Cellulose insulation in oil-filled power transformers: Part I - history and development
TL;DR: A brief discussion on the development of electrical grade paper/pressboard for transformer use from the raw materials, improvements made, and particularly the use of thermal upgrading agents to extend the useful life of transformers is presented in this article.
Abstract: This paper presents a brief discussion on the development of electrical grade paper/pressboard for transformer use from the raw materials, improvements made, and particularly the use of thermal upgrading agents to extend the useful life of transformers
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TL;DR: In this paper, acid catalyzed ageing of oil impregnated kraft paper has been studied experimentally and five carboxylic acids (formic, acetic, laevulinic, stearic and naphtenic acid) have been added to mineral oil to reach a neutralization value of 0.4 mg KOH/g.
Abstract: Acid catalyzed ageing of oil impregnated kraft paper has been studied experimentally. Five different carboxylic acids (formic, acetic, laevulinic, stearic and naphtenic acid) have been added to mineral oil to arrive at a neutralization value of 0.4 mg KOH/g. Thereafter, kraft paper of two different humidities has been allowed to equilibrate with the oil. The results show that the lower the molecular weight of the carboxylic acids is the more is absorbed by the paper. Furthermore, a clear synergy for the paper ageing rates between moisture and the lower molecular weight acids is found, while for the higher molecular weight acids almost no effects were found. It is concluded that present techniques for measuring acidity of oils do not reflect these detailed conditions. It is suggested to introduce a new measuring technique for neutralization value where water rinsing is used to identify the content of low molecular weight, water soluble acids.
173 citations
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...without oxygen, water or contaminants present) [1]....
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TL;DR: In this article, the authors proposed a preventive maintenance technique for power transformers, such as DGA, thermal monitoring, partial discharge measurement, capacitance and tan delta measurements, frequency response analysis, etc., to identify problems at an early stage before a catastrophic failure occurs.
Abstract: ower transformers are one of the most expensive elements in a power system, and their failure is a very costly event. Power transformers are mainly involved in energy transmission and distribution. Unplanned power transformer outages have considerable economic impact on the operation of electric power networks. To have reliable operation of transformers, it is necessary to identify problems at an early stage before a catastrophic failure occurs. In spite of corrective and predictive maintenance, preventive maintenance is gaining due importance in the modern era, and it must be taken into account to obtain the highest reliability of power apparatus such as power transformers. The well-known preventive maintenance techniques such as dissolved gas analysis (DGA), thermal monitoring, partial discharge measurement, capacitance and tan delta measurements, frequency response analysis, etc. are performed on transformers for a specific type of problem. DGA is a very efficient and reliable tool for the earliest detection of inception faults in transformer and other electrical equipment using insulating oil. Condition monitoring of electrical equipment, such as transformers, helps users in many ways such as planning of maintenance schedule, obtaining knowledge of the health of equipment, estimating the remaining service life of equipment, finding areas of further improvement, refining product specification, etc. Kraft paper (cellulose) immersed in mineral oil is used as the insulation system for the copper windings in large power transformers. As the system ages under load, the paper and oil can degrade, potentially leading to catastrophic failure. Partial discharge (PD) is an important tool for improving the reliability of HV insulation systems. It is a very sensitive and nondestructive method of evaluation of the health of the insulation of any HV equipment. PD always is associated with the degradation of insulation systems in HV equipment. Therefore, PDs need to be detected, measured, located, and reduced to a safe value so that the quality of the insulation system is not affected.
109 citations
TL;DR: In this paper, a case for allowing higher temperatures in transformers filled with natural ester fluids was made and the authors provided a review of data from aging studies performed on cellulose (both Kraft paper and pressboard) impregnated separately in mineral oil and BIOTEMP (ABB, USA), a high oleic sunflower based fluid.
Abstract: The article makes a case for allowing higher temperatures in transformers filled with natural ester fluids. This article will first provide a review of data from aging studies performed on cellulose (both Kraft paper and pressboard) impregnated separately in mineral oil and BIOTEMP (ABB, USA), a high oleic sunflower based fluid. Next, possible mechanisms that explain the differences in aging behavior will be discussed. The article concludes with recommendations for new temperature limits for BIOTEMP-impregnated transformers in comparison with mineral-oil-impregnated transformers.
102 citations
Cites background or methods from "Cellulose insulation in oil-filled ..."
