What are the advantages and disadvantages of an open delta transformer configuration ?

Open-delta configurations are typically deployed by utilities, typically to loads with little single-phase requirements.


  • Open-deltas only require the utility to install two transformers.
  • Future Capacity can be increased by simply installing a third similar sized transformer verses installing 2-3 larger transformers.


  • While the line to line voltages will be equal, the line to neutral voltages will have two phases being equal and one phase being 1.732 times larger.
  • Unbalanced single phase loads can cause voltage fluctuations and additional, uneven transformer heating.
  • An open delta connection only has 58% of the capacity of a full set of three transformers, that is a 42% decrease in actual capacity event though the installed capacity only drops by 33%.