Calculation of power transformer health index using the combination of principal component analysis and mass-spring-damper model

Power transformers are one of the most important and expensive equipment in power systems which could be affected by electrical stresses such as traveling waves, switching and thermal stresses such as overload and chemical reactions in dielectric oil. The DGA index expresses the dissolved gases generated due to faults in the transformer oil. The oil quality index determines the effect of electrical, physical and chemical parameters of transformer oil. Oil quality and DGA indices are important in determining the transformer health index. In this paper, the principal components analysis method used to determine the weight coefficients of DGA and oil quality indices. Also, the modes determined by CIGRE technical brochure 761 are used to calculate the mentioned indices. Then, the transformer is considered as a second-order system, and the mentioned indices are determined as parameters of the damping coefficient and natural frequency related to the mass-spring-damper model of the second-order system. Using state space matrices, the transformer system matrix of the second-order system is determined. Finally, the transformer health index is calculated using the ratio of the infinity norm matrix of the new transformer system to the infinity norm matrix of the worked transformer system.