## 2 Fault Type and Fault Feature Information of the Protection System  
### Classification of Protection System Fault Types  
When the fault diagnosis of the protection system is carried out, the fault types are properly classified, which can ensure the accuracy of judgment, reduce the amount of calculation in the process of fault diagnosis, reduce the amount of computer resources, and improve the response speed and convergence speed [12]. By analyzing the alarm information, self-checking information, sampling value information, and fault maintenance-record data of the device of the protection system, we can divide the faults into two categories. One is the simple fault, that is, there is an obvious mapping relationship between the fault type and the fault feature information. After the fault occurs, the fault type can be simply deduced according to the fault feature information. For example, if the fault feature information is \"Power failure alarm of merging unit\", it can be directly deduced that the fault is \"Power module fault of merging unit\". Another type is the complex fault, which means that the mapping relationship between the fault type and fault feature information is weak, and cannot be directly deduced by simple reasoning of fault feature information. An intelligent algorithm is needed for the reasoning and diagnosis. According to the equipment manual, fault data, and fault characteristics, the high-frequency faults are classified as shown in Tables 1 and 2. \begin{table}
\begin{tabular}{c c c} \hline
**Number** & **Fault Types** & **Fault Feature Information** \\ \hline
1 & Power module fault of merging unit & Power failure alarm of merging unit \\ \hline
2 & The RX1 receive Bus fault of the merge unit & 4–8 Bus MU frame Loss/4–8 Bus check error \\ \hline
3 & GPS timing signal of merging unit not accessed & B01 synchronous anomaly alarm of merging unit \\ \hline
4 & Device board card configuration and specific engineering design drawings do not match & Board card configuration error \\ \hline
5 & Error in merging unit memory check & Merging unit memory checking error \\ \hline
6 & Incorrect configuration of send text for merge unit & Incorrect configuration of send text for merge unit \\ \hline
7 & Errors in HTM data exchange between merging unit board boards & B01 HTM error of merging unit \\ \hline
8 & Device stall error of merging unit & BO1 report BO3 Stall error of merging unit \\ \hline
9 & B11 input power loss of merging unit & B11 optocoupler power loss alarm of merging unit \\ \hline
10 & BO3 sampling plate anomaly of merging unit & BO3 sampling plate anomaly of merging unit \\ \hline
11 & The sampling of BO3 dual AD in merging unit is inconsistent & The sampling of BO3 dual AD in merging unit is inconsistent \\ \hline
12 & GOOSE-A network storm of merging unit & GOOSE-A network storm of merging unit \\ \hline
13 & The sampling voltage of merging unit BO2 & BO2 sampling power drop of merging unit \\ \hline
14 & Error in intelligent terminal memory check & Intelligent terminal memory checking error \\ \hline
15 & BO1\_A network link N of intelligent terminal disconnected & BO1\_A network link N of intelligent terminal disconnected \\ \hline \end{tabular}
\end{table} 
Table 1: Simple fault types and corresponding fault feature information.