# HVdc Circuit Breakers: Prospects and Challenges
## 8 Summary and Future Research Needs  
In the previous sections of this article, several technical areas were identified and discussed related to the HVdc breakers. Summary of the conversed literature and future research directions are discussed in the following [72]:  
1. Improvements in the existing dc breaker topology can be fetched by optimizing the size of components such as; inductors, capacitors, varistors, etc. The goal is to reduce interruption time, size, and cost.
2. The switching arc's oscillation growth and interruption capability can be optimized by studying the arc characteristics in detail under various vacuum and gas breaker conditions. Verification and derivation of the constraints are in mathematical arc models.
3. Comsol Multiphysics(r) simulations of dc arcs are recommended for high oscillatory current and during the interruption.
4. Medium-voltage dc breakers can be employed for high-voltage levels by enhancing the technology, series connections, or by smearing dc breakers across the medium-voltage levels in multilevel converter topologies.
5. The use of hybrid dc breakers is recommended. As it can have features of both mechanical and solid-state breakers with reduced ratings of switches. Thus, size, cost, and interruption time are reduced.
6. Fast mechanical disconnectors with low on-state losses and high recovery of withstand voltage have sufficient arcing voltage for swift commutation. Such switches can be deployed in hybrid dc breakers for fast actions.
7. The use of new wide-bandgap power semiconductor devices (e.g., SiC or GaN) is recommended to have negligible on-state losses.
8. Active gate driving technologies that may improve the performance of semiconductor switches in a pure solid-state circuit breaker are recommended.
9. Integrated optimization of the whole M-HVdc system should be done to comply with the necessities of breaker-control protection.
10. The standards and norms for the operation of multi-terminal HVdc systems must be defined to develop the proper dc-grid protection.
11. New testing methods for the dc breaker or its components should be designed. As dc breakers have strong network interaction, power-hardware-in-the-loop techniques would be advantageous.
12. GE Plasma switches that may operate at high temperature, more economical, and are adjusted in confined space of smaller footprints are recommended for medium dc voltage.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of CB** & **Alstom** & **ABB** & **GE** \\ \hline Size & Large & Medium & Reduced \\ Cooling & Required & Required & Not required \\ On–state losses & Low & High (0.01\% of transmitted & \\  & Low & Power (>Alstom) & Reduced \\ Interruption speed & Medium & High (few ms \textgreater{} Alstom) & High \\ Auxiliary branch & Thyristor stacks in series with a capacitor & IGBT switch with ultra fast & — \\  & & disconnector & — \\ Cost & Lower for HVDC & Lower for MVDC & Reduced \\ Interruption capability & Uni–directional & Bi–directional & — \\ Suitability & High voltage dc/LCC & MVdc/VSC & MVdc \\ \hline \hline \end{tabular}
\end{table}
Table 6: Comparison of anticipating commercial HVdc breakers.