Eaton Power Xpert 9395P-900 Series Installation And Operation Manual Download

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Understanding UPS Operation

6-26

Eaton

Power Xpert

9395P-900 UPS Installation and Operation Manual P-164000501—Rev 09

www.eaton.com/powerquality

The distributed bypass system can be transferred from Normal mode to Bypass mode manually. However, the
distributed bypass system automatically switches to Bypass mode whenever the UPSs can no longer supply
the critical load. If the distributed bypass system transfers to Bypass mode from Normal mode due to an output
voltage deviation, the distributed bypass system automatically attempts to return to Normal mode (up to three
times within a 10-minute period). After three transfer attempts or an overload, the system locks the critical load
to the bypass source and requires operator intervention to transfer.

Bypass mode is a normal operating mode, not an alarm condition. However, if the distributed bypass system
is unable to return to Normal mode following an automatic transfer to Bypass mode, an alarm condition is
recorded.

Bypass may also be used when the UPSs or UPMs in the system must be shut down to perform routine
maintenance or repairs.

In the Parallel Redundant (N+1) arrangement, the bypass circuitry in each UPS operates to support the applied
loads on bypass. If the UPSs are online and one UPS trips offline, the remaining UPSs do not go to bypass as
long as they have the capacity to support the load.

In the Parallel Capacity (N+0) arrangement, if one UPS trips offline and goes to bypass, the remaining UPSs
also go to bypass.

6.4.4

Battery Mode - Distributed Bypass

The UPSs transfer to Battery mode automatically if a utility power outage occurs, or if the utility power does
not conform to specified parameters. In Battery mode, the battery provides emergency DC power that the
inverter converts to AC power.

Figure 6-20 shows the path of electrical power through the distributed bypass system when operating in
Battery mode.

While in Battery mode, the UPSs sound an audible horn, illuminate a visual indicator lamp on the front panel
(Online and On Battery), and create an entry into the alarm event history. As the battery discharges, the boost
converter and inverter constantly make minute adjustments maintaining a steady output. The UPSs remain in
this operating mode until the input power to the rectifier is again within the specified voltage or frequency
acceptance windows.

If the input power fails to return or is not within the acceptance windows required for normal operation, the
battery continues discharging until a DC voltage level is reached where the inverter output can no longer
support the shared loads. When this event occurs, each UPS issues another set of audible and visual alarms
that indicate a two-minute SHUTDOWN IMMINENT warning. Unless the system has a valid AC input soon,
redundant UPMs begin shutting down until there are no longer enough UPMs online to support the connected
load. When this event occurs, the system shuts down. If the bypass source is available, the system transfers
to bypass instead of shutting down.