Study on streaming electrification properties of palm fatty acid ester (PFAE) oil due to aging

Palm fatty acid ester (PFAE) is mono ester oil which has better cooling property than mineral oil and other poly esters. Recently, natural ester has been tested on extra high voltage large power transformer. Large power transformers have a risk of streaming electrification. Many studies have been conducted to investigate streaming electrification properties of mineral oil immersed transformers and their countermeasures. However, streaming electrification properties of natural esters are rarely studied. Therefore, this paper presents a study on streaming electrification properties of PFAE due to aging. PFAE and mixed oils were prepared under several conditions. Aging test was conducted by heating the oil samples at 100 °C for 360, 720, 1080 and 1440 hours. The results show that heating causes various trends of volume resistivity and positive increases in electrostatic charging tendency (ECT) with respect to aging time. At initial state, ion dissociation on additive compound decreases volume resistivity and increases ECT. However, during the heating, the dissociation is not accelerated. Additive compound is dissociated into radicals to mitigate oxidation. In the mixture of 20% mineral oil and 80% PFAE, higher changes in volume resistivity and ECT indicate that degradation is more likely to occur in mineral oil part. In addition, air circumstance has effects on volume resistivity and ECT.