In a centrifugal separator for cleaning a gas containing liquid impurities, a stationary casing encloses a separation space having an inner wall surface. An inlet is provided. A rotating member is provided in the separation space downstream the inlet rotates in a direction of rotation around an axis of rotation. The rotating member brings the gas to rotation in the direction of rotation for separation of liquid impurities from the gas. A gas outlet is provided downstream the rotating member for discharge of the cleaned gas. A first liquid outlet is provided upstream the gas outlet and downstream the rotating member for discharge of separated liquid impurities and comprises an outlet hole. A surrounding ring groove extends outwardly from the inner wall surface in the stationary casing and has a surrounding bottom surface, wherein the outlet hole extends outwardly from the bottom surface.