Thermo-Oxidative Stability of Mineral Naphthenic Insulating Oils:  Combined Effect of Antioxidants and Metal Passivator

Abstract

The oxidation of mineral oils is the most important cause of poor power transformer performance. High voltages, high temperatures, and the presence of oxygen and metallic surfaces are some of the factors that may trigger oxidation reactions. The use of antioxidant additives and metal passivators in insulating oils has the purpose of improving their performance, by increasing their stability to oxidation so as to ensure a more reliable operation of the transformer. This work presents a kinetic experimental study of the oxidation reactions of a naphthenic mineral oil (with and without additives) as a function of temperature. Oil samples were doped with phenolic antioxidants (AOX), a metal passivator (MPA), and combinations of these (AOX and MPA) in order to verify the efficiency of such additives in increasing thermo-oxidative stability. All doped and nondoped oil samples were submitted to an accelerated oxidation test according to modified ASTM D-2440 method. The level of degradation was assessed by monitoring the area under the carbonyl band (around 1713 cm -1 ) in the FTIR spectrum and comparing it to that obtained for the new nonoxidized oil. The results obtained for the oxidation of nondoped oil samples showed that the kinetic behavior may be well represented by a first-order homogeneous reaction rate law, with energy of activation around 10 kcal/mol. Our results also show that hindered phenolic antioxidants significantly reduce the formation of oxidation products. The addition of a metal passivator, even at very low levels (8 ppm), causes a synergetic effect with all antioxidants tested, leading to a significant improvement in the resistance of the oil against oxidation.

Quantifying the Effect of Catalysts on the Lifetime of Transformer Oil

“…In particular, mineral oils are mixtures of linear saturated hydrocarbons (paraffins), cyclic saturated hydrocarbons (naphthenes), aromatic hydrocarbons, and small amounts of nonhydrocarbons (sulfur, nitrogen, and oxygen combined with carbon and hydrogen) [39,40], whereas the selected oil may contain thousands of different types of paraffinic, naphthenic, and aromatic hydrocarbon molecules [40]. According to the amount ratios of basic types of hydrocarbons, and subsequently, according to the presence of specific chemical substances, the reactions that occur during thermo-oxidation of oil differ [39]. Chemical reactions may also vary significantly depending on the type of mineral oil (e.g., based on the production process and intended for the defined application) and on the environment of actual usage.…”

“…Many factors influence the continuity and interlacing of ongoing chemical reactions. Elevated temperature, high voltage [39], and the presence of impurities, including dissolved gases (not only oxygen), water, polar and ionic contaminants (traces of sulphate, sulphonates, furfural, etc. ), and particulate solid contaminants (metals, metal oxides, fibers of cellulose, etc.)…”

Suitable additives for vegetable oil‐based automotive shock absorber fluids: an overview

“…An AO is a chemical compound use to hinder or delay oxidation in lubricants. They achieve these as radical scavengers, such as aryl‐amines and hindered phenol, which can lock‐up free radicals and prevent oxidation, as peroxide decomposers like environmentally benign and effective phosphorus‐based additives, which break down peroxides, and improve oxidation stability, also as metal deactivators, which inhibit the catalytic effects of service environment components, contaminants and additive elements that are metallic based (by chemosorbing to the metal surfaces, forming a kind of film that hinders the facilitating activities of the metals in the reaction between oxygen and oil molecules to form radicals), and as UV absorbers . The activities of AOs in an ASA fluid chamber can be illustrated as in Figure .…”

Phosphorus cardanol: chemical characterization and thermal stability

“…For evaluation of the thermal properties, the authors used thermal analysis (TG-DTG, DSC and DTA) in different atmospheres [14]. Lubricant oil (naphthenic lube base oil) was used as organic substrate to study the antioxidant activity of the obtained phosphorus [24][25][26]. To study the antioxidant activity of the phosphorus compounds, the researchers used a lubricant oil as organic substrate (naphthenic lube base oil).…”