Improved method for aging assessment of winding hot-spot insulation of transformer based on the 2-FAL concentration in oil

• Published in: International journal of electrical power & energy systems Vol. 112; pp. 191 - 198
• Main Authors: Sun, Weidong, Yang, Lijun, Zare, Firuz, Lin, Yuandi, Cheng, Zhidong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2019
• Subjects: 2-FAL total generation; Hot spot; Insulation paper; Thermal aging assessment; Unequal temperature distribution; Thermal aging assessment; Insulation paper; Hot spot; Unequal temperature distribution; 2-FAL total generation
• ISSN: 0142-0615; 1879-3517
• DOI: 10.1016/j.ijepes.2019.04.026

•A linear relationship between 2-FAL total generation and (1/DPt-1/DP0) is obtained.•Method of 2-FAL concentration in oil under unequal temperature distribution is obtained.•Assessment of winding hot-spot DP based on 2-FAL concentration in oil is obtained.•The assessment is verified by aging experiment with unequal temperature distribution. 2-furfuraldehyde (2-FAL) is widely accepted as a chemical marker to indicate the degradation of cellulose insulation in oil-impregnated transformers. However, the application of 2-FAL in the aging diagnosis of transformers in operation is ineffective. The excessive dispersion of 2-FAL concentration measured in transformers is caused by many influence factors. In addition, the 2-FAL concentration in oil cannot indicate the aging of the most serious point given the temperature distribution along the winding height, that is, the insulation at the hot spot of a winding. To optimize the assessment, an improved method for the hot-spot insulation assessment based on the 2-FAL concentration in oil is proposed in this work. The 2-FAL generation in cellulose chain scission is firstly analyzed theoretically, and a new linear relationship between (1/DPt-1/DP0) and 2-FAL total generation is obtained. Moreover, the 2-FAL partitioning between an insulation paper and mineral oil influenced by temperature, moisture, and aging status in total is considered. Second, by considering the linear relationship and the 2-FAL partitioning, an equation between the insulation at hot-spot temperature and the 2-FAL concentration in oil is established for the thermal aging under unequal temperature distribution condition. Finally, to verify the proposed method, a testing platform is introduced to conduct the thermal aging experiment with temperature gradients. The proposed method demonstrates better assessment results than the conventional thermal aging test at constant temperature.