This work deals with the problem of increasing the safety of supply of 110 kV transmission network of the Sisak area as well as the problem of voltage quality in the considered part of the Croatian power system. The overall status of the transmission network is analyzed as well as the state of relay protection equipment and telecommunications connectivity. The paper examines the issue of sectioned 110 kV network in SS 110/35/6.3 kV Rafinerija in detail, as well as technical requirements and changes in the network that are due to Network Rules of power grid on interface with the system user “INA Oil Refinery” Sisak. A new concept of relay protection is proposed for the protection of the observed part of the transmission network. A problem of high voltages in transmission network in the Sisak area is also analyzed and the technical solution is proposed. The problem of voltage flicker in the transmission network in Sisak area after connecting a new electric arc furnace in CMC Sisak on 33 kV side is analyzed in detail. Preliminary analysis of the spread of flickers in the transmission network, and detailed measurements of short-term and long-term flickers is carried out. Short-circuit power at the connection of the electric arc furnace at the 110 kV node and the surrounding network is calculated. Based on the results of measurements of flicker for different switching states the expected value for the maximum power flickers furnaces of 43.5 MW is calculated. Technical solution for reducing flicker in the transmission network in accordance with the Network Rules for electricity is proposed by connecting an electric arc furnace at 220 kV level through the transformation of 220/33 kV, with the additional installation of dynamic compensation on 33 kV side. The proposed technical solution for connecting the 220 kV network is analyzed in relation to the technical solution of the dynamic compensation with maximum power. The proposed technical solution allows the use of transformer station TS Željezara for the HEP purposes, the possibility of a transformation of the 2 x 40 MVA, which would allow for the new users in the power distribution network on the grounds of former TS Željezara Sisak, as well as future users of the network. The proposed technical solution relieves the 110 kV network and permanently solves the problem of flickers and increased voltages in the Sisak area.