What is the power factor in the open delta connection of transformers? How is it determined?

In an open delta connection of transformers, the power factor is not uniform across the two remaining windings, and it does not remain at unity as it would in a standard three-phase delta configuration.

Here are the key points to understand the power factor in an open delta connection:

Power Factor of Individual Transformers

• In an open delta connection, each of the two single-phase transformers operates with a different power factor. For a balanced load with unity power factor, one transformer has a power factor of (\cos(30-\phi)) and the other has a power factor of (\cos(30+\phi)), where (\phi) is the load power factor angle4.

Internal Power Factor

• Even when the load has a unity power factor, the internal power factors of the two transformers are not unity. One transformer operates at a leading power factor and the other at a lagging power factor, resulting in internal power factors of approximately 0.866 (or (\cos 30^\circ))4.

Overall Power Delivery

• The overall power delivery of the open delta transformer is affected by these internal power factors. The maximum power that an open delta transformer can deliver is only about 57.7% of the capacity of an equivalent three-phase delta transformer with similar voltage and load current ratings. This is because the two transformers are not fully utilized due to the phase angle differences and the resulting power factor discrepancies234.

In summary, the power factor in an open delta connection is not a simple unity power factor as in a standard delta configuration. Instead, it involves complex power factor relationships between the two operating transformers, leading to an overall reduced capacity compared to a full delta connection.