Greg Cash

Condition assessment of EPDM composite insulators using FTIR spectroscopy

Two new sampling and analysis techniques for assessing the condition of EPDM (ethylene-propylene diene monomer) composite insulators are presented. Polymer oxidation is assessed by removing small amounts of surface polymer by swabbing with xylene and analyzing this material by FTIR (Fourier transform infrared) emission spectroscopy. A measure of the amount of surface chalking is obtained by scraping a small amount of degraded surface material with a blade and analyzing by FTIR absorption spectroscopy. Numerical indices quantifying the amount of oxidation and surface chalking are obtained by calculating the ratios of absorption or emission peak heights in the infrared spectra. These indices are named the oxidation index and the chalking index. Three types of field-aged 275 kV EPDM composite insulators are investigated and the results from the new techniques compared with analyzes by XPS (X-ray photoelectron spectroscopy) with good agreement. It is found that for two types of insulator that the oxidation index is increased in regions near the HV conductor.

Controlled interfaces in low‐temperature‐cured phenolic composites

The surface chemistry and interfacial adhesion of silane-treated E-glass fibers and low-power, oxygen or water plasma-treated ultrahigh-modulus polyethylene (UHMPE) fibers with acid-catalyzed, low-temperature-cured phenolic resins have been measured by X-ray photoelectron spectroscopy, (XPS) and static secondary ion mass spectrometry (SIMS), fiber bundle pullout and flexural and interlaminar shear strength properties of unidirectional composites. The most effective treatment for E-glass involved an epoxy silane rather than an amino silane owing to the protonation by the acid catalyst of the amine as well as the loss of reactive sites by the formation of carbon dioxide adducts stable at the conditions of cure. Scanning electron microscope examination of the cured phenolic resin showed phase-separated water domains; the diameter of these domains decreased towards the fiber surface in a chopped-strand mat composite owing to the lowering of the surface tension produced by the dissolution of the binder by the phenolic resin. Both water and oxygen-plasma treatments of UHMPE increased the fiber bundle pullout force by the same amount and this was attributed to direct chemical bonding to hydroxyl (and possibly epoxy) groups detected by XPS, SSIMS and derivatization. The best composite properties were obtained when oxygen plasma-treated UHMPE was used and this was attributed to the slower restructuring and higher total oxygen content enabling efficient wet-out of the fibers by the resin.

SPECTROSCOPIC CHARACTERIZATION OF LOW MOLECULAR WEIGHT FLUIDS FROM SILICONE ELASTOMERS

ABSTRACT The migration of low molecular weight (LMW) silicone fluid from the bulk to the surface of polydimethylsiloxane (PDMS) elastomers results in hydrophobic recovery after thermal or UV damage. The identification and analysis of these silicone fluids is an important step in understanding the process which ultimately affects the service lifetime of the elastomer and may provide one approach to assessing residual service lifetime in applications such as high voltage insulation. LMW silicone fluids were extracted from the bulk of four different silicone elastomers used as the weather sheds on high voltage insulators and differences were observed both in the total amount of fluid and the amounts obtained on successive extractions. MALDI-MS analysis of the extracted fluids showed significant differences in the proportions of cyclic and linear species. The extracted fluids were also analyzed by FTIR and Raman spectroscopy to determine trimethyl silyl end-group concentration using a calibrated series of PDMS standards containing known proportions of linear and cyclic species. Comparison of FTIR and Raman analysis with the MALDI-MS showed a major limitation in vibrational spectroscopic analysis of cyclic/linear content occurred when the linear species terminated in dimethylhydroxyl rather than trimethyl silyl groups.

In-situ condition monitoring of EPDM composite insulators using Fourier transform infra-red spectroscopy

Procedures for determining the amount of polymer oxidation and surface chalking occurring on composite insulators are developed using FTIR spectroscopy. Numerical indicators of surface oxidation and chalking are obtained from ratios of peak heights in the IR spectra. Results of analyses of samples from three different types of EPDM 275 kV insulators suggest that oxidation is affected by surface discharging and weathering and that the amount of surface chalking is related to leakage current.

