Testing experiences on mixed dielectric capacitors for high voltage DC filter applications

The authors give results of experiments performed to develop capacitors for DC filters of the Sardinia-Corsica-Italian mainland 200-kV DC interconnection. The tests were conducted on capacitor elements with a mixed paper-polypropylene-film dielectric. Several kinds of tests were performed to check the capacitor ability to withstand the stresses expected in service. The DC breakdown voltage was not significantly affected by the dielectric temperature in the range from -25°C to 75°C and the values obtained were about 3 U _N. The presence of a DC base stress did not influence partial discharge inception and extinction voltages, whereas it greatly reduced capacitor life when the AC voltage level was sufficient to cause inception of partial discharge. The discharge tests, both endurance and life, showed the good resistance to discharge stresses of the mixed dielectric system. With an assigned voltage equal to 1.5 U_N, several thousands of discharges were necessary to cause breakdown of elements