# Fault Detection and VSC-HVDC Network Dynamics Analysis for the Faults in Its Host AC Networks
## 5 Conclusions  
Protecting HVDC transmission systems against both AC and DC faults is a challenging task. An SST-based detection algorithm was proposed in this work, where the DTE index is computed using the output obtained from the EMD-SST. The proposed method was  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Detection Technique** & **Fault** & **SLS** & **SNR** & **Detection Time** & **Computational Burden** \\ \hline TMF & \(\surd\) & - & - & From 200 ms to 2 s & Low \\ \hline V\&I THD & \(\surd\) & - & - & 800 ms & High \\ \hline ROCOC and ROCOV & \(\surd\) & - & \(\surd\) & 200–300 ms & High \\ \hline ROCOF & \(\surd\) & \(\times\) & - & 100 ms & Low \\ \hline ROCRP & \(\surd\) & \(\times\) & \(\times\) & 100 ms & Low \\ \hline FFT & \(\surd\) & \(\surd\) & \(\times\) & 50 ms & High \\ \hline ST & \(\surd\) & \(\surd\) & \(\times\) & \textless{2 s} & High \\ \hline STFT & \(\surd\) & \(\times\) & \(\surd\) & \textless{2 cycles} & High \\ \hline WT & \(\surd\) & - & \(\surd\) & 30 ms & High \\ \hline VMD-HT & \(\surd\) & - & \(\surd\) & 10 ms & Low \\ \hline HHT & \(\surd\) & \(\times\) & \(\times\) & 10 ms & Low \\ \hline SST (Proposed) & \(\surd\) & \(\surd\) & \(\surd\) & \textless{5 ms} & Very Low \\ \hline \hline \end{tabular} \(\surd\) = condition verified, X = not considered, SLS = sudden load switching, and SNR = signal-to-noise ratio.  
\end{table}
Table 6: Comparison of the proposed method with the existing techniques.  
Figure 12: Results for the presence of noise in the signal. (**a**) Current waveform for phase A, (**b**) DTE for phase A in the presence of various SNRs.  
tested, and the results were validated for different conditions such as symmetrical and asymmetrical fault conditions, fault locations, load angles, and fault inception times. The algorithm was applied to an HVDC network connected with AC host networks. The simulation results indicate the performance of the proposed method during every stage of the disturbance. It was also found that the method was robust enough for the selected sampling frequencies, load switching conditions, and noisy conditions. For the different AC faults (i.e., AG, ABG, AB, and ABC faults) in the host AC network-1, the proposed method took 4.24, 3.85, 1.65, and 1.30 ms, respectively. For various AC faults in the other three host networks (i.e., at T\({}_{2}\), T\({}_{3}\), and T\({}_{4}\)), the time taken by the algorithm is mentioned in Table 3. A set of comparative studies was performed between the existing HHT and the proposed SST methods. For the AG, ABG, AB, and ABC fault cases, it was observed that the TFRs obtained using the SST were more suitable and concentrated, giving more accurate information about the faults, and the obtained analysis can be observed in Table 4. For all types of symmetrical and asymmetrical fault scenarios, the proposed algorithm could detect the fault within 5 ms. which was quite lower than the time taken by the other techniques mentioned in Table 6. From the analysis, it was observed that the proposed integrated approach had a higher accuracy rate with a faster response and was reliable for the relay application.  
Conceptualization, K.R.; Methodology, Software: K.R. and M.B.; Writing--Original draft preparation, K.R.; supervision, N.K., R.N. and M.B.; financial support, N.K. All authors have read and agreed to the published version of the manuscript.  
Institutional Open Access Program (IOAP): Ostfold University College.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.