In this topic, you study Open Delta Connection of Transformers – Theory, Diagram, and Derivation.
If one transformer of the delta delta connected three phase transformers is disconnected due to some fault in it, the remaining two transformers make an open-delta or V–V connection as shown in Figure 1. The open-delta connection supplied a three-phase load with a rating reduced to about 57.7
Figure 1 Open-delta connection by two single-phase transformers
Let us examine the VA rating of delta-delta connected transformers and open-delta transformers as shown in Figure 2.
(1)
(2)
The ratio of Equation 1 and Equation 2 as,
- Delta-delta connection
- Open-delta connection
Figure 2 Delta-delta connection and V–V connection for comparison (only secondary shown)
This shows that the load carried by open delta connected transformers is only 57.7 percent of the original load.