The value of stacking factor is usually-

Correct option is D

·        The stacking factor, also known as the lamination factor, is a measure used in electrical engineering, particularly in the design of transformers and electric machines.

·        It represents the ratio of the volume occupied by the core material (usually laminated steel) to the total volume of the core (including the spaces between laminations and any insulation).

$$\text{Stacking factor} = \frac{\text{effective cross sectional area of the transformer}}{\text{gross cross sectional area of the transformer}}$$​

·        The stacking factor is less than unity because the core is not a solid piece of material; it consists of thin laminated sheets with insulation between them to reduce eddy current losses.

·        The spaces occupied by the insulation reduce the effective volume of the magnetic material, hence making the stacking factor less than 1.

·        The stacking factor typically ranges between 0.9 and 0.95, depending on the quality of lamination and the thickness of insulation used.