According to the different electric field distribution […]
According to the different electric field distribution in the insulation layer, the multi-core cable is divided into the total package (or insulated) type cable and the split-phase shielding (or split-phase lead package) type cable.
First, the package (or with insulation) type cable
All-inclusive (or insulated) cables are for multi-core lower voltage cable, the package type for extrusion insulation, with insulation for oil-impregnated paper insulation.
The package type that is made of the first good insulation of each phase conductor stranded twisted wire cable, and then re-package metal layer (shield, concentric conductor, metal sheath or armor), and finally extruded outer sheath made of Insulation type is after the insulated core is stranded into a cable, wrapped around the core and then wrapped a certain thickness of the tape insulation (in order to relative and between the opposite have the same electrical strength), after drying impregnated Extruded lead sheath, and finally extruded outer sheath.
The electric field distribution of the package type or insulated cable is very uneven. The insulation and filling of each phase are affected by the changing electric field all the time. Both the radial component and the tangential component of the power line are also called non-radial cables .
Due to the tangential field strength component tends to make the plastic insulation dendrite aging, and the filler is lower than the dielectric strength of insulation, so that the electric cable is not high strength, therefore, the overall package structure for 0.6 / 1kv1.8 / 3kv voltage grade PVC insulation, XLPE insulation and EPR (HEPR) insulated power cables. 1KV cable voltage is low, the electric field strength is small, the insulation of the electrical performance of the less demanding, except for cross-sectional area of light music cable multi-core round package structure, the larger cross-sectional area of the cable fan or multi-core multi-core Structure, such as the three-phase cable system for three-phase cable, four-core cable for three-phase four-wire system, and five-core cable for three-phase five-wire cable to save material. 1.8 / 3kv cable must have a metal shield, the main three-round package round structure.
Second, split-phase shielding (or split-phase lead package) type cable
After the insulated core of each phase is made, a metal shield or a metal sheath (lead sleeve or aluminum sleeve) is first wrapped, and then filled with a cable, a spacer sleeve or an inner liner, a metal armor and an outer sheath Into the multi-core cable, called split-phase shielding (or split-phase lead package) cable.
Split-phase shielded cable can shield the electric field in each phase of the insulation layer, each phase of the metal shield without electric field, that is, low dielectric strength of the filler from the electric field, the power line along the core of each phase insulation Radial (also known as radial cable), no tangential field strength components.
Due to the phase-separation shielding insulation resistance of the cable breaking resistance than the much higher than the package type, the voltage level used to improve a lot. Therefore, 6KV and above the use of round-phase multi-phase power cable shielding structure, in order to improve the insulation resistance to breakdown strength, larger cross-sectional area of the cable can be used single-core structure.