UPS systems are standardized according to the EU standardEN 50091-3( IEC 62040-3). In this standard, UPS systems are classified according to the response time and the consideration of transient disturbances.
VI (Voltage Independent) systems are also referred to as Line Interactive. They permanently monitor the mains voltage and supply the connected devices and systems from the battery supply in the event of undervoltage or power failure. VI systems meet UPS protection class 2 and can be used economically up to power ratings of 1 kVA.