Which of the following terms describes a connection type of transformers in a voltage step-down application?

In the context of transformers used for voltage step-down applications, the open delta connection is significant. This configuration is utilized when only two transformers instead of three are used to provide a lower voltage output, and it can be advantageous in terms of cost and space for smaller loads. Though it is not as efficient as the full delta connection, it allows for the transformation of voltage while utilizing fewer resources.

In an open delta connection, the primary windings of the two transformers are connected in a way that maintains the necessary phase shift, while their secondary windings are connected to produce the desired lower voltage. This method is particularly useful in applications where full capacity is not required, allowing for two transformers to handle the load adequately while saving on installation costs and space.

Other options do not accurately represent the typical transformer connection types used specifically for stepping down voltage. Load banks are used for testing and conditioning electrical systems, series connections are generally for increasing voltage or current in specific configurations, and parallel connections do not pertain specifically to step-down applications in transformer systems. Thus, open delta is the appropriate term for this specific application.