Recent studies of long EHV cables show the importance of performing temporary overvoltage analyses. As the switching of EHV cables can trigger temporary overvoltages, it is important to find the dominant frequency component contained in the switching overvoltages of these cables. Since there are no theoretical formulas to find the dominant frequency, it is generally found by means of time domain simulations or frequency scans. The derivation of theoretical formulas has been desired as the formulas would be useful in verifying the results of time domain simulations or frequency scans. Additionally, the formulas could eliminate the necessity of building simulation models of some network components. In order to address this need, this paper derives theoretical formulas to find the dominant frequency in long cable energization overvoltages. The accuracy and practical usefulness of the formulas are confirmed by comparing with the results of time domain simulations.

No abstract

No abstract

No abstract

The Kriegers Flak combined grid solution (KF CGS) will interconnect the eastern synchronous area of Denmark and Germany by extending the existing high-voltage alternating current (HVAC) offshore wind farm infrastructure in the Baltic Sea. In contrast to conventional point-to-point interconnectors, the extension creates a meshed submarine grid (MSG) which includes an interconnector and wind farm collectors to the countries using the same equipment. Denmark East as part of the Nordic system and 50 Hertz as part of the synchronous Continental European grid are asynchronous to each other, which makes a frequency transformation necessary. The interconnection will be realised by a high-voltage direct current (HVDC) back-to-back (BtB) converter in voltage source converter technology located at the German end of the interconnector. The BtB and the entire HVAC MSG between Denmark and Germany will be controlled by a so-called master controller for interconnector operation (MIO). The KF CGS will integrate offshore wind power generation, increase the security of supply and enhance integration of regionally produced renewable energy. This study describes the overall infrastructure of the KF CGS and the MIO functions. A model-based evaluation of those shows the behaviour of the HVAC/HVDC MSG in normal operation and in the case of contingencies.