Liebert UPS System - Manual (Page 96)

Chapter 8 Parallel System
90
Fig. 8-4 Series backup mode
Note
The default value of alternative operation time is 168 hours and the range is 0-4320
hours
8.1.3 Operation modes
The parallel operation system also has operation modes such as normal mode,
battery mode, bypass mode and maintenance bypass mode. All the UPS units
inside the parallel operation system should operate in harmony. For example if one
UPS is in inverter mode, the bypass of other units should be shut down.
Normal mode: The load is powered by the inverters of all the UPS units inside the
system. If the bypass frequency is in the synchronous range, the inverter will be
synchronous with the bypass. Otherwise, the system will operate at nominal
frequency.
Battery mode: The batteries of the system powers the load through inverters of all
the UPS units. The system operates at nominal frequency.
Bypass mode: The condition to transfer to bypass mode is same with that of single
module UPS system. The bypasses of all the UPS units power the load.