A Study of the Erosion Mechanisms of Silicone Rubber Housing Composites

Silicone rubber insulators have been replacing conventional insulators made from toughened glass and porcelain in the power system, due to the non-wetting properties of silicone rubber insulation housing. However, silicone elastomers will eventually wet-out leading to leakage current and dry-band arcing giving rise to erosion of the silicone housing material, and eventually insulation failure. Well-established formulations of insulation housing composites have been developed and validated for erosion performance using the standard inclined plane tracking and erosion test, yet no such formulations have been developed and validated for DC. With the assumption that equivalent performance will be obtained, an adjustment to the creepage distance has been the measure taken in using the AC insulators for DC, without taking into consideration the differing aspects of the DC as compared to the AC dry-band arcing. This practice questions the existing DC insulators as an unknown entity that requires further investigation to ensure the reliability of the power supply. In addition recent demands have been raised to develop housing composites specifically for DC outdoor insulation, particularly with the increased interest in DC. It follows that developing a standard DC inclined plane tracking and erosion test is necessary for the development of more suitable materials for outdoor DC insulation applications. This thesis provides a thorough study of the DC dry-band arcing mechanism as opposed to the well understood mechanism of the AC dry-band arcing and provides a mechanistic understanding to the dry-band arcing leading to erosion as a foundation for the development of a standard DC inclined plane tracking and erosion test. To this end, the influence of inorganic fillers in silicone rubber on resisting erosion due to dry-band arcing is also presented, as an essential step towards obtaining more suitable silicone composite for DC outdoor insulation applications

A Study of the Erosion Mechanisms of Silicone Rubber Housing Composites

Silicone rubber insulators have been replacing conventional insulators made from toughened glass and porcelain in the power system, due to the non-wetting properties of silicone rubber insulation housing. However, silicone elastomers will eventually wet-out leading to leakage current and dry-band arcing giving rise to erosion of the silicone housing material, and eventually insulation failure. Well-established formulations of insulation housing composites have been developed and validated for erosion performance using the standard inclined plane tracking and erosion test, yet no such formulations have been developed and validated for DC. With the assumption that equivalent performance will be obtained, an adjustment to the creepage distance has been the measure taken in using the AC insulators for DC, without taking into consideration the differing aspects of the DC as compared to the AC dry-band arcing. This practice questions the existing DC insulators as an unknown entity that requires further investigation to ensure the reliability of the power supply. In addition recent demands have been raised to develop housing composites specifically for DC outdoor insulation, particularly with the increased interest in DC. It follows that developing a standard DC inclined plane tracking and erosion test is necessary for the development of more suitable materials for outdoor DC insulation applications. This thesis provides a thorough study of the DC dry-band arcing mechanism as opposed to the well understood mechanism of the AC dry-band arcing and provides a mechanistic understanding to the dry-band arcing leading to erosion as a foundation for the development of a standard DC inclined plane tracking and erosion test. To this end, the influence of inorganic fillers in silicone rubber on resisting erosion due to dry-band arcing is also presented, as an essential step towards obtaining more suitable silicone composite for DC outdoor insulation applications

The electrical tracking and erosion resistance evaluated using the inclined plane test: a critical task in the development of outdoor polymer insulating materials

Evaluating the electrical tracking and erosion resistance of polymeric housing materials is an essential task performed in the development of outdoor insulators. Tracking refers to the formation of a carbonaceous path on the surface of the insulation housing; whereas, erosion indicates weight loss of the housing material. An absolute realization of the electrical tracking and erosion resistance is not possible and therefore relative ranking of materials is the outcome that can be obtained in the standard electrical tracking and erosion tests. With the early utilization of organic insulating materials, failure due to tracking was a major concern, and therefore standard screening methods were proposed to mainly evaluate the tracking rather than the erosion resistance. Erosion is more important since the application of tracking-resistant composites compounded with high levels of inorganic fillers or possessing inorganic backbones such as silicones.Peer reviewed: YesNRC publication: Ye

Measurements of hydrophobicity for silicone rubber coating on outdoor insulators

In this paper condition assessment of silicon rubber coating applied to high voltage insulators is proposed. Electrical, thermal and chemical measurement methods are used to evaluate the condition of silicon rubber coating. From an asset management perspective, hydrophobicity is shown to be the key indicator of aging, and this the remnant life, of the coating material. The increase in the content of surface oxygen is an indicator of hydrophobicity deterioration under the power system. In addition, detecting the diffusion of the low-molecular-weight siloxane from the bulk to the surface can be utilized to indicate the relative ability to recover hydrophobicity after aging.Peer reviewed: YesNRC publication: Ye

