As a flexible and efficient distributed power system, microgrid system is widely used in data centers, industrial production, medical facilities and other fields to ensure stable power supply for critical loads. In microgrid systems, power switching devices are one of the core components that ensure power supply continuity and reliability. Among them, static transfer switch (STS) and automatic transfer switch (ATS) are two common power switching devices. They have significant differences in functionality, application scenarios, and performance. This article will delve into the roles and differences between STS and ATS in microgrid systems.
1 What is a microgrid
(1) Definition and Structure of Microgrid
A microgrid is a small power generation and distribution system composed of distributed power sources (such as solar photovoltaics, wind power, small hydropower, etc.), energy storage devices (such as batteries, supercapacitors, etc.), power electronic converters (such as inverters, rectifiers, etc.), loads, and monitoring and protection devices. It can operate in parallel with the power grid or independently in islanding mode, with flexible operation mode and high energy utilization efficiency.
(2) Operation mode of microgrid system
Grid connected operation mode: In grid connected operation mode, the microgrid is connected to the main grid, and the distributed power sources within the microgrid can supply power to local loads. Excess electricity can also be transmitted to the main grid. At the same time, when the power generation within the microgrid is insufficient, the large grid can provide power support to the microgrid.
Island operation mode: When there is a fault or planned power outage in the power grid, the microgrid can be disconnected from the power grid and enter island operation mode. In islanding operation mode, microgrids rely on their own distributed power sources and energy storage devices to maintain power supply to local loads, ensuring the normal operation of critical loads.
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2 Definition of STS and ATS
1. Static Transfer Switch (STS)
STS (Static Transfer Switch) is a power switching device based on electronic circuits, mainly used to achieve fast and seamless switching between two independent AC power sources. Its core components include an intelligent control board, high-speed thyristors, and circuit breakers.
2. Automatic Transfer Switch (ATS)
ATS (Automatic Transfer Switch) is a mechanical power switching device mainly used in emergency power supply systems to automatically switch the load circuit from one power source to another backup power source. The switching execution components are usually contactors or circuit breakers.
3 The role of STS and ATS
(1) The role of STS
1. Quick switching
STS can quickly switch to the backup power supply in the event of a main power failure, with a switching time typically not exceeding 8 milliseconds, and can even reach 1/4 cycle (≤ 5 milliseconds). This fast switching capability ensures uninterrupted operation of precision electronic devices, avoiding data loss or equipment damage caused by power outages.
2. High reliability
Power supply STS is suitable for applications that require extremely high power quality, such as data centers, communication base stations, laboratories, etc. It can provide dual bus power supply for single power loads, enhancing the redundancy of the power supply system.
3. Compatible with multiple power sources
STS can achieve seamless switching between UPS and UPS, UPS and generator, UPS and mains power, and mains power to mains power, providing reliable power support for equipment in complex power environments.
(2) The role of ATS
1. Emergency backup switching
ATS is mainly used in emergency power supply systems. When the main power supply fails, it automatically switches to the backup power supply to ensure the continuous operation of important loads. Its switching time is usually over 100 milliseconds, suitable for loads that are insensitive to brief power outages, such as lighting, motors, etc.
2. Reliability of mechanical structure
ATS adopts mechanical contact switching, which has strong anti-interference ability and high switching success rate. Its structure is simple, maintenance cost is low, and it is suitable for switching heavy loads.
3. Widely used
ATS is widely used in industrial production, data centers, hospitals, and other occasions that require continuous power supply, especially in scenarios where switching speed is not high.
4 The difference between STS and ATS
(1) Switching speed
STS: Switching speed is extremely fast, usually between 5 milliseconds and 8 milliseconds, suitable for devices sensitive to power outages.
ATS: The switching speed is slow, usually over 100 milliseconds, and can even reach 1.5 seconds, suitable for loads that are not sensitive to brief power outages.
(2) Switching method
STS: Using electronic switches (high-speed thyristors) to achieve switching, the switching process is "first off and then on", which can achieve seamless switching.
ATS: Switching is achieved using mechanical contacts (contactors or circuit breakers), and the switching process relies on mechanical action, which may result in brief power outages.
(3) Application scenarios
STS: Suitable for occasions with extremely high requirements for power quality, such as data centers, communication base stations, precision instruments, etc.
ATS: Suitable for occasions that are not sensitive to brief power outages, such as industrial production, hospitals, lighting, etc.
(4) Reliability
STS: The electronic switch switching method makes it more sensitive to factors such as electromagnetic interference and temperature, but the switching speed and safety are higher.
ATS: The mechanical contact switching method gives it stronger anti-interference ability, but faults may occur due to contact wear, temperature rise and heating issues.
(5) Cost and Maintenance
STS: The equipment cost is relatively high, but maintenance is relatively simple.
ATS: The equipment cost is relatively low, but the mechanical structure requires regular maintenance.
5 Conclusion
STS, with its advantages of fast switching and high reliability power supply, is suitable for precision equipment that is sensitive to power outages; ATS, on the other hand, is suitable for ordinary loads that are insensitive to brief power outages due to its mechanical reliability and lower cost. In practical applications, STS or ATS should be reasonably selected based on factors such as load characteristics, power environment, and budget to ensure the stable operation of microgrid systems and the reliability of power supply.