The intersheath grading in the cable are used to

Grading of a cable is nothing but the process of achieving uniform electrostatic stress in the dielectric of cable. This is achieved by making potential gradient equal throughout the dielectric layer. It can be done in two ways - (i) Capacitance grading and (ii) Inter-sheath grading.

Capacitance Grading:

• Capacitance grading is done by employing various layers of different dielectrics having different permittivity’s between the core and the sheath
• Hence the dielectric insulation provided is no longer homogeneous, but composite
• The various layers are arranged so that the permittivity decreases from the surface of the conductor to the sheath of a cable i.e. the permittivity of dielectric is inversely proportional to the distance from the center

Inter-sheath Grading:

• In this method, instead of using various dielectrics and having a composite dielectric, we use a homogeneous dielectric material
• However, in order to distribute the stress properly, we use extra metallic sheaths between the conductor and the main sheath
• These intermediate sheaths are called ‘inter-sheaths’; These inter-sheaths are then held at adequate voltage levels
• This method improves voltage distribution in the dielectric of the cable and consequently uniform potential gradient is obtained