Capacitance Grading

The grading done by using the layers of dielectrics having different permittivities between the core and the sheath is called Capacitance grading. 

In intesheath grading, the permittivity of dielectric is same everywhere and the dielectric is said to be homogeneous. But is case of capacitance grading, a composite dielectric is used.

Let d₁ = Diameter of the dielectric with permittivity ε₁

and D = Diameter of the dielectric with permittivity  ε₂

The stress at a point which is at a distance x is inversely proportional to the distance x and given by,

Hence the stress at any point in the inner dielectric is,

Similarly the dielectric stress in the outer dielectric is,

Thus the electric stress is inversely proportional to the permittivities and the inner raddi of the dielectrics.

Condition for equal maximum stress

Let us obtain the condition under which the maximum values of the stresses in the two regions are equal.