Kerala has only 2 main lines in which there is high amount of traffic. Palakkad to Thiruvananthapuram and Palakkad to Mangalore(Karnataka). If you see nearby state,especially TN, almost 900+km's of its line are under electrification.
1.Erode-Karur-Tiruchirapalli & Salem-Karur-Dindigul -300km
2.Tiruchirapalli-Thanjavur-Mayiladuthurai-Villupur am
3.Tiruchirapalli-Thanjavur-Karaikkal.
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this only main line which will be left for Electrification is Dharmapuri-Bangalore.
Even though Kerala have electrified lines but yet Trains Shoranur to Mangalore cannot be hauled with Eloco-Reason is Sub Stations not operational.
Only 4 train use Eloco till Mangalore. It will take another 4-6 months
Kerala even almost fully electrified doesn't even have a dedicated ELOCO shed. They have only ERS Dloco shed and Loco are also getting old and are limited.
Kerala is fully depended on Eloco of ED,AJJ,RPM and Dloco of ED,GOC.
Karnataka only have Dloco shed. UBL and KJM, but no Eloco shed.