Prediction of Bus-Transfer Switching in Future HVdc Substations

Abstract

Abstract-Prior research has characterized bus-transfer switching capabilities of disconnectors commonly found in ac gas insulated switchgear (GIS) by means of a limit performance prediction. A large number of dc bus-transfer tests was 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 bustransfer 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.

Improving GIS Disconnectors for Future HVDC Applications

“…In prior research on the fundamentals of bus-transfer switching in HVac [14] and HVdc GIS [13] employing widely used GIS disconnectors with slow-moving and unblown electrode systems, the authors have identified a correlation between the instantaneous recovery voltage u RV and the predicted arc voltage u arc at a current zero at time t 0 , which ensures an extinction of the switching arc:…”

“…voltage level (L ) and pre-switching current (i S ·d 1 /(d 1 +d 2 )), these times become longer [13]. Another potential application of HVdc disconnectors, which can be modelled by the equivalent circuit diagram of Fig.…”

“…in ac [14] and dc [13]. For the investigation of disconnectors at higher recovery voltages, a low pass filter (R F , C F ) was implemented, mitigating high frequency oscillations, which are otherwise excited by large changes of the current gradient between the bus-transfer inductances and parasitic capacitances of the FPDCS modules.…”

“…1. Simplified equivalent circuit diagram for bus-transfer switching, in which the disconnector is modelled as a current and time dependant voltage source u DS as used in prior investigations [11], [13], [14].…”

“…Their applications in HVdc converters have been well documented [10], however, MTdc-specific research of requirements and available technology for use in substations remains rare. The use of disconnectors to transfer load currents between parallel conductors such as bus bars of a substation or submarine cables in an MTdc grid has been investigated by Kanngiesser [11], Vinson [12] and the authors [13]. The findings of long arcing times without current zeroes for large inductances and high harmonic contents leading to multiple reignitions present dc specific challenges, which have to be investigated further and which can be mitigated by improved disconnector designs.…”