High Power Factors and Contaminants in Transformer Oil

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1 High Power Factors and Contaminants in Transformer Oil By Russ Crutcher and Ken Warner

2 HIGH POWER FACTORS AND CONTAMINANTS IN TRANSFORMER OIL Russ Crutcher and Ken Warner Microlab Northwest Abstract New transformers often begin showing elevated power factors in the first few years of operation. This early power factor increase is generally due to polar compounds extracted from paints, gaskets, adhesives, polymers, and other materials in the transformer or accessory equipment exposed to the oil. These compounds can increase the power factor of the oil even when present at a few parts per million. Special techniques have been developed to detect these materials at very low levels and identify their source. Once detected, their presence in sister units can be quickly determined. Elevated power factors later in the history of the transformer may be due to particles and breakdown products in the oil. The same techniques can be used to characterize the breakdown products, and the particles can be identified using light microscopy. A number of case histories are provided, along with a discussion of the mechanisms involved and an explanation of why power factors may rise, fall, and then rise again. Detecting Low-level Polar Compound in Oil Infrared spectroscopy is often used to characterize the presence of chemical compounds in transformer oil. The technique most often used in routine analysis is to look through a relatively thick layer of the oil. This long path method is used to detect a few peaks in the spectrogram that are typical of the additive or additives of interest (see Figure 1). This is like taking a picture of someone with the sun over his/her shoulder and intentionally overexposing the image. The image would be washed out, but you could still tell that a person was there. It would be much better if the sun was over your own shoulder and the exposure was correctly adjusted to see the person in detail. It is the same with the oil. Shooting the beam through a long path of oil is like shooting into the sun. Long-path methods work for some routine analyses. It is a relatively inexpensive technique, but it is also subject to misinterpretation and cannot detect the chemical compounds of concern at the low levels that cause changes in the power factor.

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3 %T ransm ittance Wavenumbers (cm-1) Figure 1: Bulk Spectrum of Used Transformer Mineral Oil, Thick Cell (Long Path) The main peaks are all the result of simple carbon hydrogen bonds. The signatures of the compounds of interest are all mixed in the little peaks, shoulders of peaks, or can t be seen. Some general statements can be made, such as the antioxidant is depleted. There is no specific information about sources or causes of the chemicals all mixed together creating the minor peaks to the right in this spectrum. The polar compounds of interest can be recovered from the transformer oil by taking advantage of the very properties that cause them to interfere with the power factor. In the laboratory, a number of special media similar to Fuller s Earth can be used to remove the polar compounds from the oil. These compounds can then be collected from the media by special solvents for analysis. A rough quantification of the amount of polar compounds in the oil can be determined at this stage by measuring the volume of polar compounds collected (see Photograph 1). Along with the volume of the polar compounds in the sample, other features become evident. Differences in color and the presence of some crystalline materials Photograph 1: Polar Compounds from Four Different Extractions Volumes and color become evident at this stage in the separation. become evident at this stage (see Photographs 2 and 3). The crystalline materials that appear are soluble in the bulk oil at very low levels but not sufficiently soluble in the smaller volume of the extracted polar compounds. The mixed bulk polar compounds can be characterized using infrared analysis to look for dominant chemical families. Peaks that were barely visible in the long-path analysis now stand out strongly. The carbon-oxygen bonds in the concentrated polar compounds are clearly evident in the spectrum shown in Figure 2. That can be useful if tracking a single compound that must

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4 %T ransm ittance Photograph 2: Sodium Chloride Salt Extracted with Polar Compounds Photograph 3: Organic Salt Extracted with Polar Compounds be present at significant levels relative to other polar compounds to cause important changes. Generally, a couple of peaks for that compound will be used in order to mark the presence of the compound of interest rather than a single peak that may be shared by a number of compounds. Some additives fit that description, such as the reacted antioxidants. In most cases, some further separation is required to find the material that is of concern Wavenumbers (cm-1) Figure 2: Spectrum of the Combined Polar Compounds Removed from Used Transformer Oil The carbon-hydrogen bonds are still a major functionality, but now the carbon-oxygen peaks show strongly. At this point, there are still many different compounds present. A dominant polar compound might be identifiable in this spectrum, but generally, a further separation of the polar compounds is required to find the source of the problem.

