DC traction system was introduced in Mumbai division of Central Railway in the year 1925. The section was electrified on 1500 V DC system. Conversion of DC system to 25 KV AC systems (RKM-441 & TKM-1681) has been started in 1996-97. Conversion of DC system to 25 KV AC systems has following advantages:

• Significant saving in energy cost due to introduction of three phase electric locos & EMUs.
• Introduction of higher power locomotives. WAG7 locos needs less Maintenance, are more reliable and generate higher tractive effort than DC locos. This will result in smoother operation in ghat sections at higher speeds and much lower traction current handling (16 times lesser than DC).
• Reduction in Max. power demand for same level of traffic.
• Reduction in no. of substation from 73 to 18 leading to higher reliability & lower maintenance cost.
• Energy savings due to reduced lighting load in traction substation.
• Increase life of contact wire due to lower traction current handling in AC locos.
• Higher voltage insulation level in 25 KV AC system to with stand surges with greater reliability.
• Lesser Maintenance on rail bonding in AC system.
• Improvement in safety & reliability of signalling system by way of introduction of state of art technology, audio frequency double rail track circuits.
• Improvement in communication with the provision of optical fibre cable.
• Reduction in transmission and distribution losses as current in AC system is lower as compared to DC system. There has been a reduction in net SWenergy consumption in CSTM-Thane section by approximately 5.3% from May to July.

The sections Vasai Road-Diwa-Panvel-Jasai, Pune-Kalyan, Igatpuri-Kalyan and Kalyan-CSTM sections have been converted to 25 KV AC systems. The work of Conversion in CSTM-Panvel Harbour line is in progress and expected to be completed in March-2016