Quantitative analysis ageing status of natural ester-paper insulation and mineral oil-paper insulation by polarization/depolarization current

Abstract

Polarization and Depolarization Current (PDC) technique is an effective tool to assess the condition of oil-paper insulation system in power transformers. So far the PDC behaviors of mineral oil-paper insulation have been widely investigated. However, with the increasing number of transformer choosing natural ester as its insulation oil, it is important to investigate the PDC characteristics of natural ester-paper insulation to see whether the PDC technique can also be used to assess the condition of new insulation system using natural ester in transformers accurately. In this research, natural esterpaper insulation sample and mineral oil-paper insulation sample were subjected to thermally accelerated ageing experiment at 110 °C for 120 days. The PDC characteristics of natural ester-paper insulation sample and mineral oil-paper insulation sample were compared over the ageing process. A new method for assessing the ageing condition of the oil-paper insulation in terms of the depolarization charge quantity was proposed. Results show that the polarization/depolarization current of natural ester-paper insulation sample is higher than that of mineral oil-paper insulation sample with the same ageing intervals. The depolarization charge quantity of both kinds of oil-paper insulation sample is very sensitive to their ageing conditions. There is an exponential relation between the stable depolarization charge quantity of both kinds of oil-paper insulation sample and the degree of polymerization (DP) of paper. The depolarization charge quantity can be used to predict the ageing condition of oil-paper insulation providing the measurement temperature is kept the same.

Thermally Accelerated Aging of Insulation Paper for Transformers with Different Insulating Liquids

“…The largest differences between esters and oils are in the range between 400-200 DP. In the studies [19,[40][41][42] it was shown that the paper ages more slowly in esters than in insulating oils. The reason for this is the assumption that esters dry out the paper due to their higher water solubility and thus reduce the hydrolysis processes of the paper.…”

Effect of Moisture on the Thermal Conductivity of Cellulose and Aramid Paper Impregnated with Various Dielectric Liquids

“…The insulation system is a type of "transformer heart". Due to the fact that it consists of solid (cellulose and aramid paper) and liquid (electrical insulating liquid), it may degrade mainly due to thermal stresses, but also electrical, mechanical, and chemical stresses occurring in the transformer operating state [8,9]. As a consequence, it may lead to transformer failure, i.e., affect its operational safety [10,11].…”

Aging Life Evaluation of Coal Mining Flexible EPR Cables Under Multi-Stresses

“…In addition, more attention is paid on the application of Polarization and Depolarization Current (PDC) method to evaluate the insulation state. J. Hao evaluated the natural ester-paper insulation and mineral oil-paper insulation and concluded that an exponential relation between the stable depolarization charge quantity of both kinds of oil-paper insulation sample and the degree of polymerization of paper could be obtained [11]. Based on PDC, G. Ye analyzed the aging degree of XLPE cables with water trees.…”