5 The next step is thin-layer chromatography (see Photographs 4 and 5). This separates the mixed polar compounds into much smaller groups or even individual compounds. These appear as discrete bands on the chromatogram and can be visualized under ultraviolet light of various wavelengths or by other chemical characteristics. In some cases, some of the bands are visible in normal light (top image, Photograph 4). The chromatogram itself can be used as a signature of an undesirable condition. Photograph 6 shows how oil changed with time in a transformer. The chromatogram on the right in this image corresponded to the oil with elevated power factor. The chromatogram on the left corresponded to the oil prior to its developing the higher power factor. The chromatogram on the right was taken just before reprocessing the oil to drop the power factor. There are more polar compounds shown in the chromatogram on the right, as indicated by both brighter bands and more bands. Sister units could be analyzed using this technique to see if they were experiencing a similar aging process. Photograph 4: Thin layer Chromatogram of the Polar Compounds from a Mineral Oil Viewed with Visible light (Top), Long Wave (Middle), and Short (Bottom) Wave UV Light This was an oil that had a green tint to it. The visible light chromatogram shows a blue dye from an adhesive used in this system and a strong yellow band near the right end of the chromatogram that is oxidized antioxidant. This resulted in the green color. The yellow band in visible light absorbs UV at both the long and short wavelengths. Many other polar compounds are present, as can be seen in the photographs taken with ultraviolet light.

Photograph 5: Thin-layer Chromatogram of the Polar Compounds from Three Different Mineral Oils Viewed with Short Wave (254 nm) UV Light These are the polar compounds collected from three different

6 Photograph 5: Thin-layer Chromatogram of the Polar Compounds from Three Different Mineral Oils Viewed with Short Wave (254 nm) UV Light These are the polar compounds collected from three different oils. The top chromatogram is the same as shown in Photograph 4. The other two are from different transformers. Each oil has its own additives and its own mixture of chemical products prior to being added to the transformer. Each oil then reacts or extracts different materials from the paper and other components in the transformer. Some of these bands correspond to compounds that will increase the power factor in the transformer. The analysis now progresses to the next step. The bands of interest on the chromatogram are marked and then collected from the chromatogram for analysis or further processing and analysis using micro-fourier transform infrared spectrophotometry. The infrared spectra can then be searched against a large library of spectra to try to identify the compound. Once the material is identified or at least characterized to suggest a source, the materials in the oil or in the components of the transformer can be investigated. Often, the compound causing the problem is a minor component in one of these materials. It is often a catalyst or an additive that may not even be listed as an ingredient. The materials themselves must be analyzed to see what is drawn into the oil over time. In laboratory tests to confirm the hypothesis, the time scale is shortened by increasing the surface area of the material in question per unit volume of oil rather than increasing the temperature above expected operating exposures. Photograph 6: Polar Compound from Transformer Oil Separated for Analysis on a Thin Layer Chromatographic Plate Each of the color bands indicates a different family of compounds. Each band can be collected, extracted, and analyzed. This is the same oil in the same transformer at different times.

7 Power Factor and Low-level Polar Contaminants Water is not considered here, though it can elevate power factor because it is easily detected. Once it is eliminated as a contributing factor and the power factor is high, the analysis becomes more complex. The effect that trace levels of polar organic contaminants can have on the power factor of oil in oil-filled electrical equipment has been well documented 1,2. Additives in even relatively small components can result in changes to the power factor of the oil because so little material is required. No two mineral oils used in transformers are the same, as shown in the three different chromatograms of Photograph 5 from different oils. As they age, they become even more different. This is due to the fact that each oil is made up of a different set of compounds. The different individual compounds that make up the various oils react with oxygen, nitrogen, and other materials in the transformer to form different aging products. In this mixed soup of compounds that make up each oil, some mineral oils will begin to extract a catalyst or drier from paint, plastic, or gaskets when most other mineral oils will not. Some of these extracted compounds may have a measurable impact on the oil s power factor. Power factor problems can also be caused by a degraded additive or contaminant introduced before the oil was added to the equipment. The accumulation of reacted antioxidants can elevate the power factor. Other additives may also accumulate or react to cause a change in power factor. Some of the mineral oils used in transformers contain a number of discrete compounds. They can be additives or contaminants from either specific processes or from handling at some stage between the final processing and the delivery of the oil to the equipment. Hose liners, tanker contaminants, and other pieces of equipment can introduce detrimental contaminants. Power Factor and Particles Not all power factor problems are caused by polar compounds in solution. Particles from degrading components in the transformer, sludge formation, or particles introduced from outside the transformer can result in elevated power factors. Particle counter will often indicate the presence of these particles, often indirectly. An elevated power factor due to particles early in the life of a transformer indicates contaminated oil rather than degraded oil. It is often due to contaminants from the tank farm, the tanker that brings the oil, or a failed filter. If the particles are from a failed filter, the filter media will be present. If it is from the tank farm or the tanker, it is normally small natural minerals or rust. Elevated power factors in older units may be due to the formation of polymers in the oil. The oil may still appear clear because the polymer matches the refractive index of the oil. When the oil is filtered through a membrane filter, the polymer becomes obvious as a mat of fine orange particles.

