Transmission lines are protected by special devices called distance numerical protection relays. The presence of a T-connection on a third terminal transmission line can drastically affect the performance of a distance relay at other terminals. The paper presents modeling and simulation of numerical distance protection relays using DIgSILENT software on real three terminal (T-terminal) 110 kV transmission lines. A sample case of a part of 110 kV, high voltage transmission network in HEP TSO Transmission area Zagreb, which includes a section of T-terminal transmission line is analyzed. Three phase and single line to ground faults were simulated on each 110 kV transmission line section, and a time response of polygonal characteristic of numerical distance relay was presented.