PES Meetings

This study compares cross-linked polyethylene (XLPE) cables with oil-filled cables during light load conditions and when the shunt reactors are brought into service to alleviate the problem of the high capacitance of cables. Power cables are generally single cored (i.e., single phase) at higher voltages of 275 kV and 400 kV. At 132 kV and below they may be either single cored or have three cores, one per phase. Multicore cables are generally taken to be small cross-section cables with varying standard numbers of separately insulated cores for low voltage control, protection use, etc. Like power cables, the cores lie side by side. High-voltage cables are generally insulated with many layers of special paper impregnated with oil and have free oil under pressure which is contained in a sheath. They are called "oil-filled" cables. Modem technology uses gases and plastics as insulators. Cables using XLPE have been coming into use. The capacitance of single-conductor and individually screened three-conductor cables is readily calculated. For three-conductor unscreened cables one must resort to empirical design data. Owing to the high capacitance of cables, the charging current-especially at high voltages-is an essential factor in deciding the permissible length to be used.