Countermeasures for reduction of screen currents due to cross country faults in MV cable distribution networks

Abstract

• Cross-country faults can involve large currents liable to damage MV cable sheaths. • Methodologies to reduce cross-country fault currents in cable screens are presented. • Methods are compared by means of ATP-EMTP simulations on a 20 kV test network. • Additional ground wires are effective but viable only for newly built cable lines. This paper investigates the reduction of Cross-Country-Faults currents in medium voltage (MV) cable networks in order to decrease thermal stress of cable screens, especially inside joints. Four methods are analyzed: 1) disconnection of cable screens from the earth electrode of primary substation (PS); 2) buried ground wire laid near the cable lines and connected to each earth electrode of secondary substations (SSs) and PS; 3) buried ground wire and disconnection of the bonded cable screens from the earth electrode only at sending/receiving end of each cable line between two consecutive SSs; 4) cross bonding of cable screens between two consecutive SSs. Methods are analysed by ATP-EMTP simulations of a 150/20 kV radial test system formed by eight 5 km long cable lines equipped with 50 mm 2 copper conductors per phase and 16 mm 2 copper screen per cable. Compared to the limiting reactors countermeasure presented in a previous paper by the authors, which seems the solution less burdensome both technically and economically for existing lines, method 3 is more effective but its implementation is limited only to newly built lines, whereas the main drawback of method 1 is the increase of ground potential rise at fault locations.