Ans: (D) High voltage side
Explanation:
on HV side voltage is high but current is less but in the LV side voltage is less and current is high. If we connect Tap changer on the LV side then sparking will take place. Better controlled output can be determined when we connect tap changer in LV. The HV winding generally wound over LV winding hence it is easier to access the HV winding turns instead of LV winding.