Chapter 4 Operations 41
LIEBERT APM UPS Module And Parallel System 30kVA~150kVA User Manual
5.3.3 Auto-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 if the AC mains recovers. This mode and any delay time are programmed by the commissioning
engineer.
5.3.4 Bypass Mode
If the inverter overload capacity is exceeded under normal mode, or if the inverter becomes unavailable for any
reason, the static transfer switch will perform a transfer of the load from the inverter to the bypass source, with no
interruption in power to the critical AC load. If the inverter is asynchronous with the bypass, the static switch will
perform a transfer of the load from the inverter to the bypass with interruption in power to load. This is to avoid large
cross currents due to the paralleling of unsynchronized AC sources. This interruption is programmable but typically
set to be less than 3/4 of an electrical cycle, e.g., less than 15ms (50Hz) or less than 12.5ms (60Hz).
5.3.5 Black Start Mode
If the there is no utility input and you want that UPS passes from the OFF mode to the Battery Mode you have to
push the button in front of any one of the UPS Rack module, and then push “Inverter On ” button to start the inverter.
5.3.6 Maintenance Mode (Manual Bypass)
A manual bypass switch is available to ensure continuity of supply to the critical load when the UPS becomes
unavailable e.g. during a maintenance procedure. This manual bypass switch is fitted in all UPS Rack System and
rated for full load of one UPS Rack
5.3.7 Parallel Redundancy Mode (System Expansion)
For higher capacity or higher reliability or both, the outputs of several UPS modules can be programmed for direct
parallel: a built-in parallel controller in each UPS ensures automatic load sharing. A parallel system can be composed
of up to four UPS Rack Systems.
5.3.1 Sleep Mode
To improve system efficiency, when system capacity is high and the load is light you can decide to automatically shut
down a number of power modules according to load level: if then the load increases, dormant modules are
automatically started
To ensure that each module has equal chances of being selected as dormant and of dormancy duration, and that the
life cycle of each module is consistent, the polling dormancy policy is adopted for the modules. The dormancy
duration of each module can be set from 1 to 1000 days. When the dormancy duration of a module is reached, the
module automatically starts, and the next module enters into the sleep mode.
If a system is configured to have X redundant power modules, the number of dormant modules is such that in any
case, X module more than the ones required to sustain the load are not dormant .
It takes about one minute for the rectifiers and inverters of the dormant modules to start and share the load. During
this period, the system may be overloaded and switch to bypass mode, so it is recommended to enable the sleep
mode just when it is known that load changes slowly (e.g. by system upgrade) and not dramatically (e.g. by sudden
changes of workload). Two dormancy parameters are available at the background: Intelligent UPS Dormancy
Function and Module Dormancy Time.
Prerequisites for Enabling the Sleep Mode
To enter into sleep mode, the following prerequisites must be met:
The function of monitoring and setting dormancy is enabled.
The rectifier runs on the main channel without faults. The battery is almost fully charged.
The inverter does not report any fault or alarm.
The power supply for the bypass is available. The bypass voltage and SCR are normal.
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