We have seen that thew stress in the insulation is maximum at the conductor surface and minimum at the sheath. To avoid the breakdown of the insulation, it is necessary to have uniform distribution of stress all along the insulation.
Practically some methods are used to obtain uniform distribution of stress. The process of obtaining uniform distribution of stress in the insulation of cables is called grading of cables.
The unequal distribution of stress has two effects,
1. Greater insulation thickness is required, which increases the cost and size.
2. It may lead to the breakdown of insulation.
Hence the grading of cables is done.
There are two methods of grading the cables which are,
1. Use of intersheaths for grading
2. Capacitance grading