| 2,6-Di-tert-butyl-p-cresol, (DBPC), dibenzyl disulfide, (DBDS), and 1,2,3-benzotriazole, (BTA), are additives may be found concomitantly in the matrix of the power transformer oil. DBPC and DBDS act as antioxidants while, BTA is a corrosion inhibitor that protects copper conductors inside the transformer from the effect of even traces of organic sulfur compounds such as DBDS. This work describes a unique single liquid-liquid extraction pretreatment step using n-hexane as diluent for the oil sample and acetonitrile as an extractant thus, the three components are extracted simultaneously before injection into either GC or HPLC system. DBDS and DBPC are simultaneously determined using GC technique with a dual detector (ECD and FID). Another portion of the extract is injected into an HPLC-UV to determine BTA. This quantitative procedure has the advantage of low chemical consumption as well as being less laborious and less time consuming. The results indicate that the method is sensitive, accurate, precise and linear with R2 > 0.99 for each component. The resulting detection limits 0.01% (w/v), 0.80mgL-1, and 2.04 mgL -1 for DBPC, DBDS and BTA respectively were lower than those obtained by the standard methods. The method can be used for both fresh and used mineral insulating oil. Using this analytical procedure, the behavior of DBDS as corrosive sulfur species has been investigated in mineral insulating oils. The critical DBDS concentration and temperature for copper sulfide formation were estimated kinetically to be less than 9 mgL-1 DBDS and 100° C respectively. The minimum effective BTA concentration was also determined to be 5 mgL -1 that retards copper sulfide formation. Also the study confirmed that DBDS remains in mineral insulating oil for long time before being subjected to chemical depletion when it acts as either as antioxidant or as corrosive sulfur. The synergy effect between corrosive sulfur (DBDS), primary antioxidant (DBPC) and metal passivator (BTA) in mineral insulating oil was also qualitatively and quantitatively investigated in the current work. |
