Much has been written about the final days of DC traction in Mumbai, more specifically on the Harbour line from CSTM to Vashi which was the last holdout of this form of electrification on the Indian railways. This is not exactly true – the Kolkata metro will continue to be on 750 V DC indefinitely, and it is officially a part of the Indian Railways (unlike the metro systems in Delhi and elsewhere).
At its peak, the 1500 V DC system in Mumbai covered these sections:
WR: Colaba to Churchgate to Virar
CR: CST Mumbai to Pune and Igatpuri via Kalyan
CST Mumbai to Mahim and then in parallel to WR up to Andheri
CST Mumbai to Kurla via Harbour branch and then to Mankhurd,Vashi and Panvel.
(Mankhurd was the terminus until the 1990s).
(Apart from CR and WR, some lines of the Bombay Port Trust were electrified with DC as well).
A typical news item about the conversion of the last route:
What most railfans may forget is that 3000 V DC existed on some routes out of Howrah for about a decade and 1500 V DC on one metre gauge route out of Chennai for several decades.
From an official IR publication of 1964, we can get the early history. It makes things simpler if we use the names of places which were prevalent at that time
The years of completion were:
Bombay VT to Poona and Igatpuri: 1930 (299 route km) on the Great Indian Peninsular Railway, predecessor of the CR
Churchgate to Virar: 1936 (60 route km) on the Bombay, Baroda and Central India Railway, predecessor of the WR.
Madras Beach to Tambaram: 1931 (29 route km, metre gauge) on the South Indian Railway, predecessor of the SR.
and Seoraphuli-Tarakeswar: 1958 (142 route km) on ER.
Coming back to Bombay, the VT-Reay Road section was opened in 1925 with electrification, as the 1 in 34 gradient at Sandhurst Road was felt to be an insurmountable obstacle to any other means of traction. Diesel traction existed but was not considered a serious option at that time.
Reay Road to Kurla had been running on steam since it was opened in 1910.The extension from Kurla to Mankhurd was completed by 1927 and was electrified in 1936.
The Karjat-Khopoli branch was one of the first lines opened in India (in 1856, when it became the railhead for Poona for some years). It seems to have been electrified only in the mid-90s and timetables of 1994 show diesel-hauled passenger trains on the CR main timetable (not the suburban timetable).
The Diva-Vasai Road line was built in the 1980s and was electrified with DC soon after it was opened.
On what is now the WR, electrification was completed to Borivli in 1928 and to Virar in 1936. Colaba was the terminus for long distance and local trains until Bombay Central was opened in 1930, and the lines between Colaba and Churchgate were electrified but this line itself was closed at the end of 1930. Churchgate has been the terminus for local trains since then.
The short stretch from Madras Beach to Tambaram was electrified at 1500 V DC in 1931. Apart from the EMUs on this route, long distance trains continued to run on steam from Madras Egmore. By 1967 the Tambaram-Villupuram section was electrified at the then standard voltage of 25 KV AC and the Beach-Tambaram section was converted to AC to enable through running up to Villupuram.
After independence, the first steps towards electrification of ER lines out of Howrah were taken with Howrah-Bandel-Burdwan and Seoraphuli-Tarakeswar being completed by 1958. These too were converted to AC in the mid-60s, and virtually all subsequent electrification in India was at 25 KV AC. The only exceptions were the extensions from Mankhurd to Vashi and then Panvel, Thane to Vashi and extensions, and electrification of Karjat-Khopoli in the 90s which had to match the existing DC system in Mumbai.
More about DC locos, AC/DC locos and operational aspects to follow.