User manual

Chapter 4 Operation 29
NXr UPS Module And Parallel System 30kVA ~ 200kVA User Manual
inverter frequency track that of the static bypass supply, provided that the bypass remains within an acceptable
frequency window.
A manually-controlled maintenance bypass supply is incorporated into the UPS design. It enables the critical load to
be powered from the maintenance bypass supply while the UPS is shut down for routine maintenance and repair.
Note
When the UPS is operating in bypass mode or on maintenance bypass, the connected equipment is not protected from power
failures, surges, or sags.
4.2 1 + N Parallel System
Up to four UPS modules can be parallel-connected to form a 1 + N system to increase the system capacity or
reliability, or both. The load is equally shared between the paralleled UPSs.
4.2.1 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 control 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 synchronised 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.
4.2.2 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 residual current detector (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.
4.3 Operation Mode
The UPS is an on-line, double-conversion, reverse-transfer UPS that permits operation in these modes:
 Normal mode
 Battery mode (“stored energy mode”)
 Automatic restart mode
 Bypass mode
 Maintenance mode (manual bypass)
 Parallel redundancy mode