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4
Chapter 1 Overview
Maintenance bypass
The UPS has a second bypass circuit, i.e. maintenance bypass, which provides a safe working environment for
the engineers to provide regular maintenance or repair to the UPS system and at the same time provide
unregulated mains supply to the loads. The maintenance bypass can be manually selected through the
maintenance switch. It can be disconnected by turning the switch to OFF.
1.2.4 UPS Power Supply Switch Configuration
As shown in Figure 1-2, the main input power and bypass input power of the UPS are fed from the common
input switch Q1, and the UPS provides the maintenance switch Q2 and output switch Q3 as well.
During normal UPS operation, all power switches except for the maintenance switch Q2 should be closed.
Mains input
1.2.5 BCB
The external battery must be connected to the UPS through a BCB. The BCB should provide overcurrent
protection, short circuit protection and automatic tripping functions. The BCB should be installed near the
battery.
1.3 Parallel System
As shown in Figure 1-3, two UPS modules can be parallel-connected to form a parallel system to increase the
system capacity or reliability, or both. The load is equally shared between the paralleled UPSs.
Liebert APM 150 Integrated UPS Single Module And Parallel System
Maintenance switch Q2
Rectifier
Input switch Q1
Battery switch
Battery
Figure 1-2 UPS power supply switch configuration
Static switch
Automatic
Inverter
inverter switch
Charger
Output
UPS Output
switch Q3
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