Analysis and Control of Harmonic Overvoltages during Power System Restoration

The transmission system topologies during power system restoration are quite different from the well integrated system during normal operation. Due to the parallel resonance resulting from the combination of the system impedance and the transmission line capacitance, harmonic distortions caused by the switching of lightly loaded or unloaded transformers are amplified, creating high harmonic overvoltages which may cause catastrophic equipment damages and activation of protective devices. Through detailed analysis on the cause of harmonic overvoltages, this paper focuses on control of the transformer inrush current and improvement of the system frequency response characteristics. Sensitivity analysis was performed in order to find the most efficient remedial actions. Wavelet analysis was employed to analyze the transformer inrush current in both the time and frequency domains to obtain the signal information in each frequency band. The tendency of the voltage waveform was predicted based on the energy of the signal and an algorithm was then developed to terminate the electromagnetic transient simulation in a minimum amount of time. The method proposed in this paper enables fast assessment and efficient control of harmonic overvoltages which can provide guidelines for both the development of power system restoration (PSR) plan and the real system restoration