Abstract
A high-temperature oil–paper insulation system offers an opportunity to improve the overloading capability of distribution transformers facing seasonal load variation. A high-temperature electrical insulation system (EIS) was chosen due to thermal calculation based on a typical loading curve on the China Southern Power Grid. In order to evaluate candidate high-temperature insulation systems, Nomex® T910 (aramid-enhanced cellulose) immersed in FR3 (natural ester) was investigated by a dual-temperature thermal aging test compared with a conventional insulation system, Kraft paper impregnated with mineral oil. Throughout the thermal aging test, mechanical, chemical, and dielectric parameters of both paper and insulating oil were investigated in each aging cycle. The thermal aging results determined that the thermal class of the FR3-T910 insulation system meets the request of overloading transformer needs.
Highlights
Urbanization in China has led to the population moving between urban and rural areas, which results in seasonally fluctuating electrical power demand, overloading rural transformers during the Chinese spring festival and plowing seasons
Cellulose is a kind of linear condensation polymer consisting of anhydroglucose; the degree of polymerization (DP) is the average number of glycosidic rings in a cellulose macromolecule [3]
Once mechanical fractures appear in the insulating paper, the winding will be directly exposed to the insulating oil, and electrical faults are more likely to occur
Summary
Urbanization in China has led to the population moving between urban and rural areas, which results in seasonally fluctuating electrical power demand, overloading rural transformers during the Chinese spring festival and plowing seasons. The adoption of higher-capacity transformers was considered by utilities to handle overloading. This decreases the normal loading rate and yields a lower efficiency. The State Grid Corporation of China published technical guidance for overloading rural transformers in 2014 [1], and identified the typical loading curve. China Southern Power Grid released a similar typical loading curve, shown in Figure 1 [2]. On the basis of the normal temperature-rise test requirements, the transformer should meet the requirement for continuous operation of 6 h at
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