B. Per unit impedance

When two transformers are operating in parallel, they will share the load based on their per unit impedance (PU). Per unit impedance is a value that represents the relative impedance of a transformer compared to its rated capacity. It is calculated by dividing the transformer’s actual impedance by its rated capacity.

For example, if two transformers have a PU of 0.05 and 0.1, the transformer with a PU of 0.05 will carry more of the load because it has a lower impedance. In other words, the transformer with a PU of 0.05 is more efficient at carrying the load than the transformer with a PU of 0.1.

This is because when two transformers are operating in parallel, the current flowing through each transformer is inversely proportional to its impedance. Therefore, the transformer with the lower impedance will carry more current and share more of the load.

It is important to note that the transformers must have the same voltage rating and phase angle to operate in parallel. Additionally, the load must be balanced between the transformers to avoid overloading or damaging one of the transformers.