The main reasons for aging of insulated wires and cables
Aging of insulated wires and cables is a common problem in power systems, mainly caused by the following factors:
Electrical aging: Under long-term voltage, insulation materials will generate partial discharge in areas with concentrated electric field strength, leading to material corrosion, drying, and even burning and deterioration.
Thermal aging: The heat generated when current passes through will accelerate the thermal decomposition and oxidation of insulation materials, leading to a decrease in electrical performance. Long term overload operation can cause cable temperatures to become too high and accelerate insulation aging.
Mechanical aging: Mechanical effects such as vibration and electromagnetic force can cause deformation and damage to insulation materials.
Environmental factors: including:
External force damage: mechanical damage such as non-standard construction and excavation damage.
Insulation moisture: Improper joint production or high humidity environment can cause moisture infiltration, forming "water branches" that damage insulation.
Chemical corrosion: Anti-corrosion coatings in acidic or alkaline soils or chemical environments.
Temperature and Ultraviolet Radiation: High-temperature environments and ultraviolet radiation accelerate material ageing.
Methods for Detecting Ageing in Insulated Wires and Cables
1. Destructive Testing Methods
Tensile Testing: Measures the material's elongation at break to assess ageing condition. A decrease in elongation at break indicates loss of material flexibility.
Dielectric Breakdown Strength Testing: Measures the breakdown strength of insulating materials under voltage, exhibiting a linear decline following ageing.
2. Minimally Invasive Testing Methods
Density Testing: Assesses ageing severity by measuring density changes. Initial density increases followed by rapid decline in later stages.
3. Conventional Testing Techniques
Visual Inspection: Observe whether the insulation layer exhibits cracking, hardening, discolouration, or powdering.
Insulation Testing: Measure phase-to-phase and earth insulation resistance using a 500V megohmmeter. Cables rated at 0.6/1kV require ≥10MΩ/km.
Operational Monitoring: Employ infrared thermography to detect operating temperatures. Conductor temperatures exceeding 70°C or a temperature differential exceeding 15°C relative to ambient conditions indicates insulation degradation.
Conductor Testing: Utilise a loop impedance tester to verify conductor continuity. Impedance imbalance exceeding 15% in three-phase cables or abrupt impedance changes in single-phase cables signify conductor issues.
Replacement Cycle for Insulated Electrical Wires and Cables
The replacement cycle for cables depends on multiple factors:
Design Life:
XLPE insulated cables: 30 years
PVC-insulated cables: 20–25 years
New national standard stipulates: no less than 70 years
Practical Usage Recommendations:
Household Electrical Wire: Comprehensive inspection and replacement after 15–20 years
Replacement is required immediately if any of the following occur: Cracking, hardening or brittleness of the outer sheath; frequent tripping of circuit breakers; overheating of sockets; insulation resistance below 50% of the standard value.
Influencing Factors:
Copper-core wires may last 30–50 years, while aluminium-core wires typically last 15–25 years.
Damp or high-temperature environments shorten service life.
Prolonged overloading accelerates ageing.
Maintenance suggestions for extending the service life of cables
1. Reasonable selection and installation
Select high-quality copper cables; in special environments, humidity-resistant, corrosion-resistant and high-temperature-resistant types should be chosen.
Adhere to standard wiring practices, avoiding excessive bending, twisting or stretching.
Use conduit protection to avoid mechanical damage.
2. Daily maintenance measures
Regular inspection:
Visually inspect the outer skin for damage and aging every month.
Quarterly infrared temperature measurement to detect joint temperature.
Annual insulation resistance test (for low-voltage cables ≥ 0.5M Ω).
Environmental control:
Keep the laying environment dry and avoid moisture.
Special sheathed cables are used in chemical corrosion environments.
High temperature resistant cables are selected for high-temperature areas.
Load management:
Avoid long-term overload operation (not exceeding 80% of rated current capacity).
Maintain balanced three-phase load.
3. Professional maintenance
Please have a professional electrician test the household circuit load every 2-3 years, as the circuit system may experience aging or overload risks with increasing service life. Professional electricians can use instruments to detect voltage stability, line carrying capacity, and potential hazards (such as poor contact) to ensure electrical safety. Regular inspections can prevent fire or short circuit accidents.
It is recommended to upgrade old power lines to flame-retardant wires, as the insulation layer of traditional wires can easily cause fires due to high temperature melting. Flame retardant wires are made of special materials (such as XLPE insulation layer), which can suppress the spread of flames in case of fire, buying time for escape and emergency rescue, especially suitable for high load electrical areas (such as kitchens).
If any damage or leakage is found, immediately close the main switch and ask professional personnel to handle it. Damaged circuits may cause electric shock or arc sparks. Operation priority:
Step 1: Quickly cut off the main power supply (avoid touching the damaged area directly);
Step 2: Contact a certified electrician for maintenance and do not use temporary measures such as tape wrapping on your own.
