Journal Article•
Influence of Corona Discharge on Aging Characteristics of HTV Silicone Rubber Material
TL;DR: In this paper, a comparative study was performed on the HTV silicone rubber material aged by corona discharge in laboratory and by natural environment, in regard to such parameters as hydrophobicity, surface leakage current, surface microstructure and chemical composition.
Abstract: To obtain dominant parameters of material characteristics for evaluating aging state of composite insulators effectively,a comparative study was performed on the HTV silicone rubber material aged by corona discharge in laboratory and by natural environment,in regard to such parameters as hydrophobicity,surface leakage current,surface microstructure and chemical composition.Experimental results show that the characteristic parameters of the silicone rubber material under two kinds of aging conditions exhibit similar change rules.Corona aging condition decreases hydrophobicity,and increasing corona voltage or acting time leads to a sharper drop and a slower recovery or even uncompleted recovery in hydrophobicity.Hydrophobicity decline is also observed in the naturally aged specimens from HC1 level in two years to HC5 level in 15 years.In addition,surface resistivity also decreases with aging time and thus surface leakage current increases.SEM and FTIR analyses show that both corona aging and environment aging conditions induce increasing surface defect density and deepening pits,and even cracks.Moreover,aging gets the molecular chain of silicone rubber material broken and results in the generation of strong polar groups,worsening the mechanical and insulation performances of the silicone rubber.
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TL;DR: The results show that with the effect of corona discharge, the polymer structure of the silicone rubber materials change to a certain extent, and the NMR characteristic of silicon rubber materials after corona are irreversible.
Abstract: Nuclear Magnetic Resonance (NMR) detection is a non-destructive testing method that can be used to detect the aging state of organic materials. A unilateral NMR sensor is used in this study to detect the aging state of the corona aging samples of silicone rubber materials after 100-hour’s corona aging under different humidity. At the same time, a comparative analysis is made between the NMR results and the conventional methods results such as Fourier Transform Infrared Spectroscopy (FTIR) and static contact angle test. The results show that with the effect of corona discharge, the polymer structure of the silicone rubber materials change to a certain extent. These changes are shown as the effective transverse relaxation time $T_{\mathrm {2eff}}$ of aged sample decreases in the NMR detection. The results of NMR and FTIR both show that the molecular crosslinking density of silicon rubber materials increases, and the activity of the H-containing group decreases. With the increase of relative ambient humidity, $\Delta T_{\mathrm {2eff}}$ gradually increase, and it means the corona aging state is becoming much severer. The results of NMR are consistent with the results of FTIR and contact angle tests. The $T_{\mathrm {2eff}}$ of the same sample tested at different time does not have significantly changes. This indicates that the NMR characteristic of silicon rubber materials after corona are irreversible. The NMR method can test the permanent damage of silicon rubber materials caused by corona. Compared with the static contact angle test, the NMR method can analyze silicon rubber materials from the molecular structure level, and it has good portability and orientation. Meantime, NMR method can achieve a non-destructive aging state detection. Hence the NMR method will provide reference for the operation and maintenance of the silicone rubber composite insulator.
11 citations
01 Sep 2016
TL;DR: In this paper, the insulation condition of service-aged silicone rubber insulators in grids was evaluated by measuring the hydrophobicity, infrared spectrum (IR) and scanning electron microscope (SEM) results.
