选线主机是整个系统的指挥控制中心，它主要完成以下任务：
Line selection host is the command and control center of the whole system. It mainly accomplishes the following tasks:
①四段相电压的监测，一旦发生接地故障立即进入故障分析处理程序。
(1) Four-phase voltage monitoring, once the grounding fault occurs, it immediately enters the fault analysis and processing program.
②故障分析处理程序：主机读取各数据采集分支器传来的数据，采用模糊理论的方法对数据进行分析，得出正确的选项结果。
(2) Fault analysis and processing program: The host reads the data from each data acquisition branch, and uses the method of fuzzy theory to analyze the data, and obtains the correct result of the choice.
③管理好人机接口：包括按键的处理、液晶显示画面的处理、打印机的管理等。
Managing the man-machine interface well: including key processing, LCD screen processing, printer management, etc.
④通讯处理任务：包括与各数据采集分支器的通讯处理和与外部接口的通讯处理。
(4) Communication processing tasks: including communication processing with various data acquisition branches and communication processing with external interfaces.
⑤为了实时并行处理以上多任务嵌入了RTX_51实时操作系统，以保证各任务之间的协调配合。
RTX_51 real-time operating system is embedded in order to process the above multi-tasks in real time and parallel, so as to ensure the coordination of tasks.