Decomposition Kinetics of Natural Ester and Mineral oil from Thermogravimetric Analyses

With growing environmental concerns, biodegradable insulating fluids are being investigated as alternatives to petroleum-based mineral insulating oil in power transformers. In order to optimize their use, decomposition studies of these alternative fluids are therefore of ultimate importance. This paper investigates the thermal decomposition kinetics of mineral oil and two vegetable-based ester fluids, using the thermogravimetric analyses. The initial and maximal decomposition temperatures are determined using thermal analyses. In addition, the Arrhenius activation energy is calculated for the fluids under study using the Ozawa-Flynn-Wall iso-conversional method. In addition, TGA studies are extended to mineral and natural ester impregnated paper, with the aim of assessing their impact on the thermal decomposition of insulation paper. It is found that the level of mono-unsaturated acids in esters is important for enhancing the thermal stability. The enhanced thermal stability of the esters has advantageously contributed to the improvement of the thermal performance of the insulation paper

A Novel Framework to Study the Role of Ground and Fumed Silica Fillers in Suppressing DC Erosion of Silicone Rubber Outdoor Insulation

This paper investigates the effect of ground and fumed silica fillers on suppressing DC erosion in silicone rubber. Fumed silica and ground silica fillers are incorporated in silicone rubber at different loading levels and comparatively analyzed in this study. Outcomes of the +DC inclined plane tracking erosion test indicate a better erosion performance for the fumed silica filled composite despite having a lower thermal conductivity compared to the ground silica composite. Results of the simultaneous thermogravimetric and thermal differential analyses are correlated with inclined plane tracking erosion test outcomes suggesting that fumed silica suppresses depolymerization and promotes radical based crosslinking in silicone rubber. This finding is evident as higher residue is obtained with the fumed silica filler despite being filled at a significantly lower loading level compared to ground silica. The surface residue morphology obtained, and the roughness determined for the tested samples of the composites in the dry-arc resistance test indicate the formation of a coherent residue with the fumed silica filled composite. Such coherent residue could act as a barrier to shield the unaffected material underneath the damaged surface during dry-band arcing, thereby preventing progressive erosion. The outcomes of this study suggest a significant role for fumed silica promoting more interactions with silicone rubber to suppress DC erosion compared to ground silica fillers

Towards cost-effective maintenance of power transformer by accurately predicting its insulation condition

Insulation resistance (IR) or Megger test has been commonly performed in both preventive and corrective maintenance activities to verify power transformers' insulation condition. Other insulation diagnosis tests such as oil breakdown voltage (BDV), water content and dissolved-gas-in-oil analysis have been conducted along with the IR test. In this paper, a prediction model is developed to correlate IR measurements of the power transformer with its oil quality parameters, the concentration of its total dissolved combustible gases (TDCG), and its carbon dioxide to carbon monoxide concentration (CO 2/CO) ratio. Four models, based on feed-forward artificial neural networks with back-propagation, are trained on collected data of real measurements. Accuracy levels of 96%, 84%, 88%, and 91% are obtained for BDV, water content, TDCG, and CO2/CO ratio respectively. Utilizing the proposed model can reduce maintenance costs by preventing and shortening transformers' outage times using inexpensive test, i.e. using IR test only. 2012 IEEE.Scopu

A study on the effect of inorganic fillers on the dry-band arcing erosion of silicone rubber composites

This paper investigates the erosion of silicone rubber composites filled with various fillers. The fillers under study are alumina tri-hydrate, magnesium hydroxide and silica in a liquid silicone ru bber. The inclined plane tracking and erosion test was used to compare the erosion of the composite materials at 50 wt% filler level and at 4.5 kV. Simultaneous thermogravimetric and differential thermal analyses are reported which shows various mechanisms by which the fillers can su ppress the dry\uad band arcing erosion. The effect of water of hydration in the alumina tri-hyd rate and magnesium hydroxide is investigated and its effect on the suppression of the dry-band arcing erosion is reported for the composites filled with alumina tri-hydrate and magnesiu m hydroxide.Peer reviewed: YesNRC publication: Ye