DC Disc Suspension Glass Insulator

The DC disc-type suspension glass insulator is a disc-type insulating component specifically designed for high-voltage / ultra-high-voltage DC transmission lines. It is mainly adapted for DC transmission projects of ±500kV, ±800kV, ±1100kV, etc., aiming to address the technical challenges of high DC electric field-induced surface charge accumulation and high risk of pollution flashover. It is the core insulating component for cross-regional DC transmission lines.

1) Core Structure and Design Features

• The DC adaptation type umbrella skirt design adopts an asymmetric double-umbrella / triple-umbrella configuration. The surface of the umbrella skirt is coated with semiconductor glaze or treated with gradient resistance, which can effectively suppress surface charge accumulation under DC electric fields, prevent local electric field distortion caused by uneven potential distribution, and reduce corona loss and radio interference. The creepage distance is generally ≥ 30mm/kV, and some ultra-high-voltage models can reach over 40mm/kV, far exceeding that of AC insulators, meeting the insulation requirements under DC contamination conditions.
• The basic structure and material optimization mainly consists of high-strength tempered glass components, hot-dip galvanized steel caps, alloy steel feet, and anti-corrosion cement adhesive. It inherits the inherent advantages of glass insulators such as zero-value self-breakage, arc resistance, and high mechanical strength. For the electrolytic corrosion problem under DC conditions, the steel cap and steel foot adopt double-layer hot-dip galvanizing + passivation treatment, and the adhesive is added with anti-electrolytic additives to prevent electrochemical reactions between the metal attachments and the glass components and the cement layer.
• The voltage equalization adaptation design can be equipped with voltage equalization rings to optimize the DC electric field distribution, avoid excessive local field strength at the edge of the umbrella skirt causing electrical erosion damage, and improve the overall operational stability of the insulator string.

2) Core Advantages

• Outstanding anti-dc flashover capability: Under DC electric fields, the surface of the insulator is prone to accumulate charges, and the flashover tripping rate of ordinary AC insulators is 2-3 times that of DC; The DC disc-type glass insulator optimizes the umbrella shape and surface treatment, increasing the charge dissipation speed by more than 50%, and the flashover tolerance voltage is 30% higher than that of AC type, suitable for high-pollution DC transmission scenarios.
• Resistance to electrolytic corrosion and aging: Under DC conditions, there is a continuous leakage current, which can easily cause electrolytic corrosion of metal attachments and deterioration of the cement adhesive layer; The anti-electrolytic design of this type of insulator can effectively delay this process, with a service life of over 40 years in ±800kV DC lines.
• High operational economy: The zero-value self-breakage feature enables visual inspection of deteriorated insulators without the need for pole climbing detection; The umbrella skirt has strong self-cleaning ability, and the dirt is easily removed after rain washing, reducing the frequency of manual cleaning by 60% compared to DC porcelain insulators.
• Strong mechanical stability: The rated mechanical breaking load covers 70kN - 550kN, suitable for ±1100kV ultra-high-voltage DC large-span lines, and has the ability to resist wind vibration and icing bridging, meeting extreme working condition requirements.

3) Applicable Scenarios

• ±500kV, ±800kV, ±1100kV ultra-high-voltage DC transmission lines;
• DC transmission lines for external power supply bases (such as the northwest wind / solar power bases);
• DC transmission lines in coastal high-salt fog and inland heavily polluted areas;
• Tension insulator strings for cross-regional DC interconnection projects on towers.

4) Selection and Maintenance Key Points

• Select the model with the rated mechanical breaking load that is 2.5-3 times the maximum operating tension;
• In heavy pollution / coastal salt fog areas, prioritize the model with a creepage distance of ≥ 35mm/kV, and supplement with voltage equalization rings when necessary;
• For ultra-high-voltage DC lines, select products that have passed DC aging test certification.
• In heavy pollution areas, conduct inspections once every 3 months, and in clean areas, conduct inspections once every 6-12 months;
• Focus on checking for electrical erosion marks on the umbrella skirt, rust on the steel cap and steel foot, and cracking of the adhesive layer, and replace the self-burst pieces in time;
• Regularly inspect the connection status of the voltage equalization ring to avoid electric field distortion caused by loosening;