Water by Karl Fischer

Water contamination in transformer oils is a significant problem. One of the most important functions of a transformer oil is to provide electrical insulation. Any increase in moisture content can reduce the insulating properties of the oil, which may result in dielectric breakdown. Water not only results in poor insulation and fluid degradation but plays a role in the breakdown of the paper insulation with a resulting in a loss of performance. A weighed portion of sample is heated in a sealed sample vial. A stream of dry gas, typically air is passed through the sample and carries over any water vapour that is liberated into the titration vessel containing the titration solvent. Iodine for the Karl Fischer reaction is produced coulometrically in the vessel at the anode.  When all the water has been titrated, an electrometric end point detector detects excess iodine and the titration is terminated. Results are quoted in either % w/w or ppm w/w.