System Description

1.5.5Modes of Operation

See Figure 4.

The Power-Tie Uninterruptible Power System is designed to operate in the following modes:

1.Normal - Each load bus is fed from its respective UPS and the tie breaker is open. Each inverter is synchronized to its respective bypass source. Each load is supplied by its inverter(s), with its bypass available as an alternate source.

2.Momentary Tie - The load bus and the two UPSs are momentarily paralleled through the tie breaker. Both UPSs are on-line, and the bypass source of one UPS will be selected as the primary sync source. When one UPS drops off-line, then operation reverts to the Combined Loads Mode below.

3.Combined Loads - Both loads are running on one UPS through the tie breaker. The combined loads are supplied by the selected UPS’s inverter(s), with that UPS’s bypass available as the alternate and sync source. This mode is typically used for servicing a UPS system, including its bypass and bypass transfer controls, without placing that UPS’s load on bypass.

4.Continuous Tie - The load bus and the available modules from the two UPS are continuously paralleled through the tie breaker. Both UPSs are on-line, and one UPS’s bypass source will be selected as the alternate bypass and sync source. Although not normally done from this operational mode, one of the two UPSs could be shut down and isolated at this point as well.

5.System Isolation - A selected load bus which has had all load removed (via shutdown, external maintenance bypass or downstream critical load switchover devices—dual input PDU, STS or ATS) may be isolated from one or both UPSs for maintenance.

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Liebert Series 610 user manual Modes of Operation