Improved Calculations for No Load Transformer Switching Surges

Abstract

Abstract-This paper deals with a modeling of components and calculation of transient overvoltages that build up on the transformer primary terminals after the transformer has been switched off by a vacuum circuit breaker (VCB). The transformer is connected to the circuit breaker by a cable. The transient overvoltages are calculated for different cable lengths, and the cumulative probability of different arc angles is investigated.In this study two cases are considered: transient overvoltages due to steady-state magnetizing current switching, and transient overvoltages due to inrush current switching. It is shown that the case of inrush current switching is worse, as virtual current chopping is possible. The cable is modeled by pi sections, whereas the transformer model is based on a terminal impedance. The VCB re-ignitions are modeled by means of withstand voltage characteristics and high-frequency quenching capability. Due to shortage of field tests, this work uses only literature references to compare the results with actual measurements.

Transients in collection grids of large offshore wind parks

“…In order to represent the interaction between VCB and cables, modeling of the cable using pi-links or section has been adopted, for instance in Popov and van der Sluis. 10 However, it will be shown in this study that the wave propagation of TOVs has a crucial impact on the magnitude and the time derivative of the TOVs. To analyze these fast phenomena on a very short timescale, a cable model including wave propagation and fre-quency-dependent damping must be used.…”

Internal Resonance for Power Transformer Interacted With Cable Transients

“…If the oscillating frequency of the external overvoltage surge is close to the resonance frequency of the transformer winding, internal transformer resonance occurs resulting in high frequency overvoltages with maximum value. Therefore, external transients occurring in power systems might trigger internal transformer resonance, which causes high frequency transient overvoltages leading to insulation breakdown for transformer winding [1][2][3][4][5][6][7][8][9][10][11]. Shunt capacitor banks are installed in high voltage and extra high voltage systems to achieve economic saving.…”

Research on overvoltage suppression of interrupting no load transformer

“…Most of those energy-intensive enterprises are using electric arc furnace, which would cause hidden troubles to the grid, such as line trips, equipment damages and overvoltage accidents. Among this, the overvoltage accident caused by using the vacuum breaker to cut off the arc furnace transformers is one of the most serious problems [1][2][3][4][5][6][7][8][9][10][11][12][13] .…”