Roland Gilbert

Methanol: A Novel Approach to Power Transformer Asset Management

All electrical utilities deal with the task of determining the residual life of their in-service power transformers. Given the difficulties experienced with the use of first and second generations of markers (carbon oxides and 2-furfuraldehyde), several organizations are now considering the use of methanol for this purpose. Hydro-Québec, which discovered this approach, uses this molecule on a regular basis to evaluate the state of the cellulose insulation of in-service power transformers and applies it to Électricité de Frances nuclear power plant transformers. In this paper, some examples of the application of methanol in the field are presented against the information received from the early marker generations.

Determination of pentachlorophenol and its oil solvent in wood pole samples by SFE and GC with postcolumn flow splitting for simultaneous detection of the species

An alternative approach is described for the measurement of pentachlorophenol (PCP) and its oil solvent in wood samples by supercritical fluid extraction (SFE) and gas chromatography (GC). The determination is achieved over a single chromatographic run using postcolumn flow splitting for simultaneous ECD/FID detection of the SFE extracted species. First, PCP and oil components are quantitatively extracted from a 0.3-g wood sample using 10% MeOH/CO(2) supercritical fluid at 0.65 g/mL and 120 °C. An aliquot of the SFE solution is then mixed with 10 mL of a buffered aqueous phase at pH 9.4. After PCP is acetylated by the addition of 500 μL of acetic anhydride, it is followed by its extraction with 2.00 mL of hexane along with oil. Then, 0.5 μL of supernatant organic phase is injected into the GC for a selective and simultaneous determination of the species. The method has a linear response over 3 orders of magnitude for both species with a linear regression correlation coefficient higher than 0.98 (95% confidence limit) and an absolute detection limit of 60 ng of PCP and 80 μg of oil per 0.1-g wood sample. The precision (relative standard deviation) is 4% for PCP and 1% for oil as established for a typical average concentration sample. The accuracy of the SFE GC-ECD/FID combined technique for PCP and oil was assessed by analyzing wood samples collected from newly and in-service PCP/oil-impregnated red pine poles.

Decomposition of transformer oils: a new approach for the determination of dissolved gases

The possibility of using a static headspace sampling technique for introducing gases into a chromatograph and performing dissolved-gas analysis automatically was demonstrated in a previous work. The main drawback of the method was the relatively long time that the analytes take to equilibrate between the oil and the headspace. In this paper, the application of mechanical agitation to a viscous matrix to enhance diffusion of the species during the equilibration period was investigated together with the use of an improved nickel catalyst system and a new porous-layer open tubular chromatographic column. The analytical performance of the technique is established and compared with that of method A of the ASTM D 3612 standard procedure. The comparison shows that the technique can be used to assess dissolved gases with the same precision in a much shorter time with a higher sensitivity of detection. An excellent correlation was observed between the analytical results of the two techniques applied to 35 transformer oil samples. The high sensitivity of detection achieved means that transformer fault diagnosis can now be extended to equipment newly commissioned or apparatus other than open breathing equipment, where the total gas content in oil is very low.

Static headspace gas chromatographic determination of fault gases dissolved in transformer insulating oils

Abstract The analysis of dissolved gases in power transformer oils is an efficient diagnostic tool for routine performance monitoring of power transformers. A static headspace gas chromatographic method has been developed to automate the analysis. The parametric study showed that initial equilibration time is about 200 min at 70°C and set the sample volume to 15 ml of oil. Distribution coefficient values were determined under these optimized headspace conditions, avoiding the need of subsequent calibration from oil standards. The precision of the method was better than 5% and detection limits for hydrogen, carbon monoxide and methane, carbon dioxide, and hydrocarbons were 7, 10, 5 and 1 ppm (v/v), respectively. The response is linear over 3 decades up to 1000 ppm. A comparison study between the headspace and the currently used ASTM D3612 method using on-line transformer oil samples showed a good agreement. The headspace method permits an increased number of analysis per day, as much as four times, compared to the ASTM method.

Determination of dissolved gases and furan-related compounds in transformer insulating oils in a single chromatographic run by headspace/ capillary gas chromatography

Abstract A static headspace/ capillary gas chromatographic technique has been developed allowing dissolved gases and furan-related compounds in power transformer oils to be determined in a single chromatographic run. The simultaneous determination of these two classes of compounds from a single sample injection represents a definite advantage over current procedures for the detection of impending performance failure of the unit. The method uses gas chromatography with porous-layer open tubular (PLOT) columns and a valve operated in sequence for flowpath selection. Also, comparison with the current method using packed columns showed that dissolved-gas analysis with PLOT columns provides better peak shapes and lower detection limits ( S/N b = 3): 5, 3 and 1 ppm (v/v) for hydrogen, carbon oxides and light hydrocarbons respectively. Detection of 2-furaldehyde is possible down to 0.5 ppm (w/w).

Dissolution of metal oxides accumulated in nuclear steam generators: study of solutions containing organic chelating agents

A study of the reactivity of ethylenediaminetetraacetic acid (EDTA), citric acid, and hydrazine for the dissolution of magnetite particles has allowed some steps of the different mechanisms to be identified. Two mechanisms are suggested: In acidic solutions, the chelating agents are adsorbed at the solid/solution interface followed by desorption of the complexed species FeH /SUB n/ L, where HnL is EDTA or citric acid, whereas in alkaline media, direct dissolution of the oxide particles takes place followed by complexation of the species Fe/sup 3 +//Fe/sup 2 +/ in solution. The hydrazine apparently reduces the Fe/sup 3 +/ ions via a surface complexing reaction involving the N/sub 2/H/sub +//sub 5/ ions, a reaction which is in competition with the protonation of the Fe/sub 3/O/sub 4/ crystal lattice. Finally, regardless of the type of oxide (Fe/sub 3/O/sub 4/, Fe/sub 2/O/sub 3/, FeOOH, CuO, or Cu/sub 2/O) or the composition of the complexing solutions, suspensions of these particles are highly unstable with respect to agglomeration or settling out, more because of the high concentration of chelating agents than their chemical characteristics.

