Application of silicone rubber composite insulators has increased significantly over the past 30 years and among the essential factors behind continued growth is the confidence shown in them by power utilities. This edited article, contributed to INMR by world-renowned expert, Prof. LIANG Xidong, and YAN Zhipeng of Tsinghua University in Beijing, explores key issues in this regard. It proposes that current IEC test methods and technical standards are insufficient and in need of important modifications.
Development of insulators cannot be viewed separately from development of the power sector as a whole. For example, rapid growth in length of overhead lines and the move to higher voltage levels brought not only a huge increase in demand for insulators but also new and greater requirements in terms of their performance. Because of advantages in regard to superior wet and pollution flashover performance, light weight, high strength to weight ratio, easier transport and installation, resistance to vandalism, etc., application of silicone rubber composite insulators in China realized significant growth.
Composite insulators also realized significant increase in usage worldwide and, based on trial applications, now dominate all UHV lines. Moreover, major improvement has been achieved both in their manufacture and testing. Still, given the rapid development of this technology, the key issue for the future of composite insulators is that power utilities remain confident in their expected service life and performance. That means future development of composite insulators (as shown in Fig. 1) will depend on: availability of suitable test methods to verify long-term performance; establishing different requirements when it comes to station insulators; and developing the best materials and maintenance techniques.
Fig. 1: Key issues for continued development of composite insulators.
This article will focus on the discussion of new material & maintenance techniques.
Materials with Super-Hydrophobicity
New super-hydrophobic materials are especially attractive for outdoor insulation and researchers have come up with various methods to create these. For example, Tsinghua University used a laser-ablated template and fluoroalkyl-silane-modified composite coatings to prepare a specific microstructure and nanostructure on a silicone rubber surface (see Fig. 2).
Fig. 2: Scanning electron microscope (SEM) of original & super-hydrophobic HTV silicone rubber specimens. (a) original HTV silicone rubber surface, top left; (b) nano-structure HTV silicone rubber surface, bottom left; (c, d) micro-structure HTV silicone rubber surface, top right; (e, f) micro-nano-structure HTV silicone rubber surface, bottom right.
Fig. 3: Contact angle and sliding angle of the original and super-hydrophobic HTV specimens. (a) contact angle and sliding angle; (b) contact angle of HTV specimen with micro-nano structure; (c) air pockets between water and HTV specimen with micro-nano structure.
Fig. 3 shows the results of static contact angle and sliding angle measurements on HTV silicone rubber surfaces with different micro, nano, and micro-nano hierarchically textured surfaces. The static contact angle of water drops on the unaltered HTV silicone rubber sample was 115 ± 0.7° (i.e. classified as hydrophobic). In the case of micro structured HTV silicone rubber surfaces, this increased to 151.1 ± 1.7°, while with sliding angle to 4.1°. Nano-structured HTV silicone rubber surfaces offered a static contact angle of 148.2° and a sliding angle of 4.9°. The micro-nano structured HTV silicone rubber samples yielded the highest static contact angle,153.3°, and a very low sliding angle of 2.7°. A super-hydrophobic silicone rubber shows an excellent water repellency property when water droplets impact it under electric field. The surface can also be used to solve the problem of uneven field distribution due to surface water film and electric field enhancement due to water droplets. Large area such samples have successfully been prepared and it has been found that this type of surface also offers anti-icing as well as self-cleaning properties. Clearly, high volume production of long-lasting, super-hydrophobic surfaces will be an important future development in the field of outdoor insulation.
Other New Materials
There are also other developments to watch, such as nano-fillers and modification of fillers. These may provide better solutions to improve the shed/sheath of composite insulators or the FRP rod by improving or replacing the fiber or matrix materials. Another promising development is improvement of the critical interface between sheath and rod using new coupling agents or new treatment methods. Other possibilities include self-diagnosing and even self-healing materials.
Maintenance Based on Non-Contact Monitoring
On-line monitoring represents a huge challenge for a power grid. Development of industrial robots will be a promising way to conduct non-contact monitoring of insulators, such as looking for any localized heating that could be caused by surface leakage current, internal defects or degradation of the housing-rod interface. Currently, a localized temperature rise is considered related mainly to degradation of an interface and a sign of the early stage of decay-like fracture. Non-contact monitoring methods such as IR inspection from helicopters or unmanned aerial vehicles allow such localized heating to be detected so that affected insulators can be replaced in a timely manner, based on level of temperature rise.
Maintenance Based on Big Data
Information technology will certainly change development of power grids. In the case of composite insulators, two possible properties might meet some of the needs of the future smart grid. The first is large-scale, real-time on-line condition monitoring, both at substations and on overhead lines. A new function could be added to composite insulators, namely obtaining and transmitting data. Another is failure prediction based on big data. Every insulator will need to have its own QR code where all information such as manufacturing and material details, time in operation, maintenance information, etc. will be obtained. With such data, quality maintenance will become digital and failure prediction could be based on big data.
Conclusions
Use of composite insulator has increased rapidly over the past 30 years. Looking to the future, there are still key issues for continued development of this technology. Currently, test methods and technical standards are not satisfactory and it will be important to make modifications, not only to improve composite insulator quality but also to increase utility confidence when choosing such insulators. Also, new materials and better maintenance techniques will both contribute to further development of composite insulators.
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From：http://www.inmr.com/key-issues-future-composite-insulators-view-china/
