What is a primary effect of circulating odd triplen harmonic currents in a transformer?

Circulating odd triplen harmonic currents in a transformer can lead to overheating as a primary effect. These harmonics are multiples of three (such as the 3rd, 9th, 15th, etc.), and they can cause distortion in the current waveform. This distortion results in additional losses within the transformer, primarily due to increased resistive heating in the windings and core.

When these harmonics circulate, they can create excessive heat in the conductors and core material. Transformers are designed to handle specific operational conditions, and the presence of harmonics can exceed these conditions, causing the temperature to rise past safe levels. Continuous operation under these circumstances may lead to insulation breakdown and the eventual failure of the transformer.

The other options do not accurately reflect the primary impact of odd triplen harmonics. Increased efficiency, reduced output voltage, and increased magnetic coupling are not direct results associated with the presence of these harmonics in a transformer; instead, they may imply improvements or changes in operating conditions that are not typically observed in the context of harmonic distortion.