Double-umbrella Type Glass Insulators

Double-umbrella type glass insulator is the mainstream subcategory of anti-pollution glass insulators. With its differentiated design featuring double umbrella skirts, it takes into account anti-pollution flashover, self-cleaning ability, and mechanical stability, and is suitable for complex transmission scenarios such as medium and severe pollution, damp and foggy conditions. It is commonly used in industrial pollution areas and coastal salt spray areas.

1) Core structure and design features

• The double umbrella skirt configuration adopts a combination design of large umbrella and small umbrella. The upper large umbrella has a larger diameter and a larger outward angle of the umbrella skirt, which can effectively shield the lower small umbrella and reduce the adhesion of dust, salt fog, bird droppings, etc.; the lower small umbrella is compactly arranged, significantly extending the creepage distance and enhancing the insulation performance. The edges of the umbrella skirts are all rounded for corner treatment, reducing corona loss and enhancing the self-cleaning effect during rain washing.
• The basic composition remains the same. The main body is made of tempered glass pieces, hot-dip galvanized steel caps, steel feet, and high-grade cement adhesive. It inherits the core advantages of glass insulators such as zero-value self-breakage, arc resistance, and high mechanical strength. Defective insulators can automatically burst and fall off without the need for pole climbing inspection.

2) Core advantages

• Outstanding anti-pollution flashover capability. The creepage distance can reach 25-35mm/kV, much higher than that of standard insulators. It can effectively block the conductive channels formed by pollution, significantly reducing the pollution flashover tripping rate in humid environments, suitable for high-pollution scenarios such as chemical, metallurgy, and coastal areas.
• Balances self-cleaning and operation economy. The design of large umbrella shielding and arc-shaped umbrella edge makes it less likely for dirt to accumulate, and it can quickly fall off after rain washing, reducing the frequency of manual cleaning; the zero-value self-break feature further reduces inspection costs and increases the operation efficiency by more than 50% compared to traditional porcelain insulators.
• Strong mechanical stability. The symmetrical structure of the double umbrella skirt disperses wind pressure and icing load, and its anti-wind vibration and anti-icing bridging capabilities are superior to single-umbrella type, suitable for large-span lines of various voltage levels from 110kV to 1000kV.

3) Applicable scenarios

• Transmission lines in medium and severe industrial pollution areas such as chemical parks, coal mines, and metallurgical plants;
• Transmission projects in coastal areas with high salt spray and high humidity, including near-sea and island projects;
• Transmission lines in humid and foggy areas with repeated icing and mountainous and high-altitude areas;
• Areas with combined pollution such as dense urban areas and urban-rural fringe areas.

4) Selection and operation key points

• In mild pollution areas, a model with a creepage distance of 25-28mm/kV can be selected. For severe pollution / coastal salt spray areas, models with a creepage distance of 30mm/kV or above are recommended;
• For long-span and repeated icing lines, high-strength models with a rated mechanical breaking load of ≥160kN are preferred.
• In mild and moderate pollution areas, inspections are conducted once every 6-12 months, and in severe pollution areas, inspections are conducted every 3-6 months;
• Pay special attention to rust conditions of the steel cap and steel foot, and in coastal areas, anti-corrosion coatings can be added or stainless steel accessories can be selected;
• No additional cleaning is required. Only self-burst insulator pieces need to be replaced in time.