Practical results and opportunities of evaluation of transformer diagnostic by an expert system

In the High Voltage Laboratory at Budapest University of Technology and Economics developed expert system, called Transformer Status Indicator (TSI) provide a good solution for technical and economical evaluate and for compare multiple transformer diagnostically results. The power transformer is the most important equipment in the transmission and distribution system, so the operators have to know the condition of their equipment because of the maintenance and operating too. This expert system is the principle of condition based maintenance strategy. The system consider discrete diagnostically results (e. g.: oil test, dissolved gas analyzing (DGA), recovery voltage measurement (RVM), furan content, insulation resistance, dielectric loss factor (tg delta)). For the comparison we need to consider some other parameters what do not indicate the status of the insulation but it has influence for that. These parameters are: voltage level, nominal power, weather, location in the grid, and the location: industrial or rural environment. The expert system using the data listed above and can characterize the condition of the insulation of the transformer only a few parameters (status of the insulation, reliability and theoretically minimum and maximum values of it) independently from the power, voltage level etc. to compare each transformer condition to make a best decision for change or refurbish the equipment. In the research work, after the developing process, the expert system tested by real data from the Hungarian distribution system. The source of the testing data is 13 HV/MV distribution transformers in Hungary. In this paper we are focusing the results and their evaluating possibilities. Because of the number of test transformers we can use statistical methods to get a good result. Either possible evaluating way is to calculate the average decreasing speed of the status of the insulation. If the operators know each work effect (maintenance and/or reconstruction) in the status of the insulation, the necessary time and volume of this work can calculate using the TSI expert system.