Interfacial Response of Insulating Liquids to High-Voltage Electric Fields – Contact Angle Measurements

Published: 12 March 2026| Version 1 | DOI: 10.17632/z3vg38m3sg.1
Contributor:
Bystrík Dolník

Description

This study examines the interfacial properties of transformer oils. Their wetting behavior was evaluated using static contact angle (CA) measurements and by assessing the influence of external high-voltage electric fields on droplet deformation. Two categories of high-voltage experiments were performed: (i) gradual voltage increase up to 7 kV to observe quasi-static deformation, and (ii) step-voltage excitation at 3.5 kV, 5.5 kV, and 6.5 kV to investigate dynamic droplet response. The results indicate a consistent decrease in contact angle with increasing electric field strength. Ester-based oils exhibited higher stability under electric stress, while mineral oils showed more pronounced droplet deformation. The findings contribute to understanding the interfacial behaviour of insulating liquids under electric field stress and provide insight into their suitability for advanced diagnostic evaluation of transformer insulation systems. The directories contain time records of parameters during contact angle measurements on insulating liquids used in the power industry. The time record is in a text file. The data set has six columns, separated by spaces. The first line represents the header. Individual columns represent the following quantities: 1st column: time (s), 2nd column: CA from the left (°), 3rd column: CA from the right (°), 4th column: average of CAs (°), 5th column: drop volume (μl), 6th column: baseline (mm). In the main directory, the data are measured in a static electric field generated by voltages ranging from 0 to 7 kV, with a step of 500 V. The corresponding subdirectory contains data measured during a step change in the electric field, generated by the voltage, from 0 V to 3.5 kV, 5.5 kV, and 6.5 kV, and vice versa. The names of the data files in the main directories are in the following structure: oil name_value of the applied voltage_series of measurements, e.g., Midel7131_0V_1. The names of the data files in the subdirectories are in the following structure: oil name_value of the initial applied voltage_value of the final applied voltage, e.g., Midel7131_0V_3500V. Directory designation and meaning of abbreviations: Midel7131: Midel 7131 (synth. ester) MideleN1204: Midel eN 1204 (nat. ester) Mogul_trafoCZ-A: Mogul trafo CZ-A (inhibited mineral oil) MOL_TO40A: MOL TO 40A (inhibited mineral oil) ShellDialaS5: Shell Diala S5 (biodegradable insulating oil) There are two text files in the Scripts directory: The first file, ca_prof2.py, is a Python 3 script that reads data from the data files. By default, it draws a violin plot from the read data. The user can change the plot to an error bar, and the mean of means can be calculated and drawn. The graphical output can be saved to PDF and SVG. The second file, named ca_time.py, is a Python 3 script used to plot data from subdirectories that store a ten-second record of stepwise application (or removal) of voltage to the electrodes.

Files

Steps to reproduce

The data was obtained by measuring the contact angle using a Theta Flex Optical Tensiometer. A custom two-electrode system was designed to generate a non-uniform electric field near the droplet. Droplet deformation and contact angle were recorded for 10 s.

Institutions

Categories

Electrical Engineering, Ionic Liquid, Droplet, Contact Angle, High Voltage Engineering

Funders

Licence