AC and DC performance of polymeric housing materials for HV outdoor insulators

This paper describes an investigation into the dry-band arcing mechanism leading to erosion of filled silicone rubber in the DC inclined plane test. Good correlation is obtained between the formation of surface residue, hotspots and the eroding dry-band arcing. The hotspots detected by infrared camera correlates well with the temperature of degradation determined by thermogravimetric analysis and differential scanning calorimetry. To characterize the physical mechanism of dry-band arcing, wavelet-based multiresolution analysis up to seven levels of resolution is applied to the leakage current waveforms. The analysis shows that both stable and intense discharges characterize the eroding dry-band arcing. A time-to-eroding parameter is proposed to determine the relative resistance to the formation of residue. Faster accumulation of residue is evident under -DC than +DC. Earlier inception of erosion is obtained for the silica filled-as compared to the alumina tri-hydrate filled-silicone, in which the release of the water of hydration is postulated to suppress the residue formation.Index Terms -Inclined plane test, silicone rubber, residue, dry band arcing, hotspot, erosion, wavelet transform, multiresolution analysis, alumina trihydrate filler, silica filler, HVDC insulation.

Section: Introductionsupporting

confidence: 78%

Investigation into the eroding dry-band arcing of filled silicone rubber under DC using wavelet-based multiresolution analysis

Ghunem

Jayaram

Cherney

2014

“…Literature on this subject is scarce. As reported in [34], even under humid conditions, the lifetime of positive charge implanted under positive dc corona may be longer as compared to the charge deposited by ac or negative dc corona, indicating the surface charging plays a determining role in the process of hydrophobicity loss and recovery. Besides, when charging epoxy insulator surfaces by dc corona, it was observed in [35] that at higher relative humidity the mechanism of surface charge decay was dominated by electric conduction along the surface of the insulators.…”

Section: Introductionmentioning

confidence: 68%

AC and DC zone-induced ageing of HTV silicone rubber

Gubanski

Hillborg

2011

On the way of making efforts to standardize the selection of polymeric materials for high voltage outdoor environments, the resistance to corona and ozone has been recognized as one among twelve parameters to be evaluated within the CIGRÉ Working Group D1.14 [1]. Our previous related work reported on the evaluation of the resistance of five commercially available polymeric materials to ac corona-ozone treatment, according to the test procedure recommended by this Working Group. With the same test arrangement in use, this report focuses on comparing the influences of ac and dc corona-ozone exposures on high temperature vulcanized (HTV) silicone rubbers. For this purpose, two types of HTV materials were used, each one characterized by different resistivity levels and tensile strength. For defining the treatment conditions, the ac and dc coronas were characterized by measuring the associated discharge current as well as the power released from the electrode. The intensity of ac corona discharge was found to be higher than that of dc corona, the latter being controlled by electrostatic charging of the treated polymeric surfaces, which also resulted in significant differences of the resulting ozone concentration. Experimental investigations after the treatments concentrated on evaluating dielectric properties (e.g. surface and volume resistivities, dielectric response (DR)), mechanical properties (e.g. tensile strength and elongation at break), as well as chemical and structural analyses (e.g. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR)). Results obtained from the measurements of dielectric properties indicated a strong sensitivity of surface resistivity to the treatments, though the impact of the dc corona remained less pronounced. On the other hand, the dielectric response and volume resistivity did not exhibit a high susceptibility to the exposure. No substantial differences were also found among the ac and dc corona treated samples as regards the mechanical properties. The XPS and FTIR analyses revealed proofs of surface oxidation for the samples treated by ac corona, while the samples treated by dc corona showed much less tendency for oxidation.

“…The results indicate, with corona exposure time the progressive increase in oxidation and hydroxyl group formation on the PDMS was observed. Moreno and Gorur [6,12,13,14] used single needle-plane electrode arrangement to study the corona degradation of the polymer samples. It has been shown that the severity of degradation increases with the relative humidity and the applied mechanical stress (bending stress).…”

Section: Introductionmentioning

confidence: 99%

“…Similarly a single needle-plate arrangement with tangential electrical stress has been used in [16], to accurately study the environmental factors on discharge intensity and the erosion of the material. With the advent of HVDC transmission lines and usage of polymeric insulators for HVDC applications, effort has been made in the literature [10,13,17] to study the effect of DC corona. Performance analysis of polymeric samples subjected to DC corona of both the polarities has been reported recently in [10].…”

Section: Introductionmentioning

confidence: 99%

Effect of coldfog on the corona induced degradation of silicone rubber samples

Reddy

2015

Corona is an unavoidable phenomena in high voltage power transmission system, in spite of suitably designed insulator accessories and transmission line hardware. It is a proven fact that the continuous occurrence of corona can subject the polymeric insulator to a severe degradation. Further, moisture in the air has a positive influence on the corona activity. This paper presents the methodology to evaluate the corona performance of the silicone rubber housing material with simultaneous application of cold fog. Analysis conducted after corona treatment by the Fourier Transform Infrared Spectroscopy (FTIR) present an interesting results showing a higher hydroxylation of sample surface under the moisture application than in the normal condition for both AC and DC excitation. FTIR spectrum also indicates the presence of nitric acid on the treated surface with coldfog application. Results obtained from SEM analysis are also presented.