Romanian scientists have studied the effects of acidic environments on power cables’ performance. The authors have used laboratory simulations to analyze the stresses that power cables are exposed to in the field. Their findings were published in the journal Energies.
Study: Study of the Accelerated Destruction of the Insulation of Power Cables in an Acid Environment. Image Credit: demarcomedia/Shutterstock.com
Background for the Research
Modern infrastructure is dependent on power cables. For reliable electricity supply to rural and urban areas, it is crucial to design reliable cables with minimal maintenance. However, several factors can affect the performance and lifespan of cables and change the dielectric material’s characteristics over time.
Installation type HPG70 D for high-voltage testing: (1) IT transformer; (2) Capacitor coupling and multiplication; (3) Multiplier recalcitrant diodes; (4) Connect cables; (5) Connection box. Image Credit: Preduș, M.F et al., Energies
The chemicals in high levels of acidity and pollution can penetrate the insulation coverings of cables. This can alter the insulation’s properties, which results in decreased operating times. This results in the cable being replaced and decommissioned, which increases maintenance burdens and interrupts power supply.
During cable operation, different voltages are used. Current studies on the behavior and effects of electrical insulation materials at low voltages have been done. There are many methods that can be used to highlight degradation in these conditions.
In lower-intensity electricity fields, the breakthrough phenomenon is preceded with electrical discharges. The occurrence of discharges tends not to occur in large portions of the insulation. It is crucial to monitor these partial discharges in order to assess the state and condition of insulation materials.
The Research
The lab-based experiments were used to study the degradation mechanisms in insulating materials under operating conditions. The experiments were conducted using PVC and XLPE samples. Measurements were made at predetermined intervals.
Samples were placed inside a rigid PVC pipe that contained electrolytes. The electrolyte composition was designed to simulate the environmental conditions cables will encounter over their lifespan. To mimic acid rain, the electrolyte contained sulphuric and nitric acids. It was diluted with water. To avoid contouring phenomena, a monopolar cable measuring 4m was inserted into the experimental equipment. Both ends protruded from the equipment.
Two-stage testing was done on the cables samples. The first stage involved testing the samples at voltages that were higher than the recommended voltage. Insulation resistance, conduction currents, and electrolyte temperature were monitored at intervals of 24 hours. Direct current was used to evaluate cables.
The second stage involved the testing of samples without the supply voltage. The electrolyte in the equipment was used to acidify the samples. Different voltages were used to recharge the electrolyte at regular intervals. The samples were continuously monitored until any signs of degradation.
(A) Assembly of the multilayer PVC pipe, fireproof type SN4-125×3.2, PVC elbow type D125 87°; (b) Method used for fixing the tube on the IT insulating support. Image Credit: Preduș, M.F et al., Energies
The Study’s Results
Three key findings were highlighted in the paper from an experimental analysis of electrical cables. Under normal operating conditions at nominal voltage values, the insulation is kept at a positive temperature, influenced by the circulating conduction current. In this situation, electrolyte absorption will be reduced.
Continuous insulation degradation occurs when the supply current is higher than the nominal voltage. It is caused by elevated heating. This can lead to loss of insulation properties and rapid decreases in insulation resistance. Finally, when there is no supply voltage, the degradation process increases, and the cable’s internal temperature decreases with electrolyte temperature. This is due again to the elevated absorption electrolytes, which causes insulation resistance to significantly decrease.
To confirm insulation degradation behavior, the results were validated in environments such as mines, near industrial waste, or environments with high water pH. Insulation defects were caused by the breakdown of aggressive acidic substances. The insulation material became a gelatinous material. This was especially evident in the vicinity of joint sleeves.
Visualization of the location of insulation breakdown: (A) after the removal of the outer shell; (b) after the removal of the semiconductor layer. Image Credit: Preduș, M.F et al., Energies
Recommendations of this Study
Based on their experimental findings, the authors made several recommendations. First, it is important to use superior chemical resistance materials for connection sleeves and cables. This will reduce the acidic environment effect on electrical cables.
Unpowered electrical cables should not be used for extended periods of time due to the fact that they can cause degradation without a voltage supply. Furthermore, it is best to avoid operating cables at voltages higher than the recommended values as this will accelerate the degradation process.
This study provides important insights into the behavior of insulation for electrical cables under real operating conditions. This will allow us to identify the root cause of the defects and prevent premature penetration, which can reduce the cable’s lifespan.
Further Reading
Preduș, M.F et al. (2022). Study of the Accelerated Destruction of the Insulation of Power Cables in an Acid Environment Energies 15(10) 3550 [online] mdpi.com. Available at: https://www.mdpi.com/1996-1073/15/10/3550
