Pressboard

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

Partial Discharge Characteristics in Pre-Breakdown Processes of Oil-Pressboard Insulation with Needle-Plate Defect Under AC-DC Combined Voltage

Abstract: The PD characteristics of oil-pressboard insulation with needle-plate defect at AC-DC combined voltage are unstable. In this paper, the time-variation trends of PD characteristics in pre-breakdown process at AC-DC combined voltage are studied via the tests in oil-pressboard insulation with needle-plate defect. The average PD repetition rate and average PD amplitude decrease with the PD developing, and the time-variation trends of them can be divided into fluctuation type and monotone type. The average PD amplitude has no obvious polarity effect, the average PD repetition rate has a polarity effect. In equivalent time-frequency spectrograms, most points move towards arch top with the developing of pre-breakdown processes, where PD equivalent time is 1300–1600 ns and PD equivalent frequency is 7.5-10 MHz. PD equivalent time-frequency spectrograms can be divided into half-arched type and whole-arched type at the end of pre-breakdown processes. The defect in pressboard caused by PD is a possible reason for the appearance of whole-arched time-frequency spectrogram.

Effect of Moistures on Space Charge and Trap Level Characteristics of Oil-Impregnated Pressboards

Abstract: Oil-paper insulation as an irreplaceable insulation system in the electrical power transformer is inevitably suffering the water intrusion on working condition, which will make dielectric performance degraded and insulation aging accelerated. In high interest of explaining the deterioration effect of absorbing moisture on the dielectric properties of oil-paper insulation system and corresponding mechanism, the space charge and trap level characteristics are investigated for the specially prepared oil-impregnated pressboards with different moisture contents. The Pulsed Electro Acoustic and Isothermal Surface Potential Decay experiments are performed to test the space charge distributions and evaluate the trap level depths, respectively. It is indicated that the polarity of injected space charges is alternated with the decaying rate being raised when the absorbing moisture is aggravated in oil-impregnated pressboards. The charge carriers are more prone to be captured by the shallow-level traps that have been introduced by water permeation near pressboard surface than the intrinsic deep-level traps inside pressboard. The captured charge carries accounts for the significantly exacerbated space charge accumulation as manifested by the surface charges of oil-impregnated pressboards.

Characteristics of Interface Charge on Oil-impregnated Pressboard Under Non-uniform AC-DC Combined Electric Field

Abstract: Investigating the characteristics of interface charge on the oil impregnated pressboard under non-uniform AC-DC combined electric field is helpful to provide the basis for design of converter transformer insulation. In this paper, using needle plate electrode model, the interface charge density on oil-impregnated pressboard under non-uniform AC, DC and AC-DC combined electric field was be measured based on the electrostatic capacitance probe. The study found that the polarity of interface charge in the oil-impregnated pressboard was the same polarity of DC component of the AC-DC combined voltage in AC and DC voltage(RMS) ratio of 1:1 to 1:5 combined electric field, the interface charge density increased with stress time extension, with the AC component instantaneous electric field produced fluctuations similar to power frequency voltage, and the maximum value could reached 1.8 times of the charge density average value. So the converter transformer insulation design couldn't ignored this effect.

Resistivity of pressboard immersed in mineral insulation oil

Abstract: The pressboard is an important solid insulation dielectric in AC-DC converter transformers. Thus, it is very significant to understand the dielectric properties of the oil-impregnated pressboard. In this paper, the volume resistivities of oil-impregnated pressboard under different conditions have been systematically investigated. The pressboard was immersed in two kinds of mineral insulation oil, respectively. The measuring device of resistivity was full of oil and isolated from outside. All samples were measured at temperature range of 25–80°C under the field strength range of 1–30kV/mm. The influences of the temperature and the field strength on the resistivity of oil-impregnated pressboard have been investigated. The results of the volume resistivity of oil-impregnated pressboard showed that the resistivity of oil-impregnated pressboard decreased with the increase of temperature, and the activation eneregy increased with the increase of field strength. Meanwhile, with the increase of field strength, the resistivity changed slightly at first and then decreased significantly.

Electric heat sealing machine for plastic bags

Abstract: The utility model discloses an electric heat sealing machine for plastic bags, including fixed plate, drive belt, pneumatic cylinder and collecting box, the fixed drive belt that is equipped with in the bottom of fixed plate, the top of drive belt is equipped with the hot pressboard, the inside electric heat piece that is equipped with of hot pressboard, one side of drive belt is fixed and is equipped with the collecting box, is fixed with the plectrum on the tank wall of collecting box one side, and the bottom fixed mounting of horizontal pole has the fan. The utility model discloses a be equipped with the electric heat piece in the inside of hot pressboard, the electric heat piece generates heat, heat conduction is to the surface of hot pressboard, required temperature had both been guaranteed, direct and the plastic bag contact of electric heat piece has been avoided again, cause the high temperature, messenger's plastic bag melts, bottom fixed mounting through at the horizontal pole has the fan, and the fan is towards the collecting box, the plastic bag that makes the whereabouts is under the air current effect in all by propelling movement to collecting box, prevent that the plastic bag from descending slowly and lightly in the outside of collecting box, and simultaneously, cold wind cools off the plastic bag, prevent that the plastic bag from being taken place to bond byhot pressed position and other plastic bags.