Numerical Evaluation of Natural Frequencies in Power Transformer Windings

Simple equations for numerical evaluation of the natural frequencies in transformer windings are given. The constants that enter the equations may easily be calculated from transformer data. The equations are valid for transformers with a high-voltage (HV) cylindrical disk winding, and where the turn ratio between the HV winding and the low-voltage (LV) winding is large. Only the natural frequencies in the HV winding are considered. The equations cover windings with the neutral circuit grounded and with the neutral circuit open.