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Investigation of overvoltages in distribution transformers

Nowadays voltage transients in electrical power systems can take different shapes related to properties of distortion source and physical phenomenon appearing in systems. Usually overvoltages contain oscillation components of different frequencies, which are propagating along lines reaching transformer terminals. Overvoltages impact power transformer insulation systems in spite of used overvoltage protection. Analysis of overvoltages in winding insulation systems have strong importance in proper and reliable work of transformers. Due to complex configuration of transformer winding different overvoltages levels can occur inside winding than at winding terminals. This article presents investigation of internal overvoltages in distribution transformer windings. Analysis was based on measurements results of transient voltages and frequency characteristics. Investigation of resonance frequencies based on winding admittance measurements was made also.