Intermediate connection system for ultra-high-voltage direct current power cable

An intermediate connection system for an ultra-high-voltage direct current (DC) power cable, comprising:

• a pair of DC power cables each including a conductor formed by twisting a plurality of strands, a cable inner semiconducting layer surrounding the conductor, a cable insulating layer, and a cable outer semiconducting layer, the pair of DC power cables provided such that ends thereof at which the conductors, the cable inner semiconducting layers, the cable insulating layers, and the cable outer semiconducting layers are sequentially exposed face each other;
• a conductor connection part configured to electrically and mechanically connecting the conductors exposed at the ends of the pair of DC power cables;
• and
• an intermediate connection part surrounding the connector connection part and the ends of the pair of DC power cables at which the conductors, the cable inner semiconducting layers, the cable insulating layers, and the cable outer semiconducting layers are sequentially exposed;
• wherein the intermediate connection part comprises:
• an intermediate-connection-part inner semiconducting layer surrounding the connector connection part;
• an intermediate-connection-part insulating layer surrounding the intermediate-connection-part inner semiconducting layer;
• an intermediate-connection-part outer semiconducting layer surrounding the intermediate-connection-part insulating layer;
• and
• an intermediate-connection-part protective sheath layer surrounding the intermediate-connection-part outer semiconducting layer,
• the intermediate-connection-part insulating layer is formed of an insulating composition containing a polyolefin resin and a crosslinking agent, and
• the intermediate-connection-part insulating layer is divided in a thickness direction thereof into three equal parts to obtain an inner layer, an intermediate layer and an outer layer,
• wherein a total amount of α-cumyl alcohol (α-CA), acetophenone (AP) and α-methyl styrene (α-MS) among crosslinking by-products contained in each of the inner layer, the intermediate layer, and the outer layer is 4,000 ppm or less.