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Introduction
2
1.0 INTRODUCTION
1.1 System Description
The role of the parallel-redundant multi-module UPS system is to supply uninterruptible, clean
power to the critical load. The UPS maintains a full-voltage, low-distortion output, even if the utility
source power sags, becomes distorted or fails.
If there is an outage of the source power, the UPS maintains power to the load until an alternate
source of power is activated or until the original power source is restored. If input AC power is not
restored, the UPS maintains the load (with a storage battery plant) long enough that the critical
equipment can be shut down in an orderly manner or an alternate power source (e.g., Genset) can be
brought on line. The Liebert Series 610 UPS module displays the rate of battery discharge and calcu-
lates the amount of battery time remaining based on the actual connected load. The time that the bat-
tery will maintain the load depends on the capacity of the battery backup plant and the size of the load.
The system control logic automatically manages critical bus operation. System logic is resident in dig-
ital control logic for precise control and improved reliability.
If the critical load current exceeds the rated load of the Liebert Series 610 UPS system, the control
logic determines the magnitude of the overload and reacts appropriately. Overloads are usually the
result of inrush current requirements. The UPS system supports loads that are 150% of the rated load
for up to 30 seconds and 125% of the rated load for up to 10 minutes. If the system is operating in the
non-redundant mode (e.g., a UPS module is off line), the overload limits are automatically adjusted.
Figure 1 Multi-Module UPS, 100-500kVA
If the load surpasses the overload capacity of the UPS, the load is automatically transferred to bypass
without interruption. When the load returns to within the UPS rating, it is either automatically or
manually returned (retransferred) to the UPS. How and when the load is returned to the UPS
depends on several factors: how long the overload lasted, how many overload conditions occurred
before transfer, whether there is an imminent failure of any part of the UPS, etc. Refer to 3.5 - Auto-
matic Operations.
100-500kVA