Comparison between porcelain and silicone rubber for external insulation on high-voltage bushings

In the current high-voltage insulating bushings market, porcelain bushings and composite material bushings are engaged in differentiated competition. Porcelain bushings, relying on mature manufacturing processes, high insulation reliability, and aging resistance, still maintain a dominant position (accounting for approximately 60%-70% of the market share), widely used in traditional power transmission and transformation scenarios. Composite material bushings (such as epoxy-impregnated paper and silicone rubber), featuring lightweight, pollution flashover resistance, and maintenance-free advantages, are rapidly penetrating the market. Their share has increased to 30%-40% in emerging applications like new energy grid integration and urban dense power grids, emerging as the main driver of the incremental market. Additionally, Hewei Power has summarized the advantages and disadvantages comparison of the two types of bushings. Please refer to the following table:

Composite Silicone Rubber Bushing vs. Porcelain Bushing Comparison Table

The silicone rubber used by Hewei Power for high voltage equipment is made of a specially formulated HTV, High Temperature Vulcanising, silicone rubber which has several advantages compared to porcelain. This instruction lists the most important properties for outdoor insulation and a short comparison between the characteristics of High Temperature Vulcanizing silicone rubber and porcelain both as materials and as an integral part of the bushing.

Hydrophobicity

The surface of silicone rubber maintains a high level of hydrophobicity even during severe environmental conditions. If the hydrophobicity of the surface is decreased, the surface will recover its hydrophobic properties since the silicone rubber continuously emits molecules of silicone oil to the surface. The layer of silicone oil is only a few molecules thick and provides the hydrophobic properties of the surface. The hydrophobicity of porcelain on the other hand is reduced already after a few days with medium severe pollution levels and will not recover unless the surface is cleaned. The design criteria for porcelain insulators according to standards is 31 mm/kV at severe pollution levels. In order to fulfil the standard requirements, the same design criteria for specific creepage distance for silicone rubber insulators as for porcelain is used which provides an even more robust design regarding the limitation of leakage currents.

Leakage currents

Thanks to the improved performance during and after severe environmental conditions with silicone rubber, the leakage current level along the insulator is very low compared to porcelain. A typical value for porcelain is 10 mA and for silicone <1 mA. This property also reduces the risk for flash-overs and thus increases the reliability of the product and eliminates the disturbances in the power grid resulting from such events.

Lightweight

The density of silicone rubber is aprox.1530 kg/m3 and 2500 kg/m3 of porcelain. The electrical insulation inside the silicone rubber is made of FCRG core or RIF core. The high mechanical strength of the insulation material supports the silicone rubber, which needs to be just 5 mm thick with the exception of the sheds. Thus the weight of the bushings is reduced to approximately half of its equivalent oil impregnated bushings with porcelain as outdoor insulation. With a more light weight design, the ability to withstand earthquakes is increased as well.

Sans entretien

The need for cleaning the bushing insulator is almost eliminated when using silicone rubber. Only in extreme environmental conditions may the insulator need to be cleaned. Porcelain, on the other hand, might have to be cleaned more often in medium-polluted areas as well.

Non-shattering material

The material has a non-shattering failure mode if subjected to vandalism, mechanical shocks, etc. The polymeric bushings are well suited for applications where vandalism by, for example, stone or brick throwing can be expected. The risk of transport damage is almost eliminated as well. The safety of personnel is increased due to the non-shattering material in the case of an unexpected failure on site.

Self-extinguishing

Silicone rubber is proven to be self-extinguishing even if a test sample is held vertically over an open flame. With this feature, the bushing with its silicone rubber insulator will not cause fire, not even maintain or develop a fire. Porcelain will not burn but it can explode or crack by extensive heating from fire sources, and consequently increase the fire when the oil is let out from the bushing.

Summary

Both porcelain bushings and composite silicone rubber bushings have their respective advantages and limitations – engineers should select based on specific project requirements regarding voltage class, environmental conditions, and lifecycle costs.

Hewei Power produces both #PolymericBushings and #PorcelainBushings undergo rigorous testing per international standards (IEC 60137). The long-term performance of outdoor composite bushings has been validated through extended testing at specialized stations under severe conditions, including coastal salt fog, desert UV exposure, and polar temperature cycles.