Pressboard

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

Effect of Temperature on Space Charge Distribution of Oil–Paper Insulation under DC and Polarity Reversal Voltage

Abstract: The electric field distortion caused by space charge is an important factor affecting the operation reliability of oil–paper insulation in a converter transformer. To study the accumulation and decay characteristics of the space charge within oil-impregnated pressboard under DC and polarity reversal voltage, and consider the possible operating conditions of the converter transformer, the space charge behavior of oil-impregnated pressboard was measured by the pulsed electro-acoustic (PEA) method in the temperature range from −20 °C to 60 °C. The effect of temperature on the accumulation and decay characteristics of space charge is also analyzed. The space charge accumulated within the pressboard at low temperature is mainly homocharge injected by the electrode, while heterocharge formed by ion dissociation counteracts some of the homocharge at high temperature. Thus, the space charge of pressboard first increases, then decreases, with an increase in temperature. However, slow decay of the space charge causes severe distortion of the electric field distribution in the pressboard during voltage polarity reversal.

Precise Measurements of the Temperature Influence on the Complex Permittivity of Power Transformers Moistened Paper-Oil Insulation

Abstract: The reference characteristics of complex permittivity of the transformers insulation solid component were determined for use in the precise diagnostics of the power transformers insulation state. The solid component is a composite of cellulose, insulating oil and water nanoparticles. Measurements were made in the frequency range from 10−4 Hz to 5000 Hz at temperatures from 293.15 to 333.15 K. Uncertainty of temperature measurements was less than ±0.01 K. Pressboard impregnated with insulating oil with a water content of (5.0 ± 0.2) by weight moistened in a manner maximally similar to the moistening process in power transformers was investigated. It was found that there are two stages of changes in permittivity and imaginary permittivity components, occurring for low and high frequency. As the temperature increases, the frequency dependencies of the permittivity and imaginary permittivity component shifts to the higher frequency region. This phenomenon is related to the change of relaxation time with the increase in temperature. The values of relaxation time activation energies of the permittivity ΔWτe′ ≈ (0.827 ± 0.0094) eV and the imaginary permittivity component ΔWτe″ = 0.883 eV were determined. It was found that Cole-Cole charts for the first stage are asymmetric and similar to those described by the Dawidson–Cole relaxation. For stage two, the charts are arc-shaped, corresponding to the Cole-Cole relaxation. It has been established that in the moistened pressboard impregnated with insulating oil, there is an additional polarization mechanism associated with the occurrence of water in the form of nanodrops and the tunneling of electrons between them.

Predicting the remaining life of a transformer

Abstract: Method of assessing the remaining lifetime of a transformer operating at temperatures above IEC 60°C/65°C/78°C or IEEE 65°C/65°C/80°C comprising a core, a winding conductor covered by high temperature insulation material and pressboard material arranged as an insulation barrier and/or a supporting structure, wherein said covered winding conductor and said pressboard material are immersed in a fluid having a fire point of at least 300 °C, said method comprising the steps of: a) at least twice measuring the temperature of the fluid at its top surface and registering the time of each measurement; and b) assessing the remaining lifetime of the transformer as a function of the measured temperatures and the corresponding registered times, and/or a') obtaining a sample of pressboard material that has been in contact with the fluid at its top surface; and b') analysing the sample to assess the remaining lifetime of the transformer, wherein the high temperature insulation material is as defined in IEC 60076-14:2009 or IEEE 1276:1997.

Charge storage and transport in oil-impregnated pressboard at polarity reversal under HVDC

Abstract: Space charge plays an important role in the breakdown and conduction processes of a high voltage direct current (HVDC) insulation system. Electrical breakdown due to charge accumulation in transformer oil and pressboard can cause failures of power transformers, especially at DC polarity reversal. In this paper, we focus our attention on the charge accumulation and movement in an transformer-oil-impregnated pressboard under DC polarity reversal at 60/spl deg/C. Using a pressure wave propagation (PWP) technique, the distribution of space charge in the sample was measured both at stationary and transient conditions.

Influence of oil property on the space charge characteristics and electric field distortion in oil-paper insulation

Abstract: The formation of space charge in oil/paper insulation system can lead to material degradation in the high electric field region and affect system reliability. It is important to understand factors that affect space charge formation in oil/paper insulation system. All the researches on the space charge characteristics of oil-paper insulation are all based on the oil impregnated insulation paper. In this paper, the space charge dynamic behavior of the oil impregnated insulation pressboard and the mixed insulation with a combination of oil gap and oil impregnated insulation pressboard were both studied. The oil property effect on the charge and electric field distribution behavior were discussed. The injected charge in aged oil impregnated insulation pressboard has a higher migration rate than that in new oil impregnated insulation pressboard. Compared with the oil impregnated insulation pressboard, a lot of space charges accumulate at the interface between oil and pressboard, which leads to obvious electric field distortion in oil gap and in oil impregnated insulation pressboard. The charge injected in new oil-paper insulation is more difficult to dissipation than that in aged oil-paper insulation.