Operating Principles; Operation Modes Summary; Installing Parallel System; Conditions For Parallel System - Emerson Liebert NX 10-30kVA Installation Manual

5.2.3

Operating Principles

Redundancy Paralleling
The 1+N parallel redundant system can noticeably improve system reliability. In normal condition,
none of the UPS modules work at full load. That means that even if the load is increased, the system
will not transfer to bypass. And when a UPS module shuts down due to any failure, the remaining
UPS modules can still power and protect the load. When redundancy is lost due to module failure or
load increase, the parallel system will trigger an alarm.
5.2.4

Operation Modes Summary

The parallel system also has operation modes such as normal, battery, bypass and maintenance
bypass. All UPS modules in the 1+N parallel system operate in coordination.
• Normal Mode Operation
The load is powered by the inverters of all the UPS modules in the system. If the frequency of
bypass is within the synchronous range, the inverter will be synchronized with the bypass. Other-
wise, the system will operate at nominal frequency.
• Battery Mode Operation
The batteries of all UPS modules power the load through their inverters. The system operates at
nominal frequency.
• Bypass Mode Operation
The condition to transfer to bypass mode is essentially the same as that of single module system.
The bypass of all the UPS modules powers the load.
• Maintenance Bypass Mode Operation
The sequence to transfer to maintenance bypass mode is the same as for transferring a single-
module system. The maintenance bypass switches should be switched on as synchronously as pos-
sible. Thus the system can be repaired without interrupting the power supply to critical load.
5.3

Installing Parallel System

The basic installation procedure of parallel system is the same as that of single module system. The
following sections introduce only the installation procedures specific to the parallel system.
5.3.1

Conditions for Parallel System

• Each UPS module should have the same rating, the same firmware and hardware version.
• Each UPS module must have the same bypass source.
• The outputs of all UPS modules are connected altogether.
• The main inputs can be from different sources, but the phase rotation sequence of main inputs,
bypass inputs and outputs must be correct and the same.
• The parallel logic cable and load sharing cable must be connected in a ring correctly (see
Figure 23).
5.3.2

Cabinet Installation

Parallel system composed of two or more UPS modules using parallel cabinet
The UPS modules that will form the 1+N system should be placed side-by-side. Each battery cabinet
is placed next to its corresponding UPS module.
The parallel cabinet should be placed in the middle of the system.
5.3.3

Preliminary Checks

Each UPS module should have the same rating, the same firmware and the same hardware version.
Refer to the instructions in 5.3.1 - Conditions for Parallel System.
5.3.4

Protective Devices

For each UPS, refer to Table 10. For each system, refer to Table 31.
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Appendix