Scientific paper ID 2499 : 2024/3

Sofia-city has the most developed transport system for public urban electric transport, including ground (trams, trolleybuses, electric buses) and underground (subway) transport. To power the electric vehicles, a traction network has been built, including feeder cables and catenary, which work under variable load regimes and weather conditions. The traction network of the ground urban electric transport powered by 24 stationary rectifier substations /RSS/, and that of the subway - by 39 traction step-down substations /TSDS/. 70% of RSS and 15% of TSDS have morally and physically outdated protective equipment of the DC outputs. A significant part of the traction network of the ground urban electric transport has not yet been rehabilitated in the last 35-40 years. All this d modernization of the protection of the traction network in RSS and TSDS, in order to improve the control of the mode electrical parameters of the cable feeders and catenary and increasing their operational reliability.

In the report, a brief analysis of the state of the traction network of urban electric transport in the city of Sofia is made. The protection and control functions of different models of digital protection devices for direct current /DC/ traction networks Sitras of the company Siemens, which are installed in 6 RSS and 26 TSDS, have been analyzed. On the basis of the analyzes carried out, an assessment of the possibilities for improving the control of the regime parameters has been made and relevant conclusions and recommendations were formulated.