Features of technology of manufacture of power high voltage cables with thermoplastic polymeric insulation

Abstract

The problem of high-voltage power cables is associated with complex technological processes in their manufacture. One of the main processes in the manufacture of cables is extrusion. There is a huge number of parameters (known as process parameters) at the stage of extrusion process that directly affect the performance of isolation and cable as a whole. It is shown that the important parameters of the process of extrusion are the melt temperature, speed, pressure, screw speed, the type of matrix used and the cooling medium in the extruder. The temperature and pressure of the melt are among the largest important parameters in the process of extrusion that determine the productivity of the process. The influence of temperature, pressure and fluctuations of these parameters on a complex of mechanical and electrical characteristics of the cable are analyzed. It is substantiated that the rheological properties of polymers are prone to oscillations, which causes problems in the production of cables. The complexity and large number of process parameters involved in the production of cables are complicated by the process of control, which determines the appearance of defects in the form of cracks, air cavities and porosity in high-voltage isolation. It is argued that the use of power cables with a cross-linked polyethylene, which is a thermosetting insulating material, causes the complexity of processing both in the manufacturing stage and in operation. Development of technology for the introduction of thermoplastic isolation provides secondary processing to implement projects of power-high-voltage variable and direct current cables. A comparative analysis of electrical, mechanical and thermal parameters of cross-linked polyethylene and thermoplastic polymers as an alternative of thermosetting isolation is presented. The article presents the features of the technological regime of extrusion of polymer isolation based on thermoelastoplasts, in particular, polypropylene compositions, which are due to the lower values of the coefficient of thermal conductivity of such compositions in comparison with polyethylene. Models are presented to describe the process of extrusion of thermoplastic isolation of power cables, taking into account the flow of molten polymeric material as a non-Newtonian, uncompressive, isothermal fluid. The necessity of determining the values of the coefficients of thermal conductivity and heat capacity of polypropylene compositions in a wide temperature range to reduce the likelihood of technological defects in high-voltage thermoplastic isolation is substantiated.