Telsius Prime was the inhabited prime planet in its star system. This system was located in the Delta Quadrant. This was the homeworld of the Telsians, and was located 30,342.4 light years from Earth.
A mine on Telsius was visited by con artists Dala, Mobar, and Zar in 2376. Disguised as USS Voyager officers, they cheated the miners out of ten kilotons of bolomite when the station was having a dilithium shortage. The mine's Chief of Mining Operations was Orek.
It was also the location of Telsian Security, which was known for having "persuasive methods of determining the truth". (VOY: "Live Fast and Prosper")
According to a map seen in season 7 of Star Trek: Voyager, the distance from Earth places the Telsius system within the galactic core. [1]