Pressboard

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

Frequency dependent propagation characteristics of partial discharge acoustic emission signal

Abstract: Oil pressboard insulation used in transformer deteriorates due to partial discharge (PD) leading to premature failure. Online monitoring of PDs can reduce the risk of catastrophic failure of transformers. Being non invasive and non interference prone, acoustic technique based PD on-line monitoring is advantageous. Acoustic emission (AE) signal produced by PD are detected by sensors mounted on the tank surface. AE signal attenuates while propagating from source to sensors. This attenuation is frequency dependent. Higher frequency component attenuates more than lower frequency components. PDs are classified according to frequency components of PDAE signal. This paper presents experimental results and analysis for frequency dependent propagation characterization of PDAE signal of laboratory simulated PDs in oil pressboard insulation system using point plane electrode system. The measured PDAE signals are analyzed using Discrete Wavelet Transform (DWT). The results highlight the possible use of frequency dependent propagation characteristics of PDAE signal for source location and for avoidance of misclassification.

Moisture and temperature effects on power transformer winding clamping pressure

Abstract: This paper presents findings from a finite element modelling based simulation study conducted to understand the moisture and temperature dependency of power transformer winding clamping pressure. Set of laboratory experiments were used to measure moisture dependent mechanical properties of high-density pressboard. First, 400 kVA disc type transformer winding was simulated to separately study the effects of moisture and temperature on clamping pressure. After that, fluctuations in clamping pressure under the combined effects of moisture and temperature of a field-installed autotransformer were studied. Simulation results revealed that winding clamping pressure is highly dependent on both temperature and moisture content. Finally, it was concluded that inclusion of moisture and temperature effect is important when analysing the results of winding clamping pressure estimation techniques.

Characteristics of Oil-pressboard Insulation Under Polarity Reversal Voltage

Abstract: The failure often happened to the oil-pressboard insulation in converter transformer during the polarity reversal voltage testIn order to look for the causes,the polarity reversal characteristics of the oil-pressboard insulation were analyzed by the RC modelA three-electrode test model and a type of polarity reversal voltage experiment unit were designedThe characteristics of mean currents and breakdown voltages of the oil-pressboard insulation were experimentally studied under different polarity reversal waysThrough analysis on experiment results and comparison with analytical results,it is indicated that the relationship between residual currents received in test and applied voltages is linear scalingThe initial values of absorption currents increase along with the applied voltages in an exponential law,and the attenuation function is an exponential function with a power function variable of time,which is different from rules determined by the RC modelBreakdown voltages decrease clearly with the increasing of the polarity reversal speedThe accumulated charges also increase along with the increasing of applied voltages in an exponential lawBased on the results,it is considered that the differences of changing regulations of absorption currents are due to the changes of strength and polarity of the internal electric field formed by space chargesThe reason causing the breakdown happened easily to the oil-pressboard insulation by the polarity reversal is the rapid increase of electric field in oil immersed pressboard

Breakdown Characteristics of Oil-pressboard Insulation in Converter Transformer Under Composite Electric Field and Its Test Method

Abstract: In order to achieve the breakdown characteristics of the oil-pressboard insulation in converter transformer under combined AC-DC electric field,breakdown characteristics of transformer oil gap,oil-impregnated pressboard and oil-pressboard complex insulation under composite electric fields,including AC,DC and combined AC-DC electric field,are tested.Results show that breakdown field strength of oil gap hardly changes with the variation of AC voltage components.Breakdown field strength of oil-impregnated pressboard decreases rapidly with the increase of AC voltage components.With the influence of the characteristics of oil-impregnated pressboard,the breakdown field strength of oil-pressboard complex insulation increases dramatically with the decrease of AC voltage components.It is demonstrated that the breakdown field strength of oil gap is almost independent of AC voltage components,but that of oil-impregnated pressboard is highly influenced by AC voltage components.Accordingly,the effectiveness of AC and DC voltage tests on converter transformer is further discussed.It is found that the ceiling voltages which occur on oil gap and oil-impregnated pressboard of the converter transformer main insulation under operating voltage are still combined AC-DC voltages.The requirements of voltage amplitude of AC or DC voltage test can be satisfied,but the waveform is different from that of the operating voltage subjected by insulation.It is concluded that applying AC voltage test to check the oil gap insulation dielectric strength is effective.However,applying DC voltage test to check the oil-impregnated pressboard insulation dielectric strength is not adequate.