Why does the following sentence use НСВ готовил
instead of CB приготовил
Повар 3 часа готовил обед.
If I use готовил
doesn't that mean I regularly cooked for 3 hours?
This use implies the process of cooking, i.e. he was physically doing something (cooking, cutting, washing, waiting, checking) for 3 hours.
But one can say Повар приготовил обед за 3 часа. - This is the statement of fact, i.e. It took him 3 hours to make the dinner.
Повар три часа готовил обед.
It means exactly the process that in English is expressed with present perfect continuous
The chef has been cooking lunch for three hours.
We do not speak about the result.
Strictly, "СВ" means truly finished action, "НСВ" doesn't. Let's replace "Повар" with "Рыбак" (fisherman) and "готовить" with "тащить рыбу" (land the fish? - action between fish is in water and fish is in corf). So, we can say either "Рыбак тащил рыбу 3 часа, но не вытащил" (He tried for 3 hours, but unsuccessfull), or "Рыбак тащил рыбу 3 часа и вытащил" (He tried for 3 hours, and successfull) (It is "НСВ"). Or, we can say ("Рыбак вытащил рыбу за 3 часа") (he is truly did it, "СВ"). In general, in many cases there is no difference between of "СВ" and "НСВ", if we're talking about of action with known result. "Повар 3 часа готовил обед" and "Повар приготовил обед за 3 часа" can be equal, if cooker was successfull. Sorry for my English.