The Application Of Solid Phase Extraction And Headspace Gas Chromatography To Methanol Detection In Transformer Oils

At present,the main methods for judging the aging state of power transformers at home and abroad are mainly focused on the measurement of the degree of polymerization of insulator paper and the concentration of furfural in insulating oil,methanol is proposed as a new insulation aging product to evaluate the aging condition of power transformers.However,the detection of methanol is mainly concentrated in the field of food,and the methanol analysis in oil matrix is not comprehensive.Therefore,we discussed the detection of methanol in insulating oil and the relationship between methanol concentration in insulating oil and insulation aging.This article is divided into two parts.Firstly,we proposed a sample pretreatment method for the determination of methanol concentration in insulating oil which combines solid phase extraction with headspace injection,detected by gas chromatography.Under the optimal experimental conditions of traditional headspace injection and this method,we compared the effect of the two detection results.Secondly,we detected the methanol concentration of insulating oil in simulated aging experiment,investigated the relationship between methanol concentration,aging and polymerization degree.The optimum conditions for solid-phase extraction headspace injection were obtained by experiments.The best filler of solid phase extraction column is C18,it should be baked90 min at 90?before extraction,and the flow rate of sample is controlled around1.6ml/min.Take out the filler and put it into headspace vial after the extraction,inject the headspace into GC by headspace sampler after heating 48min at 90?.When the methanol content in insulating oil is in the range of 50~1000?g/L,there is aLinear correlation between methanol concentration and chromatographic peak area,the linear equation is y=76.556x+19871,and R~2=0.9961.The method has good reproducibility that RSD is 4.67%.Comparing with the headspace injection,it was found that the new method is advantaged in both reproducibility and sensitivity.After detecting the methanol content in transformer oil and the degree of polymerization in simulated aging test,it was known that methanol concentration in transformer oil increases with aging time.At beginning of the test,the increasing speed of methanol concentration was faster,and then it slowed down with the increase of time.Meanwhile,the methanol concentration increased with the increase of aging temperature.The concentration of methanol decreased with the increase of the degree of polymerization of insulator paper.There was a linear relationship between the two,and it changed when the degree of polymerization was around 500.When the polymerization degree is less than 500,the change of methanol concentration with polymerization degree is larger than that when polymerization degree is greater than 500.