Liebert NX UPS System user manual Modes of Operation

Operation

5.2.1Features of NX Multi-Module UPS Configurations

1.The hardware and firmware of single module UPS units is completely compatible with the requirements of a multi-module system. Multi-module configuration is achieved merely through settings in configuration software.

2.Parallel control cables are connected in a ring, providing both performance and redundancy. Dual-bus control cables are connected between any two UPS modules of each bus. The intelligent paralleling 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 –recovering e.g. following overloads and their clearance.

3.The total load of the multi-module system can be queried from each module’s LCD display.

5.2.2Requirements 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. In order to assure 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 the main input sources must be referenced to the same neutral potential.

3.Any RCD, Residual Current monitoring device, if installed, must be of an appropriate setting and located upstream of the common neutral bonding point. Alternatively, the device must monitor the combined 4-wire rectifier and split-bypass input currents of the system. Refer to the High Leakage Current Warning on page 1.

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.

5.3Modes of Operation

The NX UPS is an on-line, double-conversion, reverse-transfer UPS that permits operation in these modes:

•Normal Mode

•Battery Mode (Stored Energy Mode)

•Auto-Restart Mode

•Bypass Mode

•Maintenance Mode (Manual Bypass)

•ECO Mode

•Parallel Redundancy Mode

•Hot-Standby Mode

•Frequency Converter Mode

5.3.1Normal Mode

The UPS inverter continuously supplies the critical AC load. The rectifier/charger derives power from the AC mains input source and supplies DC power to the inverter while simultaneously FLOAT or BOOST charging its associated backup battery.

5.3.2Battery Mode (Stored Energy Mode)

Upon failure of the AC mains input power; the inverter, which obtains power from the battery, sup- plies the critical AC load. There is no interruption in power to the critical load upon failure or restora- tion of the AC mains input power after which the “Normal Mode” operation will continue without the necessity of user intervention.

5.3.3Auto-Restart Mode

The battery may become exhausted following an extended AC mains failure. The inverter shuts down when the battery reaches the End Of Discharge voltage (EOD). The UPS may be programmed to “Auto Recovery after EOD” after a delay time. This mode and any delay time are programmed by the commissioning engineer.

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