Non-ceramic insulators, particularly those made of silicone rubber (SIR), are increasingly being used in both distribution and transmission systems. They exhibit several advantages over ceramic insulators. The low surface energy of SIR insulators maintains a hydrophobic surface that facilitates a good performance in polluted outdoor service conditions. Moreover, these SIR insulators cost less and weigh less than the heavy ceramic insulators. However, non-ceramic insulators still have certain disadvantages like aging, their unknown long-term reliability, and the difficulty in detecting defective insulators. Aging, which leads either to tracking/erosion or to flashover under contaminated conditions at normal operating voltage, is still the main cause of registered failures for non-ceramic insulators.

Leakage current (LC), leading to dry-band arcing, is considered one of the most important causes of aging in SIR insulators. For this reason, the LC peak value has been measured in the field and during aging tests. However, no correlation has been found between the LC peak value and aging in SIR insulators. In addition, most of the aging studies have concentrated on the influence of the SIR material composition on the aging performance of SIR insulators. Very few investigations have been conducted to explore the influence of SIR insulator profiles on performance. In this investigation, salt-fog tests are conducted to test the influence of SIR insulator profiles on their aging performance. Since it is well known that dry-band arcing is associated with distortion in the LC, LC low frequency components are used as a diagnostic tool to assess the influence of the profiles on the aging performance of SIR insulators. Three forms of aging are identified during the study:​ no visible damage, erosion, and failure. A very good correlation is discovered between these three forms of aging and the LC low frequency components. In addition, time series modelling is employed to identify the onset of dry-band arcing by using the third harmonic component of the LC.

Shed spacing, shed diameter, alternate shed design and shed profile are the SIR profile parameters investigated in this study. As the shed spacing decreases, the performance of the SIR insulator improves. However, shed spacing less than 30 mm leads to shed bridging by water droplets. Also, shed profile proves to be pivotal in the design of the SIR distribution class insulators. Moreover, it is discovered that as the shed diameter increases, the protected area beneath the shed increases, resulting in an improved aging performance.

Electric field calculations, conducted with FEMLAB®, reveals that as the shed inclination angle increases, the field enhancement beneath the shed increases as well. Moreover, the field enhancement beneath the shed is relatively high for the sheds near the high voltage end of the insulator. However, the simulation results demonstrate that the electric field on the insulator surface is less than the onset value to initiate corona in both dry and wet conditions. Consequently, dry-band arcing is the main electrical cause for aging in distribution class insulators.

Two different methods to compute the current density along the contaminated and wet SIR insulator's surface are investigated. The first method, based on the field theory approach, uses the commercial software FEMLAB® to compute the current density. The conductivity of the contamination layer used in the calculations is extracted from the measured equivalent salt deposit density (ESDD) for each of the different regions of the insulator surface. The second method is based on the circuit theory approach, and the insulator surface is divided into different sections for resistance calculations to account for different contamination levels. The rankings, based on the calculated current densities from the segmentation of the insulator surface for the ESDD measurements, match those extracted from the measured leakage currents.

In summary, the LC low frequency components are employed to study the relationship between SIR insulator profiles and aging, and it is demonstrated that LC low frequency components can be correlated with aging in SIR insulators. In fact, the results indicate that the SIR insulator profile has an enormous influence on the aging performance of SIR insulators.