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Design Optimization of Ferrite Rings for VFTO Mitigation

Very fast transient overvoltage (VFTO)-related problems are raising growing concerns in China with the development of ultra-high voltage. The practice of fitting ferrite rings on gas-insulated switchgear busbars for VFTO mitigation has long been proposed but few investigations on its' design optimization were conducted. Based on theoretical analysis of the simplified model, the optimal damping condition of ferrite rings is proposed, which is conducive to the type selection. The number of rings to be employed to ensure visible suppressing effects is given through simulations and the influence of the saturation is discussed. The impact on power frequency is analyzed to be negligible. Finally, comparisons are made between theoretical conclusions and existing experiment results, which approve the optimal damping condition and agree in the number of rings to be employed.