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

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.

本研究针对变压器油（transformer oils）的界面特性展开分析。通过静态接触角（static contact angle, CA）测量，以及评估外部高压电场对液滴变形的影响，对其润湿行为进行了表征。本研究开展了两类高压实验：(i) 逐步升压至7 kV，以观察准静态液滴变形；(ii) 在3.5 kV、5.5 kV及6.5 kV下进行阶跃电压激励，以探究液滴的动态响应特性。结果表明，接触角随电场强度升高呈现持续降低的趋势。酯基油（ester-based oils）在电场应力下表现出更高的稳定性，而矿物油（mineral oils）的液滴变形则更为显著。本研究成果有助于深入理解绝缘液体（insulating liquids）在电场应力下的界面行为，并为变压器绝缘系统的先进诊断评估提供了理论参考。

本数据集包含电力工业用绝缘液体接触角测量过程中的参数时间记录。该时间记录存储于文本文件中，数据集共包含6列数据，以空格分隔，首行为表头信息。各列对应的物理量如下：
1. 第1列：时间（s）
2. 第2列：左侧接触角（°）
3. 第3列：右侧接触角（°）
4. 第4列：接触角平均值（°）
5. 第5列：液滴体积（μl）
6. 第6列：基线（mm）

主目录下的数据为在0至7 kV、步长500 V的静电场中测得的结果。对应子目录中的数据则为电场阶跃变化过程中测得的结果，电场可由0 V阶跃至3.5 kV、5.5 kV及6.5 kV，亦可反向阶跃。

主目录下的数据文件命名规则如下：油样名称_施加电压值_测量序列，例如 Midel7131_0V_1。子目录下的数据文件命名规则如下：油样名称_初始施加电压值_最终施加电压值，例如 Midel7131_0V_3500V。

目录命名及缩写含义如下：
Midel7131：Midel 7131（合成酯基油）
MideleN1204：Midel eN 1204（天然酯基油）
Mogul_trafoCZ-A：Mogul trafo CZ-A（含抑制剂矿物油）
MOL_TO40A：MOL TO 40A（含抑制剂矿物油）
ShellDialaS5：Shell Diala S5（可生物降解绝缘油）

Scripts目录下包含两个Python 3脚本文件：
第一个文件为ca_prof2.py，可读取数据文件中的信息，默认绘制读取数据的小提琴图。用户可将图表类型修改为误差棒图，同时可计算并绘制均值的均值。图形输出可保存为PDF或SVG格式。
第二个文件为ca_time.py，用于绘制子目录中的数据，此类数据记录了电极施加（或移除）电压的10秒阶跃过程中的相关参数。