Voltage Stresses Produced by Aperiodic and Oscillating System Overvoltages in Transformer Windings

This paper investigates the internal voltages produced by various types of system overvoltages with special consideration to part winding resonance phenomena19297 which can result in very high voltage stress but may not be: adequately considered in design and test practice. A case of oscillating voltage excitation is reported which caused the failure of a generator step-up transformer due to internal resonance. According to theoretical considerations, internal oscillation and resonance voltages depend on the damping of the excitation voltage and of the windings. For a 500 kV single phase generator step-up transformer, it is demonstrated that favorable damping characteristics of the windings can reduce to a large extent the risk of excessive internal voltages