Influence of insulation eccentricity to cables

For rubber plastic insulated power cable, due to the reason of the manufacturing process, its surrounding the conductor insulation thickness may not be equal, namely, insulation eccentricity.
In the structure of radial electric field H cable shielding layer on the surface of the conductor insulation layer is the end point of the electric field, when the insulation thickness, the electric field for coaxial cylinder electric field. The electric field of rubber cable insulation layer distribution is uniform, that is in the same radius of insulation on the circumference of a circle of electric field intensity are equal.
When the uneven thickness of insulation and eccentric, electric field is no longer a coaxial cylinder electric field, the electric field distribution within the insulation layer is not uniform, deterioration of the electric field will be concentrated in insulating thin place, where the insulation of the thinner of the electric field intensity. Visible, insulation eccentricity for the radial electric field of the structure of the H cable, it is very harmful, when serious can cause insulation breakdown.
The current cable in the national standard GB/T 12706, demand for cable insulation layer is:
(1) the insulation thickness shall be not less than 6 average nominal thickness.
(2) the minimum insulation thickness shall be not less than 90% of the nominal value -- 0.1mm.
(3) for more than 35kv voltage grade of cable, the eccentricity (maximum thickness) divided by the difference between the maximum and minimum thickness thickness should be not greater than 15%.
In low voltage cable, is using the radial electric field structure, namely each phase no shielding layer insulation surface, such as PVC cable, etc. This cable will not because of excessive deteriorating insulation eccentricity and electric field, the insulation thickness as long as the foot against the requirements of the former two.