The medium voltage cables market is growing steadily and covers urban and rural power distribution networks, mining power sources, and railroads. The expected service life of the cables is therefore directly relevant for them to achieve stable operation. So how long do they last? This is what most people are concerned about. According to practical evidence the expected life of medium voltage cables is generally about 25-35 years. In practice, however, they often last longer than this. Over time, cables can experience unexpected failures leading to costly repairs and power outages. And what causes these premature failures?
A thorough and deep analysis should be done to identify the crucial aspects that affect the life expectancy of MV cables, and we will write about our recommendations for retaining and prolonging the lifespan for your cables.
Cable Life Expectancy
The life expectancy of a cable is the number of years that a cable is designed to be expected to continue to function properly under ideal or standard conditions of use. The period is influenced by multiple factors such as cable materials, design, manufacturing quality, operating environment, load conditions, maintenance conditions, etc. For example, XLPE (cross-linked polyethylene) cables are known for their durability, with a service life of 40 years or more. On the other hand, paper-insulated cables, which were widely used in the past, tend to have a shorter service life due to aging and degradation.
Taking a 25kV medium voltage cable, it was installed in a newly developed industrial area that was originally expected to be free from extreme chemical contamination. However, a few years later, a chemical plant is established nearby and the emissions of acids and alkalis penetrate the soil, causing the environment around the cable to become a corrosive chemical environment. This chemical corrosion gradually eroded the outer sheath of the cable, which in turn affected the inner insulation. Over time, the insulation of the cable deteriorates and partial discharges may occur, eventually leading to cable failure and the need for early replacement. This illustrates the significant impact that environmental factors, particularly chemical corrosion, can have on the service life of MV cables. Even poor consideration during initial design and installation can result in a significantly shorter cable life.
What affects the service life of MV cables? – 5 major factors
Studies have shown that 35kV and below medium voltage cables have more than 90% of the number of power cables running breakdown faults due to external factors.
1. External damage and mechanical stress
During the installation phase, irregular laying operations, such as excessive bending, stretching or scratches from sharp objects, can lead to damage to the physical structure of the cable. Secondly, during laying and operation, MV cables may suffer physical damage, such as accidental damage from excavation operations, compression by heavy objects or frequent mechanical vibration. These external damages can lead to cracks in the cable sheath and insulation layer, which in turn accelerates the aging process and reduces its service life.
2. Environmental factors
It including temperature, humidity and chemical corrosion environment. Higher temperatures will promote faster deterioration of cable insulation materials. On the other hand, humid environments may cause water infiltration which promotes the occurrence of water dendrites and degrade insulation performance. If a cable is buried in soil with acidic and alkaline properties, they contribute to electrochemical and chemical corrosion and damage the outer sheath of the cable which leads to damage of the internal structure of the cable.
3. Overloading and thermal effects
As soon as the user starts the cable “overloading” usage, the life will be substantially diminished. This effect aggravates especially during the summertime and can result to insulation failure. It is the outer layer of insulation that is sub-standard, the rating for aging resistance is reduced, the rupture of outer skin will be quite easy; the life span is only within a few years.
4. Electrical stress
Uneven electric field distribution or excessive voltage levels can lead to partial discharges, which are a serious problem in medium voltage cables. Prolonged partial discharges can gradually erode the insulation and eventually lead to cable failure and shortened service life.
5. Quality of joints and terminals
Cable joints and terminals are its weakest link. Improper installation or material quality problems can cause localized overheating, insulation failure or moisture intrusion. These seriously affect the overall life of the cable.
Are there specific maintenance practices that can extend the life of MV cables?
Indeed there are! Just like any other essential part of the infrastructure, medium voltage cables need correct caring and maintenance processes in order to prolong their life and keep reliability. The working-life of a cable significantly differs from its design lifespan in specific working conditions. The line failures are frequent and the wire begins to age, replacement must occur in a timely manner. So, what are the effective methods for prolonging the life span of wires and cables? Here best practices are provided for you.
- Periodic health checks – Cables are scrutinized for cracks, rust, and signs of deterioration. They are then maintained, overhauled, or replaced whenever needed.
- Cable installation – Cable laying should take into account environmental factors. Avoid direct sunlight, humidity or chemically corrosive environments. Where necessary, outdoor cables should be appropriately protected, for example through waterproofing. According to the different use of the environment, choose the right type of cable, such as underground, outdoor or special environment for ensuring that the characteristics of the cable and the environment to match.
- Insulation testing to protect the “core” – Regular insulation resistance tests and partial discharge tests are conducted. This is the electrophysiological equivalent of a heart check; it is concerned with ascertaining whether the internal circuits of the cable are functioning properly, and whether any problems that might occur have been solved.
- Proper setup and storage -During installation and daily use, prevent cables from excessive bending, crushing by heavy objects or mechanical damage. At the same time, further safeguarding of cables laid on external walls should be done to prevent accidental damage. Regarding how to store the method should be remembered: do not directly contact with acid, alkali and mineral oil, and keep away from corrosive substances.
- Prevent cables from operating in the overuse conditions – The temperature of the cables will increase rapidly in such situation and will trigger insulation aging which will lead to short circuits.
One of the most basic protection measures while also considering the most crucial thing is to begin by sourcing for the nationally accepted top ten brands of cables. For example, we will find that the poor quality of the cable will have gaps in the copper wire. First of all, the copper wire is not pure enough and does not meet national standards. Standard wires and cables can be used for a long time and save time and energy. In this point of product quality, the industry is recognized by customers ZW cable does a very good job. Its 3.6KV～36KV mv cable since the official production has been strictly control product quality. Each process is strictly controlled to ensure that each wire and cable meets the national standards.
Identifying Signs of Cable Faults and Aging
The identification of cable aging and degradation involves multi-dimensional monitoring and analysis. First, a visual external inspection can reveal cracks, color changes, swelling or physical damage. These are signs of the early stages of aging.
Electrical testing includes dielectric loss measurements and partial discharge analysis. Degradation of insulation indicates higher energy loss and potential deterioration. Partial discharge assessment identifies localized electrical breakdown within the insulation, which is a precursor to failure. Frequency domain analysis and impedance spectroscopy help to understand changes in the electrical characteristics of cables, revealing degradation that may not be apparent to the naked eye. These methods provide a comprehensive view of the health of the cable.
Cable service life problems can be controlled by the production of a relatively small range, we need to choose a good manufacturer in the prerequisite to obtain reliable products. The rest of the “human factor” as well as “natural factors” can be prevented or avoided as much as possible. The service life can be longer.
Should there be any other inquiries presented or the need for additional electrical cable types, feel free to reach out to our representatives!
