Types of insulation

Power cables:
advantages and disadvantages of different insulation types

 

At present, power cables insulated with Cross-Linked Polyethylene (XLPE) are more commonly used instead of the traditional with impregnated paper (the BPI) and polyvinyl chloride (PVC) plastic insulation. Therefore, most manufacturers of power cable master manufacture of such products. Let's look at the advantages and disadvantages of different types of insulation power cables.

Power cables with all the above insulating materials have decent dielectric characteristics. However these insulation materials are significantly different from each other. This is due to their different chemical compositions and properties. For example, plasticized PVC, being a polar polymer has reduced dielectric characteristics as compared with non-polar polyethylene or impregnated paper, which leads to increased losses in the insulation. However the PVC plastic compound is non flame retardant.

Power cables with paper insulation must include a metal shell in its structure to mechanically protect the insulation and to prevent radial penetration of water into the power cable. Power cables with paper insulation and lead sheaths are suitable for installation in damp soil, and in the presence of special protective covers, and under water. Power cables with XLPE insulation for protection against radial penetration of moisture requires a special metal layer of alumopolymer tape or aluminum or lead sheath. In Russia XLPE-insulated power cables with 10-35 kV voltage are currently predominantly produced as single-core versions. Power cables with XLPE insulation are designed for installation only in channels or trenches, with the installation of additional protection against damage to the cable, due to this design the use of steel is not allowed in the cable protective covers.

 

Power cables with paper insulation have another advantage. In power cables with paper insulation, the cable armor manufactured from steel strips or wires protects the cable from being damaged during installation or operation. The paper Power cable has a sector-shaped conductors, which can significantly reduce the size of products as compared to cables having a circular core form.

At the same time power cables with paper insulation have one major drawback: the laying of cables on vertical and steeply inclined roads with high levels of laying difference, the oil colophonium composition will absorb into paper insulation,  causing it to be impoverished and which can cause premature aging of the cable. To reduce this effect, the power cable is applied with a nondrip impregnating composition. Power cables with polymer insulation (XLPE) have no such disadvantage.

One of the main characteristics of insulation materials is permissible heating temperature of conductors which is the maximum temperature at which the insulating material does not lose its properties for a extended periods of time. The higher the score, the higher the permissible load current which can be passed through power cable for a long time. Long permissible temperature XLPE-insulation has a higher score than other materials used for power cable insulation, as XLPE is a thermoset material.

In conclusion, the different cable designs have their advantages and disadvantages due to their design and material used for insulation. Therefore, when using these cables, conditions for installation, operation, and requirements for the reliability of cable lines must be considered.