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Loading and Thermal Performance
Published in Leonard L. Grigsby, Electric Power Transformer Engineering, 2017
Robert F. Tillman, Don A. Duckett
With overly conservative loading practices, cellulose insulation life due to thermal stress is practically limitless, theoretically more than 1000 years. In practice, deterioration of accessories and nonactive parts limits the practical life of the transformer. These elements include the tank, gauges, valves, fans, radiators, bushings, LTCs, etc. The average, practical life of a transformer is probably 30–50 years. Many fail beyond economical repair before 30 years. Therefore, it is reasonable and responsible to allow some thermal aging of the cellulose insulation system. The key is to identify the risk. Loss of insulation life is seldom the real risk. Most of the time, risks other than loss of insulation life are the limiting characteristics.
Insulation materials
Published in Arthur Lyons, Materials for Architects and Builders, 2019
Cellulose insulation is manufactured from shredded recycled paper and other organic waste. It is treated with borax for flammability and smouldering resistance; this also makes it unattractive to vermin and resistant to insects, fungus and dry rot. Unlike mineral fibre and glassfibre insulation, it does not cause skin irritation during installation. Recycled cellulose has a low embodied energy compared to mineral and glassfibre insulation, and when removed from a building it may be recycled again or disposed of safely without creating toxic waste. (Treatment with the inorganic salt borax ensures that cellulose insulation conforms to BS 5803 Part 4: 1985 – Fire Test Class 1 and Smoulder Test Class B2.)
Foam forming of fiber products: a review
Published in Journal of Dispersion Science and Technology, 2020
Tuomo Hjelt, Jukka A. Ketoja, Harri Kiiskinen, Antti I. Koponen, Elina Pääkkönen
Building products should meet fire safety regulations. The Euroclass is a classification system for building products based on the reaction-to-fire performance and used widely in the member countries of the EU. In the Euroclass system, A1 and A2 are noncombustible materials and materials certified from B to F are combustible in ascending order. One challenge is that poor reaction-to-fire properties of foam-formed materials need to be improved to meet the fire safety regulations. Zheng et al.[160–162] showed that foamed cellulose insulation panels with commercial fire retardants (20% expandable graphite or 25% synergetic) passed fire class E according to the standard EN 13501-1. They also tested if coating of foam-formed materials would improve fire retardancy. A few bio-based fire retardants (sulfonated kraft lignin, kraft lignin, and nanoclay) and commercial fire retardants were mixed with MFC binder. The cellulose thermal insulation panels were then coated with those formulations. Nanoclay-coated samples showed the best fire retardancy properties. The coatings, however, increased the thermal conductivity compared to the reference without coating.
Embodied energy data implications for optimal specification of building envelopes
Published in Building Research & Information, 2020
Shahaboddin Resalati, Christopher C. Kendrick, Callum Hill
Analysing the GWP results (Figure 6) demonstrate that there is a clear distinction between different insulation groups (e.g. MW and GW with similar values compared with hydrocarbon-based insulation materials such as EPS, XPS, PU and PF). Amongst each group there is no significant statistical difference in the median GWP per unit weight values. This is also in line with the findings in the Hill et al. (2018) study. It is evident that although median points are very close in all groups, the ranges of probability distribution for PU and MW are considerably larger than those for XPS and GW respectively. The EE values however show slightly different scenarios. For example, the associated EE values for EPS are significantly higher than those of the same nature such as XPS and PU. Also the median EE values for cellulose insulation escalate to almost similar values to MW median points. The probability distribution for EE values for cellulose products cover a wider range compared with all other insulation types due to the distinct nature of the products categorized under the same insulation group.
Assessment on Oil-Paper Insulation Aging of Transformer Based on Dielectric Response Model
Published in Electric Power Components and Systems, 2019
Mingze Zhang, Ji Liu, Menghan Yin, Haifeng Jia, Jialu Lv
The polarization of transformer oil is mainly electronic polarization, the proportion of the relaxation polarization is small [21]. While the polarization of the oil-impregnated paper is composed of two parts: the electronic polarization and relaxation polarization. With the aging of oil- impregnated paper, the major molecular chains of cellulose insulation paper are broken, and the polar substances such as glucose and organic acids are generated. So relaxation polarization has a major proportion. Each polar molecule has its own relaxation time, the aging leads to increase of the polar small molecules and it will inevitably increase the dispersion degree of relaxation time. Therefore, in Figure 8(a) changing law of β of oil-impregnated paper is more obvious than the transformer oil. Meanwhile, the appearance of the polarity of small molecules increases dielectric polarization degree, which causes the increase of static permittivity (εs). The optical frequency permittivity (ε∞) is basically unchanged in same frequency range. Therefore, in Figure 8(b) values of Δε increases with aging time. In addition, with the increase of the aging time, the dielectric strength of oil-paper insulation is reduced, and the relaxation polarization is easier to be established. The process mentioned above illustrates the phenomenon in Figure 8(c) which relaxation time τ decreases gradually with the increase of the aging time. There is an obvious linear relationship between relaxation time and aging time.