It could not be ignored that the system impedance have an influence on recovery voltage of main break when the value of parallel resistance across the main break is close to the value of system impedance. Under this condition it is considered that the phase voltage

the power frequency recovery voltage and the transient recovery voltage of main break on first pole to clear would reduce. It is suggested that the influence of the system impedance and the parallel resistance on power frequency recovery voltage should be characterized by means of the "first pole to clear factor of main break" and the "voltage distribution factor of main break".