Application and limitations of the Karl Fischer technique of moisture analysis in electrical plant insulation

A major utilities´ (Queensland Electricity Company) experiences with moisture determination in electrical insulation via the coulometric and titrimetric Karl Fischer technique are revealed. The importance of maintaining confidence in the reliability of this determination in relation to electrical plant contractual acceptance, maintenance and overhaul is discussed and sources of error in the overall determination of insulation dryness are examined. Major sources of error in moisture determinations are the sampling process, subsequent sample handling, inadequate knowledge of material composition and generally unrecognised characteristics of the Karl Fischer technique. The paper describes the approach taken in the authors organisation to reduce such errors in the determination of the relative humidity of insulation systems. One approach to a methodology for identification and measurement of accuracy, precision and bias is also presented