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Introduction
3
1.0 INTRODUCTION
1.1 System Description
The role of the UPS system is to supply uninterruptible, clean power to the critical load. It maintains
a full-voltage, low-distortion output, even if the utility source power sags or becomes distorted.
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 the battery plant) long enough that the critical equipment
can be shut down in an orderly manner. The Npower UPS module displays the rate of battery dis-
charge and calculates the amount of battery time remaining based on the actual connected load. The
time that the battery 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 Signal Processors (DSPs) for precise control and improved reliability.
If the critical load current exceeds the rated load of the Npower UPS system, the control logic deter-
mines 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 60 seconds, 125% of the rated load for up to ten minutes, and 104% of the rated load indefinitely.
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. In the unlikely
event of a fault within the UPS, the control logic, which continuously monitors all critical circuits
within the UPS system, transfers the load to bypass without interruption and simultaneously sets off
local and remote alarms. For a few specified faults, the UPS is shut down. The UPS can be manually
returned to service when the fault has been corrected.
The Npower UPS display system provides precise monitoring of the UPS, fast alarm response, and
quick troubleshooting. For easy manual operations, menu-driven software provides access to several
step-by-step help screens. All operator functions are performed using menu-prompted displays and a
minimum number of operator controls. Available options include external communication capability
with both automatic dial-out and dial-in features for early warning and diagnosis of abnormal condi-
tions.
The system software allows the operator or Liebert Global Services to enter application specific infor-
mation. Overload, overvoltage, battery discharge, and shutdown limits can be set by the operator. In
effect, the software is tailored for each site.
The UPS system protects critical equipment from source power disturbances and outages, load faults,
and UPS malfunctions. This triple protection virtually eliminates computer and computing equip-
ment downtime as a result of utility source power problems.