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The strength of electrical insulation in gaseous compressed SF6 is determined by various parameters, like pressure, polarity, field homogeneity, surface roughness of the electrodes, particulate contamination, and voltage wave shape. The dependence of the involved physical phenomena on accessible design parameters, like e.g. pressure, geometry, is of interest for the prediction of partial discharge...
Dielectric response measurements are an important technique to characterize dielectric materials. However, the electrode arrangements as well as the accuracy of the measurement setup limit the precision of this characterization, especially in case of solid dielectric materials. An air reference method and a contact-free electrode arrangement are described in this paper to enhance the dielectric characterization...
A study of the emission spectra from discharges on an ice surface and a discussion of its implication on local thermodynamic equilibrium are presented. Rotational temperatures were measured using OH (A-X) emission bands. The variation of rotational temperature, which is similar to that of gas temperature with discharge current, was studied. The excitation temperature of the arc column was determined...
Partial discharge (PD) characteristics of hexadecane were studied in a needle-plane electrode geometry under AC field with a 20 μm tip radius tungsten needle. PD experiments were conducted on samples containing known concentrations of aromatic and corrosive sulfur compounds. Partial discharge inception voltage (PDIV), streamer repetition rates, and phase resolved PD (PRPD) patterns were acquired....
Composite insulators have been used in power system for more than 20 years in China. Compared to porcelain and glass insulators, the pollution flashover performance of composite insulators is better, whereas the icing flashover performance is worse. Shed configuration is a key factor that influences flashover voltage of composite insulators covered ice or snow in icing regions. The DC flashover tests...
The flashover phenomenon for the unilluminated case along the interface of solid dielectric in vacuum is the main factor which restricts the performance of high pulsed power devices, and there are plenty of investigations devoted into determining which parameters are important in predicting flashover behavior and the theoretical understanding involved in the process in the past several decades. In...
In this paper, polydimethylesiloxane (PDMS) as a candidate for high voltage insulation applications is investigated as to the aging behavior at different temperatures in air. Three models according to ISO 11346, to Gillen et al, and to Hoang and Lowe were applied to determine endurance limits in terms of a time-to-failure after aging in hot air. Aging was performed in air from 150 to 170°C. Tensile...
On the background of the peculiar technology problems with the external insulation of UHV dc equipment in China, caused by high altitude and heavy pollution, this paper presents the pollution flashover performance of full-scale ??800 kV converter station post insulators at actual high altitude area. The tests were carried out according to the solid layer method, and the 50% withstand voltage (U50%...
Transformer mineral oil has been replaced by alternative oils such as synthetic oil and natural esters due to their biodegradability and environmentally friendly nature. This paper presents performance of coconut oil as such an alternative. Generally, as the other alternative oils, coconut oil has high conductivity due to the presence of free fatty acids. In this study, three different types of coconut...
The presence of partial discharges is one of the most prominent indicators of defects and ongoing degradation processes of electrical insulation. As a high percentage of failures are associated with partial discharges, the need for the classification, extraction and evaluation of partial discharge signals is essential. Consequently, an electrical model of a breakdown void, modeled as part of the power...
The lightning protection design of a substation is generally based on the surge overvoltage incoming to the substation, which is generated by the back-flashover across an insulator string of the transmission tower that is closest to the substation and struck by a lightning return stroke. In this case, surges propagate along non-horizontal or non-uniform lines such as the tower and the inclined lines...
Partial discharge (PD) monitoring plays an important role in the maintenance of the high voltage (HV) apparatus, such as transformer and gas-insulated substation (GIS). In recent years, the ultra high frequency (UHF) method for PD detection arouses great interest of many researchers because of its high sensitivity and anti-interference capability. The coupling of UHF signal and process of the signal...
On-line Partial Discharge (PD) monitoring is being increasingly adopted in an effort to improve asset management of the vast network of MV and HV power cables. This paper presents a novel method for autonomous recognition of PD patterns recorded under conditions in which a phase-reference voltage waveform from the HV conductors is not available, as is often the case in on-line PD based insulation...
Bipolar charge transport (BCT) model has been widely used to simulate time/space evolution of space charges in insulating materials. The BCT simulations are performed to investigate the relationships between space charge accumulation and conduction, electroluminescence (EL), charge packet formation, electrical breakdown, and surface potential decay (SPD) properties. Accordingly, the charge advection-reaction...
Partial discharge (PD) diagnostics can be used to diagnose insulation defects in medium voltage cables and thereby inform required maintenance planning to extend the lifespan of ageing assets. High frequency current transformers (HFCT) installed on the earth strap at the cable termination are widely used to detect the fast varying pulses resulting from PD. Due to constructional reasons earth strap...
We present an efficient method of predicting the electric strength (ES) of insulating gases in comparison to sulfur hexafluoride. Different molecular properties (descriptors) of a comprehensive set of 67 predominantly electronegative or electron attaching molecules were calculated ab-initio by means of density functional theory (DFT). For the same list of molecules, we compiled a data set of experimental...
This paper presents a feature extraction algorithm for partial discharge (PD) pulses separation using S transform (ST)-based time-frequency representation. Firstly, the algorithm acquires a series of base vectors in the frequency domain and location vectors in the time domain obtained by applying a non-negative matrix factorization (NMF)-based matrix decomposition technique to compress ST amplitude...
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