Analysis of distance protection setting by performing primary trials

In the territory of the western part of the Croatian electrical power system (EPS) lines 110 kV of the transmission network have been reconstructed for the purpose of improvement of safety and drive quality. The particularity of the observed part of the EPS is that its environment includes only one powerful power supply source. Those are two thermal power plants on the same location, Plomin 1 with the voltage level of 110 kVand Plomin 2 with the voltage level of 220 kV. The fault which occurred in the observed network is charged almost entirely from one supply point. The said inconsistence in the fault currents distribution often results in the occurrence of such conditions that do not guarantee proper operation of the transmission lines’ protection relays. Relay protection of the transmission lines has become a complex system. The use of telecommunication resources together with numerical protection relays has given rise to the need for verification of the entire system as a whole and not only its individual parts. The performance of primary trials in the transmission network 110 kV was used to test the operation of the protection system in the fault ambience. The work describes the preparatory work and the very performance of primary trials at the T-junction of the 110 kV transmission line of Plomin thermal power plant − Šijana substation − Vinčent substatio.