Tamil Nadu will soon move in top position because
300 km of Erode-Karur-Tiruchirapalli and Salem-Karur-Dindigul is under electrification and work of Erode-Karur-Tiruchirapalli is almost complete.
150 km of Thanjavur-Thiruvarur-Karaikal Port is under electrification and work is going good.
196 Km of Omalur-Dharmapuri-Baiyyappanahali tender is also out with RVNL
similarly...
more... Mayiladuthurai-Cuddalore-Villupuram and Mayiladuthurai-Thiruvarur is also out.
Only Rameswaram line will be left which doesn't matter because Rameswaram line is difficult to be electrified (Pamban bridge Part)
Arakkonam-Takkolam should be done,but all is in the hands of Indian Air force.