## 7 Annotations on Topological Evaluation of HVdc Circuits
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Topology** & **No. of DCCB** & **No. of HVdc Link** &
\begin{tabular}{c} **Extra Offshore** \\ **Substation** \\ \end{tabular} & **Flexibility** & **Stability** & **Redundancy** & **Comm** & **Remarks** \\ \hline PPT & Zero & \(\text{N}_{\text{WP}}=\text{N}_{\text{BS}}\) & No & No & Yes & No & No & Single terminal, not flexible \\ \hline GRT & & \(\text{N}_{\text{WP}}+\text{N}_{\text{BS}}\) & \(\text{N}_{\text{WP}}+\text{N}_{\text{BS}}\) & No & Excellent & Moderate & Excellent & Yes & Flexible but the dc-link have to be rated \\ \hline \multirow{3}{*}{ST} & WF side & \(\text{N}_{\text{WP}}+\text{N}_{\text{BS}}\) & \(\text{N}_{\text{WP}}\) & Yes & Bad & Excellent & Moderate & No & The rating of dc circuits of GS-VSC and \\  & SS side & Zero & \(\text{N}_{\text{SB}}\) & No & Excellent & Bad & Moderate & No & WF-VSC are equal. Fault in the central \\  & Total & \(\text{N}_{\text{WP}}+\text{N}_{\text{BS}}\) & \(\text{N}_{\text{WP}}+\text{N}_{\text{BS}}\) & Yes & Moderate & Moderate & Moderate & No & star mode will collapse the system. \\ \hline \multirow{3}{*}{SCRT} & WF side & \(\text{N}_{\text{WP}}+\text{N}_{\text{BS}}\) & \(\text{N}_{\text{WP}}\) & Yes & Bad & Excellent & Moderate & No & Full power rating dc-link required in the \\  & SS side & Zero & \(\text{N}_{\text{SB}}\) & No & Excellent & Bad & Moderate & No & contrast ring. Moderately flexible and \\  & Total & \(\text{N}_{\text{WP}}+\text{N}_{\text{BS}}\) & \(\text{N}_{\text{WP}}+\text{N}_{\text{BS}}\) & Yes & Moderate & Moderate & Moderate & No & stable \\ \hline \multirow{3}{*}{WERT} & WF side & \(\text{N}_{\text{WP}}\) & \(\text{N}_{\text{WP}}\) & No & Excellent & Excellent & Excellent & Yes & Requires a number of DCCB equal to \\  & SS side & Zero & \(\text{N}_{\text{SB}}\) & No & Bad & Bad & Moderate & Yes & PFS. Flexible on the WFS side. Poor \\  & Total & \(\text{N}_{\text{WP}}\) & \(\text{N}_{\text{WP}}+\text{N}_{\text{BS}}\) & No & Moderate & Moderate & Moderate & Yes & stability during fault inside the GS-VSC. \\ \hline \multirow{3}{*}{SSRT} & WF side & Zero & \(\text{N}_{\text{WP}}\) & No & Bad & Bad & Moderate & Yes & Good stability but poor redundancy and \\  & SS side & \(\text{N}_{\text{SB}}\) & \(\text{N}_{\text{SB}}\) & No & Excellent & Excellent & Excellent & Yes & flexibility. The HVdc CB is equal \\  & Total & \(\text{N}_{\text{SB}}\) & \(\text{N}_{\text{WP}}+\text{N}_{\text{BS}}\) & No & Moderate & Moderate & Moderate & No & No \\ \hline \multirow{3}{*}{2 WF-ISS} & WF side & Zero & \(\text{N}_{\text{WP}}\) & No & Moderate & Moderate & Moderate & Yes & The number of DCCB is half to WFs. \\  & SS side & \(\text{N}_{\text{SB}}\) & No & No & Bad & Bad & Bad & Yes & Moderate flexibility and stability \\  & Total & \(\text{N}_{\text{SB}}\) & \(\text{N}_{\text{WP}}+\text{N}_{\text{BS}}\) & No & Moderate & Moderate & Moderate & Yes & \\ \hline \multirow{3}{*}{WFS-SSRT} & WF side & Zero & \(\text{N}_{\text{WP}}\) & No & Excellent & Excellent & Excellent & Yes & Excellent flexibility, stability, and \\  & SS side & \(\text{N}_{\text{SB}}\) & \(\text{N}_{\text{SB}}\) & No & Excellent & Excellent & Excellent & Yes & redundancy with the same number of \\  & Total & \(\text{N}_{\text{SB}}\) & \(\text{N}_{\text{WP}}+\text{N}_{\text{BS}}\) & No & Excellent & Excellent & Excellent & Yes & HVdc CB as in 2 WF-ISS \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of MT-HVdc system topologies.