...For the given equilibrium temperature, the relative humidity in the paper is estimated from Oommen’s version of the moisture sorption curves for cellulose (see Figure 15) [19]....
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...Oommen’s redrawing of moisture in wood pulp as a function of relative humidity of the ambient by Jeffries [19]....
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TL;DR: A comprehensive literature review on the applications of nanotechnology concepts for transformers, especially investigations related to insulating materials, dielectric fluids, outdoor insulators, monitoring systems and other components is presented in this article.
90 citations
TL;DR: In this paper, the dielectric properties of two nanocellulose types from wood, namely, nanofibrillated cellulose (NFC), and algae, viz., Cladophora cellulose, for electrical insulator applications were characterized with X-ray diffraction, nitrogen gas and moisture sorption isotherms.
Abstract: Cellulose is one of the oldest electrically insulating materials used in oil-filled high-power transformers and cables. However, reports on the dielectric properties of nanocellulose for electrical insulator applications are scarce. The aim of this study was to characterize the dielectric properties of two nanocellulose types from wood, viz., nanofibrillated cellulose (NFC), and algae, viz., Cladophora cellulose, for electrical insulator applications. The cellulose materials were characterized with X-ray diffraction, nitrogen gas and moisture sorption isotherms, helium pycnometry, mechanical testing, and dielectric spectroscopy at various relative humidities. The algae nanocellulose sample was more crystalline and had a lower moisture sorption capacity at low and moderate relative humidities, compared to NFC. On the other hand, it was much more porous, which resulted in lower strength and higher dielectric loss than for NFC. It is concluded that the solid-state properties of nanocellulose may have a substantial impact on the dielectric properties of electrical insulator applications.
78 citations
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TL;DR: In this article, a laboratory method for evaluating the thermal stability of chemically treated insulating paper is presented that measures the performance at various stages of deterioration, makes direct numerical comparisons, and can be used to establish specifications for the treated paper used to build 65°C-rise transformers.
Abstract: Transformers with a variety of chemically treated insulating papers are being offered for 65°C operation. However, there are no industry standards for qualifying treated insulation for the new rating and it is impossible to compare the performance of different brands of insulation on the basis of published literature because of differences in the test conditions. A laboratory method, for evaluating the thermal stability of insulating paper, is presented that measures the performance at various stages of deterioration, makes direct numerical comparisons, and can be used to establish specifications for the treated paper used to build 65°C-rise transformers. Insulating paper is aged in oil in a sealed cylinder in the presence of copper, iron, and carefully controlled amounts of oxygen and water. Deterioration, as measured by loss in tensile and bursting strength, is plotted against time for each temperature. Insulation life is then plotted as a function of temperature. Evolution of gases is also measured. Tests indicate there are significant differences in the performance of the brands of treated insulation tested. The effects of water, oxygen, and competitive brands of transformer oil on insulation life can be studied independently.
26 citations
TL;DR: In this paper, the basic elements of transformers, including two independent coils and a closed iron core, are described and compared to the transformer energy distribution networks that are used today, from experimental devices of the 1830s to the first transformer systems of the 1880s.
Abstract: he apparatus Michael Faraday constructed in 1831, by which he invented electromagnetic induction, contained all basic elements of transformers: two independent coils and a closed iron core. Nevertheless, another 54 years passed before the appearance of the transformers and transformer energy distribution networks that are generally used today. From experimental devices of the 1830s to the first transformer systems of the 1880s
25 citations
25 citations
"Cellulose insulation in oil-filled ..." refers background in this paper
...Kohan of Bell Telephone Laboratories in New York wrote an article in AIEE Transactions on cellulose as an insulating material for various electrical applications: paper capacitors, paper-insulated power cables, telephone cables [1]....
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TL;DR: In this article, a 100-year review examines the development of electrical insulation subdivided into materials, test methods and standards, and concludes that electrical insulation can be classified into three categories:
Abstract: This 100-year review examines the development of electrical insulation subdivided into materials, test methods and standards.
19 citations
TL;DR: A brief history of the early days of the transformer's development is presented in this paper, where the first commercial installation of a transformer was celebrated 75 years ago, and the first transformer was installed in a commercial building.
Abstract: Last year marked the 75th anniversary of the first commercial installation of the transformer. In this article a brief history of the) early days of the transformer's development is presented.
19 citations