Cross-linked polyethylene insulated cables (XLPE cables) are widely used not only in low-voltage power supply systems below 6kV, but also in transmission and distribution line systems with voltage levels from 6kV to 500kV. The structure of XLPE cables below 6kV is basically the same as that of PVC low-voltage cables. (See diagram)
Single-core cross-linked polyethylene cable structure diagram
(a) Single-core cross-linked polyethylene insulated cable; (b) Single-core cross-linked polyethylene insulated steel tape armored cable; (c) Single-core cross-linked polyethylene insulated steel wire armored cable; (d) Outline diagram: 1, 8, 17 - Conductor; 2, 9, 18 - Conductor shield; 3, 10, 19 - Insulation; 4, 11, 20 - Insulation shield; 5, 12, 21 - Copper tape shield; 6, 13, 22 - Wrapping tape; 7, 16, 26 - Outer sheath; 14, 23 - Inner sheath; 15, 24 - Steel tape armor; 25 - Copper wire
Three-core cross-linked polyethylene cable structure diagram:
(a) Unarmored cable;(b) Steel tape armored cable;(c) Steel wire armored cable;(d) Outline diagram:1, 9, 19 - Conductor;2, 10, 20 - Conductor shield;3, 11, 21 - Insulation;4, 12, 22 - Insulation shield;5, 13, 23 - Copper tape shield;6, 14, 24 - Filler;7, 15, 25 - Wrapping tape;8, 18, 28 - Outer sheath;16, 26 - Inner sheath;17, 27 - Steel tape/steel wire armor
Compared to other low-voltage plastic cables, the most significant difference in structure between 6~35kV cross-linked polyethylene (XLPE) cables is the addition of inner and outer semi-conductive shielding layers and a copper tape (wire) metal shielding layer. Both inner and outer semi-conductive shielding layers use carbon black-added XLPE material, typically 1~2mm thick, with a volume resistivity of approximately 10⁴ Ω·cm. The copper tape (wire) forms a circuit for the cable's ground fault current and provides a stable ground potential. Therefore, the ground wire of XLPE cables is led out via copper tape (wire) rather than armored steel tape, which is crucial. Cables with a conductor cross-sectional area of 240m² or less generally use a copper tape shielding structure; while cables with a conductor cross-sectional area greater than 240m² use a copper wire shielding structure.
Representative models of 6~35kV XLPE cables include aluminum core YJLV or YJLY types, and copper core YJV or YJY types.
The figure shows two typical structures of cross-linked polyethylene cables with voltage levels of 66kV and above. In addition to YJLY/V type and YJV/Y type, the representative models also include YJQ, YJLQ type, YJLW, and YJLLW type.
Schematic diagram of 66~220kV cross-linked polyethylene cable structure (I)
(a) Cross-sectional view; (b) Outer view 1- Conductor; 2- Inner shield; 3- Insulation; 4- Outer shield; 5- Copper wire shield; 6- Longitudinal water-blocking layer; 7- Comprehensive waterproof layer; 8- Outer sheath
Schematic diagram of 66~220kV cross-linked polyethylene cable structure (II) (a) Cross-sectional view; (b) Outer shape view 1- Conductor; 2- Inner shield; 3- Insulation; 4- Outer shield; 5- Longitudinal water-blocking layer; 6- Non-magnetic metal sheath; 7- Outer sheath
Compared to cables of 35kV and below, cables of 66kV and above do not use steel tape for their armor layer. Instead, they employ non-magnetic metals such as corrugated aluminum (copper, aluminum alloy, stainless steel) sheaths, which also provide excellent waterproofing. The outer sheath of the cable is generally made of PVC material, with a layer of conductive graphite coated on top. This graphite layer serves as the ground terminal, facilitating withstand voltage tests on the outer sheath.
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