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Static transfer switch (STS)

A static transfer switch uses power semiconductors such as Silicon-controlled rectifiers (SCRs) to transfer a load between two sources. Because there are no mechanical moving parts, the transfer can be completed rapidly, perhaps within a quarter-cycle of the power frequency. Static transfer switches can be used where a reliable and independent second source of power is available and it is necessary to protect the load from even a few power frequency cycles interruption time, or from any surges or sags in the prime power source.

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