Why the transformers input current is non sinusoidal?

The input current of a transformer is non-sinusoidal primarily due to the presence of non-linear loads connected to the transformer, which introduce harmonics into the system. Additionally, the transformer itself can exhibit non-linear characteristics, especially when operating near saturation or under varying loads. These factors result in a distorted current waveform that deviates from a pure sinusoidal shape, leading to increased losses and potential overheating in the transformer and connected equipment.