Pressboard

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

Comparison of partial discharge inception voltages for ester and mineral oils under divergent fields

Abstract: Ester oils are making their way into the transformer market, but still some doubts exist about their ability to be successful fluids for high and extra-high voltage transformers. In this paper, we compare the PDIV of two commercially available fluids: a natural ester and mineral oil. Two different setups were considered: Point to plane in oil and point to plane on a pressboard sheet immersed in oil. Fluids and pressboard sheets were fully conditioned prior testing. Results suggest that ester oils perform slightly better with simple point-to-plane electrodes, independently of the gap length. When testing oil/plane electrode configurations with pressboard, ester oils perform much better at short gaps. This behavior has been explained considering the hydrophilicity of ester oils, which helps in further drying the pressboard prior testing. Therefore, ester oils could prove superior to mineral oils in suppressing creeping discharges.

Characteristics of leakage current during surface disharge at the oil-pressboard interface

Abstract: Surface discharge at the oil-pressboard interface leads to the development of a conducting path that is generally accepted as white marks due to localized heating. The visible white marks are believed to be due to partial discharge (PD) energy that is high enough to dry out the pressboard through vaporizing the moisture and breaking oil molecules to generate gases in the pressboard pores. A long period of electrical stress applied to a surface discharge experiment using a needle-bar electrode configuration has led to the formation of full-gap white marks on the pressboard surface that bridged the needle tip and earth bar. During the surface discharge, leakage current may occur intermittently that sometimes is visible in the form of full discharge of arcing at the oil-pressboard interface bridging the needle tip and earth bar. This condition is expected to be similar to that of dry-band arcing from inclined-plane tracking experiments for outdoor insulation. This paper explains the surface discharge experiment and details the obtained leakage current characteristics in terms of waveforms and frequency spectra. Correlation between leakage current measurements using a shunt resistor and PD signal detection has been undertaken in order to identify the useful information for condition monitoring of surface discharge in a large transformer. An equivalent circuit to represent the leakage current occurrence at the oil-pressboard interface without considering the superimposed pulses due to individual PD events is also proposed. The effect of moisture on the experimental results is also discussed

Charge behavior in flowing oil at oil/pressboard interface by electro-optic field measurement

Abstract: In this paper, the authors directly measure the electric field strength in an oil/pressboard composite insulation system using an electro-optic method of Kerr effect. They investigate electric field distribution in both flowing uncharged and charged oil by flow electrification. From the measurement results, they quantitatively discuss the electric field distribution and the charge behavior.

Creepage discharge performance for high moisture pressboard

Abstract: To research the creepage performance of high moisture pressboard, possible high moisture of pressboard in service power transformer has been analyzed, a creepage discharge simulation and test equipment and measurement system have been set up in laboratory, which were consisted of creepage discharge model, test tank, UHF sensor, gas-phase chromatographic instrument and partial discharge detector. Creepage discharge growth from inception to stop has been simulated by raised voltage step by step up to 50kV, ultra high frequency signal, apparent discharge magnitude and dissolved gases in oil have been measured in the growth. The results show that moisture of pressboard in part may reach 7% in service power transformer; creepage discharge inception voltage has a remarkable decrease under this high moisture; creepage discharge appeared at small oil gap firstly and bright spark can been observed; creepage discharge was intermittent and even stop at some time; lots of bubbles were generated in the creepage growth; C2H2 and H2 generated by creepage discharge was very high.