This paper deals with a comparative study of the negative and positive DC breakdown voltages of different insulating liquids namely two natural esters (an extra virgin olive oil (OO) without additive and rapeseed oil), two synthetic ester fluids (a methyleolate obtained by transesterification of olive oil and tetraester), and a naphthenic mineral oil (MO); an oils mixture namely 80% OO + 20% MO is also investigated. Statistical analysis of the experimental data is also performed. The obtained results are also compared with those obtained in our previous work under AC and lightning impulse voltages. It is observed that the negative and positive DC breakdown voltages of natural esters are higher than those of mineral oil. On the other hand, the DC breakdown voltage of (80% OO + 20 % MO) mixture shows comparable behavior to that of mineral oil. The DC negative breakdown voltages are higher than the positive ones in the tested liquids. It is also shown that the DC breakdown voltage values of the investigated liquids generally obey the normal distribution.

中文翻译：

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直流电压下植物油与矿物油、天然和合成酯液体的击穿电压比较

本文涉及不同绝缘液体的正负直流击穿电压的比较研究，即两种天然酯（一种不含添加剂和菜籽油的特级初榨橄榄油 (O​​O)）、两种合成酯液（一种通过酯交换获得的甲醇酯）。橄榄油和四酯），以及环烷矿物油（MO）；还研究了一种油混合物，即 80% OO + 20% MO。还对实验数据进行了统计分析。获得的结果也与我们之前在交流和雷电冲击电压下的工作中获得的结果进行了比较。据观察，天然酯的正负直流击穿电压高于矿物油。另一方面，(80% OO + 20% MO) 混合物的直流击穿电压表现出与矿物油相当的行为。直流负击穿电压高于被测液体中的正击穿电压。还表明，所研究液体的直流击穿电压值通常服从正态分布。