2 Chapter 1 Overview
Liebert NXC 30kVA And 40kVA UPS User Manual
When the mains is abnormal, the rectifier stops working, and the battery supplies power to the loads through the
inverter. If the battery voltage falls to end of discharge (EOD) voltage and the mains still has not been recovered, the
UPS will shut down (if the system uses split bypass configuration and the bypass is normal, the system will transfer to
bypass). The battery EOD voltage is preset. When the mains is abnormal, the battery maintains the UPS operation till
the battery voltage is reduced to EOD voltage and the UPS shuts down, this time is called ‘Backup Time’. The length of
backup time depends on the battery capacity and the loads.
1.2.2 Bypass
Through the intelligent control of the ‘Static Switch’ module (as shown in Figure 1-1) containing the controllable
electronic switch, the loads can be supplied by the inverter or the bypass. In normal situation, the loads are supplied
by the inverter, in which case the inverter switch at inverter side is closed. In the case of overload (the overload delay
time expires) or inverter failure, the inverter switch is opened, and the ‘Static Switch’ module will automatically transfer
the loads to the bypass.
In normal operating state, to realize the uninterrupted transfer between inverter and bypass, the inverter output must
be synchronized with the bypass.
Therefore, when the bypass frequency is within the synchronization range, the inverter control circuit will synchronize
the inverter output frequency with the bypass frequency and phase.
Besides, the UPS has a manual maintenance bypass switch for shutdown of the UPS upon maintenance. In this
situation, the bypass will directly supply the critical loads through the maintenance bypass.
Note
When the load is supplied by the bypass or maintenance bypass, the power supply quality will be uncertain.
1.2.3 System Control Principle
Normal operation
Normal mode: It means that the UPS has normal input mains, the rectifier and inverter operate normally, the load is
supplied by the inverter, the battery circuit breaker is closed, and the battery is in stable floating charge state.
(Parallel System)
Note: As the single UPS module outputs are connected in parallel, the system checks that the
inverter control circuits are perfectly synchronized with one another and with the bypass in terms of both frequency
and phase, and that they have the same output voltages. Current supplied to the load is automatically divided among
UPSs. A warning message appears while synchronization is in progress.
Mains abnormal
When the mains fails or is abnormal, the rectifier will stop working automatically, and the system will transfer to battery
output (through inverter). The length of the operation time in battery mode depends on the load and the battery
capacity. During this period, if the battery voltage falls to the EOD voltage and the mains still has not been recovered,
the inverter will stop working automatically, and the UPS operator control and display panel will display corresponding
alarm messages. If the system uses split bypass configuration and the bypass is normal, the system will transfer to
bypass.
Mains recovery
When the mains resumes normal within allowable time, the rectifier will start automatically (at this time its output power
will increase gradually) and supply the load and charge the battery again. Therefore, the power supply to the load will
not be interrupted.
Battery disconnection
To disconnect the external battery from the UPS system for maintenance, use the external isolating switch. At this time,
except for the battery backup function upon mains failure, other functions and all the steady state performance of the
UPS will not be affected.
UPS module failure
In case of inverter failure, inverter switch failure, output fuse blowout and bypass STS failure, the load will
automatically transfer to the bypass, and the output power supply will not be interrupted. In this situation, please
contact the local customer service center of Emerson Network Power Co., Ltd for technical support.
Summary of Contents for NXC 30kVA
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