Determination of Criteria for Assessing the Oil Quality of Current Transformers Type TFZM 110 kV

Objective of research was to determine the criteria for assessing the technical condition of oil of current transformers (CT) type TFZM 110 kV. These CT make up most of the CT fleet. The influence of the structural-group composition of the oil and the life time of the CT on variation of following parameters was studied: moisture content and the tangent of dielectric loss of oil at 90°C, breakdown voltage, acid number (H2O, Ubr, Tgoil90°C, KOH). The analysis was carried out on a representative sample (24517 measurement results), which was collected for 30 years. The measurement results were divided into 9 groups (with different structural-group composition of the oil and different periods of CT operation). For each group, the mathematical expectation value, dispersion, permissible value and maximum permissible values of the studied parameters were determined. Further, the impact of the service life and mark of oil on each of the oil quality parameters was evaluated. More accurate criteria for evaluating the quality of the oil are determined, considering the operating time of the CT and the characteristics of the mark of oil. The obtained dependences of the parameters on the operating time can be used with the help of predictive analytics for medium-term planning of oil regeneration (replacement), determination of the optimal frequency of oil quality control.