Laboratory ferroresonance measurements in power transformers

The paper analyzes laboratory ferroresonance measurements taken on an example of a three-phase three-legged power transformer. Ferroresonance occurrs due to a nonlinear inductance, capacitance and periodic voltage source in the network. A transformer becomes ferroresonant during an irregular circuit-breaker operation, when the interaction between the transformer nonlinear magnetizing inductances and phase-to-ground capacitances generate sustained distorted overvoltages. The measurement results and voltage waveforms show the presence of high and sustained ferroresonant overvoltages and a harmonic spectrum containing higher harmonics.