Characteristics of XLPE Cable
Permissible operating temperature:
For permanent (normal) operation: + 90°C/+194°F
In short circuit: +250°C/+482°F
In overload operation and damage by sea: up to +130°C/266° F
Specific heat resistance: 3.5 K x m/W
Dielectric constant: 2.4
Specific resistance (20°C): min. 1016 Ohm x cm
Loss factor (tan δ) (20°C): max. 0.5 x 10-3
Density: 0.92 g/cm3
Breaking strength: min. 200%
Tensile strength: min. 12.5 N/mm2
Conductor & Inner Semi-Conducting Layer
Conductor
• Copper or Aluminum, round, multi-wire stranded and compact, according to VDE 0295 and HD 383.
Inner Semi-Conducting Layer
• Semi-conducting compound, cross-linked, min. wall thickness 0.3 mm.
Insulation
• Cross-linked Polyethylene (XLPE), compound type 2XI1 according to DIN VDE 0207 part 22 an HD 620.1
• Insulation nominal wall thickness
6/10 kV = 3.4 mm
12/20 kV = 5.5 mm
18/30 kV = 8.0 mm
Outer Semi-Conducting Layer
• Outer semi-conducting layer is extruded together with the inner semi-conducting layer and the insulation in one working process and are spliced with each other
• Semi-conducting compound, cross-linked, wall thickness 0.3 to 0.6 mm
Concentricity of Conductor
•The difference between the maximum and minimum value of 0.5 mm should not be exceeded.
Semi-Conducting Type
•Over the outer semi-conducting layer, a semi-conducting tape must be used.
Shielding
• Shielding of copper wires must have a minimum diameter of 0.5 mm and over that a copper tape applied helically with a minimum thickness of 0.1 mm.
• Copper cross-section according to DIN VDE 0273 and 0276.
Separator
• Over the shielding as well as under the outer jacket a separating layer must be used (e.g. tape).
Outer Jacket
• PE compound DMP2 according to HD 620.1 and 2YM3 to DIN VDE 0276 part 3, black, or
• PVC compound DMV6 according to HD 620.1 and YM5 to DIN VDE 0207 part 5, red
• Wall thickness = 2.5 mm, for 1 x 500 mm2 / 30 kV = 2.6 mm
Cable Installation
In order to avoid any damage, the XLPE insulated medium voltage power cables should be carefully laid and installed. It must be ensured that the cables should not be pulled over hard or sharp edges. The cable ends must be sealed water-tight. After cutting the length both ends must be sealed immediately.
An installation depth of 60 to 80 cm is recommended. Single conductor cables are normally arranged in a trefoil touching or triangular shape.
For installation in conduits, especially the influence of thermal insulation of air space between the cable and the inner wall of the conduit should be considered. The inner diameter of the conduit should be at least 1.5 times that of the diameter of the cable.
Bending Radius
During the installation of XLPE cables, the bending radius should not be below the following values:
Cable without metal jacket = 15 x cable Ø
Cable with aluminum-laminated jacket = 30 x cable Ø
Temperature Range
During the installation, the temperature should not be below the following values:
For XLPE insulation + PVC jacket = - 5°C
For XLPE insulation + PE jacket = -20°C
Max. Permissible Tensile Strength
By pulling the conductors with a pulling head (not for armored cables)
P = No. of conductors x conductor cross-section x δ
δ = permissible pulling tension N/mm2
- for copper conductor: 50 N/mm2
- for aluminum conductor: 30 N/mm2
Current Carrying Capacity
According to VDE 0276 part 620, -5C or HD 620 S1
Laying Underground
Laying depth: 0.7 - 0.8 m
Ground temperature in laying depth: +20°C/+68°F
Specific heat resistance: 1.0 K m/W
Load factor: 0.7 (EVU-load)
Outdoor Installation
Air temperature: +30°C/86°F
Load factor (permanent load): 1.0
Installation in Conduits
Cables for conduit system installation in ground, a reduction of the current carrying capacity with a factor of 0.85 is recommended.
Test Voltages
Kind of Voltage Test | Voltage Test in kV | ||
U0/U = 6/10 kV | U0/U = 12/20 kV | U0/U = 18/30 kV | |
Voltage Test a.c. in kV | 15 | 30 | 45 |
Voltage Test d.c. in kV | 48 | 96 | 144 |
Voltage Test a.c. (1000 h) | 18 | 36 | 54 |
Voltage Test of Cable System
During the operation or after installing the medium voltage power cables, the dielectric can be tested with alternating or direct current. The test duration continues 30 minutes.
Kind of Voltage Test | U0/U = 6/10 kV | U0/U = 12/20 kV | U0/U = 18/30 kV |
Voltage Test a.c. in kV | 12 | 24 | 36 |
Voltage Test d.c. in kV | 34 up to 48 | 67 up to 96 | 76 up to 108 |
