## 5 Future Challenges
Reaching better times for MCBs is very difficult, so researchers around the world are focusing their efforts on obtaining SSCBs or HCBs. Despite their arc-extinguishing difficulties and low operating times, MCBs are still used in DCMGs because of their low losses and low cost. SSCBS constitute a good alternative for DCMG protection due to several advantages: (1) operating times lower than 100 \(\upmu\)s; (2) that it does not generate arcs under faults since there are new technologies that permit galvanic isolation; (3) that it does not produce sound \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Type** & **Advantages** & **Disadvantages** & **Operation Speed (ms)** & **Ref. N°** \\ \hline \multirow{3}{*}{Fuses} & \multirow{3}{*}{Low Cost} & Not able to distinguish between a transient and a permanent fault. & \multirow{3}{*}{\textless{100}} & \multirow{3}{*}{[21]} \\  & & Fuse need to be replaced for successful operation & & \\ \hline \multirow{3}{*}{MCBs} & Low cost. & Slow operating speed. & \multirow{3}{*}{\textless{60}} & [21] \\  & Low contact resistance. & Limited current interruption & & [92] \\  & Very low power losses. & capability. & & [20] \\  & & Low life time. & & [64] \\ \hline \multirow{3}{*}{SSCBs} & Fast operation. & High on-state losses. & \multirow{3}{*}{\textless{0.1}} & [21] \\  & No arc, no sound. & Relatively high cost. & & [92] \\  & No gas emissions. & Big size due to heatsink. & & [20] \\  & Very long lifetime. & & [31] \\ \hline \multirow{3}{*}{SSCBs} & Compared with Si SSCBs: & \multirow{3}{*}{\
\begin{tabular}{} \end{tabular} } & \multirow{3}{*}{\textless{0.1}} & \multirow{3}{*}{[78]} \\  & Higher speed. & & \\  & Higher thermal conductivity. & & & \\  & smaller heat sinks. & & & \\  & Withstand higher voltages. & Still evolving towards its maturity. & & [103] \\  & Thinner for the same voltage. & & & \\  & very low switching losses. & & & \\ \hline \multirow{3}{*}{HCBs} & Low power losses. & Complex technology. & \multirow{3}{*}{\textless{0.1}} & \multirow{3}{*}{[94]} \\  & No arcing on mechanical contacts. & Current commutation relies on the arc voltage. & & \\  & Relative fast operation speed. & Very expensive & & \\ \hline \multirow{3}{*}{ZSCBs} & Fast operation. & \multirow{3}{*}{
\begin{tabular}{} \end{tabular} } & \multirow{3}{*}{\textless{0.1}} & \multirow{3}{*}{[58]} \\  & Natural commutation. & & & \\  & Control circuit simplified. & & & \\  & Cascaded breaker coordination is & & & \\  & inherently automatic. & & & \\  & Relative lower cost. & & & \\  & Fast operation. & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of CBs. because the trigger does not use any mechanical systems for operation; (4) that it does not emit gases, since there is not any chemical reaction during the operation; (5) that it has long life service for the use of semiconductors; (6) that it presents high reliability; and (7) that it correctly works for a great variety of DCMG applications (generators, loads, batteries). However, to be fully developed, there is still the challenge of reducing power losses due to the modulation effect of the finite conductivity of semiconductors [31], as well as the reduction of the current-balancing problem and construction cost in parallel technology to improve the interrupting capability [104]. Moreover, the family of SSCBs is very broad (SCR, GTOs, Mosfets, IGETs, IGCTs, and CS-MCTs) and there is a lot of research to improve them, as evidenced in this review. In general terms, trying to put together the most relevant aspects of all papers consulted, SSCBs have, as a future challenge, the reduction of the commutation losses, while simultaneously safely increasing the switching frequency in order to decrease the harmonic frequency currents injected to the system.