Emerson 30-200kVA Manuel D’Utilisation

The Liebert NXa Uninterruptible Power System is connected between the Mains AC input source and 

the critical load to provide uninterruptible power to the latter. The power from the UPS is free from 

voltage and frequency variations and from disturbances experienced at the Mains AC input supply. 

This is achieved through high frequency double conversion power pulse width modulation (PWM) 

associated with full digital signal processing control (DSP).
As shown in Figure 63, the AC input mains source is supplied at Q1 and converted into a DC source. 

This DC source feeds a DC/DC Bidirectional Battery Converter (that ensures the battery to remain 

charged at all times) and at the same time feeds the Inverter that converts the DC source into a clean 

and input independent AC source. The battery powers the load through the bidirectional battery con-

verter and through the inverter in case of an AC input mains power failure. In case of Inverter 

unavailability or excessive overload, the load may also be powered from an external AC Bypass source 

through input isolator Q2 and the static bypass. Besides this, if maintenance or repair of the UPS is 

necessary, the UPS can support the load through the internal and manually controlled maintenance 

bypass isolator Q3. With the exception of the maintenance bypass isolator, all the isolators shown are 

closed during normal UPS operation. 

Hazardous mains and / or battery voltage present behind covers. 
No user-serviceable parts are located behind covers that require a tool for their removal. Only 

qualified service personnel are authorised to remove such covers.