There is a lecture called fundamentals of electric and electronics and there is a new topic in that lecture I have to learn but I have little information on it. Topic is three phase systems or three phase power calculations or something like that. There are big letter such as R,S which confuses me and systems called star or triangular.Can somebody guide me please how to learn that topic. there are physics books called physics 2 which all of them explains the electrical forces,fields RLCs but they do not cover that three phase topic. Can you give me book names about it for examples does that topic belongs to circuit theory?