Advantages of open delta connection of 3-phase transformer:
1. When one of the phase in case of delta-delta bank is out of order by any reason, the service will be continued till the faulty phase is repaired or a new transformer is installed.
2. In case of future, increase in the load demand can be anticipated by using open delta connection. The present load can be supplied by using open delta connection and the additional demand in future (about 33%) will be supplied by converting open delta connection to delta-delta connection.