Prediction of Bus-Transfer Switching in Future HVdc Substations

Prior research has characterized bus-transfer switching capabilities of disconnectors commonly found in ac gas insulated switchgear by means of a limit performance prediction. A large number of dc bus-transfer tests were conducted on a modified bus-transfer test setup in order to study the applicability of these findings for the use of disconnectors in future HVdc substations. It was found that the ac extinction criterion based solely on the instantaneous recovery voltage and the expected arc voltage at current zero is also valid for dc bus-transfer switching. However, due to the high-frequency harmonics inherent to HVdc power transmission, the process of reaching the initial current zero and the extinction of the switching arc at current zero have been discovered to be independent to a certain degree. For negligible harmonic content of the switching current, arcing times below 20 ms have been predicted for reasonable sizes of substations and realistic dc current magnitudes, which is certainly within the capabilities of existing ac disconnectors. The previously devised limit performance prediction can be applied to gauge influences of different harmonic current contents and small modifications to the disconnector in simulation by applying the reignition criterion at the initial and all subsequent current zeros. Ultimately, however, exact knowledge of frequency and magnitude of the harmonic currents is needed in order to perform accurate predictions.