Medium Voltage Power Cables Catalogue - AEC Online

Introduction to XLPE Insulated Cables
The modern manufacturing process for XLPE insulation consists of triple extrusion of peroxide-cross-linkable polymeric
cable component layer on a copper or aluminum conductor, followed by a continuous vulcanization process and a cooling
step. The peroxide containing polymer compounds are extruded in the range of 110 °C to 140 °C at various line speeds,
followed by vulcanization under 100~200 psi of dry hot nitrogen in a tube with a residence time to obtain the desired
cross-linking of the compounds. The temperature is the key factor to induce decomposition of the peroxide, which
initiates the cross-linking process in the polymer compounds. Therefore, the cross-linking condition is very sensitive to
the heat transfer condition of the continuous vulcanization (CV) tube and cable construction.
The quality of the vulcanizable insulation compounds is strongly dependent on the efficiency of an organic peroxide
concentration level. It is very important to understand the cure kinetics to define a proper cross-linking performance in
the commercial CV tube conditions for optimum cable manufacturing process.
One of the critical elements in the processing of XLPE insulation for medium voltage cables is the perfection of the
interfaces between the insulation and the semi-conductive inner and outer shields forming the three layers of insulation.
This concern rises up the importance of the simultaneous extrusion of the inner semi-conductive, insulation and outer
semi-conductive layers, which is achieved by the specially developed high performance triple heads using super smooth,
extra clean raw materials with immediate curing on the continuous vulcanization (CV) line.
The one step continuous process guarantees the following features:
• Homogenous insulation, free from micro-voids
• Very smooth interfaces between the insulation and the semi-conductive layers
• High impulse and AC breakdown strength
• Long life and service reliability
Fig. 2 Continuous Vulcanization (CV) Line
Fig. 3 Triple-Head Extrusion System
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