Case Study - Calculation of DGA Limit Values and Sampling Interval in Power Transformers

The predictive maintenance in power transformers aims to manage the risk of the asset. This is achieved through the calculation and control of the health index of the power transformers. A very important parameter for calculating the health index in power transformers is the dissolved gas analysis (DGA). The current trend is online DGA monitoring, in addition to continuing to perform analyzes in the laboratory. In spite of the fact the DGA is well known, there is a lack of real data outside the guides. This case study uses a method for calculating the limits of the gas levels and of the annual increase in the concentration of combustible gases, in order to establish the optimum sampling interval and the alarm limits of the continuous monitoring equipment for each power transformer.