Pressboard

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

Influential factor analysis and computation on electric field of converter transformer barrier

Abstract: Bushing and barrier system are the critical components in ultra high voltage (UHV) converter transformer for safe operation. Electric field distributions within bushing and barrier system are complicated in UHV converter transformer under combined AC and DC voltages, which, as a consequence, results in some technical difficulties in insulation structure design and manufacture. The paper presents the FEM electric field simulation of busing barrier structure under AC, DC and polarity reversal operation voltages. Firstly, the research results show that transformer oil with lower relative dielectric constant undertakes higher field strength under the AC voltage, whilst the insulating pressboard with higher resistivity bears higher field strength under the DC voltage, and the maximum field strength occurs in the insulating coating on the shielding ring surface. Moreover, extremely high field strength appears in transformer oil due to the space charge accumulation during voltage polarity reversal. Secondly, the research indicates that temperature has a big influence on electric field distribution of barrier system under DC voltage, specifically, with reduction of temperature the electric field distribution among oil and pressboard becomes increasingly uneven. Finally, the feasibility of applying nonlinear insulating pressboard to replace tradition pressboard in barrier system insulation structure is discussed and concludes that the nonlinear pressboard could improve electric field distribution dramatically.

Relationship between carbonized traces and space charges in oil-paper insulation

Abstract: Among all the types of transformer insulation deterioration, partial discharge is relatively a direct one that may lead to carbon traces which have negative effect on insulation. We believe that the relationship between the trace length and total appearance charge of partial discharges is a key to diagnose the oil paper insulation's remained life, even though the carbon trace in paper or pressboard cannot be seen directly like the transparent material such as XLPE. In this paper, we put forward an electrical method based on the hypothesis that the space charges just stay where the partial discharge happened before. Based on a distributed potential measuring system, we pay attention to carbon traces developed in a single electrical tree. After a series of high voltage experiments, we calculate the position of the space charges by their electric field and then we get the trace length by the farthest space charges. Finally, we get the result of experiment consisted with that of the theory calculations.

Surface flashover studies on precompressed pressboard insulation under superimposed AC/DC voltages

Abstract: The scale down models of pre-compressed mineral oil insulation system have been studied under surface flashover of the surface of insulation. The experimental investigations have been dealt with for conventional AC, DC and superimposed voltages of AC/DC at different electrode gap distances. Two types of models using cylindrical embedded electrodes and stuck electrodes on the surface are employed. The studies relating to different conditions of the insulation system namely dry pressboard, impregnated pressboard in air medium, impregnated pressboard in oil medium are detailed. The surface flashover voltages under AC, DC and superimposed voltages have predominant effect on small electrode gaps causing sufficient damage to the surface of insulation. The time to failure of insulation due to discharges are presented. The discharges are more severe on dry pressboard as compared to oil impregnated pressboard.

Effect of nanoparticles on streamer propagation and breakdown of vegetable oil-pressboard interface in non-uniform electric field

Abstract: Electrical equipment is always subjected to various of operating conduction and voltage waves which cause insulation failure on the surface of pressboard (PB). In this paper, pre-breakdown streamers of surface discharge on the interface of PB in vegetable oil based Fe3O4 nanofluids (NFs) were observed by the shadowgraph method under lightning impulse voltage. The images indicate that streamers of NFs impregnated PB show more branches than that of pure oil impregnated PB. The stopping length of streamers propagation is calculated by shadowgraph images for NFs and pure oil. Results suggest that the stopping length of NFs impregnated PB is shorter under the same extra voltage. Secondary reverse streamer is generated at the dissipation process by the reverse electric field, which is caused by residual space charge imparted by primary streamer. Results indicate that the Fe3O4 nanoparticles have reduced the length of secondary reverse streamer. The positive and negative lightning breakdown voltage of Fe3O4 NFs impregnated PB is increased by 24% and 12% at 50mm gap, respectively. In addition, nanoparticles have effectively changed the electric field distribution resulting in the alleviation of streamer concentrated along the parallel direction of PB, and increased the lightning impulse breakdown voltage.

Electrical breakdown in transformers due to flow electrification

Abstract: The authors describe physical modeling and experimental measurement techniques with well instrumented laboratory models that simulate physical processes at work in power transformers. Scenarios involving coupled interactions between electrical charging, chemistry, moisture, and temperature are being studied. In order to understand how these mechanisms can lead to transformer failure, well-controlled experimental facilities and sensors for continuous monitoring of charge density, oil conductivity, oil moisture, and temperature have been developed. Dielectrometry sensors for pressboard which can monitor pressboard conductivity and moisture distributions are also being developed. A Couette flow facility is used to experimentally model the flow regimes in transformers that are similar to pumps and plenums, primary flows through conduits, and secondary flows around spacer blocks, protuberances, and bends.