Theoretical and experimnental studies of the critical line length for the interruption of short-line faults

For the clearing of short-line faults by SF6 circuit-breakers, the maximum rated current interrupted is calculated as a function of the short-line fault parameter p, using an extended Mayr equation. In agreement with experimental results it is shown that for SF6 circuit-breakers the curves have a minimum at p=0.9 for a rated voltage of 245 kV and at p=0.93 for 420 and 550 kV. For a air-blast circuit-breaker the minimum shifts to a lower value of p, namely p=0.8.