# Environmental Effects on HV Dielectric Materials and Related Sensing Technologies
## 2 Analyses and Discussions
Self-healing HV insulators with similar weather resistance properties throughout the used material were also reported [57] which are also suitable for high-voltage electrical insulators by using a silicon rubber composition. Figure 2: Method for analysing the risk of failure of HV insulators leading to substation failure [42]. Systems that can attach to the top or the bottom of the HV insulators to prevent surface leakage currents, corona discharges and the corrosive and erosive effects thereby produced were also proposed [58] to extend the operation life of the insulators. The devices, which attach to the region of the junction of insulators and their end fittings, have a disk-shaped semiconductor element with rounded edges and rounded-edge surface conduction. The system prevents surface currents and corona discharges by shunting the current through the semi-conductive disk and its surface conduction layer. The round configuration of the device also avoids any high-field points which might otherwise produce corona discharge on the surface of the device. In spite of the development of improved insulators for polluted environments in many parts of the world, insulator contamination has become an important impediment to the supply of electrical energy. The typical electrical discharges present on high-voltage insulators--partial discharge, dry band arching and corona discharge--can compromise the security of the power network. Corona discharge occurs on the surface of insulators or adjacent insulators when the intensity of the electric field exceeds the breakdown strength of the surrounding air. The products of corona discharge are electromagnetic (EM) radiation, heat, and chemical compounds such as ozone (O\({}_{3}\)), nitrogen dioxide (NO\({}_{2}\)), and nitric acid (HNO\({}_{3}\)) [59]. The combined contribution of chemical and electromagnetic stresses increases the degradation of the HV insulators. Experimental and theoretical studies have assessed corona discharge in high-voltage systems [60; 61; 62]. Early investigations addressed the behavior of HV cables under low-level radiation and thermal aging conditions [63] and reported that failure of insulators can occur under prolonged electrical and thermal conditions. Life prediction tools were proposed to estimate the age profile of HV cables and insulators based on low-level radiation, flashover voltage, and surface resistance [15; 63]. The majority of studies have been concerned with electrical activities only around one insulator to quantify the power losses and electric field around the insulator [64; 65; 66; 67; 68]. The field transfer from an electrical discharge along the surface of a faulty insulator to other insulators in a cross-arm structure was investigated [69]. The study showed that the intensity of the field around adjacent insulators on the cross-arm can be between 5% and 30% of the intensity in the immediate proximity of the corona discharge. The computational and experimental results indicated that the field level at different locations along the cross-arm depends on the physical size and intensity of the discharge. The electrical stress due to this field increases together with inclement environmental conditions and can contribute to the electrical aging of the insulators, ultimately leading to their breakdown. The influence of water droplet pollution on the discharge activity of insulating materials is of relevance to the power industry. The presence of water on the surface of insulators has been shown to significantly increase partial discharge activity [70]. This can lead to the aging of insulating materials and ultimately can cause the failure of high-voltage insulators. The presence of current channels, caused by carbonization, saline crystals, or water, can support the discharge events between water droplets, which are linked to these current paths. Extensive studies have been carried out to recognize the parameters that facilitate this type of discharge activity for droplets situated on horizontal surfaces [71; 72; 73].