Kelvas Prime was the inhabited prime planet in the Kelvas system.
Following the supposed demise of Damar, Mila overheard a rumor that someone's cousin had seen Damar on Kelvas Prime. (DS9: "The Dogs of War")
This planet was only mentioned in dialogue.
Since Kelvas V and the Kelvas facility were both Cardassian, this might have been a Cardassian planet.
This planet's quadrant of origin is inferred based on the position of the Cardassian Union as seen in the star chart appearing in the Star Trek: Picard episode "Maps and Legends".