Ups Power Supply Switch Configuration - Liebert NXC 30kVA User Manual

(Parallel System) In the event of a fault in a UPS module, it will automatically exit from the parallel system. If the
system is still capable of providing the required load, the remaining modules will continue to supply the load with no
interruption. If the remaining modules are no longer capable of fulfilling power requirements, the load will automatically
transfer to the bypass.
Overload
If the inverter is overloaded or the inverter current remains outside the specifications (refer to Table 11-6) longer than
the specified time, the load will automatically transfer to the bypass without power interruption. If both the overload and
the current are reduced to a level within the specified range, then the load will be transferred back to the inverter. In
case of output short circuit, the load will be transferred to the bypass, and the inverter will shut down. Five minutes
later, the inverter will start up automatically. If the short circuit is removed at this point, the load will be transferred back
to the inverter. The transfer is determined first of all by the features of the protective device of the system.
In the above two situations, the UPS operator control and display panel will display alarm messages.
(Parallel System) The control logic system constantly monitors load requirements and controls the power supplied by
each UPS module. In the event that an overload condition is sustained for greater than a preset time, the load will
transfer to the bypass, when the number of active modules is unable to satisfy load requirements. The load returns to
the inverter if the power is reduced to a value that can be sustained by the number of active modules in the system.
Maintenance bypass
The UPS has a second bypass circuit, i.e. maintenance bypass, which provides a safe working environment for the
engineers to provide regular maintenance or repair to the UPS system and at the same time provide unregulated
mains supply to the loads. The maintenance bypass can be manually selected through the maintenance bypass
switch, and it can be disconnected by turning the switch to OFF.
If the UPS system is composed of two or more parallel UPS modules, and the load capacity exceeds the single module capacity,
do not use the internal maintenance bypass switch.

1.2.4 UPS Power Supply Switch Configuration

Figure 1-2 describes the block diagram of the UPS module. The UPS has split bypass configuration (that is, the
bypass adopts independent mains input) and common input configuration. In split bypass configuration, the static
bypass and maintenance bypass share the same independent bypass power supply. Where a separate power source
is not available, the input supply connections of the bypass input switch (Q2) and rectifier input switch (Q1) would be
linked together (linked before delivery) to make the bypass input and rectifier input use mains power of the same route.
During the normal operation of the UPS, except for the maintenance bypass switch Q3, other switches shall be closed.
Liebert NXC 30kVA And 40kVA UPS User Manual
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