UPS units. VI stands for Voltage
Independent from mains supply. Other names for this UPS types are line-interactive, single-
conversion or delta-conversion UPS units.
The input utility power is passed through the UPS directly to the load. A Bidirectional inverter
generates from the AC input voltage the DC voltage for charging the batteries as required and
AC voltage from the UPS batteries in case of utility power failure.
An automatic voltage regulator, AVR, can correct abnormal voltages on the input utility AC
without the need to switch to battery operation. The AVR will engage when input AC is
outwith a preset lower or higher input voltage window. In case of the input voltage being
below the lower threshold the UPS will boost the voltage and in case it is above the maximum
input threshold it lower or buck the voltage. These voltage corrections are achieved with
transformers.
Noise filters and suppressors in the UPS can also protect from electromagnetic line noise as
well as unexpected surge in utility power due to e.g. lighting strikes.
The frequency of the input voltage, if it is present, is identical to that of the output voltage.
Due to the design of this UPS topology switching times from utility power to battery power
occurs. The switching time can be between 2 ms to 10 ms.
6U Rack or Tower UPS RT8kVA and RT11kVA IUOMG
249
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