Novel Sensor for Determining the Aging Condition of Insulation Paper in a Transformer

The online monitoring is becoming increasingly important for operators of high voltage assets. One of the most important assets are transformers, especially power transformers, which are mainly insulated with paper together with an insulating liquid for impregnation. An important parameter is the aging condition of the insulating paper, which allows an estimation of the operational safety. This variable is determined by the degree of polymerization (DP-value) and provides information about the mechanical stability of the paper. However, paper samples are currently required for the measurement, which is carried out in a laboratory in accordance with IEC 60450, whereby the paper is destroyed. This study is conducted to determine the DP-value of a paper insulation using a novel, patented optical sensor. The investigation shows that oil-free paper samples have very strong linear correlation between the value measured with the sensor and the DP-value. Therefore, a condition assessment is possible within seconds, as the measurement by means of the optical method is significantly faster and more precise than the conventional viscometric method. It also shows that the assessment is independent of the insulating oil, in which the paper is aged. The sensor could be used for an improved condition assessment of transformers to increase the operational safety.