Moisture Equilibrium Charts for Transformer Insulation Drying Practice

A set of moisture equilibrium charts applicable to transformer insulation is presented. These may be used for the estimation of dryness levels in transformer insulation during the preparative and operational stages, and also during storage. A critique on the well known Piper chart is provided. Techniques to construct equilibrium curves for the combined paper-oil system from indirect measurements are outlined, and the interpretation of these curves for practical situations is discussed.