Filter
Top Products
Operation
80
3.5.2 Automatic Transfers to Bypass (Overload Condition)
The UPS system will initiate an automatic load transfer to the bypass line if an overload condition
exceeds the current-versus-time curve of overload capacity or if specified UPS system faults occur.
Load On Bypass is illustrated in Figure 42.
The Overload Transfer and Output Undervoltage alarm messages will initiate an automatic transfer
to bypass and the Load On Bypass message will be displayed. The status report screens will include
the Automatic Transfer to Bypass message. Other UPS system faults will initiate an automatic trans-
fer to bypass followed immediately by the shutdown and isolation of the UPS system. Refer to 3.5.4 -
Automatic Transfers to Bypass (UPS System Faults).
In an automatic transfer to bypass the output and bypass circuit breakers do not overlap as they do in
a manual transfer. The static bypass switch is fired (closed), the output circuit breaker is opened, and
the bypass circuit breaker is closed. Bypass power is supplied to the critical load through the static
bypass switch during the short time while both circuit breakers are open.
3.5.3 Automatic Retransfers to UPS
Automatic Retransfer to UPS is an option that you can select from the System Configuration screen.
If you do not want the UPS system to initiate any automatic retransfers, set Max Auto-Rexfer
Attempts to zero (0).
In an automatic retransfer, the two motorized circuit breakers (bypass and inverter output) are both
closed simultaneously for a short period of time (overlap).
The following critical bus conditions must be present to initiate an automatic retransfer of the critical
load from the bypass source to the UPS inverter:
1. The number of Auto-Rexfer Attempts selected must be greater than zero (0). If zero (0) is selected,
no automatic retransfers will occur.
2. Critical load was initially transferred to the bypass source due to a system overload only. A
manual retransfer from bypass is required if the transfer to bypass was caused by any condition
other than output overload.
3. Overload has since dropped below 100% of the rated load.
4. Both the Input and the Battery (MBD) circuit breakers have remain closed since the overload
transfer.
5. OK to Transfer signal received from the control logic for at least 10 seconds, within 5 minutes of
the system overload transfer. A manual retransfer from bypass is required for overloads lasting
5 minutes or more.
6. Cyclic-type overloads, which occur up to five (select range is 0 to 5) times in 60 minutes, are
automatically returned to the inverter for each event including the Nth overload. A manually
initiated retransfer from bypass is required for the N + 1 overload.
NOTE
A load transfer to the bypass line will be completed whenever an automatic transfer to bypass
is initiated. If the OK to Transfer condition is present, the load transfer will be uninterrupted.
If the Static Switch Unable alarm message is present for any reason, the automatic transfer
will be interrupted for 40 to 120 milliseconds. Because of the reliability of the UPS components,
an interrupted load transfer is a very unlikely occurrence.