CABLE STRESS RELIEF
When the semi-conducting core screen is cut, the electrical field distribution changes radically. The surrounding air becomes overstressed as does the dielectric material in the cable immediately in the vicinity of
the cut screen.
To prevent rapid breakdown of the cable it is necessary to apply a stress cone or a linear stress relief tube at the end of the screen.
The cone has an insulating portion to reinforce the primary cable insulation and a conductive portion to mate with the semi-conducting core screen.
This controls the lines of equipotential so that when they finally emerge into the air they are sufficiently far apart not to cause ionisation.
Electrical stress control The stress control tubing at each cable end in combination with the yellow stress grading mastic at the screen cut provide a precisely defined impedance characteristic which smoothes the electrical field. For ease of installation, a stress control patch is applied around the mechanical connector to provide a similar function.
The design and construction of screened power cable is primarily based on two types of electrical stress :

A radial stress which can be represented by lines of flux and a longitudinal stress which can be considered as lines of equipotential