In a tap changing transformer, the tappings are provided on

Tap changing transformers are used to regulate the output voltage by changing the turn ratio.

Tappings are typically provided on the high voltage winding rather than the low voltage side.

This is because the current in the high voltage winding is lower, making it easier and safer to implement tap changes without handling large currents.

Changing taps on the high voltage side also reduces the size and cost of the tap-changing equipment.

Option A and Option B are incorrect because although technically possible, it is not common practice to place tappings on the primary or secondary specifically unless they are also the high voltage side.

Option D is incorrect because while taps can theoretically be placed on any winding, they are practically and most commonly placed on the high voltage winding.

Therefore, Option C: High voltage winding is the correct answer.