Electric traction in Nepal; self-contained vehicles

Importance of electric traction in Nepal

Electric traction uses electric motors to drive vehicles, with energy from overhead lines, rails or batteries. It is very relevant to Nepal because:

1. Hydropower surplus: Nepal has large hydro potential (about 83,000 MW theoretical, ~42,000 MW economically feasible) and now spills energy in the wet season. Traction gives a domestic market for this clean energy.
2. Reduced fuel imports: petroleum products are a large part of the import bill and trade deficit; electric vehicles cut this.
3. Pollution: the Kathmandu valley has severe air pollution from diesel vehicles; electric traction has zero local emissions.
4. Efficiency and cost: electric motors are 85–95 % efficient; the running cost per km is much lower than for diesel.
5. Hilly terrain: high starting torque and regenerative braking suit steep gradients.
6. Projects: the planned Mechi–Mahakali electric railway, the Kerung–Kathmandu and Raxaul–Kathmandu railway studies, metro/monorail studies for Kathmandu, electric buses (Sajha Yatayat), e-rickshaws and the earlier Kathmandu trolley bus (1975–2009). (The existing Janakpur–Jaynagar railway is diesel-operated, so electrifying it is a further opportunity.) Government tax incentives promote EVs.
7. Energy security and employment in the electricity sector.

Challenges: high capital cost, reliability of supply, charging/feeder infrastructure, and difficult terrain for railways.

Self-contained vehicles

A self-contained vehicle produces or stores its electrical energy on board, so no overhead line is needed. Examples: diesel-electric locomotives, battery electric vehicles (e-buses, e-cars, mine and shunting locos), and hybrid vehicles. They can run on any route but are heavier, costlier per kW and less efficient than line-fed vehicles.

Transmission systems

 DC-DC: Diesel -> DC generator -> DC series motors -> gear -> axle
 AC-DC: Diesel -> alternator -> rectifier -> DC series motors
 AC-AC: Diesel -> alternator -> rectifier -> VVVF inverter -> IM
 Battery: Battery -> chopper/inverter -> motor -> gear/differential

• DC–DC: the generator field controls the voltage; simple, but the generator commutator limits the rating.
• AC–DC: lighter alternator with silicon rectifier; most common in diesel locos.
• AC–DC–AC: rugged three-phase induction motors, better adhesion, regenerative or rheostatic braking.
• Battery vehicles: chopper control (dc motor) or inverter with PMSM/induction motor; regenerative braking recharges the battery.

The final mechanical drive is a single-reduction gear from motor pinion to axle (axle-hung, nose-suspended motor), or a differential in road vehicles.