Automatic devices in power systems include Automatic Reclosing Devices, Automatic Transfer Switches, Automatic Frequency Regulation Devices, Automatic Excitation Regulators, among others. These devices perform their respective operations automatically by monitoring and evaluating the system in real-time, reducing the need for manual intervention, and enhancing the efficiency and stability of the power system.

1.Automatic Reclosing Device (ARD) 

An Automatic Reclosing Device is an automatic system that re-engages a circuit breaker after it has been tripped due to a fault. It is a widely used anti-failure measure on overhead lines. When temporary faults occur on transmission and distribution overhead lines, such as transient lightning strikes or wind damage, relay protection causes the breaker to trip. Generally, the line's insulation performance can recover, and the ARD recloses the breaker after a short interval (0.5-1.5 seconds), improving power supply reliability, reducing outage losses, and enhancing the transient stability of the power system. In some cases, the function of reclosing can delay the need to set up double-circuit lines, saving investment. Additionally, it can correct false trips caused by malfunctioning breaker mechanisms or relay misoperations.

2.Automatic Transfer Switch (ATS) 

The Automatic Transfer Switch activates when the main power supply fails for any reason, automatically and swiftly (0.2-0.5 seconds) connecting the backup power supply to the electrical equipment or switching the equipment to the backup power, ensuring continuous power to the load and users. The ATS operates only when the working power supply is indeed disconnected and the backup power supply has voltage, and it can activate only once. The accuracy and reliability of the ATS directly impact the reliability of power supply in power plants and substations. ATS devices are typically used in power systems with two or more power sources. When the main power source fails, the ATS detects changes in electrical parameters and, after certain logical evaluations and delays, automatically connects the backup power to ensure continuous supply to critical loads.

3.Automatic Frequency Regulation Device (AFRD) 

The Automatic Frequency Regulation Device monitors grid frequency variations and, within a preset frequency range, automatically adjusts the output power of generating units to maintain grid frequency within a reasonable range. AFRDs ensure stable operation of the power system, improve power supply quality, and maintain frequency stability through automatic adjustments. Common AFRDs include speed governors and frequency converters. The principle of AFRD operation involves generating a deviation signal when the system frequency deviates from the nominal value. This signal is input into the AFRD, which calculates the required power adjustment based on the magnitude and direction of the deviation and adjusts the relevant parameters of the prime mover or generator to achieve power adjustment.

4.Automatic Excitation Regulator (AER) 

The Automatic Excitation Regulator adjusts the excitation current of a generator based on the power system's operating state to maintain the generator terminal voltage at a specified level and achieve reasonable reactive power distribution, thereby improving system stability. An AER typically consists of measurement units, comparison units, amplification units, and execution units. The measurement unit measures parameters such as the generator's terminal voltage and current; the comparison unit compares these measurements with set values to derive a deviation signal; the amplification unit amplifies this deviation signal to drive the execution unit; the execution unit adjusts the exciter's excitation current, thereby altering the generator's excitation current. The AER operates by automatically adjusting the excitation current when the generator terminal voltage deviates from the set value, restoring the terminal voltage to the set value. In the event of system faults or disturbances, the AER can quickly increase the excitation current to enhance the generator's transient stability.