Emerson Liebert APS Installation Manual download pdf (Page 25)

Chapter 2 Operation 17

Liebert APM Modular UPS User & Installation Manual

During normal operating conditions, the inverter output and bypass supply must be fully synchronized so as to

achieve a clean (no-break) load transfer between the inverter output and static bypass line. The synchronization

between the inverter output and static bypass is achieved through the inverter control electronics, which make the

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 or surges and sags.

2.2 Operation Mode

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

Normal mode

Battery mode

Auto-restart mode

Bypass mode

Maintenance bypass mode (manual bypass)

ECO mode

2.2.1 Normal Mode

The UPS rectifiers derive power from the AC mains input source and supply DC power to the inverters, which

continuously supply the AC load. Simultaneously, the charger, which derives power from the rectifiers, float or boost

charges the associated backup battery of the UPS.

2.2.2 Battery Mode

The UPS is operating in battery mode when the battery is supplying backup power to the load through the inverters.

Upon mains failure, the UPS automatically transfers to battery mode without power interruption to the load. Upon

restoration of the AC mains, the UPS automatically transfers back to normal mode without the necessity of user

intervention, without power interruption to the load.

Note: Battery start function is available for switching the UPS on into Battery (charged) mode directly during mains

failure. Thus, the battery power can be used independently to increase the UPS utility.

2.2.3 Automatic Restart Mode

The battery becomes exhausted following an extended AC mains failure. The inverters shut down when the battery

reaches the EOD voltage. The UPS can be programmed to automatic restart after EOD after a set variable delay time.

This mode and any delay time are programmed by the commissioning engineer.

During the delay time before automatic restart, the UPS charges the battery so as to avoid power interruption to load

in case of a following power failure.

In case the UPS is not programmed to automatic restart, you can use the FAULT CLEAR key to manually start the

UPS.

2.2.4 Bypass Mode

During normal mode operation, if the inverters fail, are overloaded or turned off, the static switch will perform a

transfer of the load from the inverters to the bypass source, with no interruption in power to the load. Should the

inverters be asynchronous with the bypass, the static switch will perform a transfer of the load from the inverters to

the bypass, with interruption in power to the load. This is to avoid paralleling of unsynchronized AC sources. This

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