Topic
Pressboard
About: Pressboard is a research topic. Over the lifetime, 1123 publications have been published within this topic receiving 9089 citations.
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30 Sep 2001
TL;DR: In this paper, the authors studied the physical chemistry of charge generation in power transformers and found that the chemical composition of the board, with regard to their content in chemical functional groups (hydroxyl or carboxyl groups) or radical nature (lignin), as well as board manufacturing parameters (pulp refining, layer composition) and surface properties seem to be at the origin of the electrification phenomenon.
Abstract: As part of a research program in the field of flow electrification in power transformers, some fundamental studies have been undertaken on the physical chemistry of this phenomenon. The two main constituents involved in the process of charge generations are oil and pressboard. As oil composition is difficult to deal with, the choice has been made to understand the overall chemistry through the role played by the pressboard, whose composition is better mastered. In order to identify the chemical species in the pressboard responsible for the charge generation, in view of perfecting additives to neutralize the phenomenon, the French Institute of Pulp and Paper carried out modifications on commercial pressboards, and manufactured some others. Charge accumulation, measured from capacitive currents on insulated electrodes facing the pressboard ducts, has been observed for modified and manufactured pressboards with regard to oil flow rate and temperature. All the experiments have led to various behaviors in terms of kinetics and magnitude of the charge accumulation. The obtained results tend to prove that chemical composition of pressboards, with regard to their content in chemical functional groups (hydroxyl or carboxyl groups) or radical nature (lignin), as well as board manufacturing parameters (pulp refining, layer composition) and surface properties seem to be at the origin of the electrification phenomenon.
23 citations
01 Aug 2005
TL;DR: In this paper, the authors investigated the breakdown process in transformer oil/cellulose insulation under a LI (lightning impulse) voltage and showed that a streamer propagates from the needle-axis direction to that along the surface of the solid insulation and carries electrical charges onto the solid surface and thus redistributed the electric field in the insulation.
Abstract: The work contributes to the understanding of breakdown processes in transformer oil/cellulose insulation under a LI (lightning impulse) voltage. The breakdown mechanism associated with streamer propagation, space charge distribution, material properties and insulation geometry is studied. The observed phenomena lead to a qualitative model which adds insight into the breakdown process in composite transformer insulation. Oil-impregnated pressboard, paper or polymeric material was inserted into a needle/plane electrode geometry in which oil gap distances exist between the solid insulation and the electrodes. Breakdown processes related to streamers were observed both in the oil gap and on the surface of the solid. Experiments showed that two important phenomena occurred when a streamer was initiated in oil and propagated to the surface of a solid insulation: the streamer changed its propagation from the needle-axis direction to that along the surface of the solid insulation; the streamer carried electrical charges onto the solid surface and thus redistributed the electric field in the insulation. The breakdown data were compared with those from a turn-to-turn model of transformer windings. It is found that it is the "average field" in the solid insulation after streamer development that governs puncture of the solid. A streamer can also puncture the solid insulation with no discharge pattern being observed on its surface, which happened when a large ratio exists between length of the oil gap and thickness of the solid insulation. The breakdown process is related to material type of the solid insulation.
23 citations
TL;DR: In this article, a distributed parameter model was proposed to reveal the correlation between moisture distribution (under nonequilibrium conditions due to thermal transients) and dielectric response parameters (dielectric losses and permittivity).
Abstract: Dielectric response measurement has recently been adopted by utilities for evaluating moisture content in cellulose insulation (paper and pressboard) of transformers. Moisture distribution is highly dependent on temperature. Since the temperature inside a transformer may change during the dielectric response measurement, the moisture in the transformer’s cellulose and oil insulation can hardly attain an equilibrium state. Instead, moisture dynamics exist inside the transformer: 1) cellulose absorbs (desorbs) moisture from (to) oil with the changes in temperature and 2) moisture migrates inside cellulose due to a moisture gradient. This paper investigates moisture dynamics and its effect on the dielectric response of a transformer’s cellulose insulation. It proposes a distributed parameter model to reveal the correlation between moisture distribution (under nonequilibrium conditions due to thermal transients) and dielectric response parameters (dielectric losses and permittivity) of cellulose insulation. It then estimates these parameters under moisture nonequilibrium conditions. The accelerated ageing and moisture diffusion experiments are conducted on a prototype transformer to verify the proposed model. The methodology developed in this paper can help the proper interpretation of dielectric response measurement of field transformers under thermal transients.
22 citations
TL;DR: In this article, the surface discharge injected current was measured by using High Frequency Current Transformer (HFCT) and it was observed that the rise time of the current pulse is about 800ps.
Abstract: The surface discharge injected current were measured by using High Frequency Current Transformer (HFCT). It is observed that the rise time of the current pulse is about 800ps. In addition, the rise time of the current pulses has not altered in copper sulphide (CuS) diffused Oil Impregnated Pressboard (OIP) material, but the width of the current signal has increased with the increase in the amount of copper sulphide diffusion into the pressboard. It is confirmed that the injected current pulse radiates Ultra High Frequency (UHF) signal and the dominant frequency of the UHF signal formed due to the surface discharge injected current is about 0.9 GHz. The characteristic frequency contents of the UHF signal formed due to surface discharge activity is the same with the virgin and copper sulphide diffused pressboard material. The surface discharge inception voltage is high with the virgin specimen compared with copper sulphide diffused oil impregnated paper insulating material and is the same irrespective of the amount of diffusion of copper sulphide to it. The Phase Resolved Partial Discharge (PRPD) analysis indicates that at the point of surface discharge inception, the discharge occurs at the peak of the applied AC voltage and when the applied voltage magnitude is increased, the discharge occurs at the rising portion of the applied AC voltage. The characteristics of the surface discharges formed are the same with the copper sulphide diffused oil impregnated pressboard material. It is noticed that with increase in ageing time, a reduction in partial discharge magnitude is observed. Attenuated total reflectance Fourier transform infra-red spectroscopy (ATR-FTIR) analysis was carried out to understand the characteristic changes that occur in the degraded zone formed due to surface discharges. The measurement of surface charge indicates that ageing of oil impregnated paper material increases the surface charge accumulation. Energy Dispersive Spectroscopy (EDS) confirms the presence of copper and sulphur in the aged Oil Impregnated Pressboard material. The Atomic Absorption Spectroscopy (AAS) results indicate that the amount of copper content in pressboard material have increased with ageing time.
22 citations