Pressboard

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

Space charge dynamics in oil and thick pressboard combined system under polarity reversal voltage

Abstract: In this study, the space charge dynamics in an oil and oil impregnated pressboard combined insulation system are investigated by the means of pulsed electroacoustic (PEA) technique under voltage polarity reversal conditions. To be closer to the real case in convertor transformers, a 1mm thick pressboard covered with a 0.5mm thick oil film were used as the testing sample. For comparison, three types of oil with different aging stages were used: fresh oil, medium aged oil and severely aged oil. The external electric field was firstly applied +10kV/mm for 1hour, then reversed to -10kV/mm in 1min period. After that, the -10kV/mm was applied for 1 hour. The results have clearly shown the impact of the oil film and the interface between oil and pressboard on charge dynamics under polarity reversal conditions. The electric field enhancement and the time constant of the 'mirror image effect' have been analyzed for different cases.

Study of Oil/Pressboard Creeping Discharges under Divergent AC Voltage—Part 1: Fundamental Phenomena and Influencing Factors

Abstract: This paper presents an experimental study of the fundamental phenomena of progressive creeping discharge as well as the influences of pressboard ageing and voltage amplitude under divergent AC voltages. A ramp-stress test is used to determine the partial discharge inception voltage (PDIV) and the flashover voltage of oil/pressboard interface versus pressboard ageing. Constant-stress tests are carried out to investigate the partial discharge (PD) behaviors, the pressboard surface temperature, and the oil-dissolved gases of progressive creeping discharges. It is found that the pressboard ageing affects only the interface PDIV. The progressive creeping discharges concentrate at the triple-junction and comprises probably oil corona discharges and surface discharges in pressboard dimples. If no pressboard damage is present, the progressive discharges exhibit in general a constant PD pattern but a diminishing intensity, and nevertheless can be sustained for the severely-aged pressboards under strong voltages. The underlying causes are correlated with the competing effects of pressboard ageing on interface moisture and the triple-junction field intensification. Gas analyses indicate the hydrogen is the principal faulty gas and the Duval's Triangle diagnoses the progressive creeping discharges as either low-energy or high-energy discharge fault. No pressboard overheating is observed during the discharges.

Effect of the oil-paper insulation aging on partial discharge characteristics in a hemispherical surface model

Abstract: To investigate the effect of aging on surface discharge of the pressboard on the shielding electrode at the end of bushing, a thermal aging preparation methods of different aging degrees of pressboard samples, surface defect model, and the associated hemisphere are designed and the step-up method is used for subsequent experimental work. Finally, the partial discharges (PDs) under different degrees of aging are compared and combined with Fourier Transform Infrared spectra and electric field simulation. Results show that the pre-discharge occurs mainly in the oil gap between the hemispherical electrode edge and the pressboard. The aging of the pressboard exerts no obvious effect on the discharge characteristics in the initial stage of PD; with the development of the discharge, the development of aging of pressboard leads to a higher electric field intensity acting over a greater area, the more intense the discharge, the faster the relative discharge increases and the larger its amplitude. This discharge will cause decomposition of the oil in the pores of the aging pressboard thus generating gas bubbles which will move as discharge develops. When the bubbles reach the surface of the pressboard, the local electric field intensity will increase and the discharge will become more intense.

Fractal analysis of creeping discharge propagating over pressboard immersed in mineral and vegetable oils

Abstract: The paper is aimed at the fractal analysis of the real (i.e., observed experimentally) creeping discharge patterns propagating over pressboard immersed in mineral and vegetable rape-seed oils, under lightning impulse voltages, using a pointplane electrode arrangement. By using the box counting method, we show that the discharge patterns present a fractal dimension D which depends on the thickness of pressboard (e) and the kind of oil; D decreases when e increases. The value of the density of branches increases when the thickness of pressboard decreases. D is generally higher in mineral oil than in vegetable rape-seed oil. This dependency on the thickness and nature of oil reveals the existence of a relation between the fractal dimension and the physical parameters.

Investigation on the performance of thermally aged natural ester fluid impregnated pressboard material

Abstract: This paper reports the key findings from an experimental study carried out on thermally aged natural ester fluid impregnated pressboard (EOIP) material. The results show that the surface discharge inception voltage (SDIV) with thermally aged EOIP material is higher under negative DC voltage compared with positive DC and AC voltage. The SDIV increases with AC voltage frequency and a minimal reduction in voltage was observed under harmonic AC voltages with different total harmonic distortion (THD). The rate of change in voltage due to ripple content in DC voltage affects the SDIV of EOIP material, initiating discharges at lower voltages. The UHF signals radiated during the surface discharge process have a bandwidth in the range 0.9 to 2 GHz. Surface potential variation studies indicated the formation of high trap sites and trap density due to thermal aging. A reduction in the oxidation onset temperature and the activation energy of thermal decomposition were observed with thermally aged EOIP material. A pyrolysis study showed high composition of levoglucosan and acidic residue with the thermally aged specimen, which reduces its degree of polymerization. Impedance spectroscopic analysis indicates a non-Debye type of relaxation with thermally aged EOIP material. The mobility and charge transfer characteristics were also inferred from the modulus spectroscopy which showed less change for thermally aged pressboard material.