Pressboard

About: Pressboard is a research topic. Over the lifetime, 1123 publications have been published within this topic receiving 9089 citations.

Quantitative aging assessment method for cellulose pressboard based on the interpretation of the dielectric response mechanism

Abstract: Cellulose pressboard is used as a key element in various power equipment insulation structures and determines the operational safety of electric equipment and power systems. This paper aims to increase the application of a pressboard aging assessment method based on frequency domain spectroscopy, a promising nondestructive method for power equipment diagnosis, through in-depth theoretical analysis and accurate data fitting. To achieve this purpose, first, based on classic theoretical models in the field of dielectric physics, a mathematical deduction is proposed to separate each dielectric process in the overlapping frequency band. Second, a novel analysis approach that considers both the pressboard dielectric response and the thermally stimulated current is proposed and demonstrated to be effective in determining the physical meaning of pressboard microscopic dielectric processes. Third, a function model based on a specific microscopic mechanism is established to fit the frequency domain spectra of pressboard samples with different aging degrees. Based on this approach, the variations in charge carrier motion characteristics in the frequency domain with increasing pressboard aging degree are clarified. Moreover, the function model provides characteristic parameters that are clearly related to the degree of polymerization of the material, which represents a quantitative method for evaluating the aging degree of cellulose pressboard by indirectly obtaining its frequency response curve.

Influence of temperature on developing process of surface flashover in oil-paper insulation under combined AC-DC voltage

Abstract: In order to study the influence of temperature on surface flashover behavior with oil-paper interface under combined AC-DC voltage, a discharge test assembly was established to investigate the influence of temperature on developing process of surface flashover of oil-paper interface from 25 °C to 90 °C. Based on impulse current method, the process of surface flashover of oil-paper interface under combined AC-DC voltage was studied by electrodes configurations that simulated the tangential electric field and radial electric field of surface of pressboard, in which the voltage was increased step-by-step. Meanwhile the partial discharge (PD) spectrums at whole flashover stages were studied. Moreover, high speed camera was used to record the whole process of surface flashover which was divided into 4 stages: (1)Inception stage, (2)Streamer stage, (3)Intermittent breakdown stage, (4) Surface flashover stage. The experiments results shown that flashover voltage and PD inception voltage at high temperature (HT) was lower than the voltage at low temperature (LT). The average amplitudes of PD at LT were lower than at HT. The growth rate and repetition rate of PD at HT was faster than at LT. It was easier to develop the flashover at oil-paper interface under combined AC and DC voltage at HT. So the flashover voltage was lower at HT. the surface of pressboard was destructed severely at HT, the track of surface discharge was obvious at HT.

On electric stresses at wedge-shaped oil gaps in power transformers with application to surface discharge and breakdown

Abstract: The problem of a high-voltage applied to a wedge-shaped oil gap in power transformers is considered as far as induced distortions and tangential electric stresses are concerned Near-tip distortions and electric stress concentration occur due to the essentially difference in the relative permittivity between the insulating oil and the pressboard When the magnitude of tangential electric stress intensity reaches a critical threshold value, surface discharge and breakdown occurs at the oil/pressboard interface In this work, a simplified computation model is developed for the quantitative analysis of the distribution of electric stress and the breakdown electric field strength in the wedge-shaped oil gap in power transformers The detailed computation results on the effects of pressboard permittivity and thickness on the surface discharge inception voltage are presented It shows that the surface discharge inception voltage is a function of pressboard permittivity and thickness; and the value of surface discharge inception voltage decreases with increasing dielectric permittivity

The Correlation between Surface Tracking and Partial Discharge Characteristics on Pressboard Surface Immersed in MIDEL eN

Abstract: This paper presents the investigation of the surface tracking on pressboard surface immersed in MIDEL eN oil. In this work, the development of surface discharge was analyzed by correlating the visual records of surface tracking on impregnated pressboard and the partial discharge (PD) activities. The PD activities during the surface tracking process were analyzed in terms of Phase Resolved Partial Discharge (PRPD) patterns. Throughout the experiment, surface discharge is found as the development of tree-like patterns in the form of white marks occurring on the oil-pressboard interface. This phenomenon is generally accepted as the drying out process that involves evaporation and decomposition of the oil molecules in the pressboard pores due to the surface discharge activities on the pressboard surface layer. The development of surface discharge on the pressboard surface can continue from minutes to months or even years until failure. Thus, condition monitoring system is important to characterize this type of faulty condition. The experimental results show that there is the decreasing trend of PD magnitude during the development of white mark hallway of a gap distance which is eventually suffered from an unexpected fault.

Measurement of moisture spatial profiles in transformer pressboard

Abstract: Moisture concentration was measured in a 1.5 mm thick transformer pressboard as a function of time and position during moisture diffusion process. A flexible interdigital three-wavelength sensor was used to provide the necessary information regarding pressboard dielectric properties at different depths from the sensor-pressboard interface. Results were obtained by processing the signals from the three-wavelength sensor, air humidity sensor, and thermocouple installed in the experimental chamber. Air-pressboard equilibrium curves were used to provide boundary conditions and the relative moisture level magnitude. The proposed technology has significant potential for measurement of diffusion processes in various dielectrics.