The Effect of Electronic Scavenger Additives on the AC Dielectric Strength of Transformer Mineral Oil

Abstract

This paper is devoted to the influence of two types of electronic scavenger additives/compounds, namely, carbon tetrachloride (CCl4) and methyl iodide, which is also called iodomethane (CH3I), on the dielectric strength of transformer mineral oil. The tests are achieved in a sphere-sphere electrodes arrangement under AC voltage according to the IEC 60156 standard. The investigated additive concentrations range from 0 to 600 ppm. The verification of the conformity of the experimental results with normal and Weibull probabilistic distributions as well as the estimation of the breakdown voltage with risk probabilities of 1%, 10%, and 50% are also performed. It is shown that there is an optimum concentration of each type of electronic scavenger compound at which the dielectric strength of the mineral oil is significantly improved (i.e., it reaches a maximum value). This improvement is of 98% with 500 ppm of CH3I and 93% with 200 ppm of CCl4. It is also shown that the breakdown voltage values of all of the investigated samples with and without additives conform to a Weibull distribution but not to a normal distribution. The obtained results are discussed with regard to the possible mechanisms that may be responsible, particularly the two phases of inception and propagation of the streamers.

Influence of electronic scavenger additives on AC breakdown voltage of synthetic ester

“…The obtained results with SE confirm the beneficial effect of electronic scavenger additives on AC U BDV are observed with mineral oil [4] even if the improvement is much less important. For the optimal amount (concentration) of CH 3 I, the improvement is of 27% in SE against 98% in mineral oil.…”

“…To check whether the data obey one and/or the other distribution law, the used method is the same as that one in the previous work [4].…”

“…Among the investigations dealing with these kinds of additives and their influence on the breakdown voltage (BDV) of insulating oils, the aromatic compounds [1]. Unfortunately, the reported results are contradictory [1][2][3][4]. According to Zaky et al [1], the addition of aromatic compounds improves the dielectric strength of insulating liquids while Mathes and Rouse [3] observed that the BDV of naphthenic oil significantly decreases when adding a small concentration of poly-aromatic additives.…”

“…In recent work [4], it was showed that under AC voltage, the addition of a given amount of electronic scavenger compound significantly improves its dielectric strength and there is an optimum concentration of additive for which the BDV reaches a maximum value. Indeed, by considering three kinds of electronic scavenger additives, namely methyl iodide (iodomethane), CH 3 I, and carbon tetrachloride CCl 4 , it was observed that with 500 ppm of CH 3 I, the enhancement is about 98%, whereas it is about 93% with 200 ppm of CCl 4 .…”

“…These properties enable to ensure fire security, transformer performance improvement, and environmental protection by extending the life of devices. In addition, the very low-pour point and excellent oxidation stability, make SE suitable for cold climates and breathing power transformer [1][2][3][4][5][6]. Mineral oils have poor bio degradability (<30%) and have negative effect on aquatic sources and a high-pour point what presents some issues on the environment.…”