Porcelain insulators have been an integral part of power systems for more than a century due in large part to their rigidity, which assures alignment of components in substation equipment. Moreover, in recent years there have been great advancements in understanding the seismic events that impact such insulators at substations. Resonant frequencies from these events can cause immense dynamic forces and, due to its weight and brittle nature, porcelain is more susceptible to destructive harmonic frequencies. But with good design practice, advanced materials and modern manufacturing methods, porcelain insulators can still prove a dependable form of insulation in seismic service environments. Material characteristics play a major role in equipment design under such dynamic forces and, while steel and aluminum are ductile and offer predictable strength, porcelain is non-ductile and can vary greatly in strength. Seismic performance of porcelain insulators can therefore be enhanced through maximizing strength and reducing weight.

Since weight is a key factor when calculating the force/energy that goes into the equipment during a seismic event, the challenge is optimize design and maximize strength to weight ratio.

Weight Reduction

There are ways to reduce the weight of a porcelain insulator of given strength. First of all, insulators should ideally be specially designed for the need. Moreover, maximizing section lengths helps reduce weight on multi-stack insulators. Manufacturers also have material choices that offer higher strength and maintaining tight quality assurance standards can further enhance overall strength.

Optimizing Design

The design of an insulator needs to account for its application under seismic conditions. Often, insulators used at substations are based on standard designs intended to perform across a range of applications. An example is an insulator with uniform cylindrical cores that can be applied upright but is considerably heavier when under-hung. While tapered insulators are increasingly used in HV applications, determining optimal taper is important.

Shed Weight

Shed profile is a means to increase creepage distance, yet sheds contribute weight to an insulator. In the past, sheds have typically been up to 19 mm at the core tapering down to 12 mm at the tip. With improved material science, shed size can be reduced, resulting in a 20% reduction in shed weight.

Reduced Sections

Insulators are comprised of single or multiple sections bolted together. Insulators are typically single piece construction up to 750 kV BIL. High voltage insulators can be made up of many sections depending on the voltage level. Stress concentrations are found at the joints where the cast iron fittings are cemented onto the porcelain. The diameter of the porcelain at the fitting is increased due to the concentrated stress levels. Reducing number of sections will reduce high stress locations as well as the weight of the additional fittings

Material

Porcelain insulators are technical ceramics containing a mix of kaolin, alumina, feldspar and silica (quartz). IEC 60672-3 refers to three main types: C-110, C-120 and C-130. C-110 is known as quartz porcelain while C-120 and C-130 are alumina porcelains. C-120 contains 20%-30% alumina whereas C-130 normally has alumina content greater than 30%. Insulators manufactured with C-130 clay with higher than minimum levels can offer up to 40% reduction in weight.

Production Process

Manufacture of clay materials has an inherently wide range of resulting material strengths. Such variation can occur within a batch or between batches. Achieving consistent body strength is difficult, especially if processes are not tightly controlled. Indeed, it has been demonstrated that strength of ceramic materials can have over 35% standard deviation. The larger the deviation, the heavier the design of the insulator needed to ensure meeting the Specified Mechanical Load (SML). Reducing standard deviation directly reduces weight of any given manufacturer’s design parameters.

Conclusions

Improving the performance of porcelain insulators under seismic service conditions is possible mainly through weight reduction methods. Optimizing design based on specific actual application, using high strength materials and maintaining a consistent manufacturing process will all ensure the best performance possible.

From：https://www.inmr.com/seismic-performance-of-porcelain-at-substations/