Shield T3 60 – 500KVA User Manual
11
1.4.3
Bypass Mode
If the inverter overload capacity is exceeded under Normal mode, or if the inverter
becomes unavailable for any reason, the static transfer switch will perform a transfer
of the load from the inverter to the bypass source, with no interruption in power to the
critical AC load. Should the inverter be asynchronous with the bypass, the static switch
will perform a transfer of the load from the inverter to the bypass with power
interruption to the load. This is to avoid large cross currents due to the paralleling of
unsynchronized AC sources. This interruption is programmable but typically set to be
less than 3/4 of an electrical cycle, e.g., less than 15ms (50Hz) or less than 12.5ms
(60Hz). The action of transfer/re-transfer can also be done by the command through
monitor.
Rectifier
AC/DC
Main
Static Bypass
Manual Bypass
Inverter
DC/AC
Charge/
Discharge
Output
Battery
Bypass
Figure1-5 UPS conceptual diagram in Bypass Mode
1.4.4
Maintenance Mode (Manual Bypass)
A manual bypass switch is available to ensure continuity of supply to the critical load
when the UPS becomes unavailable e.g. during a maintenance procedure.
Rectifier
AC/DC
Main
Static Bypass
Manual Bypass
Inverter
DC/AC
Charge/
Discharge
Output
Battery
Bypass
Figure1-6 UPS conceptual diagram in Maintenance Mode
