Conduction characteristics of MIDEL eN 1204 insulating liquid under DC non-uniform conditions

Wong, T. and Timoshkin, I. and Given, M. and Wilson, M. and MacGregor, S. (2018) Conduction characteristics of MIDEL eN 1204 insulating liquid under DC non-uniform conditions. In: 11th Universities High Voltage Network Colloquium, 2018-01-15 - 2018-01-16, University of Southampton.

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In the continued search for environmentally friendly mineral oil alternatives for industrial applications, the present study expands on previous studies as in [1,2], with the addition of rapeseed based dielectric fluid MIDEL eN-1204. The conduction characteristics of MIDEL eN-1204, both fresh and thermally aged, have been measured and compared with well-known synthetic ester liquid MIDEL 7131 and mineral oil Diala D. The mobility of charge carriers under high voltage in a point-plane electrode topology, and the temperature dependence of conductivity under low-field conditions for each fluid sample have been obtained. Charge carrier mobility in the tested liquids was found through I1/2-V curves in the method described in [3]. I-V curves were obtained in the standard cylindrical test cell with electrode separation of 1 mm, energised with voltages up to 70 V at room temperature (20 Co), 45 Co and 75 Co to analyse the conductivity increase with temperature. The above was also repeated with thermally aged (with presence of copper) fluid samples. Obtained results agree well with theoretical conduction models and existing studies. It is therefore found that MIDEL eN 1204 natural ester fluid possesses a similar carrier mobility in the 0-10 kV range when compared to MIDEL 7131 synthetic ester liquid, but exhibits a much higher mobility with aging. In the low-field region, it is found that MIDEL eN possesses a lower conductivity across the temperature ranges, and a lower conductivity increase with aging compared with the other two fluids. The conduction data for Diala D are found to demonstrate a transient character under low-field conditions, with potential viscous and electrohydrodynamic processes being dominant, rendering the obtained data uncertain and difficult to analyse as a means of comparison, and opening a definite opportunity for further study.