I'm not sure, but I think you have made a mess of some of them. (a) When I arrived at the station the train left -- 'Left' is simple past; the train left after she arrived (b) When I arrived at the station, the train was leaving-- ' Was leaving is past progressive'; the arrival and departure are simultaneous. (c) When I arrived at the station the train had left-- 'Had left' is past perfect; the train left before she arrived.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.