- 2082 Baisakh · 6 marks
Advantages of electric traction; trains, trolley, tramways
Short answer
Electric traction is clean, provides high starting torque, regenerative braking, low maintenance, and high efficiency. Electric trains use dedicated rails, high speed and voltage; tramways run on street rails at DC 500–600 V; trolley buses have rubber tyres, no rails, steerable, and use two overhead wires for supply and return.
What are the advantages of electric traction? Compare between electric trains, trolley and tramways.
Electric traction is the system of driving vehicles (trains, trams, trolley buses) by electric motors, with energy taken from an overhead line, third rail or on-board source.
Advantages of electric traction
- Clean: no smoke or exhaust; ideal for cities and tunnels.
- High starting torque and fast acceleration, so higher schedule speed and more trains per track.
- Regenerative braking saves 15–30 % energy and reduces brake wear.
- Low maintenance: about half the maintenance cost of steam or diesel locomotives.
- High overall efficiency when power comes from central (e.g. hydro) stations.
- Higher coefficient of adhesion and no fuel storage on board; lower centre of gravity.
- Locomotive is ready to start at once; no idle running.
- In Nepal, uses domestic hydropower instead of imported fuel.
Disadvantages: high capital cost of overhead lines and substations, interference with telecommunication lines, and dependence on supply.
Comparison
| Point | Electric train | Tramway | Trolley bus |
|---|---|---|---|
| Track | Own rail track | Rails on city streets | No rails; road |
| Steering | Rails | Rails | Driver steers |
| Current collection | Pantograph / third rail | Trolley pole or bow | Two trolley poles |
| Return path | Running rails | Running rails | Second overhead wire |
| Supply | 25 kV ac or 600–3000 V dc | 500–600 V dc | 550–750 V dc |
| Speed, distance | High, long distance and suburban | Low, short urban | Low, urban |
| Flexibility | Least | Low (fixed route) | Can move around traffic |
| Tyres / noise | Steel wheels | Steel wheels, noisy | Rubber tyres, quiet |
| Capacity | Very high | Medium | Low–medium |
| Braking | Regenerative/rheostatic | Rheostatic, mech. | Regenerative possible |
Example: Kathmandu's trolley bus (Tripureshwor–Suryabinayak, 1975–2009) used two overhead wires, as the rubber tyres cannot return current through rails.
✓ Answer checked by Claude Opus 5.5 (high effort)
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