This paper presents a brief introduction to the emergence of differential protection of power transformers. In this paper, the techniques used in implementing the 2nd harmonic restraint, the artificial neural network (ANN) and the latest wavelet packet transform-based disturbance detection and classification are reviewed. Moreover, the response of these different protection techniques is simulated for the same conditions. Finally, a comparison between these techniques is made and to identify the technique that offers the optimal power transformer protection. A list of references provide a state-of-the-art survey of significant as well as some incremental contributions in chronological order of appearance over the past 50 years.