Recently established working groups (WGs) within CIGRE deal with a number of aspects of polymeric outdoor insulation. For example, WG B2.57 of Study Committee B2, Overhead Lines, conducts a survey of operating experience with composite insulators and proposes an application guide dealing with key topics based on practice by user utilities. This WG, headed by Frank Schmuck, has a membership of more than 30 experts. Similarly, WGs D1.58 and D1.59 within Study Committee Materials & Emerging Test Techniques deal with evaluating the dynamic hydrophobicity of polymeric insulating materials under AC and DC voltage stresses as well as methods for characterizing the dielectric performance of polymeric insulating materials for outdoor applications. Both are headed by Dr. Jens Seifert.
Two other WGs have also been formed to cover related topics. One of these – D1.61 – deals with Optical Corona Detection & Measurement. This subject is now of growing interest because, in certain cases, use of composite insulators is being questioned due to a claimed insufficiency of applicable diagnostic techniques, especially when it comes to live-line-work. However, as shown in Technical Brochure 545, Assessment of In-Service Composite Insulators by Using Diagnostic Tools, a number of methodologies are available that can be used to evaluate the condition of components and equipment under operating voltage. Their use and applicability is summarized in the Table.
For example, UV measurements can be made during daylight (see Fig. 1) or using night vision cameras (Fig. 2) that employ different wavelengths for measurement – the first 240…280 nm and the second, 230…450 nm. Being able to make use of such equipment during daytime is a big advantage hence this measurement principle has grown increasingly popular. In recent years, several different types of UV cameras have become available. However, in most cases they do not offer a clear ‘yes’ or ‘no’ result in terms of identifying defective components. Rather, their use often requires knowledge and experience when it comes to correctly interpreting data, especially when the focus is on polymeric surfaces susceptible to ageing.
Also, ambient conditions such as humidity, temperature, wind and pollution by other sources of photons, are all critical to correctly interpreting findings. Based on this, the main duties of this WG will be defining measurement parameters and calibration and, if possible, deducing thresholds for specific line components as well as demonstrating typical applications. The work of this group is mostly experimental and the Convenor is Nishal Mahatho from Eskom.
The other new WG, D1.62, Surface Degradation of Polymeric Insulating Materials for Outdoor Applications, has a designation that might sound alarming but should not be. In some cases, different types of degradation were observed on polymeric insulating surfaces after only a relatively short period in service. Some work in this regard was started within D1.27 and continues in this WG. For the few cases known so far, there has been no common root cause or scientific model since the interaction between degraded material and operational stress factors has been mostly case-dependent. As such, it is important to generate more information about these phenomena in order to better understand destructive degradation mechanisms and offer recommendations on how to improve the specific material groups being affected. Beside a ‘theoretical’ risk evaluation by Failure Mode Effect Analysis (FMEA), this work is also driven by experimental work including Round Robin tests, where degradation mechanisms are identified in principle. An example of such a degradation mechanism is acid attack on a polymeric surface. The Convenor of this WG is Dr. Bernd Komanschek.
Dr. Frank Schmuck