Power frequency secondary arc current in uncompensated EHV AC mixed cable-overhead lines

The paper deals with the secondary arc current and recovery voltage in Extra-High Voltage (EHV) ac mixed lines (MLs), i.e. solidly series-connected overhead line (OHL) and underground cable (CL) sections, during the dead time of single-pole auto-reclosure (SPAR) cycles, following single-phase-to-ground faults in the overhead line sections. Secondary arc current and recovery voltage are investigated at first by an analytical approach, assessing power-frequency quantities on a simplified equivalent circuit model of MLs. A parametric analysis of uncompensated 400 kV–50 Hz mixed lines and the comparison with overhead lines of equal length have been subsequently carried out by a multiconductor simulation program. Results show that the inclusion of short underground cable stretches in mixed lines has two main effects: an increase of secondary arc current and a concurrent reduction of the recovery voltage in comparison to overhead lines. The study evidences possible criticalities during SPAR

The paper deals with the secondary arc current and recovery voltage in Extra-High Voltage (EHV) ac mixed lines (MLs), i.e. solidly series-connected overhead line (OHL) and underground cable (CL) sections, during the dead time of single-pole auto-reclosure (SPAR) cycles, following single-phase-to-ground faults in the overhead line sections. Secondary arc current and recovery voltage are investigated at first by an analytical approach, assessing power-frequency quantities on a simplified equivalent circuit model of MLs. A parametric analysis of uncompensated 400 kV–50 Hz mixed lines and the comparison with overhead lines of equal length have been subsequently carried out by a multiconductor simulation program. Results show that the inclusion of short underground cable stretches in mixed lines has two main effects: an increase of secondary arc current and a concurrent reduction of the recovery voltage in comparison to overhead lines. The study evidences possible criticalities during SPAR in some typical 400 kV–50 Hz mixed line configurations and operating conditions: secondary arc currents may be 50% higher than in 400 kV OHLs of equal length and can be greater than 50 ÷ 60 A.