Liebert UPS System - Manual (Page 95)

Chapter 8 Parallel System
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Fig. 8-2 Redundancy operation mode
This system can improve the system reliability noticeably. In normal condition, each
UPS does not work at full load, so even if the load is increased, the system will not
transfer to bypass.
When X number of UPS shuts down due to failure, the remaining N numbers of
UPS can still powers the load. At this time, the system will give out the alarm.
3. Paralleling for Capacity Expansion
In this system, X is zero then if the rating of each UPS unit is Po and the total load
capacity is Pmax, then (N-1) x Po < Pmax < N x Po, as shown in Figure 8-3. This
system cannot improve the reliability, but can improve the system capacity to
support an increased load.
Fig. 8-3 Capacity expansion
4. Series “Hot-Standby” parallel system
Two UPS units are connected in series, one is the Master and the other Slave.
The Slave output is the bypass source of the Master, as shown in Figure 8-4. In
normal condition, both UPS are in normal mode with the inverter supporting the
load. If one unit fails, the other will power the load. In order for the system to rotate
powering the load, the alternative operation time must be set. If two different UPS
are connected in series, the load capacity must be smaller than the UPS with the
smallest rating.