The maximum efficiency of a distribution transformer is

The maximum efficiency of a distribution transformer is at full load. This is because the transformer is designed to operate at its most efficient point when it is fully loaded. When the transformer is not loaded, or is only partially loaded, it is less efficient. This is because there is more heat loss in the transformer when it is not fully loaded.

Here is a brief explanation of each option:

• Option A: At no load, the transformer is not transferring any power, so its efficiency is 0%.
• Option B: At 50% full load, the transformer is transferring some power, but it is not operating at its most efficient point.
• Option C: At 80% full load, the transformer is transferring more power than at 50% full load, but it is still not operating at its most efficient point.
• Option D: At full load, the transformer is transferring the most power and is operating at its most efficient point.