History of Electrification in Indian Railways:-
The first electric train ran in India with the inauguration of services between Bombay VT and Kurla Harbour on 3rd Feb 1925 on ex-GIP Railway system. The section was electrified on 1500 Volt DC. Electric traction was subsequently extended on Central Railway upto Igatpuri on Northeast line and Pune on Southeast line where heavy gradients on the Western Ghats compelled introduction of electric traction. 1500 Volt DC traction was introduced on the Suburban section of Western Railway between Colaba and Borivili on 05.01.1928 and between Madras Beach and Tambaram of Southern Railway on 15.11.1931.Thus, before dawn of Independence, India had 388 KM of DC electrification.
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the post Independence era, the work of electrification of Howrah - Burdwan section of Eastern Railway taken up on 3000 Volt DC during the Period of 1st Five year Plan was completed in 1958. As a result of the extensive research and trials in Europe, particularly in French Railways (SNCF), 25 kV AC system of traction emerged as an economical system of Electrification. Indian Railways decided in 1957 to adopt 25 kV AC system of electrification as a standard with SNCF as their consultant in the initial stages.
The first section to be electrified on 25 kV AC system was Raj Kharswan - Dongoposi of South Eastern Railway in the year 1960. with a view to provide continuity of traction system. Howrah - Burdwan section of Eastern Railway and Madras Beach - Tambaram section of Southern Railway were converted to 25 kV AC system by 1968.
Source: CORE website