What type of Transfer Switch do I need for my UPS Installation?
In an uninterruptible power supply (UPS) application, an automatic transfer switch (ATS) and a static transfer switch (STS) serve the critical function of transferring electrical loads between power sources, but they operate in fundamentally different ways and are suitable for different scenarios.
Automatic Transfer Switch (ATS)
Operation Mechanism:
An ATS uses electromechanical relays or motorised breakers to switch the load between different power sources (e.g., from utility power to ups or generator power).
The transfer involves a brief interruption of power, typically in the range of milliseconds to a few seconds, as the mechanical components move.
Typical Applications:
ATS is commonly used in scenarios where brief power interruptions are acceptable, such as for non sensitive equipment in residential, commercial, and some industrial settings.
Speed:
The transfer speed is relatively slow compared to STS due to the mechanical movement required. The typical transfer time is around 100 milliseconds to a few seconds, depending on the system.
Complexity and Cost:
- Generally less complex and less expensive than STS.
- Easier to maintain due to fewer electronic components.
Static Transfer Switch (STS)
Operation Mechanism:
An STS uses solid-state devices, such as thyristors or silicon-controlled rectifiers (SCRs), to switch the load between power sources.
The transfer is virtually instantaneous, typically within a quarter of a cycle of the power waveform (around 4 to 5 milliseconds at 50 Hz or 60 Hz).
Typical Applications:
STS is used in critical applications where even the smallest interruption in power can be detrimental, such as in data centres, telecommunications, and other mission-critical environments.
Suitable for systems requiring high availability and minimal downtime.
Speed:
The transfer speed is extremely fast, almost instantaneous, making it ideal for sensitive equipment that cannot tolerate power interruptions.
Complexity and Cost:
- More complex and more expensive than ATS due to the use of advanced solid-state technology.
- Requires more sophisticated monitoring and control systems.
- Typically involves higher maintenance due to the complexity of electronic components.
Key Differences
Transfer Mechanism:
ATS: Electromechanical (relays or motorised breakers).
STS: Solid-state (electronic switches).
Transfer Speed:
ATS: Slower (milliseconds to seconds).
STS: Faster (milliseconds, typically within one power cycle).
Suitability:
ATS: Suitable for applications where short interruptions are tolerable.
STS: Suitable for applications requiring uninterrupted power and minimal transfer times.
Cost and Complexity:
ATS: Less expensive and less complex.
STS: More expensive and complex.
In summary, the choice between an ATS and an STS depends largely on the specific requirements of the UPS application, particularly regarding acceptable transfer times and the critical nature of the load being powered.