Analytical Instrumentation
that might adversely affect Cl/PCB measurement capability.
In order to check for water interferences, a study was completed to shed additional light on what result bias might be documented for transformer oil containing water at various levels. Eight separate sample materials were prepared to closely approximate 25 mg/kg Cl in a fresh (unused) transformer oil (specified to be <10 mg/kg water) Water at various concentration levels was then spiked into the 25 mg/kg chlorine containing material and analysed in order to determine what water contamination level might affect MCXRF Cl measurement capability. Water visibility was judged as a film or as droplets of water obviously observable on the surface of the Mylar®
sample cup
film, following the analytical run (see figure 3). The results of ASI’s testing can be found in table 4.
Table 2: MCXRF and WDXRF result comparisons
results were derived from the average of two consecutive 180 second analyses of 5 mls of transformer oil in the same sample cup. This data is illustrated in Figure 2.
Figure 4: Photo of Instrument Utility – Ease of Use
The instrumentation requires only a reliable electrical source (100-250 VAC), no other utilities are required for the non-destructive and non-spark producing MCXRF technique. The apparatus features a large and responsive touch screen display that is easy to use and sample analysis can be initiated with minimum user inputs. Sample preparation and handling are eased by Mylar®
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Table 4: Cl in transformer oil, water contamination effects Figure 2: Precision Data
The repeatability data was then analyzed using a modified EPA method detection limit (MDL) technique to estimate level of detection (LOD) and level of quantification (LOQ) and MDL at the 95 percent confidence level. These estimates are shown in Table 3. It should be noted the elevated signal-to-noise (S/N) ratio of 84.4 indicates that a much lower concentration can be analysed and that detection limits are likely to be lower than indicated.
film-sealed disposable plastic cups, allowing instrument use by non-laboratory trained technicians. A powerful on-board computer enables a full line-up of data handling, printing, and processing features needed for contemporary data transfer and compliance with good-laboratory practice require- ments. For safe operation the instrument has an automatic control that de-powers the X-ray tube anytime the sample compartment is opened and optimum X-ray tube operating status is also ensured by an integrated, self-testing scheme that is initiated each time the instrument is started. Although not often a requirement in transformer oil applications, when desired, users can also simultaneously measure sulphur content from weight percent down to part per million levels.
Conclusion Table 3: Estimate of detection limits Moisture Contamination Effects
Typically water contamination in new unused transformer oil is less than 10 mg/kg because of strict dielectric constant specifications and other application reasons. Additionally, water contamination can be readily visible because of its insolubility in transformer oil. However, one concern for the analyst can be the presence of a not easily visible water contamination
Figure 3: Photo of water droplets on cup film (Top). Cup (Bottom) spiked with water.
Wat er in Transformer Oil Contamination
• No discernable affect on MCXRF Cl/PCB measurement capability was noted up to 2000 mg/kg
• Contaminations up to 100 mg/kg were not readily visible to the eye
• Contaminations at 250 mg/kg and above were visible
Electrical transformers are removed from service for a whole host of reasons. Primary causes are mechanical or electrical damage, capacity upgrades, and age. For wet (oil-containing) transformers, depending on the transformer size and type of service, the condit-ion of the fluid it contains may not be fully known and may not have been analysed or characterised in any way since being placed in service. In this case, the party having custody of the used transformer oil needs a reliable, fast and easy-to-use screening methodology. This reduces the need to analyse large numbers of materials with more expensive and time consuming test- ing techniques. Based on the independent ASI test findings and the performance features described, the HORIBA MESA 6000 chlorine analyser readily demonstrates the ability to meet all the fitness-for-use criteria commonly needed when inspection and classification of a large number of transformer oil materials is required.
Fully Automated Determination of TAN/TBN in Oil Samples
Metrohm presents the 864 Robotic Balance Sample Processor, an advanced system for fully automated TAN/TBN determinations in petroleum products. Capabilities include weighing, solvent addition, waiting times for complete dissolution and optimised electrode conditioning procedures between samples, as well as convenient collection of all data in a database. Results are available within minutes and even very low TAN/TBN values can be determined with reproducibilities better than 2%.
ASTM D 664 and ASTM D 2896 describe two methods for the determination of TAN and TBN based on potentiometric titration of the acidic and basic constituents, respectively.
If carried out manually, these procedures are time-consuming and labour-intensive. Further drawbacks are the handling of toxic solvent mixtures and the tedious cleaning of oil- smeared beakers and electrodes. All of this can be avoided with the 864 Robotic Balance Sample Processor, as it allows the complete automation of these procedures from sample preparation all the way to collecting and processing results in a comprehensive database. A unique feature of the system is the patented technique of weighing the sample directly on the rack. There is no simpler way to prepare a sample – just position it on the rack and press START, all other steps are carried out fully automatically. This includes taring of the titration beaker as well as transferring the correct amount of sample. This technique significantly improves the accuracy and reproducibility of results.
Reader Reply Card No 31
February/March 2010
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