DEVELOPMENT OF 500-KV XLPE CABLES AND ACCESSORIES FOR LONG-DISTANCE UNDERGROUND TRANSMISSION-LINE .3. ELECTRICAL-PROPERTIES OF 500-KV CABLES

500-kV XLPE-insulated cable with an insulation thickness of 27 mm has been developed for long-distance transmission lines. Basic studies on 500-kV XLPE cable have shown that contaminants in the insulation may b e the factor determining electrical performance. This hypothesis is ju stified by the good correlation obtained between statistical estimatio ns of the size of the largest contaminant in the insulation and the el ectrical characteristics of full-sized cables. Voltage-withstand and l ong-term tests have confirmed the design values for minimum breakdown stress, for AC and impulse voltage, and for the degradation coefficien ts.