Characterisation of Dynamic Stresses on HVDC Cables upon DC Current Interruption in Meshed Grid Applications

Photo adopted from the TenneT TSO 2GW program - The 2GW program (tennet.eu)

An interconnected DC network brings value by improving the utilization of transmission infrastructure. The availability of the grid is improved, and DC side connections are optimized by reducing the number of necessary converters. The DC grids are, however, faced with a novel interface between DC cables and fault separation devices, such as DC circuit breakers. To harness the benefits and to realize a sustainable DC grid, the requirements of such an electrical interface must be investigated and specified for its technical requirements. This necessitates a thorough understanding of dynamic stresses, such as transient voltages and currents, under various operational modes of the circuit breaker. This research intends to provide a detailed analysis of the prospective dynamic stresses in meshed DC grids that would potentially be experienced by cable systems when implemented together with DC circuit breakers.

The energy transition aims to guarantee the security of supply, along with minimizing environmental impact and cost of energy to consumers. In case of a contingency, DC grids would experience a relatively faster decay in voltage due to lower overall system impedance. The fault current would increase owing to higher line discharge currents, along with a contribution from multiple fault-feeding sources. Therefore, higher fault currents and subsequent transient voltages can be expected in DC grids. Additionally, DC circuit breakers would be needed for quickly and selectively isolating faulty cable sections. This selectivity is essential to avoid the total loss of a multi-terminal DC network in case of a fault. Cables are the preferred transmission choice, especially for realizing offshore DC grids. To improve reliability, technical requirements must be specified for the DC cables for an electrically robust interface with a DC circuit breaker. A knowledge gap currently exists in defining a representative transient stress profile affecting the cables in meshed DC grids, especially due to the implementation of DC circuit breakers. This research would contribute to filling this gap.

This project is realized in cooperation with TSO TenneT, and the results will provide a detailed analysis of the electrical interface between DC cables and DC circuit breakers. Practice-based DC cable system modeling and the use of existing verified models of the DC circuit breakers will be developed accordingly.

Project Partners

The research is conducted by Tanumay Karmokar who holds a full-time position at TenneT TSO GmbH in Germany. The responsible supervisor at TU Delft is Prof.Dr.Ir. Marjan Popov. TenneT, is the main stakeholder in the results, and financially supports the project.