Obiettivo
Medium voltage polymeric power cables are subject to the phenomenon of water treeing when installed and operated in a wet environment. From studies on a test cell, it has been shown that water tree growth and ion penetration in polymer plaques were dependent on time, electrical stress and the nature of the electrolyte solution, but the role of oxidation proved difficult to establish. Structural changes and mechanical behaviour of the amophorous phase also showed dependence on temperature, tree growth being observed in this region and along spherulite surfaces. Morphological changes in cables manufactured under different conditions did not result in differences in either electrical performance or water tree growth after cable tests, but the change in manufacture had resulted in a change in the water tree distribution. Incorporation of additives to provide ion traps proved difficult but the benefits of clean insulating and semiconducting materials were demonstrated.
EUROPE SUPPLIES ABOUT 50 % OF THE EXTRUDED POLYMER MEDIUM VOLTAGE POWER CABLES TO A COMPETITIVE AND GROWING WORLD MARKET (1,200 MECU PER ANNUM). THE LIFE OF CABLES CAN DEGRADE FROM THE REQUISITE 40 TO LESS THAN 10 YEARS THROUGH THE FORMATION OF "VENTED WATER TREES" AT THE SEMI-CONDUCTING SCREEN.
CURRENT SOLUTIONS ARE BASED ON THE USE OF TREE GROWTH INHIBITORS WHICH HAVE YET TO DEMONSTRATE THEIR LONG TERM BENEFITS.
THE SOLUTION PROPOSED HERE IS BASED ON RECENT WORK ON ELECTROCHEMICAL OXIDATION AND ON ION PENETRATION WHICH SUGGESTS THAT CONTROL OF THE IONIC CONTENT AND PERMEABILITY TO IONS OF THE SCREEN MATERIAL, COUPLED WITH INCLUSION OF ION TRAPS IN THE POLYMER, SHOULD SUPPRESS WATER TREEING. THIS WOULD INCREASE THE COMPETITIVENESS OF EUROPEAN MANUFACTURERS WHILE REQUIRING ONLY LIMITED MODIFICATION OF THE MANUFACTURING PROCESS. TO GAIN ACCEPTANCE FOR THIS NOVEL TECHNIQUE MANUFACTURERS MUST ESTABLISH THE LINKS BETWEEN OXIDATION PROCESSES, ION PENETRATION AND TREE GROWTH AND DEMONSTRATE TO CABLE PURCHASERES THROUGH MUTUALLY ACCEPTABLE CABLE TESTS THAT SHEAT CONTROL AND ADDITIVES WILL OVERCOME THIS PROBLEM.
Campo scientifico
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CSC - Cost-sharing contractsCoordinatore
92115 Clichy
Francia