A circuit switcher is a switching device like a circuit breaker. It interrupts the power flow.
It is typically installed on the high voltage side of the transformer.
Historically the fault interruption capability was lower (~5kA) and therefore was only operated for faults occurring on the load side of the transformer. New-generation switchers can interrupt up to 40kA, making it comparable to a circuit breaker and therefore can be operated for faults occurring on the source and load side.
Figure 2: Circuit switcher for transformer protection, installed on high voltage side
Circuit switchers may also be installed at the transmission line terminal. Normally, motor-operated disconnects are installed. However, when opening, the line charging current magnitude can overwhelm the interruption capabilities of the whip of a disconnect. A switcher when sized correctly, using its SF6 chamber, can safely interrupt the line charging current.
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