6 Chapter 1 Overview
NX UPS Single Module And Parallel System 250kVA ~ 800kVA User Manual
Moreover, two UPS module systems or parallel systems can comprise a dual bus system. Each UPS module or
parallel system has independent output. Output synchronization is achieved through LBS, thus enabling seamless
load transfer between the two systems.
1.3.1 Parallel System Features
1. The hardware and software of parallel system are completely the same as those of single UPS module. The
parallel configuration is achieved through settings in configuration software. The parameter settings of each UPS
module in parallel system should be the same.
2. Parallel cables are connected in a ring, providing both system reliability and redundancy. Dual bus control cables
are connected between any two UPS modules of each bus. The intelligent parallel logic provides the user with
maximum flexibility. For example, shutting down or starting up UPS modules in a parallel system can be done in any
sequence. Transfers between normal and bypass modes of operation are synchronized and self–recoverable, for
example, following overloads and their clearance.
3. The total load of the parallel system can be queried from each UPS module’s LCD.
1.3.2 Requirements For Paralleling Of UPS Modules
A group of paralleled modules behave as if it were one large UPS with the advantage of presenting higher reliability.
To ensure that all modules are equally utilised and to comply with relevant wiring rules, the following requirements
apply:
1. All UPS modules must be of the same rating and must be connected to the same bypass source.
2. The bypass and main input sources must be referenced to the same neutral potential.
3. Any RCD, if installed, must be of an appropriate setting and located upstream of the common neutral bonding point.
Alternatively, the device must monitor the protective earth current of the system. Refer to
Warning: high earth leakage
current
before
Contents
.
4. The outputs of all UPS modules must be connected to a common output bus.
Note
Optional isolation transformers are available for applications where sources do not share the same neutral reference or where the
neutral is not available.
1.4 Operation Mode
The UPS system permits operation in these modes:
Normal mode
Battery mode
Bypass mode
Maintenance mode (manual bypass)
Automatic restart mode
Parallel redundancy mode (system expansion)
Normal mode
As shown in Figure 1-7, the UPS rectifier derives power from the AC mains input source and supplies DC power to
the inverter, which continuously supplies AC power to the load. Simultaneously, the charger, which derives power
from the rectifier, float or boost charges the associated backup battery of the UPS.
