Chapter 1 Overview 7
NX UPS Single Module And Parallel System 250kVA ~ 800kVA User Manual
Mains input
Rectifier
Inverter
Battery charger
Battery
UPS output
Main input switch
Output switch
Figure 1-7 Schematic diagram of normal mode
Battery mode
As shown in Figure 1-8, the UPS is operating in battery mode when the battery is supplying backup power to the load
through the inverter. Upon mains failure, the UPS automatically transfers to battery mode without power interruption
to the load. Upon restoration of the AC mains, the UPS automatically transfers back to normal mode without the
necessity of user intervention, without power interruption to the load.
Output switch
Inverter
Rectifier
UPS output
Battery
Figure 1-8 Schematic diagram of battery mode
Bypass mode
As shown in Figure 1-9, during normal mode operation, if the inverter fails, is overloaded or turned off, the static
switch will perform a transfer of the load from the inverter to the bypass source, with no interruption in power to the
load. Should the inverter be asynchronous with the bypass, the static switch will perform a transfer of the load from
the inverter to the bypass, with interruption in power to the load. This avoids large cross current caused by paralleling
of unsynchronized AC sources. This interruption is less than 20ms.
Bypass switch
Static switch
UPS output
Output switch
Bypass input
Figure 1-9 Schematic diagram of bypass mode
Maintenance mode
As shown in Figure 1-10, if UPS maintenance or repair is needed, you may use the maintenance switch to transfer
the load to the maintenance bypass, with no interruption in power to the load. This maintenance switch is fitted in all
UPS modules and rated for full load of one module.
Bypass input
Maintenance switch
Maintenance bypass
UPS output
Figure 1-10 Schematic diagram of maintenance mode
Automatic restart mode
The UPS provides automatic restart function: Following an extended AC mains failure, when the battery reaches the
EOD voltage, the inverter shuts down; upon mains restoration, the UPS can restart automatically after a delay time.
This function and any delay time are programmed by the commissioning engineer.