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As the modernization of people’s production and daily life in our country progresses, demand for electricity and reliance on it are increasing exponentially. At the same time, requirements regarding power quality are becoming more stringent, and power supply and distribution systems in various fields are continuously moving toward automation, unattended operation, remote control, and uninterrupted power supply. Some electricity users have particularly heightened demands for uninterrupted power supply. In our country, electricity supply relies mainly on the power grid, and the gap in electricity supply is continuously increasing; shortages are particularly severe during peak usage periods. As a result, many large enterprises build their own power plants or equip themselves with generators. Therefore, the seamless switching between different power sources to ensure uninterrupted power supply and high reliability has become an important aspect of the protection and control systems in modern power distribution systems. Chapter 11 of GB50062, the \"Design Code for Relay Protection and Automatic Devices in Electrical Installations,\" also specifies the detailed requirements for the automatic activation of backup power sources and backup equipment. The microcomputer-based automatic transfer switch protection device combines automatic system devices with relay protection devices; it is an economical and effective technical solution that ensures uninterrupted power supply for users, and it is widely used in modern power supply systems. Here, only the two backup self-switching methods and basic principles of the microcomputer-based backup self-switching protection device in power systems are discussed. The core component of the microcomputer-based automatic transfer switch protection device (hereinafter referred to as auto transfer switch) is a high-performance single-chip microcomputer, which consists of a CPU module, a relay module, an AC power supply module, a human-machine interaction module, etc. It boasts advantages such as strong interference resistance, stability and reliability, as well as ease of use. The liquid crystal digital display and the buttons on the automatic transfer panel make operation simple and convenient; remote control is also possible through the RS485 communication interface. The device collects signals using AC uninterruptible sampling and then performs Fourier analysis in real time, enabling accurate determination of the power supply status and facilitating delayed switching of the power supply. The standby auto-transfer device has an online operating status monitoring function, allowing for the observation of various input electrical values, digital signals, set values, and other information. It also features reliable software and hardware watchdog functions as well as an event recording function. When the product is used in power supply and distribution circuits of different voltage levels such as 110kV, 10kV, and 0.4kV systems, different electrical parameters need to be set, which must be specified at the time of ordering. When selecting the automatic transfer switch function, low-voltage protection must not be enabled to avoid failures or incorrect operations caused by conflicts. The widespread use of microcomputer-based automatic reclosing protection devices in modern power systems has provided a more reliable guarantee for uninterrupted power supply, playing a significant role in the advancement of power automation. Although the models and appearances of microcomputer-based automatic transfer switch protection devices from different manufacturers and brands vary, their functions and principles are generally the same. It should be emphasized here that users must refer to the corresponding user manual when designing the secondary control schematic, and connect the wires according to the functions of the terminals specified in the manual. Conditions for automatic transfer to a backup system: First, there must be a backup power source or backup equipment. Secondly, when the voltage of the working bus drops, the standby power supply or equipment can be activated only after the circuit breaker that supplies the working power is switched off by the automatic standby switch ； Another scenario is a system failure in the main power supply; in such cases, the protection mechanism operates by tripping the circuit breaker for the main power supply before activating the backup power supply or equipment. The third condition is that the bus voltage of the backup power supply meets the requirements. $ v; _, t2 A3 N2 z, `The voltage transformer should be installed at the busbar. If it is a double-bus system, they should all be installed. In some places, voltage transformers are also installed on the line side to enable reclosing.