Chapter 8 Parallel System; System Introduction; Basics - Liebert UPS System User Manual

8.1 System Introduction

8.1.1 Basics

The Liebert UPS uses intelligent and reliable decentralized parallel operation
technology. A maximum of four single units of the same capacity can operate in
parallel.
The UPS system has two paralleling modes:
Paralleling for redundancy
Paralleling for capacity
1. Conditions for parallel operation
Each UPS unit has the same capacity, same software and hardware version
Each UPS in the system must share the same bypass source
The UPS output are connected together. The rectifier input can be from a different
source, but the phase rotation of the rectifier input, bypass input and output must
be the same
The parallel logic cable and load sharing cable must be connected
2. Features of parallel systems
1）The hardware and firmware of each unit in the system must be compatible and
changing the operation mode can be done only with changing the software setting.
2）The parallel signal bus is simple, reliable and designed for redundancy, which
provides the user with maximum flexibility. Shutting down or starting up the UPS in
the parallel system can be done in any sequence. If an overload occurs, the
system can recover automatically from bypass mode after the overload is cleared.
3）The operation status can be queried from each UPS's LCD display.
4）The UPS monitoring module (optional) can monitor the system parameters of
the whole system.
5）Any single module UPS system in the parallel system can be designated as the
host for communication with remote computer. The total load current, number of

Chapter 8 Parallel System

Chapter 8 Parallel System
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