Pressboard

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

Effects of DC prestressing on partial discharge in oil-impregnated pressboard insulation

Abstract: The AC (50 Hz) partial discharge (PD) characteristics of oil-impregnated pressboard (OIP) insulation are severely influenced by the DC voltage component in the converter transformer. Therefore, this study investigates the effect of different DC prestressing voltage (DCPV) amplitudes, prestressing time, and repetitions times of the applied AC voltage on the OIP insulation AC PD characteristics. Meanwhile, the space charge characteristics of distribution and dissipation are measured by pulsed electro-acoustic method. The experimental results show that the PD inception voltage (PDIV) and PD extinction voltage (PDEV) after DCPV were lower than that under AC voltage without DCPV. The PDIV decrease with higher DCPV at prestressing time from 30 to 60 min. But it increase with higher DCPV at prestressing time from 90 to 120 min. However, PDIV initially increase then decrease with the increasing repetition times of the applied AC voltage. The space charge distribution in 1 mm OIP insulation takes 60 min to reach a balanced condition. The residual space charge is relatively higher at a longer prestressing voltage time and higher DC voltage when the DC voltage was turn off. The PDIV and PDEV after DCPV is improved by Joule heating with longer prestressing time and higher DCPV. The space charge had negative effect on them.

Influence of surface roughness and thickness of pressboard on the charging characteristics of transformer oil

Abstract: Flow electrification has been found to be the principal cause of at least a dozen of failures of forced oil cooled power transformers. Despite considerable research efforts worldwide, the phenomena is still posing a threat to the service reliability. The present study carried out employing pressboards and presspapers of varying compositions, roughness and thickness, adopting Rotating Disc Electrode (RDE) and Rotating Cylindrical Electrode (RCE) systems revealed higher charging of Paraffinic based oil with pressboards composed of cotton pulp. Charging of the oil also increased with thickness of the solid insulating material. It was noticed that the charging of the oil increased with pressboards and presspapers with their surface calendered. The surface roughness (Ra) of pressboards investigated varied from 2 /spl mu/m-10 /spl mu/m. The investigation carried out using RDE failed to influence the charging of oil with roughness of pressboard. The study was carried out over rotational speed of 120-2000 rpm and temperature ranging from 27/spl deg/C-60/spl deg/C. >

Propagation of creepage discharge on solid insulator in insulating oil

Abstract: In relation to the optimum design of internal insulation for HV oil-filled power apparatus, studies of the creepage discharge on the surface of a solid insulator in insulating oil are of practical importance, so much research on this subject has been carried out. In the present paper, the propagation aspects of a creepage discharge on a hard glass (thickness: 3 mm) in insulating oil such as transformer oil are observed in detail under an impulse voltage condition in a point-plane electrode geometry, by using a high-speed schlieren method. In addition, turning our attention to a surface state of a pressboard, the creepage discharge on it is investigated by using a video camera and an image-fiber observation system.

Breakdown behavior of liquid-solid systems. A comprehensive model

Abstract: Composite Liquid-Solid Insulation systems have been used in transformers ever since. Optical investigations of the breakdown behavior were carried out over the last years using lightning impulse voltage. Gaps with Solid-liquid barrier systems show specific behavior in the breakdown process. Gap insulation ability increases with barriers and the breakdown process is influenced by the appearance of predischarges in the liquid gap with subsequent micro-discharges at the board surface. Micro-discharges lead to surface-charges on the board creating Lichtenberg-figures with charge-accumulation on the board surface. These charges in turn reinfluence streamer inception and propagation in the liquid. The breakdown process itself is due to degradation processes of the board and depends strongly on prestressing phenomena. In order to get towards a breakdown model for the composite insulation system, liquid-breakdown and solid-breakdown have to be modelled according to the chemico-physical properties of the liquid and the impregnated pressboard. Attention has to be paied to interdependences between the respective processes. This contribution will present a model for the breakdown-behavior of the composite system based on experimental findings. Influence of the investigated parameters will be discussed.