BRANCHED CIRCUIT OF 6 kV OPERATION WITH INSULATED NEUTRAL UNDER PHASE-TO-EARTH FAULT

Line-to-earth faults which occur in branched circuit 6-10 kV with insulated neutral are the most spread type of fail-ure. Overvoltage under line-to-earth faults leads to the failure of electric equipment and extra expenses. Mathematical models considering branched circuit parameters changes are developed. The mathematical model considering linear arms’ active resistances of a branched circuit is studied. It was found that these resistances can be neglected under transient processes evaluation while arcing. The analysis based on the mathematical model considering branched circuit phase insulation was performed. Calculations show that these parameters do not affect overvoltage level significantly. Different cases of voltage level calculation in circuit phases under arcing and voltage recovery process with different circuit parameters and earth circuit resistance values are considered. It was found that overvoltage levels depend on earth circuit resistance value, arc blowout moment and voltage value of secondary initiations. Earth circuit resistance value is determined by the number of high-frequency current zeros and correspondingly determines transient processes’ character. The highest overvoltage levels can exceed fourfold values.