Besides delta, what are the other two types of three-phase transformers used by the Air Force?

The correct answer is grounded wye and ungrounded wye. These configurations are important in three-phase transformer applications because they offer different benefits for electrical systems, particularly in terms of grounding and balancing loads.

The grounded wye configuration provides a neutral point that can be connected to ground, which enhances safety by offering a path for fault currents and helps in minimizing over-voltages during transients. This grounding also aids in the protection of electrical equipment and improves the voltage stability in the system.

On the other hand, the ungrounded wye configuration allows for a system that remains operational even if one phase becomes grounded, which is especially valuable in critical applications where continuous operation is necessary. However, it can lead to high line-to-ground voltages that may pose risks to equipment if not managed properly.

The use of these configurations helps in ensuring reliable power distribution, reducing the risk of electrical faults, and maintaining equipment longevity, making them suitable choices for various applications, including those used by the Air Force.