Under low voltage, the insulation thickness mainly depends on the mechanical stress when the wire is bent, and the grade increases with the increase of the conductor cross section; the indicator for assessing whether the cable insulation layer can continue to work is still the voltage resistance level. Under high electric field, the insulation thickness increases with the increase of the working electric field strength; the same insulation thickness is used for different cross sections at the same voltage level. The insulation for transmitting high-frequency electromagnetic waves is only a kind of isolation, but it has strict requirements on resistance and capacitance. Although it is very thin, it has high mechanical strength requirements, and a composite structure combined with air is often used.
At high voltage, the insulation thickness decreases as the wire cross-section increases, because the wire diameter increases as the wire cross-section increases, and the maximum working field strength on the wire surface decreases exponentially as the wire diameter increases according to the distribution law of the cylindrical electric field.
Insulation thickness indicates:
A. Nominal thickness: the thickness controlled by the process
B. Thinnest insulation thickness: the thinnest thickness; 90% of the nominal thickness minus 0.1mm C. Thickest thickness
D. Average thickness: measure 6 points along the same cross section in six equal parts and calculate the average value
E. Out-of-roundness: (thickest point - thinnest point) / average thickness * 100%, generally not more than 15%
