Abstract
This paper presents a health analysis technique for transformer winding insulation through thermal monitoring and Fast Fourier Transform (FFT) power spectrum. A novel thermal model for the Kraft paper insulation of transformer is proposed by using the transformer’s top-oil and winding hot-spot temperature models. The relationship between the temperature rise of oil inside the transformer tank and the winding insulation degradation are considered by utilizing the data-sets and daily load cycles of a 10/13 MVA, 132/11 kV, 50 Hz, ONAF grid power transformer. The model based on IEEE Guide for loading mineral-oil-immersed transformers is developed in Simulink. The hotspot temperature rise from the thermal model is used as a reference to analyze the winding insulation degradation in the form of high frequency partial discharges (PDs) upon the output parameters of the transformer. Using data analysis techniques, a correlation is presented between the load cycles and the hot-spot temperature through which the health status of the transformer winding insulation is estimated. Moreover, the high frequency transients were detected using the Fast Fourier Transform (FFT) spectrum analyzer tool in MATLAB. The preliminary study shows that high frequency PDs are detected for the overheated and deteriorated state of the winding insulation. The results show that the proposed technique is feasible for the health analysis of power transformers and successfully predicted the deterioration of the transformer winding insulation.
Highlights
The valid and relevant approaches reported for the subject matter are; Partial discharge (PD)(IEC-60270), Ultra High Frequency (UHF) partial discharges (PDs) measurement, Frequency Response Analysis (FRA), Frequency Domain Spectroscopy (FDS) and Thermal monitoring
A novel thermal monitoring technique for the health analysis of the power transformer winding insulation is presented in this paper
The thermal model is trained with the ambient temperature and load cycles of a 10/13 MVA, 132/11 kV, 50 Hz, ONAF grid power transformer
Summary
Power transformer’s health is an important aspect in defining the reliable operation of the power system. The root cause of these failures is the winding insulation, its real-time condition monitoring and health assessment is very crucial for power system operation. The kraft paper provides the electrical insulation to the transformer windings whereas the oil provides the thermal stability by acting as an insulation medium [7,8,9]. The quality of the kraft paper deteriorates both physically and chemically with nonlinear loads, transient voltage surges, switching and internal heating of the transformer caused by the heavy overloading [10,11,12,13], reducing the transformer life time. The analysis of the failure percentage of large oil-immersed power transformer and their winding insulation is an important factor to assess the health of power transformers.
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