Which of the following is NOT a type of transformer loss?

Dielectric loss is the correct answer because it refers to energy loss that occurs in insulating materials when subjected to an alternating electric field. This type of loss is not associated with the operation of transformers directly.

Transformers primarily experience losses that are attributed to their core and windings. Copper loss arises from the resistance of the copper windings when electric current flows through them, resulting in heat generation. Hysteresis loss occurs in the magnetic cores of transformers due to the continuous magnetization and demagnetization of the core material. Core loss is a combination of hysteresis and eddy current losses and signifies the energy lost as heat in the magnetic core when the transformer is in operation.

Thus, dielectric loss, being related to insulating materials rather than the functioning of transformers, makes it the option that does not qualify as a type of transformer loss.