Protection system studies for ENEL Distribuzione's MV loop lines

The paper describes some of the fault studies performed for the protection system of ENEL Distribuzione's experimental MV loop lines. The system consists of a pilot relaying scheme using directional overcurrent relays for ground and phase fault detection. With reference to an actual implementation (a MV distribution network including a loop line, in Southern Italy), attention is focused on phase fault detection, aiming at the determination of magnitude and phase angle settings for relays. The effects of fault location and fault resistance are investigated by detailed simulations, resulting in tentative phase relay settings for the new protection scheme.