Which of the following factors must be considered when determining transformer capacity?

When determining transformer capacity, the kVA rating based on primary and secondary operations is crucial because it directly reflects the amount of power the transformer can handle continuously without overheating. The kVA rating represents the apparent power in kilovolt-amperes, which considers both voltage and current on both the primary and secondary sides of the transformer.

This rating ensures that the transformer is adequately sized for the electrical load it will serve, taking into account factors like voltage levels, phase differences, and load characteristics. Scaling the transformer appropriately using this kVA rating helps maintain efficiency, reliability, and safety in electrical systems.

Other factors like earth resistance, ambient temperature, and wiring length can influence the overall performance and efficiency of the transformer but do not directly indicate its capacity. Earth resistance affects grounding effectiveness during fault conditions, ambient temperature can impact thermal performance, and wiring length relates more to voltage drop considerations than transformer sizing itself. Hence, while these factors are important for overall system design and operation, the primary consideration for transformer capacity remains the kVA rating based on its operational parameters.