Liquid chromatographic determination of morpholine and its thermal breakdown products in steam-water cycles at nuclear power plants

Abstract Morpholine and its amine breakdown products in aqueous samples were derivatized with dabsyl chloride in the presence of sodium bicarbonate and the resulting precolumn derivatives determined by high-performance liquid chromatography with visible detection at 456 nm. The analytical column was a μBondapak C18 reversed-phase device. The breakdown products were determined in the concentration range of 0.25–10 μg/ml in water, with a relative standard deviation of 0.38–7.08%. The amine detection limits were 0.01–0.03 μg/ml for 20-μl injections. Chromatographic analysis of 100-ml grab samples after acidification and concentration demonstrates the sucess of this technique for determining the quantity (ng/ml) of ammonia, methylamine, ethylamine, ethanolamine and 2-(2-aminoethoxy)ethanol in the thermal cycle at Gentilly 2 nuclear power plant. The recovery for the complete assay procedure varied between 92.0 and 106.0% depending on the product studied.

Arc degradation of SF 6 in the presence of polymeric insulating materials

An investigation has been made of the degradation reactions due to the application of an electric are at the polymeric insulating material/SF6 interface. Polyethylene, Teflon, epoxy and phenolic resins were used as the solid insulating materials in the study. The degradation process was observed to occur in two separate steps. In the first step, the polymeric materials are pyrolyzed by the are (are degradation). The second step involves a gas-phase reaction between the SF6 and the volatile products generated by the are degradation. Analysis of the arc-degradation products by gas chromatography, mass spectrometry and infrared spectrophotometry indicates a significant difference between the composition of the various reaction products and the corresponding products of a degradation reaction carried out thermally. The principal reaction products of the gas-phase reactions between SF6 and the volatile degradation products were identified as CF4, SOF2, SF4, SiF4, HF and also CO in the cases of epoxy and phenolic resins. General reaction mechanisms for the formation of these products are proposed. The implications of these results regarding the use of such insulating systems in electrical apparatus are discussed.

Determination of the analytical performance of a headspace capillary gas chromatographic technique and karl Fischer coulometric titration by system calibration using oil samples containing known amounts of moisture.

Over the past few years, concerns have been raised in the literature about the accuracy of the Karl Fischer (KF) method for assessing moisture in transformer mineral oils. To better understand this issue, the performance of a static headspace capillary gas chromatographic (HS-CGC) technique was compared to that of KF coulometric titration by analyzing moisture in samples containing known amounts of water and various samples obtained from the National Institute of Standards and Technology (NIST). Two modes of adding samples into the KF vessel were used:  direct injection and indirect injection via an azeotropic distillation of the moisture with toluene. Under the conditions used for direct injection, the oil matrix was totally dissolved in the anolyte, which allowed the moisture to be titrated in a single-phase solution rather than in a suspension. The results have shown that when HS-CGC and combined azeotropic distillation/KF titration are calibrated with moisture-in-oil standards, a linear relation is observed over 0-60 ppm H(2)O with a correlation coefficient better than 0.9994 (95% confidence), with the regression line crossing through zero. A similar relation can also be observed when calibration is achieved by direct KF addition of standards prepared with octanol-1, but in this case an intercept of 4-5 ppm is noted. The amount of moisture determined by curve interpolation in NIST reference materials by the three calibrated systems ranges from 13.0 to 14.8 ppm for RM 8506 and 42.5 to 46.4 ppm for RM 8507, and in any case, the results were as high as those reported in the literature with volumetric KF titration. However, titration of various dehydrated oil and solvent samples showed that direct KF titration is affected by a small bias when samples contain very little moisture. The source of error after correction for the large sample volume used for the determination (8 mL) is about 6 ppm for Voltesso naphthenic oil and 4 ppm for toluene, revealing a matrix effect on the measurement. Finally, the results revealed that HS-CGC is a good technique for measuring moisture in oil samples and that the use of azeotropic vapors for introducing moisture into the titrator almost completely eliminates the matrix effect observed with the oil components. Direct KF injection could also be used provided the system is calibrated with moisture-in-oil standards prepared in the same matrix which is to be used for the determination.

Comparison between headspace and vacuum gas extraction techniques for the gas chromatographic determination of dissolved gases from transformer insulating oils

The conventional headspace sampling technique is highly efficient for analyzing dissolved gases in transformer oil apart from the relatively long time that the analytes take to equilibrate between the sample and vapor phases. By mixing the sample during the equilibration period, the equilibration time was shortened by a factor of 15. Under these conditions, analysis of the gases of the first sample is completed in 32 min, while analysis of each subsequent sample takes only 20 min. The results of the analysis of dissolved-gas standards by the headspace sampling technique were compared to those obtained by four labs using the ASTM D3612 method. Our technique compares well to the vacuum gas extraction technique with a number of accurate analyses higher than the best results obtained by the participating labs. An average relative standard deviation of 4% for all gases studied was observed. Excellent correlation between the results of the analysis of 80 transformer oil samples by these two techniques was noted for all gases of interest.<<ETX>>