When we choose the power cable, power cable the most basic structure you know?
Core ① role is used to transmit electrical energy, commonly used materials for copper, aluminum.
② cross-sectional area (unit of measurement square millimeters): in order to facilitate the manufacture and use of the cross-section of the cable to take a standard series of specifications, China’s regulations are: 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300, 400, 500, 630, 800, 1000, 1200, 1400, 1600, 2000, 2500, etc. ③ Core structure: take more than one fine wire stranded into a bundle, after the mold for compression, so that the tight pressure coefficient from 0.73 to 0.9 or more, conducive to crimp connection.
④ Cable conductor resistance: the conductor itself has a resistance, through the current will heat up, and its temperature rise value is the key factor limiting the capacity of the cable. We hope that the conductor resistance is as small as possible.
Conductor shielding layer (also known as internal shielding layer, internal semi-conductive layer) ① Conductor shielding layer is extruded in the cable conductor on the non-metallic layer, and the conductor equipotential, volume resistivity of 100 ~ 1000Ω – m. With the conductor equipotential.
② general situation 3kV and the following low-voltage cable without conductor shielding layer, 6kV and above the high-voltage cable must have conductor shielding layer.
③ conductor shielding layer main role: to eliminate the unevenness of the conductor surface pits; to eliminate the tip effect of the conductor surface; to eliminate the porosity between the conductor and the insulation; so that the conductor and the insulation between the close contact; to improve the distribution of the electric field around the conductor; for the crosslinked cable conductor shielding layer also has the inhibition of the growth of electric trees and heat shielding effect.
Insulation layer (also known as the main insulation) ① cable main insulation has a specific function to withstand the system voltage, in the life cycle of the cable, to withstand the rated voltage and system failure over-voltage, lightning impact voltage, to ensure that in the work of the heat state does not occur relative to the ground or between the phase of the breakdown of the short-circuit. Therefore, the main insulation material is the key to the quality of the cable.
② cross-linked polyethylene is a good insulating material, now widely used, its color is greenish-white translucent. Its characteristics are: high insulation resistance; can withstand high frequency, impulse field breakdown strength; low dielectric loss angle tangent value; stable chemical properties; good heat resistance, long-term allowable operating temperature of 90 ℃; good mechanical properties, easy to process and technology.
Insulation shielding layer (also known as outer shielding layer, outer semi-conductive layer) ① Insulation shielding layer is extruded in the cable main insulation on the non-metallic layer, the material is also cross-linked materials, with semi-conductive properties, volume resistivity of 500 ~ 1000 Ω – m. Equipotential with grounding protection.
② general situation 3kV and the following low-voltage cable without insulation shielding layer, 6kV and above, high-voltage cables must have insulation shielding layer.
③ insulation shielding layer role: the transition between the main cable insulation and grounding metal shielding, so that there is close contact, to eliminate the insulation and grounding conductors between the pores; to eliminate the tip effect of the surface of the grounding of the copper strip; to improve the distribution of electric field around the surface of the insulation.
④ insulation shielding in accordance with the process is divided into peelable and non-peelable type, general medium-voltage cables, 35kV and the following peelable type, good peelable insulation shielding has a good adhesion, no semi-conductive particles remain after peeling. 110kV and above non-peelable type. Non-strippable type shielding layer and the main insulation of the combination of more closely, the construction process requires more.