Abstract: To evaluate the insulation condition of service-aged silicone rubber insulators in grids, the hydrophobicity, infrared spectrum (IR) and scanning electron microscope (SEM) of service-aged chalking and no chalking silicone rubber insulators are measured. The results show that chalking service-aged silicone rubber insulators have greater hydrophobicity than no chalking silicone rubber insulators. Microstructure changes of the silicone rubber insulators were respectively analyzed by infrared spectrum (IR) and scanning electron microscope (SEM). The IR results show that service-aged chalking silicone rubber insulators have greater main-chain fragmentation and methyl-group loss than no chalking silicone rubber insulators. Meanwhile, the IR resultants of chalking insulators aged under AC or DC voltages are similar. The SEM results show similar microstructure of chalking insulators. The aging mechanisms between chalking composite insulators under AC or DC voltages are similar, which lead to the same surface topography of service-aged silicone rubber insulators. Therefore, even though service-aged rubber insulators were aged under different voltages, there are similar IR and SEM results. They both have the microstructure changes on the surface, because of the mobility of silicone molecules, the service-aged chalking silicone rubber insulators still can keep good hydrophobic.
10 citations
Cites background from "Influence of Corona Discharge on Ag..."
...The decrease of hydrophobicity is used as an important indicator to evaluate the aging state of silicone rubber insulators [8]....
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03 Nov 2014
TL;DR: In this article, the authors presented a new criterion on aging diagnosis of silicone rubber composite insulators using conduction current test and surface electron microstructure (SEM) analysis.
Abstract: This paper presents a new criterion on aging diagnosis of silicone rubber composite insulator. Taking being operated composite insulators as the object, the electrical degradation threshold was obtained by the conduction current test, then the hydrophobic of samples was obtained by static contact angle measurement and the surface micro of samples was analyzed by surface electron microstructure (SEM). Preliminary tests indicates that the electrical degradation threshold of samples changing from 5 to 10 kV/mm with different aging degree, the more severe the degree of aging of the sample, the deeper its trap level, the lower the electrical degradation threshold, the greater the conduction current value. Research shows that electrical degradation threshold obtained by conduction current test of silicone rubber composite insulators can basically reflect material's aging degree, electrical degradation threshold may become the new criterion for diagnosing aging condition of silicone rubber composite insulators.
5 citations
Cites methods from "Influence of Corona Discharge on Ag..."
...At present, there are some methods are used to diagnosis the aging condition of silicone rubber composite insulators[5-6]....
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01 Sep 2016
TL;DR: After a large number of samples training, PNN model can accurately distinguish the hydrophobic level of bushing composite insulator bushing, which has great significance for monitoring composite insulators reliably.
Abstract: As the growth of the operating life and the influence of the environment, the hydrophobic of transformer composite insulator bushing will decline and pollution flashover accident happened easily, which can affect the safe operation of lines. This paper using machine vision to monitor the transformer composite insulator bushing surface, first, recognition and preprocessing the images of hydrophobic of composite insulator bushing, then extracting the characteristic value, finally, using probability neural network (PNN) to evaluate the hydrophobic of the transformer composite insulator bushing, after a large number of samples training, PNN model can accurately distinguish the hydrophobic level of bushing composite insulator bushing, which has great significance for monitoring composite insulator reliably.
4 citations
01 Sep 2016
TL;DR: In this paper, the relationship between micro structure and hydrophobicity is presented for service-aged silicone rubber insulators in order to evaluate the insulation condition of service aged silicone rubber.
Abstract: Silicone rubber insulators aged after years of operation. To evaluate the insulation condition of service-aged silicone rubber insulators, the relationship between micro structure and hydrophobicity is presented for service-aged silicone rubber insulators in this paper. According to industry standards, the hydrophobicity property of silicone rubber insulators are classified by contact angle method and water spray classification. Results showed the silicone rubber insulators still kept good hydrophobicity after 7∼9 years' service. Microstructure changes of the silicone rubber insulators were respectively analyzed by infrared spectrum (IR), and energy dispersive spectroscopy (EDS). The IR results showed that service-aged silicone rubbers had main-chain fragmentation and methyl-group loss. The EDS results indicated that small organic silicon molecules (hydrophobic groups) moved to the surface of sheds and improved the hydrophobicity. Therefore, even though the surface microstructure of silicone rubber insulators changed in service, silicone rubber insulators still can keep good hydrophobicity because of the migration of small organic silicon molecules.
4 citations