## 19 Comparison of Traveling Wave and Non-Traveling Wave Based Methods
### Traveling Wave (TW) Based Methods for Internal and External Faults  
When an internal fault \(F_{1}\) occurs, the process of propagation of TW is shown in Figure 30. According to the fault superposition principle, a voltage source \(U_{F1}\) is superimposed at \(F_{1}\) from where TWs spread towards the end terminals of TL. Initial TWs detected by the protection equipment installed at end terminals are backward TWs i.e., \(U_{Rb}\) and \(U_{Ib}\). Later on, these backward TWs are reflected as forward TWs i.e., \(U_{Rf}\) and \(U_{If}\)[109; 110; 111; 112].  
However, when an external fault \(F_{2}\) occurs, the corresponding process of propagation of TWs is presented by solid line in Figure 31. Forward TW \(U_{Rf}\) is detected at the rectifier station which further propagates towards the inverter station and is detected as backward TW \(U_{Ib}\) while at the inverter station, backward TW \(U_{Ib}\) is reflected as forward TW \(U_{If}\). Further, \(U_{If}\) is detected as backward TW \(U_{Rb}\) at the rectifier station. Hence, first TW is detected as forward TW at rectifier station while first TW detected as backward TW at inverter station in case of external fault at ac side of rectifier station.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Serial Number** & **Parameters** & **Traveling Wave Based Method** & **Non-Traveling Wave Based Method** \\ \hline
5 & Transmission line parameters & Arrival time of traveling wave is greatly influenced by transmission lines. & Transmission line resistance influence the post voltage and current values. \\ \hline
6 & Information of fault & First traveling wave wavefront contains maximum information of fault & Only a section of line’s data from fault transient to steady state is sufficient to estimate fault over the entire dc transmission line. \\ \hline
7 & DC faults near converter stations & Difficult to identify or locate. This is because of small variation in amplitude of traveling wave wavefront. & Significant change in post fault dc current value enables identification and location of fault. \\ \hline
8 & DC faults characteristics closed to zero crossings & Inaccurate detection. Transformations are required & rapidly to steady state value. No such issue exists in this method. \\ \hline
9 & Accuracy in fault estimation & High & Low as compared to traveling wave method \\ \hline
10 & Speed of detection with same data length & High & Low \\ \hline
11 & Time and frequency domain analysis & Accuracy is increased by time and frequency domain analysis for fault estimation & Time domain increases accuracy and speed of fault estimation \\ \hline
12 & Knowledge based methods & Applicable with both pre and post fault voltage and current values & Applicable with only post fault voltage and current values \\ \hline
13 & DC transmission line model & It works well for both lumped and distributed parameter line model & It works well with distributed parameter line model. \\ \hline \hline \end{tabular}
\end{table}
Table 2: _Cont._Similarly, when an external fault occurs at \(F_{3}\), the corresponding process of propagation of TWs is presented by dotted line in Figure 31. Forward TW \(U_{If}\) is detected by inverter station which propagates towards the rectifier and is detected as backward TW \(U_{Rb}\). At rectifier station, backward TW \(U_{Rb}\) is reflected as forward TW \(U_{Rf}\) which is then detected as backward TW \(U_{lb}\) at the inverter station. Hence, first TW is detected as forward TW at inverter station while first TW detected as backward TW at rectifier station in case of external fault at ac side of inverter station.