No Need of loco change at Nagpur, as the Nagpur - Channai line is electrified (even PDY). Also, A train coming from Bhusawal, Badnera line and going to BZA, MAS line does not require to go to Nagpur. It can take MAS route after departing from Wardha and that too without reversal. You may refer a map or check the TT of Navjeevan Express (12655 / 56).