A damping circuit is connected in series with the triggered spark gap and is not always stressed by the ac-line current. In parallel to the spark gap the bypass-breaker is located to provide current commutation for times when the current capability of the Spark gap or MOV is exceeded.During internal faults (faults occuring on the HV-line to which the capacitor bank is connected to) the spark gap and the bypass-breaker are allowed to operate and to protect capacitor and MOV from overload.
In some cases a MOV only protection scheme is used (i.e. no spark gap) however this usually requries a much higher MOV energy which is more costly than a Spark Gap Solution. A typical single line diagram for a FSC is shown below.