The degree of polymerization of cellulosic insulation: Review of measuring technologies and its significance on equipment

In this paper, at first the term and the technical significance of the degree of polymerization (DP) of cellulose insulation is explained. Factors influencing the DP of new, unused insulation products are detailed. An overview of commonly used DP measuring techniques and standards is given. Depending on the method, the measured DP value of cellulose insulation can vary considerably. The DP loss at transformer drying in the factory is examined and the correlation of the DP with functional properties and lifetime of solid insulation is detailed. The issue of minimum DP requirement of insulation of new transformers is discussed, considering the assessed loss-of-life due to transformer drying.