The minimum rating for a power transformer is considered to be _________ kVA.

• A. 500
• B. 2500
• C. 750
• D. 3750

Answer: (A)

Power transformers are the larger class of transformers used for bulk power transfer in substations, as opposed to smaller units that serve local distribution. In many practical references, 500 kVA is the minimum rating that distinguishes a power transformer from a distribution transformer. At this size, the equipment is built to handle higher currents, fault levels, and more demanding cooling and protection, which are typical of substation and transmission applications. Below 500 kVA, transformers are generally used for local distribution with lighter construction and simpler protection. So, 500 kVA is the cutoff used here to define the minimum rating for a power transformer.