High voltage direct current cable with impregnated tape insulation

A direct current, electric, submarine cable for an operating voltage of at least 200 kilovolts and adapted for use in lengths of at least 100 kilometers and at substantial depths under water, said cable comprising:

• a conductor;
• an inner, semi-conductive screen around, and conductively connected to, said conductor;
• an outer, semi-conductive screen around and spaced from said inner semi-conductive screen;
• a metallic sheath around said outer semi-conductive screen;
• and
• solid insulation intermediate said inner semi-conductive screen and said outer semi-conductive screen;
• said insulation comprising insulating material which is impregnated with a compound comprising at least a viscous hydrocarbon oil and at least one substance containing polar groups, said compound having a resistivity in the temperature operating range of the cable at least 100 times lower than the resistivity of said insulating material impregnated with said compound;
• said cable being characterized by a voltage breakdown resistance with voids in the insulation which is greater than the voltage breakdown resistance of the same cable without said compound.