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8.2 Operating Modes
The UPS is designed to operate as an on-line, double-conversion, reverse-transfer system in the
following modes:
•Normal Mode
•Battery Mode
• Auto-Restart Mode
• Bypass Mode
• Battery Start Mode
• Maintenance Mode (Manual Bypass)
•Sleep Mode
• Paralleling Mode
Normal Mode
Operating in normal mode, the Liebert
®
APM
™
’s rectifier derives power from a utility AC source and
supplies regulated DC power to the inverter, which regenerates precise AC power to supply the
connected equipment. The rectifier also uses the utility source power to charge the batteries.
Battery Mode
When utility AC power fails, the Liebert APM protects the critical load by instantaneously channeling
battery power to the inverter which continues supporting the critical load without interruption. When
utility power returns and is within acceptable limits, the Liebert APM automatically shifts back to
Normal mode, with the rectifier powering the critical load.
Auto-Restart Mode
The battery may become exhausted following an extended AC utility 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 utility recovers. This mode and any delay time may
be programmed by the commissioning engineer.
Bypass Mode
When the Liebert APM is in bypass mode, the load is directly supported by utility power and is
without battery backup protection.
The Liebert APM’s static transfer switch will shift the load from the inverter to bypass mode without
an interruption in AC power if the inverter is synchronous with the bypass and any of the following
occurs:
• inverter fails
• inverter overload capacity is exceeded
• inverter is manually turned off by user
Battery Start Mode
The battery start option permits starting the Liebert APM with power supplied only by the batteries
(at charged condition).
NOTE
If the inverter is asynchronous with the bypass, the static switch will transfer the load from the
inverter to the bypass WITH interruption in AC power to the critical load. This interruption
will be less than 15ms (in 50Hz), or less than 13.33ms (in 60Hz). This interruption time may be
altered by modifying the Output transfer interrupt time setting.