## 2 Distribution Network Reliability Evaluation Method
### Fault Impact Analysis  
The distribution automation sensing and control terminal is mainly divided into two types: TUs without tele-control function terminals and TUs with tele-control function terminals. The TUs without tele-control function distribution terminal only have the functions of telemetry and remote communication and have the functions of current telemetry and information reporting, which has little effect on the improvement of power supply reliabil  
Figure 2: System state sequence. ity. The TUs with tele-control function distribution terminal have the functions of telemetry, remote communication, and remote control, which can realize the automatic control of the disconnector and then quickly isolate the fault area, effectively improving the power reliability. Based on the three stages of fault handling (fault location, fault isolation, and power restoration), this section analyzes the consequences of the fault of the sense-control terminal. Firstly, the composition of fault handling time is defined. Secondly, based on the whole process of fault handling, the influence of sensing terminal faults on fault partition and outage time is analyzed in detail. (1) Fault Handling Time  
The fault processing time T includes fault location time \(t_{1}\), fault isolation time \(t_{2}\), load transfer time \(t_{3}\), and fault repair time \(t_{4}\), specifically:  
\[T=t_{1}+t_{2}+t_{3}+t_{4} \tag{10}\]  
1. Fault location time \(t_{1}\)  
It includes the time when the TUs without tele-control function terminal or the TUs with tele-control function terminal upload the fault information and the time when the master station determines the fault area. 2. Fault isolation time \(t_{2}\)  
Including automatic isolation time \(t_{2,r}\) and manual isolation time \(t_{2,s}\). The automatic isolation time is the time for the staff to remotely control the segmented switch with the TUs with tele-control function terminal. The manual isolation time is the time when maintenance personnel arrive at the scene to manually isolate the fault. 3. Load transfer time \(t_{3}\)  
Including automatic transfer time \(t_{3,r}\) and manual transfer time \(t_{3,s}\). The automatic transfer time is the time when the staff remotely controls the contact switch equipped with the TUs with tele-control function terminal downstream of the fault isolation area. The manual transfer time is the time when maintenance personnel manually close the contact switch. 4. Fault repair time \(t_{4}\)  
Time for the maintenance personnel to repair the fault on site. (2) Analysis of the influence of fault mode considering the fault of sense-control terminal  
The application of the sense-control terminal effectively improves the automation level of the system, which is conducive to improve the safety of the distribution network's operation and the reliability of the power supply. However, in the actual operation of the distribution network, the fault of the sense-control terminal component may lead to the wrong location of the fault area, which will lead to the expansion of the power outage area, which will not be conducive to the reliable operation of the distribution network. Therefore, it is necessary to consider the impact of terminal equipment failure on the reliability. In the actual medium-voltage distribution network, due to the consideration of investment and construction costs, the TU with tele-control function terminal equipment is usually only installed at the important load point, while the sensing and control terminals at other load points are the TUs without tele-control function terminal equipment. Because only the TUs with tele-control function equipment have the function of automatic fault isolation, the impact of different types of terminals on the outage time is different, and the reliability evaluation of multi-voltage levels distribution network needs to be discussed separately. This paper will discuss the influence that results after the failure of the sense-control terminal in three stages.