During the annual maintenance of ultra-high voltage (UHV) lines, there are arc erosion marks on the wire at the grounding clamp. In severe cases, it can lead to strand breakage, wire breakage, and even grounding clamp shedding, which is easy to cause safety accidents. However, the arc ablation characteristics of the wire at the grounding clamp and the process of strand breakage during the maintenance of UHV lines remain unclear. Therefore, based on the induced current calculation result from an actual case of arc ablation on an UHV blackout line, this paper uses the current action integral equivalent method to build a research platform for the arc ablation characteristics of the wire at the grounding clamp. The results show that the discharge arc is accompanied by a large number of heat, light and shock wave effects. The arc generates severe arc ablation along the discharge channel between the lower end of the wire and the clamp, and there are multiple arcing processes. By increasing the contact area between the wire and the grounding clamp, the local arc energy density is reduced, and the ablation degree is obviously weakened. By reducing the gap distance between the wire and the grounding clamp, the arc discharge ablation and impact are more concentrated and severe, and the degree of wire ablation damage is more significant. Under the cumulative effect of arc ablation, the test wire exhibits broken strands, and the fracture is up to 5 mm at the severe melting point, which aggravates the ablation of the adjacent strands. When the arc current action integral is the same, the cumulative effect of wire arc ablation energy under small amplitude, low frequency and long time action current is more obvious, and the damage to wire ablation is stronger. The research results provide a reference for ensuring the personal safety of maintenance staff and prolonging the operating life of transmission equipment.

Heavy rainfall can bridge the sheds of insulators on transmission lines, substations, and converter stations with continuous water columns, leading to electric field distortion. At the same time, the porcelain insulator is easily deteriorated due to its own weight and wind load during long-term operation. The formation of zero-value insulators leads to the occurrence of rain flashover accidents. To investigate the lightning impulse discharge characteristics of porcelain insulator strings containing zero value insulators under heavy rainfall, lightning impulse tests are conducted on XWP2-160 porcelain insulator strings under various zero-value configurations. The results show that, both with and without zero-value insulators, the lightning rain flashover voltage of the porcelain insulator string decreases with the increase of rainfall intensity and rainwater conductivity. The flashover voltage of insulator strings without zero-value insulators is more significantly influenced by rainfall intensity and rainwater conductivity. As the number of zero-value insulators increases, the influence of rainfall intensity and rainwater conductivity on the lightning impulse flashover voltage becomes smaller. When zero-value insulators are located at different positions along the string, the lightning impulse flashover voltage gradually decreases with increasing rainfall intensity and rainwater conductivity, showing a tendency toward saturation. When the zero-value insulator is arranged at the high-voltage end, the rain flashover voltage is obviously greater than that at the middle and grounded end, and the degree of influence by the rainfall intensity and rainwater conductivity is also greater than that at the middle and grounded end. The research results can provide important guidance for the design and configuration of external insulation systems of transmission lines to cope with thunderstorms.

Thermally induced defects in the encapsulated insulation layer of dry-type transformers are prominent. To detect abnormal heating of winding insulation materials in a timely manner, this paper proposes an inorganic thermochromic coating-based temperature measurement method for the encapsulated insulation layer of dry-type transformer windings and investigates its performance. The inorganic temperature-indicating material is synthesized via the liquid-phase method, and its structure and micromorphology are characterized by Fourier transform infrared spectroscopy, thermogravimetry-differential thermogravimetry (TG-DTG), and other techniques, revealing the discoloration mechanism of the material. Considering the discoloration temperature range and sensitivity, the optimal mass ratio of the components (oxalic acid, potassium oxalate, and cobalt carbonate) is determined. Temperature-indicating coatings are prepared using two different basecoats, and their composition ratios are optimized according to discoloration, adhesion, hydrophobicity, and electrical properties. The results show that coatings using RTV-Ⅱ as the basecoat have a discoloration temperature of 103~120 ℃ and a grade 1 adhesion level. The static contact angle is greater than 100° both before and after discoloration, and the surface flashover voltage exceeds 9 kV/cm. The coating achieves the best comprehensive performance when the ratio of the basecoat to thermochromic material is 10∶3. After thermal aging at 60~80 ℃ for 168 h, no obvious degradation is observed in its discoloration and electrical insulation performance. The results can provide technical support for the temperature detection and overheating warning of thermally induced defects in the encapsulated insulation layer of dry-type transformer windings.

Lightning weather is frequently accompanied by heavy rainfall, resulting in the bridging of the insulator umbrella skirt of the transmission line by rain columns. Under the impact of lightning, the "bridging effect" may occur. Simultaneously, under the influence of multiple factors, the internal insulation of porcelain insulators deteriorates, forming zero-value insulators and further reducing the insulation performance. In this paper, 35 kV porcelain insulators on transmission lines with an operating life exceeding 15 years are selected, and tests on the lightning impulse discharge characteristics under heavy rainfall conditions in different zero-value positions are conducted. The research indicates that for the porcelain insulator string, whether with or without zero-value insulators, the rain flashover voltage decreases as a power function with the increase of rainfall intensity and the conductivity of rainwater. The rain flashover voltage of the intact insulator string is more significantly affected by rainfall intensity and the conductivity of rainwater. When the zero-value insulator is in different positions, the rain flashover voltage gradually decreases with the increase of rainfall intensity and the conductivity of rainwater, and a saturation trend is observed. When the zero-value insulator is located at the high-voltage end, the rain flashover voltage is the highest, and the influence of rainfall intensity and the conductivity of rainwater are significant. In this paper, the parameters of the rain shield are optimized. After its arrangement, the rain flashover voltage significantly increased by an average of 100.2%, and a clear saturation trend is presented with the increase of the outer diameter. Before and after the installation of the rain-shedding shields, obvious changes occurr in the development path of the electric arc, and the development time is significantly shortened. Compared to the condition before installing the rain-shedding shields, the arc length decreased by 39.99% and the arc propagation speed increased by 180.02% after installation.