Study on Voltage Response Method of Transformer Condition Assessment

Accurate condition assessment of power transformer is needed to guarantee transformer operation safely and reliably. In this paper the technique and application of return voltage measurement and some results of dielectric response measurements of several transformers was introduced. Voltage response measurements were performed on various transformers with different voltage grades, various operating periods, different moisture contents and aging degrees on site. Derived moisture contents from return voltage measurement were compared with the corresponding moisture contents obtained from the analysis of oil samples. Based on on-site experiments and theoretical analysis, the criteria for insulation state of transformer are proposed. Moisture condition of transformer insulation can be determined by using return dominant time constant, and a good correlation between aging degree and the return voltage initial slopes of the aged transformers. Field test performed on several transformers, its interpretation of results are also presented, which proves that RVM measurements can be used as a reliable tool for evaluating moisture content in transformer insulation.