All over the world, we are observing the development of cable lines at all voltage levels. Despite being more expensive and labor-intensive to install, their laying is definitely worthwhile—especially due to safety and their invisibility in urban spaces. However, it is important to remember to follow a number of rules during operation.

Quality of Cable Lines – Damage Rate

The damage rate is one of the most important parameters defining the quality of a cable line. It expresses the number of failures recorded per year per 100 km of line. In the case of polymer-insulated cables, in European countries the coefficient usually remains at the level of 0.2–0.4. During the laying of lines, accessories such as a cable stocking are used to prevent damage at this stage.

Failure rate naturally depends mainly on the material used. Earlier first-generation cables (thin outer PVC sheath, thermoplastic polyethylene insulation) were relatively prone to water treeing. In some cases, such damage can be mitigated by impregnating the insulation with silicone-based liquids. Such procedures are effective, for example, in areas with high humidity. Silicone simultaneously performs several functions:

  • it slows down the growth of water trees that have already appeared,
  • it fills gaps, preventing moisture from further penetrating inside,
  • silicone binds water, thus minimizing damage occurring inside the cable.

Insulation regeneration helps reduce costs – it is much cheaper than replacement. However, this method will not work if the insulation is already in very poor condition.

Second-Generation Cables

They have extruded semiconductive screens and, usually, cross-linked polyethylene (XLPE) insulation. The manufacturer is responsible for ensuring and documenting high quality. However, responsibility also lies with the user, as proper installation and diagnosis of potential damage (e.g., due to assembly errors or improper transport) are necessary. For storage and transport, cable stands, often equipped with wheels, are used. Using stands and drums is the safest method of transporting cables – not only to prevent damage but also for safety regulations. Tests are also performed during operation to ensure that no damage has occurred. Diagnostics primarily involve checking the overall condition of the insulation and locating potential faults that could lead to a more serious failure in the future.

When Is Cable Line Replacement Necessary?

Elements of cable lines, like all other devices, cannot be used indefinitely – after some time, they must be replaced. When deciding on cable line replacement, several factors must be taken into account. Primarily, these are technical aspects. Even properly operated cable line components undergo natural wear. Signs of aging include deteriorating parameters, an increase in the number of failures or disruptions during operation, and rising maintenance costs.

A decision to replace a cable line may also be made for strategic reasons. This is often related, for example, to increasing load capacity, which makes a line with specific parameters insufficient. It may also involve increasing the voltage level, introducing newer technology, or adapting to changing environmental protection standards. The most common problems leading to cable line replacement are a lack of spare parts or personnel with the skills required to operate it. It also happens that the fire risk increases, making it necessary to implement newer technology.

Sometimes a cable line is replaced because its repair becomes uneconomical. New technologies are often much cheaper to operate. New materials and more modern designs make it possible to reduce losses to a minimum. In some cases, repairing an old cable line is exceptionally costly, so replacing it with a new one—at least on a specific section—is a better solution. Using equipment such as an electric hydraulic pump and heads for laying cable lines helps minimize the risk of damage during installation.

Expected Service Life of a Cable Line

A broader analysis is required to determine this parameter. Lifespan depends on the components that make up the line (e.g., cable joints, terminations). For each part, it is worth identifying the most probable defects. Test methods must also be selected to determine the extent of potential damage. Cable lines are usually assessed using diagnostic measurements (directly on the line), visual inspection, analytical considerations, statistical data, and expert opinions.

Proper operation of a cable line allows potential irregularities to be detected in time before the problem becomes more advanced and more expensive to repair.