Liebert UPS System Paralleling for Capacity Expansion, Series Hot-Standby parallel system

Chapter 8 Parallel System

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.

89