Direct current (DC) electrification system
DC electrification history
In 1926 electrification of the first railway line in USSR was complete. It was railway line Baku - Sabunchi. It was electrified to run suburban electric-multiple unit trains.
But 20th September 1924 first electric train began to operate on Tallinn-Pääsküla route (11,2 km long). The system power was 1200 V DC.
The first electrified line for cargo transportation was open on August 16, 1932 via Surami pass, Hashuri - Zestafoni 63 km long. All passenger and freight train was pulled here by electric Ss series electric locomotives
By 1935 there was 1907 km if electrified railways and 84 electric locomotives in service.
In 1933 new conception of railway electrification was adopted. Railway lines were electrified in 3 cases:
- Railway lines with heavy suburban traffic, where steam locomotives were too uneffective.
- Railways that cross mountain passes.
- Railway lines with a heavy freight traffic in large industrial regions.
In 1950-1955 many lines electrified using the 1,5 kV voltage were re-electrified using 3 kV voltage.
Nowadays 3 kV DC scheme is still widely used on exUSSR railways. But some lines electrified with DC were re-electrified using AC 25 kV 20 Hz scheme.
DC electrification advantages
- Simpler construction of the rolling stock. As a result rolling stock is cheaper.
- Simpler way to use regenerative braking
DC electrification disadvantages
- To achieve the sampe power significantly larger current is needed (in comparison with AC 25 kV) as a result catenary wire size is larger and it's more expensive
- More tracktion substantions are needed (one per 15-30&km
- Electricity losses in rolling stock with rheostart start (in most of cases)