New Techniques for Estimating the Condition of High Voltage Polymeric Insulators

Insulators manufactured from polymeric materials are widely used by many electricity companies although there is concern about how degradation of the polymeric material of insulators might affect their lifetime. The question arises as to how utilities might best manage large populations of degrading composite insulators that are often dispersed over great geographical areas. In this paper the complete life cycle costs of polymeric insulators in large electricity networks are examined and it is concluded that failures of inexpensive components can generate significant real costs to the network owners and great indirect costs to the community. The policy of replace on failure is discussed and it is suggested that the application of condition based maintenance is needed to reduce costs. Failure modes of insulators are reviewed and a new technique for determining numerical indicators of insulator condition, developed by the author and co-researchers, is described that is based on analysis of samples of polymeric insulation taken ‘live’ from the high voltage network. The condition indicators developed for EPDM and silicone rubber insulation are described and results from sampling in 11 kV and 132 kV networks are presented.

MALDI-TOF/MS characterisation of LMW PDMS in high voltage HTV silicone rubber insulators

This paper reports the results of the characterisation of low molecular weight polydimethylsiloxane (LMW PDMS) extracted from four different brands of high temperature vulcanised (HTV) silicone rubber insulators designed for high voltage applications. LMW PDMS material was obtained from the insulators by sequential soxhlet extractions and mass changes were recorded for each extraction. The insulator extracts were thoroughly characterised using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS), which provides identification of individual molecular species allowing differences in molecular structure to be identified. The extracts were found to contain both linear and cyclic species. Some variations in end groups of the linear species were also noted. These spectra were used to calculate the relative proportions of these species as well as the average molecular weights of the extracts. Significant differences were observed in molecular composition and the speed of recovery of the insulators studied.

Diagnostics of EPDM polymer insulators

In this paper the application of pattern recognition techniques as a tool for diagnostics of ethylene-propylene diene monomer (EPDM) polymer insulators is discussed. Assessment of degradation is carried out by taking small samples of insulator shed material in-situ with subsequent analysis of the samples by Fourier transform infrared spectroscopy (FTIR) method. Chemical indicators of insulation condition obtained from FTIR are fed to a pattern recognition program, cluster analysis, which is shown to successfully discriminate between insulators from different locations, manufacturers and with varying degree of degradation. A database linking the numerical indicators of insulation condition and type, age and location of insulators has also been developed.

Dehydroxylation of intercalated kaolinite an infrared emission spectroscopic study

Intercalation of kaolinites with organic substances provides a method of expansion for a typically non-expanding clay. The dehydroxylation process is affected by the interaction of the kaolinite with the organic molecules, providing a mechanism for the dehydroxylation to occur at a decreased temperature. The dehydroxylation of the Birdwood kaolinite and its intercalates has been investigated by Fourier Transform in-situ infrared emission spectroscopy over the temperature range 200 °C to 600 °C at 25 °C intervals. Dehydroxylation of the intercalated kaolinite was observed by the decrease in intensity of the bands at 3670 cm−1, 3650 and 3600 cm−1 (inner surface hydroxyl bands) and 3620 cm−1 (inner hydroxyl band). The first two bands represent the out-of-phase vibrations of the hydroxyl stretching region of the kaolinite. The band at 3605 cm−1 is assigned to the inner surface hydroxyl hydrogen bonded to the acetate ion. It is proposed that the infrared emission process occurs through the loss of energy throu...

New Techniques for Life Cycle Management of Polymeric Insulators in High Voltage Electricity Networks

Abstract Insulators manufactured from polymeric materials are widely used by many electricity companies although there is concern about how degradation of the polymeric material of insulators might affect their lifetime. The question arises as to how utilities might best manage large populations of degrading composite insulators that are often dispersed over great geographical areas. In this paper the complete life cycle costs of polymeric insulators in large electricity networks are examined and it is concluded that failures of inexpensive components can generate significant real costs to the network owners and great indirect costs to the community. The policy of replace on failure is discussed and it is suggested that the application of condition based maintenance is needed to reduce costs. Failure modes of insulators are reviewed and a new technique for determining numerical indicators of insulator condition, developed by the author and co-researchers, is described that is based on analysis of samples of polymeric insulation taken ‘live’ from the high voltage network. The condition indicators developed for EPDM and silicone rubber insulation are described and results from sampling in 11 kV and 132 kV networks are presented.

Chemical and electrical techniques for condition assessment of composite insulators

In this paper, the results of fog tests on eight different surface-coated 11 kV EPDM insulators were presented. The objective of tests is to examine electrical characteristics of composite insulators during degradation. Leakage currents were found to be determined by shed surface condition. The electrical test results were compared with results of chemical surface analysis, which gave two numerical indicators: oxidation index and ester/ketone ratio. Surface condition of insulator was also examined by scanning electron micrograph. The electrical and chemical analysis results give useful and related indicator of surface condition.