The operational parameters of power cables are largely determined by the insulation of conductive conductors. Therefore, the electrical industry pays great attention to both the selection of insulation materials from the existing ones and the development of new compositions. EPR is one such insulating material.
Benefits of EPR (Ethylene Propylene Insulation)
Ethylene-propylene rubber as a material is well suited for use as insulation for cable cores with operating voltages up to 35 kV. Referencing it provides the cable product with good flexibility. Chemical stability of the material, incl. in relation to ozone and UV radiation, it can guarantee at least 5 years of service life even in harsh industrial conditions, subway tunnels, construction sites, and mining facilities.
An important advantage of cables with EPR insulation is the extended operating temperature range with a lower permissible temperature of -60 ° C. EPR-insulated cable fully retains its original properties when heated to + 90 ° С, i.e. the power supply line built on its basis has good resistance to short circuits.
At the same time, zero moisture absorption and chemical inertness are ensured, even in aggressive ambient atmospheres. Moreover, the ethylene-propylene cable insulation does not impose restrictions on its use in hazardous areas.
Of no small importance is the relatively low density, which, other things being equal, reduces the linear mass of the product. The application of insulation does not require changes in well-established technological processes.
Comparison of EPR cables with XLPE cables
Cross-linked polyethylene as an insulating material is well mastered by the cable industry and is widely used in the serial production of cables oriented to harsh operating conditions. The transition to ethylene propylene in the products of this group allows:
- to increase the short-circuit resistance by about 20% according to the value of the short-term maximum temperature;
- shift (for some formulations) to -40 ° C the lower limit of the permissible installation temperature without the need to preheat the cable;
- radically (up to four outer diameters) reduce the value of the minimum allowable bending radius during laying;
- improve parameters for non-propagation of combustion.
- Use EPR cables in hazardous areas and at the same time, the other characteristics of the cable remain at least at the same level.
In cable production, various materials are used to insulate wire elements. The main condition for the insulation of cables and wires is that it should not conduct current, therefore, materials are traditionally used here: rubber, PVC, polyethylene, fluoroplastic, or paper. In some cases, also used as insulating materials: magnesium oxide, varnish, silk, or polystyrene.
The conductor is a round, stranded, sealed conductor of class 2 copper or aluminum wires according to the CEI 20-29 standard.
Crosslinked elastomeric compound (EPR) insulation complies with CEI 20-11; insulation thickness complies with the requirements of the CEI 20-13 standard.
The cable for rated voltage over 6 kV is made with extruded semiconducting layers located between the conductor and the insulation, as well as over the insulation.
The semi-conductive layer over the insulation can be easily removed at room temperature.
In a single-core cable, the metal shield is made of copper wires, over which a copper tape is spirally applied. In a 3-core cable, each core is shielded with copper tape. Three-core cables with voltage up to 6 kV can have one common screen. Cable shields comply with CEI 20-13 standard.
In a three-core cable, the armor provides mechanical protection and is made of galvanized steel strips overlaid on three cores in accordance with the CEI 20-13 standard.
The outer shell is made of a thermoplastic PVC composition, has a red color, and meets the quality requirements of the CEI 20-11 standard.
If required, Nexans can supply a cable with the following specifications:
- flame retardant in accordance with CEI 20-22 part 2, as well as with a reduced amount of toxic and corrosive vapors (CEI 20-37 part 1) or (CEI 20-38 / CEI 20-37);
- with non-magnetic armor (single-core cables).
EPR cable sleeves
Couplings for EPR cables are divided into connecting (intermediate) and end couplings. The former is used to connect individual building lengths of cables in the linear part of the trunk, the latter – provide the normal supply of wires of individual phases to the input device or directly to the load.
Couplings have a traditional cylindrical structure, their design is developed taking into account the peculiarities of the cable structure.
The installation of couplings requires a certain correction of the technology used for cables with paper insulation, and the installation time increases and the need to remove additional semiconductive coatings from the conductive core. At the same time, the consumption of intermediate couplings increases due to the shorter face-to-face length.