Comparison between Shunt Capacitive Effect of XLPE and Oil-Filled Cables with the Utilization of Shunt Reactors during Light Load Conditions

Large cities usually have underground systems and are likely to be 132 kV, 500 mm². Under normal operation with the highest season of loads, the capacitive effect of the cables is neutralized by the voltage drop in the reactance of the cables. Disconnecting loads from the system produces lighter loads. This changes the balance of the capacitive and inductive effects of the underground system, creating higher voltages on the cable in addition to pulling the generators into their underexcited mode to meet the resulting leading power factor. Normally static shunt reactors are brought into service to alleviate this effect. 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 [1]. 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 [1] .