SURGE PROTECTION OF BUILDINGS CONNECTED TO AN OVERHEAD LOW-VOLTAGE NETWORK

U prenaponskoj zaštiti na niskom naponu postoje tri klase uređaja prenaponske zaštite. Predstavljena metoda izbora uređaja prenaponske zaštite može se koristiti pri donošenju odluke koje klase treba biti uređaj prenaponske zaštite koji se postavlja u priključni mjerni ormarić objekta. Metoda je testirana na jednoj tipičnoj nazemnoj niskonaponskoj mreži u Hrvatskoj. S obzirom na dobro iskustvo s uređajima prenaponske zaštite klase II u transformatorskim stanicama u toj mreži, može se zaključiti da je uređaj prenaponske zaštite klae II sasvim primjeren i za objekte spojene na niskonaponsku mrežu.There are three clases of surge protective devices for low-voltage system. The method for the selection of surge protective devices presented can be used to determine which class of surge protectice device should be inastalled in the service entrance of a building. The method has been tested on a typical ovehead low-voltage network in Croatia. Based upon good experience with Class II surge protective devices in the transformer stations of this network, it can be concluded that Class II surge protective devices are quite suitable for buildings connected to a low-voltage network

EVALUATION OF ENERGY STRESS ON LINE ARRESTERS

Line Surge Arresters (LSAs) are efficient means for the improvement of the lightning performance of transmission lines. Determination of optimal LSA number, location and rating is important for the improvement of the reliability and availability of a transmission system. In selection of the LSA special attention should be paid to their energy stress which depends on complex interactions between the arrester locations, grounding, shielding and the local lightning environment. LSAs experience higher energy stress compared to station arresters, because the incoming surge to a station is limited by insulator flashover on the transmission line and impulse corona. In this paper calculations of energy stresses were carried out for a double-circuit 220 kV line with a single shielding wire. Parametric studies were conducted in which arrester discharge energy was a function of: time to half value of stroke current, number of towers with arresters, footing resistance, span length and angle of power frequency voltage. Arrester energy stress is analyzed in case of stroke to tower and shielding failure. From conducted analysis it can be concluded that energy stress on LSAs is lower for shorter span lengths. Tower footing resistance has only minor effect on the discharge energy. Arrester discharge energy strongly depends on time to half of the stroke current, number of towers with installed arresters and angle of power frequency voltage

EVALUATION OF ENERGY STRESS ON LINE ARRESTERS

Line Surge Arresters (LSAs) are efficient means for the improvement of the lightning performance of transmission lines. Determination of optimal LSA number, location and rating is important for the improvement of the reliability and availability of a transmission system. In selection of the LSA special attention should be paid to their energy stress which depends on complex interactions between the arrester locations, grounding, shielding and the local lightning environment. LSAs experience higher energy stress compared to station arresters, because the incoming surge to a station is limited by insulator flashover on the transmission line and impulse corona. In this paper calculations of energy stresses were carried out for a double-circuit 220 kV line with a single shielding wire. Parametric studies were conducted in which arrester discharge energy was a function of: time to half value of stroke current, number of towers with arresters, footing resistance, span length and angle of power frequency voltage. Arrester energy stress is analyzed in case of stroke to tower and shielding failure. From conducted analysis it can be concluded that energy stress on LSAs is lower for shorter span lengths. Tower footing resistance has only minor effect on the discharge energy. Arrester discharge energy strongly depends on time to half of the stroke current, number of towers with installed arresters and angle of power frequency voltage