University of Manchester

X-Ray analysis of Composite Insulator materials for outdoor overhead line insulators

Riccardo Giussani
Project Completed

Scientific Case

The mechanical longevity of an overhead line insulator is dependent on the strength and quality of the rod which is usually made out of glass reinforced polymer. The connections of end fittings are also very important since they provide protection to the rod from the elements of nature.
The exposure of the rod to water contaminated with salt in the presence of electric field can lead to the formation of acids which attack the glass fibres, making them weaker. This phenomenon is progressive and depends upon the degree of exposure of the rod, the strength of the electric field, the mechanical load on the insulator and the environmental conditions. Exposure can result from erosion of the sheath due to discharge activity on the surface of the insulator, puncture of the sheath or from poor bonding between the sheath and the end fittings. It has been observed that under such conditions it is possible for a brittle fracture to occur in a matter of weeks.
To summarise, the rod must have a low void percentage (i.e. not be porous) to decrease the risk of puncture and reduce the probability of electrical discharges that result in long term degradation. These properties of the rod material are validated by the dye penetration and water diffusion tests specified in the IEC 61109 standard [1].
Despite the fact that this IEC standard has been used by the industry for the last few decades, the phenomena is still not fully understand plus the standard’s requirements, with the development of new materials, are becoming obsolete since virtually all the new materials can pass the above-mentioned test ( IEC standard [1] has been updated in 2008 but the “Dye penetration test” and the “Water diffusion test” have never been updated [2]).
To improve the understanding of the phenomena we are, within the University of Manchester, running some alternative tests to quantify the properties of the materials.
With the intention of support the current findings/results we would like to analyze the morphological structure of different materials exposed to the test as in [1,2] and examine how the moisture absorption actually affect the phenomena.
Objectives are to compare the moisture absorption (measured through X-Ray tomography) with the result from the alternative tests currently ongoing within the EEE department.
Accordingly to the standard the likelihood of the material to absorb moisture is directly related to the performance of the overhead line insulator, we would like to verify if for the new material this assertion is still valid. If so it is aims of the authors to quantify this relationship (moisture absorption/porosity/performance).
[1] BSI, "IEC 61109 Insulators for overhead lines. Composite suspension and tension insulators for a.c. systems with a nominal voltage greater than 1000 V. Definitions, test methods and acceptance criteria," 2008.
[2] BSI, "Composite insulators for a.c. overhead lines with a nominal voltage greater than 1000 V - Definitions, test methods and acceptance criteria," 1992.

Experiment Design

analyze the morphological structure of different materials for overhead lines insulators

5 microns
Scanners and Rigs
Nikon XTH225
Not Required

Sample & Safety

Low Hazard

Scan Records

Project Report