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Solid insulating materials are good insulators, can be easily adopted for practical applications, but their mechanical and electrical properties deteriorate rapidly when the temperature exceeds 100°C.
The performance of organic insulating materials can be improved by treating them with varnish or impregnating them with oil to enhance their thermal stability.
Examples of organic insulating materials include paper and press board, which are commonly used in cables, capacitors, and transformers.
Inorganic materials do not show any appreciable reduction in their electrical and mechanical properties up to 250°C, unlike organic materials which deteriorate rapidly at lower temperatures.
Important inorganic materials used for electric applications include glasses and ceramics, which are utilized for manufacturing insulators and bushings due to their resistance to atmospheric pollutants.
Chemical actions such as chemical instability at high temperatures, oxidation, cracking, and hydrolysis can lead to progressive chemical degradation of insulating materials.
Treeing is a phenomenon where visible markings appear on solid dielectrics due to electrical stresses, resulting in the formation of conducting paths that resemble tree branches.
Tracking occurs when a conducting film, formed due to moisture on the surface of solid dielectrics, starts conducting under voltage, generating heat and leading to the formation of dry conducting tracks.
The cumulative process leading to insulation failure in organic materials involves carbonization at the region of sparking, where carbonized regions act as permanent conducting channels bridging the distance between electrodes.
Thermal breakdown is influenced by the frequency of the applied voltage, with higher frequencies resulting in more serious thermal breakdown due to increased power loss under a.c. conditions.
Intrinsic breakdown occurs due to the inherent properties of the material, while thermal breakdown occurs after prolonged exposure to high temperatures and electrical stresses.
Moisture contributes to the formation of a conducting film on the surface of solid dielectrics, which can lead to tracking and eventual breakdown when voltage is applied.
Electrochemical breakdown is caused by chemical transformations such as electrolysis and the formation of ozone, which can lead to the degradation of insulating materials over time.
Partial discharges can create localized areas of high electric field strength, leading to material degradation and eventual failure of the insulation.
Thermal breakdown stresses are generally lower under a.c. conditions compared to d.c. due to higher power loss associated with a.c. fields.
The temperature threshold of 100°C is significant because it marks the point at which the mechanical and electrical properties of organic insulating materials begin to deteriorate rapidly.
Treeing leads to the roughening of the surface of solid dielectrics, creating irregular paths that can result in the formation of conducting channels and eventual breakdown.
Understanding the breakdown mechanisms of solid dielectrics is crucial for improving the reliability and longevity of electrical insulation systems in various applications.
Preventive measures include proper material selection, regular maintenance, environmental control to minimize moisture, and the application of protective coatings.
Contaminants can create conductive paths on the surface of solid dielectrics, increasing the risk of tracking and treeing, which can lead to insulation failure.
The relationship is that thermal breakdown becomes more serious at higher frequencies due to the proportional increase in heat generated, leading to faster degradation of the material.