Prediction of the in-plane biaxial strength of paper by the Tsai-Wu failure criterion has in general proved to be in good agreement with experimental data. However, the Tsai-Wu criterion ...overestimates the strength in some parts of the biaxial tension region. This shortcoming can be corrected by adding a pair of cubic terms to the existing Tsai-Wu criterion. The modified Tsai-Wu criterion presented here predicts the biaxial strength of paper more accurately than the Tsai-Wu criterion. The extra pair of parameters introduced is determined ftom data obtained by standard tests.
Viscometric Degree of Polymerization (DPv or DP for short) is a well-established method used in the transformer industry to track degradation of the paper insulation used inside transformers. The DP ...method works well for both new, unprocessed paper, and for aged paper. But in recent years it has become an established fact that there are unclear issues related to measurements of DP on new paper after factory drying. This phenomenon has been observed for different paper types, paper dried using different drying methods, different types of pulp and measurements made at different laboratories. Cigré has recently published a reference paper on the subject 1, written by experts from different transformer manufacturers, paper manufacturers, independent laboratories and utilities. It is further noted in Cigré brochure 738 (WG D1.53) that at times, new paper after factory drying does not dissolve well in the Cuen solution used for DP measurement. This difficulty introduces tremendous uncertainties in the average DP numbers reported by laboratories for such papers. In this article we seek to shed some light on this problem and its effect on reported DP values.