8 %T Case History 1: Drier from Paint in Transformer Radiators Driers in paint perform a number of important functions. They affect the bond to the substrate, the rate and depth of cure, and the physical properties of the paint at final cure. There are a number of driers in paint, each responsible for some aspect of the cure. Driers are not part of the final polymer in the cured paint film; therefore, they can become mobile in the film and enter the oil if the paint polymer is permeable to some components in the oil. Some of these driers can result in an elevated power factor, even when present at only a few parts per million. In this case, a paint formulation had been modified to reduce the solvent exposure to employees and the amount of hazardous waste on the part of the company producing the paint. The name of the paint had not changed. It was still stable in mineral oil. The assumption was that all mineral oils were the same and that they age the same. That assumption was wrong. The paint was stable in the new oil just as it had been in the standard mineral oil. When the oil showing the high power factor was run through Fuller s Earth, the power factor dropped down to low levels. When this aged oil now with a low power factor was exposed to the cured paint, its power factor went back up over time. The infrared analysis of the polar compounds from the paint that had moved into the oil was the same as that of the polar compounds removed from the original oil that had the elevated power factor (see Figure 3). No other client using a different mineral oil had a problem with this paint Wav enumbers ( cm- 1) FIGURE 3: Overlay of the IR Spectra from the Paint Extract (Red) and the Extract from the High Power Factor Oil (Green) The remarkable similarity of these spectra would seem to implicate extractables from the paint as the same material, causing the high power factor in the oil when present.

The high power factor oil had an additional band caused by a plasticizer that had come from an overheated gasket in the pump housing.

9 Case History 2: Plasticizer from a Gasket Used in a Transformer A transformer had a pump failure and an elevated power factor. The thin-layer chromatogram of the oil with the high power factor was compared to the oil from a sister unit that had a low power factor (see Photograph 7). The high power factor oil had an additional band caused by a plasticizer that had come from an overheated gasket in the pump housing. Processing the oil through Fuller s Earth removed that band, and the power factor dropped back to normal. Photograph 7: Thin layer Chromatogram of Oil with High Power Factor (Top) and Oil from a Sister Unit with Normal Power Factor (Bottom) Case History 3: Particle Contamination from Oil Storage A new transformer was showing an elevated power factor. An analysis of the oil indicated a very high concentration of fine natural minerals (see Photograph 8). The size distribution and types of minerals indicated that this was due to ground contamination and not the degradation of a mineral-filled polymer or an ion exchange medium. Filtering the particles out of the oil returned the power factor to an acceptable level. Photograph 8: Natural Mineral Particles from Delivered Oil Causing Elevated Power Factor The minerals include clays, limestone, quartz, and other natural minerals.

Case History 4: Particles from Polymerization of the Oil This material can form in transformers over time. This unit began service in 1970.

10 Case History 4: Particles from Polymerization of the Oil This material can form in transformers over time. This unit began service in At 100 o Celsius, much of this material went back into solution in the oil. The material was a complex of oxidized oil and paper degradation products. The oil appeared clear, though it was distinctly orange. The system had been in operation for 32 years at the time of testing. Photograph 9: Polymerized Oil Particles Cold Filtered from the Oil Conclusion A new approach to the analysis of polar compounds and particles that cause an elevation of the power factor in electrical equipment has been presented here. This technique has been evolving over the last 15 years and has been effective in isolating the cause of power factor problems in a number of cases. The analytical procedure can identify these compounds at parts per million levels. Once the compound is identified, candidate sources can be tested for the presence of these compounds. Materials used in transformers, bushing, and other oil-filled electrical equipment often contain compounds that are not obvious. Catalysts, driers, curing agents, antioxidants, pacifiers, and other additives are often not listed for these materials. Some of these compounds used in a material can have adverse effects on equipment performance over time. Those effects may be oil specific. These problems can now be identified and appropriate action taken. Particles introduced as contaminants or that form in oil over time can also contribute to the power factor. These particles can be identified and their source located. The identification of their source will permit the selection of an effective remediation program. Elevated power factors can result from anything that changes the dielectric constant as a function of frequency. Polar compounds or particles in suspension will change the dielectric constant. These contaminants can often be identified and, more importantly, their source can be identified. The ability to identify their source provides an ability to control their effect on the system.

11 References 1. Crutcher, E.R., Phil Hopkinson, Ray Rettew, Steve Smith, Ken Warner, and Jaime LaFave. Paint Induced Elevation of Oil Power Factor in Electrical Equipment, Doble Conference, Boston, MA, April 11, Oommen, T.V. Flow Electrification Properties of Certain High Charging Polymeric Materials in Transformer Oil, IEEE International Symposium on Electrical Insulation, Arlington, VA. pp , June 7 10, 1998.

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